Дисертації з теми "Strength of Jointed Specimen"

Closely jointed greywacke rock masses are widespread throughout both the North and South Islands of New Zealand and much of New Zealand's infrastructure is constructed upon greywacke rock masses. This thesis deals with determining the rock mass strength of unweathered closely jointed New Zealand greywacke rock masses. Currently, the estimation of rock mass strength and deformability is reasonably well predicted through the use of such empirical failure criteria as the Hoek-Brown failure criterion and empirical expressions to predict deformability. However, previous studies upon predicting the strength and deformability of unweathered closely jointed New Zealand greywacke rock masses has shown that existing empirical methods of determining strength and deformability are unsatisfactory. The problem with predicting rock mass strength and deformability moduli of New Zealand greywacke and the lack of adequate data to calibrate a failure criterion was the starting point for this work. The objective of this thesis was to increase the knowledge of intact and defect properties of closely jointed greywacke, develop reliable rock mass data with which to calibrate a failure criterion and improve the ability to estimate the rock mass strength of greywacke rock masses. A review of existing failure criteria for rock masses was conducted and of these criteria, the Hoek-Brown rock mass failure criteria was selected to calibrate to both the intact rock and rock mass failure data, because of its broad acceptance in the rock mechanics community. A database of greywacke properties was developed based on previous studies upon unweathered greywacke around New Zealand and is attached to the thesis as an Appendix. The database included descriptions of greywacke defect properties and mechanical properties of the intact rock and joints. From this database, inputs could be justified for numerical modelling and later analyses of failure criteria. Records from the construction archives of the Benmore and Aviemore hydroelectric power projects in the South Island of New Zealand were reviewed to obtain information and results from a series of shear tests carried out on unweathered closely jointed greywacke in the 1960s. Data on rock mass strength at failure and rock mass deformability were extracted from these records to assess the predictability of the failure criterion and deformability expressions. Problems experienced during the shear tests at the Aviemore dam site created doubt as to the actual rock mass strengths achieved at failure. The behaviour of these tests was studied using the finite difference code FLAC. The work was aimed at investigating the potential for transfer of shear force between the two concrete blocks sheared in each test and the impact shear force transfer had upon the likely normal stresses beneath each block at failure. The numerical modelling results indicated that a combination of preferential failure occurring in one direction, and doubt in the actual normal load applied to the concrete blocks during testing lead to premature failure in the blocks sheared upstream. The blocks sheared in the opposite direction failed at normal stresses that are reflective of the strength of an unweathered greywacke rock mass, but these results could be explained by failure occurring along defects therefore not satisfying the assumptions of homogeneity typically required of a rock mass failure criterion. The Hoek-Brown failure criterion for intact rock was investigated by fitting it to the largest intact greywacke datasets. For a full set of test data (i.e. including tensile data), the Mostyn & Douglas (2000) variant of the Hoek-Brown failure criterion gave the best fit for a full set of rock mass data. A multiple regression method was developed which improved the fitted curve to intact data in the tensile region and gave the best estimate of tensile strength if no existing lab results for tensile strength were available. These results suggest that the Hoek-Brown failure criterion is significantly limited in its applicability to intact NZ greywacke rock. Hoek-Brown input parameters different to those suggested by Hoek et al (2002) are recommended for using the Hoek-Brown failure criterion for intact NZ greywacke. For closely jointed NZ greywacke rock masses, the results from the shear tests at Aviemore and Benmore were separated into different GSI classes and Hoek-Brown envelopes fitted to the datasets by multiple regression. Revised expressions were proposed for each Hoek-Brown input parameter (mb, s, ab) as a function of the GSI. The resulting revised Hoek-Brown failure envelopes for NZ greywacke offer a significant improvement on the existing criterion used to predict the strength of NZ greywacke intact rock and rock masses. The differences in the behaviour of the reaction blocks that failed before the test blocks and the reduction in rock strength due to sliding along defects from that predicted could be reasoned from recorded observations and the behaviour of the concrete blocks during the shear tests. This study has clearly illustrated the need for continued research in this area. This includes (1) a means of assessing the role of defects upon the shear strength of closely jointed greywacke rock mass into a failure criterion, (2) further modelling of the in-situ shear tests by a discrete element procedure to expressly determine the role of the defect on failure, (3) more testing on rock masses to obtain more data to calibrate a rock mass failure criterion, and (4) more studies on predicting the strength of extremely disturbed rock masses.

The deformability and strength properties of jointed rock masses are two of the fundamental parameters needed for the design and performance estimation of rock structures. Due to the presence of complicated minor discontinuity patterns (joints, bedding planes etc.), jointed rock masses show anisotropic and scale (size) dependent mechanical properties. At present, satisfactory procedures are not available to estimate anisotropic, scale dependent mechanical properties of jointed rock. Because of the statistical nature of joint geometry networks in rock masses, the joint patterns should be characterized statistically. The available joint geometry modeling schemes are reviewed. One of these schemes is used in this dissertation to generate actual joints in rock blocks. Three dimensional distinct element code (3DEC), which is used to perform stress analyses on jointed rock blocks in this study, is introduced and its shortcoming is identified. To overcome the shortcoming of 3DEC, a new technique is developed by introducing fictitious joints into rock blocks. Concerning the introduced fictitious joints, their geometry positions are mathematically determined; the representative mechanical properties for them found at 2D level are reviewed and verified at 3D level. By using the new technique, the deformation and strength properties of the rock blocks with many different joint configurations are found. Then effects of joint geometry parameters on the mechanical properties of jointed rock blocks are investigated. It is found that the joint geometry patterns have significant influences on the mechanical properties of rock blocks. All the joint geometry parameters are then integrated into fracture tensor. The relationships between the mechanical properties of jointed rock blocks and the fracture tensor parameters (its first invariant and directional component) are investigated. The possibility of obtaining the equivalent continuum behavior (REV properties) of jointed rock blocks is explored by using the aforementioned relationships. Finally, based on the research results, a new 3D constitutive model for jointed rock masses is developed to describe their pre-failure behavior. The constitutive model includes the effects of joints in terms of fracture tensor components and it shows the anisotropic and scale dependent natures of jointed rock masses.

In this study, the pre-failure behavior of a jointed rock block is modeled by an incrementally linear elastic anisotropic constitutive model (using an orthotropic model in 2D). In order to estimate the parameters in the constitutive model, a new technique was used in this dissertation. A 2D joint geometry generation code was used to generate finite size actual joint networks in 2D rock blocks. A 2D distinct element code (UDEC) was chosen as the stress analysis tool in this study. Fictitious joints were introduced into the rock blocks which contain finite size actual joints to discretize the problem domain into polygons. A number of stress analyses of rock blocks which contain only persistent joints were performed to estimate representative values for mechanical properties of fictitious joints to simulate the intact rock behavior. Finally, the rock blocks having different deterministic actual joint configurations with fictitious joints were subjected to 2D stress analysis under various stress paths using UDEC. Results of these stress analyses were used to estimate the deformational and strength properties of these rock blocks. Influence of joint geometry parameters on the mechanical properties of jointed rock blocks were found to be very significant. Plots are given to show how mechanical properties of rock blocks vary with joint intensity and joint size/block size for different joint orientations. These plots can also be used to estimate REV (Representative Elementary Volume) size and REV properties for rock masses. It is important to note that these REV property values depend on the chosen constitutive models for intact rock and joints. The concept of fracture tensor is reviewed at the 2D level. Relationships between the mechanical properties of jointed rock blocks and the fracture tensor parameters (its first invariant and components) are established. These relationships can be used to estimate the parameters of the chosen constitutive model for the rock block. This constitutive model has captured both scale dependent and anisotropic behaviors of rock masses. The possibility of obtaining the equivalent continuum properties (REV properties) of jointed rock blocks is explored by using the aforementioned relationships. (Abstract shortened by UMI.)

Mechanical strength in wood has always been compromised due to the complex behaviours of the material when interfered with moisture and heat. These factors has always limited the use of the material. However, the will of using more sustainable materials such as wood has contributed to a wider use of the material and several new ways that lead to improvement. Several of these methods emphasizes the joining of two wood components together endwise, where finger-joints are the most commonly used method. Several studies regarding how well finger-joints can withstand external load has been made over the years. However, many of these studies focuses on geometrical properties or strength varying in different species. This study focuses on how relative humidity and temperature affects mechanical strength in finger-jointed wood products. There were beliefs before the research started that increasing temperature would affect mechanical strength greatly. However, it turned out to only affect the mechanical strength marginally, and that relative humidity was the largest contributor to decreasing tolerance levels. It is important to notify that mechanical strength seemed to be directly affected to moisture content (MC), which is a result of an interactive relationship with both temperature and RH. It was particularly MC-levels above 9.2% that showed a decrease in mechanical strength. This research also focused on estimating the relative MOR per cross-section in varying conditions. This method could be used to better understand to which degree hygroscopic factors affects mechanical strength relative to the glued-surface area between finger-joints. Even though the findings in this study indicates that there seems to be possible to estimate strength in regards to relative MOR per cross-section, the results were not sufficient to be viewed as scientifically proof. The findings could however be used as ground for future studies.

The aim of this work is to evaluate the mechanical strength of a co-polymer of 2-hydroxyethylmethacrylate (HEMA) and methylmethacrylate (MMA), so that it can be applied as an interfacial layer between bone cement and steel implants to improve their performance and life. Finite element (FE) analysis techniques are used to assess the behavior of the interface layer under static and dynamic loading conditions. The material property of the co-polymer is a function of its composition and water saturation. The factors affecting the strength of the bone-implant interface are many. Implant interfacial fracture can lead to decreased stability. Fatigue life is a very important process in failure. The results obtained from static and dynamic analyses show that increasing the percentage of HEMA improves the strength of the interface by reducing the stiffness of the implant, absorbing more energy and by reducing the interfacial stress peaks and making the stress distribution more nearly uniform.
M.S.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical, Materials and Aerospace Engineering

The diploma thesis deals with the determination of the influence of size, shape and type of test specimen on values of modulus of elasticity of light-weight concrete. A lot of different specimens were prepared from two concrete’s mixtures for the experiment. Tests for measurement of static modulus of elasticity and dynamic modulus of elasticity by ultrasonic impulse velocity method were made. The results were assessed and summarized in tabular and graphical form.

In the present work, the effect of variation in specimen orientation and heat treatment on the Stress Corrosion Cracking (SCC) susceptibility of 7050 aluminum alloy was investigated in 3,5% NaCl solution and under freely corroding conditions. For this purpose, Constant Extension Rate Tests (CERT) was performed on precracked Compact Tension (CT) specimens and the Direct Current Potential Drop technique was applied to measure the crack lengths. In addition to crack length versus time curves, the relationship between the crack growth rate and the stress intensity factor was determined. Fractographic analysis was utilized extensively to support the findings related with basic mechanisms of cracking. The alloy was found to be in the most susceptible state in the SL orientation, in which the crack propagation direction is parallel to the rolling direction. The resistance to SCC is higher in the TS but at maximum in LT orientation where the loading direction is parallel to the rolling direction. In the peak aging treatment, T651, alloy is susceptible to SCC in SL orientation. When the over aging treatment, T7651, is applied the resistance is increased and the two step over aging treatment, T73651, has resulted in an additional improvement in this orientation. On the other hand, the alloy showed higher resistance to SCC in TS and LT orientations in T651 condition compared to the T7651 and T73651 treatments. In these orientations, the alloy is less susceptible in T73651 condition than in T7651 treatment.

Two new three-dimensional rock mass strength criteria are developed in this dissertation by extending an existing rock mass strength criterion. These criteria incorporate the effects of the intermediate principal stress, minimum principal stress and the anisotropy resulting from these stresses acting on the fracture system. In addition, these criteria have the capability of capturing the anisotropic and scale dependent behavior of the jointed rock mass strength by incorporating the effect of fracture geometry through the fracture tensor components. Another significant feature of the new rock mass strength criterion which has the exponential functions (equation 6.7) is having only four empirical coefficients compared to the existing strength criterion which has five empirical coefficients; if the joint sets have the same isotropic mechanical behavior, the number of the empirical coefficients reduces to two in this new strength criterion (equation 6.10). The new criteria were proposed after analyzing 452 numerical modeling results of the triaxial, polyaxial and biaxial compression tests conducted on the jointed rock blocks having one or two joint sets by the PFC3D software version 5. In this research to have several samples with the same properties a synthetic rock material that is made out of a mixture of gypsum, sand and water was used. In total, 20 joint systems were chosen and joint sets have different dip angles varying from 15 to 60 at an interval of 15 with dip directions of 30 and 75 for the two joint sets. Each joint set also has 3 persistent joints with the joint spacing of 42 mm in a cubic sample of size 160 mm and the joints have the same isotropic mechanical behavior. The confining stress combination values were chosen based on the uniaxial compressive strength (UCS) value of the modeled intact synthetic rock. The minimum principal stress values were chosen as 0, 20, 40 and 60 percent of the UCS. For each minimum principal stress value, the intermediate principal stress value varies starting at the minimum principal stress value and increasing at an interval of 20 percent of the UCS until it is lower than the strength of the sample under the biaxial loading condition with the same minimum principal stress value. The new rock mass failure criteria were developed from the PFC3D modeling data. However, since the joint sets having the dip angle of 60 intersect the top and bottom boundaries of the sample simultaneously, the joint systems with at least one of the joint sets having the dip angle of 60 were removed from the database. Thus, 284 data points from 12 joint systems were used to find the best values of the empirical coefficients for the new rock mass strength criteria. λ, p and q were found to be 0.675, 3.16 and 0.6, respectively, through a conducted grid analysis with a high R2 (coefficient of determination) value of 0.94 for the new criterion given by equation 6.9 and a and b were found to be 0.404 and 0.972, respectively, through a conducted grid analysis with a high R2 value of 0.92 for the new criterion given by equation 6.10. The research results clearly illustrate how increase of the minimum and intermediate principal stresses and decrease of the joint dip angle, increase the jointed rock block strength. This dissertation also illustrates how different confining stress combinations and joint set dip angles result in different jointed rock mass failure modes such as sliding on the joints, failure through the intact rock and a combination of the intact rock and joint failures. To express the new rock mass strength failure criteria, it was necessary to determine the intact rock strengths under the same confining stress combinations mentioned earlier. Therefore, the intact rock was also modeled for all three compression tests and the intact rock strengths were found for 33 different confining stress combinations. Suitability of six major intact rock failure criteria: Mohr-Coulomb, Hoek-Brown, Modified Lade, Modified Wiebols and Cook, Mogi and Drucker-Prager in representing the intact rock strength was examined through fitting them using the aforementioned 33 PFC3D data points. Among these criteria, Modified Lade, Modified Mogi with power function and Modified Wiebols and Cook were found to be the best failure criteria producing lower Root Mean Square Error (RMSE) values of 0.272, 0.301 and 0.307, respectively. Thus, these three failure criteria are recommended for the prediction of the intact rock strength under the polyaxial stress condition. In PFC unlike the other methods, macro mechanical parameters are not directly used in the model and micro mechanical parameter values applicable between the particles should be calibrated using the macro mechanical properties. Accurate calibration is a difficult or challenging task. This dissertation emphasized the importance of studying the effects of all micro parameter values on the macro mechanical properties before one goes through calibration of the micro parameters in PFC modeling. Important effects of two micro parameters, which have received very little attention, the particle size distribution and the cov of the normal and shear strengths, on the macro properties are clearly illustrated before conducting the said calibration. The intact rock macro mechanical parameter values for the Young’s modulus, uniaxial compression strength (UCS), internal friction angle, cohesion and Poisson's ratio were found by performing 3 uniaxial tests, 3 triaxial tests and 5 Brazilian tests on a synthetic material made out of a mixture of gypsum, sand and water and the joint macro mechanical parameter values were found by conducting 4 uniaxial compression tests and 4 direct shear tests on jointed synthetic rocks with a horizontal joint. Then the micro mechanical properties of the Linear Parallel Bond Model (LPMB) and Modified Smooth Joint Contact Model (MSJCM) were calibrated to represent the intact rock and joints respectively, through the specific procedures explained in this research. The similar results obtained between the 2 polyaxial experiments tests of the intact rock and 11 polyaxial experimental tests of the jointed rock blocks having one joint set and the numerical modeling verified the calibrated micro mechanical properties and further modification of these properties was not necessary. This dissertation also proposes a modification to the Smooth Joint Contact Model (SJCM) to overcome the shortcoming of the SJCM to capture the non-linear behavior of the joint closure varying with the joint normal stress. Modified Smooth Joint Contact Model (MSJCM) uses a linear relation between the joint normal stiffness and the normal contact stress to model the non-linear relation between the joint normal deformation and the joint normal stress observed in the compression joint normal stiffness test. A good agreement obtained between the results from the experimental tests and the numerical modeling of the compression joint normal test shows the accuracy of this new model. Moreover, another shortcoming associated with the SJCM application known as the interlocking problem was solved through this research by proposing a new joint contact implementation algorithm called joint sides checking (JSC) approach. The interlocking problem occurs due to a shortcoming of the updating procedure in the PFC software related to the contact conditions of the particles that lie around the intended joint plane during high shear displacements. This problem increases the joint strength and dilation angle and creates unwanted fractures around the intended joint plane.

In this study, low temperature cracking of asphalt concrete is investigated based on a laboratory experimental program including the design variables of aggregate type, gradation, asphalt content, binder grading, binder modification, and the experimental variables of cooling rate, and specimen size. The design of experiment is proposed according to the fractional factorial design principles to reduce the required number of test specimens. Mix designs are performed according to the Superpave mix design guidelines using materials obtained from the Turkish General Directorate of High-ways. In the course of this study, a test setup for thermal stress restrained specimen test for asphalt concrete is developed and used successfully to test a number of as-phalt concrete beam specimens. The same setup is also used for measuring the glass transition temperatures to obtain various thermo-volumetric properties of mixtures. Statistical methods are used to identify the effect of experimental variables on frac-ture strength, fracture temperature and other dependent variables obtained from the testing program. Statistical models are also developed to predict the fracture strength, fracture temperature and other thermo-volumetric properties of mixtures. Results of analyses show that aggregate type, binder modification, and asphalt content significantly affect both the fracture strength and fracture temperature of asphalt concrete. While the glass transition temperature is affected by only aggregate type, coefficients of contraction before and after the glass transition temperature are not influenced by any of the experimental variables. The results of this study provide an important basis to prevent low temperature cracking in asphalt concrete pavements.

Este trabalho visa o refinamento do procedimento para estimativa dos parâmetros elasto-plásticos de tenacidade à fratura, integral J e CTOD, incorporando o efeito de dissimilaridade mecânica devido à introdução de juntas soldadas utilizando a metodologia eta, tal efeito não é previsto na formulação das atuais normas de avaliação de tenacidade à fratura, porém a dissimilaridade mecânica afeta fortemente a relação entre o carregamento global do espécime e as forças motrizes na ponta da trinca. Para o desenvolvimento das análises foi empregada a geometria normalizada C(T), compacta, pois esta pode apresentar potencias vantagens sobre a geometria SE(B), flexão três pontos, como menor consumo de material para a confecção dos espécimes, menor capacidade do aparato experimental e fácil manipulação na prática dos testes laboratoriais, porém carece de fatores eta quando comparados ao tradicional espécime SE(B). Os principais objetivos deste trabalho são gerar um compêndio de fatores eta e propor uma formulação robusta que incorpore os efeitos de dissimilaridade mecânica para o cálculo de integral J e CTOD. Para tal intento a matriz de análise deste trabalho abrange diferentes comprimentos de trinca, níveis de dissimilaridade mecânica e larguras de cordão de solda, 0.45a/W0.6 e 1M y 1.3, 10 mm2h20 mm respectivamente. As análises numéricas foram realizadas nas condições de estado plano de deformação (2D) e tridimensional (incluindo o efeito acoplado entre os campos de tensões e deformações no plano e fora do plano), os resultados fornecem um bom suporte ao uso da geometria C(T) com trinca central no cordão de solda para avaliação de tenacidade à fratura em juntas soldadas de materiais comumente aplicados na construção de dutos e vasos de pressão.
This work focuses on the evaluation procedure to determine the elastic-plastic J integral and CTOD fracture toughness based upon the eta-method for C(T) fracture specimens including overmatched weldments. Since fracture toughness test protocols do not address weld strength mismatch effect, this effect strongly alters the relationship between global loads and crack driving forces. The objectives of this investigation are to enlarge plastic eta-factor data base for C(T) specimen and to develop a robust formulation to address weld strength mismatch. The present analyses enable the introduction of a larger set of plastic eta-factors for a wide range of crack sizes (as measured by the a/W-ratio) and material properties, including different levels of weld strength mismatch, applicable to structural, pipeline and pressure vessel steels. Very detailed non-linear finite element analyses for plane-strain and full 3D models of standard C(T) fracture specimens provide the evolution of load with increased crack mouth opening displacement (and LLD) required for the estimation procedure. The results provide a strong support to use the plastic eta-factor in J integral and CTOD estimation procedures for center notch welded C(T) fracture specimen.

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Even though the different sizes of cylindrical specimens for tests in concrete are standardized to get the simple compressive strength and the modulus of elasticity, this factor is not usually studied in most researches. So, the goal of this thesis was to evaluate the influence of the size of the specimens in the initial tangent modulus of elasticity (Eci) and in the compressive strength (fc), correlate the values of fc and Eci, and compare the values of modulus of elasticity that were estimated by the equations proposed by the Brazilian code (NBR 6118/2003) and by the American norm (ACI 318/2002). Concretes with three levels of strength were used after 28 days: 25MPa, 30MPa and 40MPa. They were all proportionally mixed with materials of the region and supplied by only one concrete batching plant of Goiânia GO. The tests of compressive strength and initial tangent modulus of elasticity were done in cylindrical specimens of 100 x 200 mm and 150 x 300 mm after 28 days. The samples were collected during the delivery of the concrete in the construction sites. For each truck, ten specimens were molded, five of 100 x 200 mm and five of 150 x 300 mm. Of the 600 specimens that were molded, 240 tests of compressive strength and 360 tests of modulus of elasticity were done. The cure was in a tank with water saturated with limestone. After the tests were done, the statistical analysis of the results was done. The variance analysis (ANOVA) indicated that the size of the specimen exerts influence only on the results of the initial tangent modulus of elasticity (Eci). There is a tendency for the specimens of 100 x 200 mm to show greater results for the modulus of elasticity of the concrete than the specimens of 150 x 300 mm. In the compressive strength, only the level of strength significantly exerted influence on the results. It was also observed that the NBR 6118/2003 overestimates the values of modulus of elasticity of the researched concretes and the results are better adequate to the model proposed by the ACI 318/02.
Apesar dos parâmetros de ensaios, como o tamanho do corpo de prova, influenciarem nos resultados do módulo de deformação e da resistência a compressão, normalmente esse fator não é estudado na maioria das pesquisas. Assim, esta dissertação objetivou avaliar a influência do tamanho dos corpos de prova no módulo de deformação tangente inicial (Eci), e na resistência a compressão (fc), correlacionar os valores de fc e Eci e comparar os valores de módulo de deformação alcançados com os valores estimados pelas equações propostas pela norma brasileira (NBR 6118/2003) e pelo amaericana (ACI 318/2002). Utilizaram-se concretos com três níveis de resistência aos 28 dias: 25MPa, 30MPa e 40Mpa, todos dosados com materiais da região e fornecidos por uma mesma central de concreto de Goiânia - GO. Os ensaios de resistência à compressão e de módulo de deformação tangente inicial foram realizados em corpos de prova cilíndricos de 100 x 200 mm e 150 x 300 mm aos 28 dias. As amostras foram coletadas durante a entrega do concreto nas obras. A cada caminhão, eram moldados dez corpos de prova, cinco de 100 x 200 mm e cinco de 150 x 300 mm. Foram moldados 600 corpos de prova, onde realizaram-se 240 ensaios de resistência à compressão e 360 de módulo de deformação. A cura foi em tanque com água saturada com cal. Após a realização dos ensaios, fez-se a análise estatística dos resultados obtidos. A análise de variância (ANOVA) indicou que o tamanho do corpo de prova exerce influência apenas nos resultados do módulo de deformação tangente inicial (Eci). Houve uma tendência dos corpos de prova de 100 x 200 mm apresentarem maiores resultados para o módulo de deformação do concreto que os corpos de prova 150 x 300 mm. Na resistência à compressão, como já era esperado, apenas a classe de resistência influenciou significativamente nos resultados. Observou-se também que a NBR-6118/2003 superestima os valores de módulo de deformação dos concretos estudados e que os resultados obtidos se adequam melhor ao modelo proposto pelo ACI318/02.

Dreiaxiale Druckprüfungen können als Einstufenversuche, als Mehrstufenversuche oder als Versuche mit kontinuierlichen Bruchzuständen ausgeführt werden. Bei der Anwendung der Mehrstufentechnik ergeben sich insbesondere Fragestellungen hinsichtlich der richtigen Wahl des Umschaltpunktes und des optimalen Verlaufs des Spannungspfades zwischen den einzelnen Versuchsstufen. Fraglich beim Versuch mit kontinuierlichen Bruchzuständen bleibt, ob im Versuchsverlauf tatsächlich Spannungszustände erfasst werden, welche die Höchstfestigkeit des untersuchten Materials repräsentieren. Die Dissertation greift diese Fragestellungen auf, ermöglicht den Einstieg in die beschriebene Thematik und schafft die Voraussetzungen, die zur Lösung der aufgeführten Problemstellungen notwendig sind. Auf der Grundlage einer umfangreichen Datenbasis gesteinsmechanischer und petrophysikalischer Kennwerte wurde ein numerisches Modell entwickelt, welches das Spannungs-Verformungs-, Festigkeits- und Bruchverhalten eines Sandsteins im direkten Zug- und im einaxialen Druckversuch sowie in dreiaxialen Druckprüfungen zufriedenstellend wiedergibt. Das Festigkeitsverhalten des entwickelten Modells wurde in Mehrstufentests mit unterschiedlichen Spannungspfaden analysiert und mit den entsprechenden Laborbefunden verglichen.

ABSTRACT Several, complicated and difficult structures are constructed or in planning stages under complex geological conditions around the world. Even small variation in analysis and design can cost significantly. It is well recognized that the strength of rock masses depends upon the strain history, extent of discontinuities, orientation of plane of weakness, condition of joints, fill material in closely packed joints and extent of confinement. Several solutions are available for strength of jointed rock mass with a set of discontinuities. There is a great multiplicity in the proposed relationships for the strength of jointed rocks. In the present study, the author conceives the effect of increasing stresses to induce permanent strains. This permanent strain appears as micro crack, macro crack and fracture. A fully developed network of permanent deformations forms joint. The joint may contain deposits of hydraulic and hydrothermal origin commonly known as a fill which may have cementing tendency. The joint factor numerically captures varied engineering possibilities of joints in a rock mass. The joints grow as an effect of loading. The growth of the joints is progressive in nature. It increases the joint factor, which modify the failure stresses. After extensive experimentation significant joint properties affecting the strength of jointed rocks with unfilled joints and joints with cemented fill has been evolved. This factor is called joint modified factor in which number of joints per meter length, orientation of joints and strength along joints and strength along joints are clubbed together. As the in situ determinations of jointed rock mass is costly and time consuming attempts are being made to predict the strength and deformation of rock mass through model test under controlled laboratory conditions In the present work jointed rocks are simulated by preparing specimens of mortar and cemented joints containing PoP were created artificially by inducing paste of PoP inside the joints. The experimental investigations have been carried on PoP cemented at varied joints possibilities specimen. The specimen made of cement and standard sand in the ratio of 1:3 to simulate the rock mass. The samples were cured at the interval of 7 days to create weakly cemented rock mass and at 28 days to make a comparatively stronger rock mass. The strength changes on 7 days and 28 days are incorporated in relation to their peak compressive strength in presence of PoP cemented joints. The specimen was tested under uniaxial compression to determine the various parameters. The results have been analysed in relation to the modified joint factor Trivedi(40) and a simple empirical approach has been found to predict unconfined compressive strength of jointed rocks with PoP cemented joints. The investigation indicates that the results are in conformity with the recent analyses proposed by Trivedi [40].

碩士
國立成功大學
土木工程學系碩博士班
98
Generally in the stability of slope analysis,when consideration of slideing failure surface shear force resistance is often using the residual shear strenght for the failure surface on the material shear strenght. Therefore, the discussion on slopes material's residual shear strenght is quite important. To find the slope on the material shear strenght,it is often using the tradition direct shear test in the laboratory. But the tradition direct shear test in the shaering process, there is changeing small in the area of cross section ofthe shear plane and to limit the shear displacement by the specimen size, can't obtain true residual strength. Bishop et al. (1971) development use ring-shear apparatus, applies in the original condition and the remolded clay shearing test improvement tradition direct shear shortcoming, there is no change in the area of cross section of the shear plane and it can do big shear displacement test. Although ring shear apparatus can improvement tradition direct shear two shortcoming, it is more difficult in the instrument operation, the instrumentation equipment to be complex, the price is soaring, generally the laboratory is rare. In order to avoid the ring-shear apparatus expensive and complex can improve the tradition direct shear test the shortcoming,this article attempts the cyclic shear test to discuss the large-scale siding slope's residual shear strenght. Mainly take the Tsaoling landslide as the object, researching into Tsaoling landslide's Chaolan formation sandstones of residual shear strenght.It has artificial jointed rock by different size specimen to discuss the area of cross section of the shear plane and shear displacement which regarding residual shear strenght influence. And scans the shearing test before and after jointing using the laser profiler to jointed specimen, calculating JRC of value its jointed specimen,which understand in the shearing test before and after Chaolan formation sandstones of jointed specimen rough change situation. In addition, by Sufer software jointing section plane plan block diagram, development jointing section plane situation, and using the geography information system analysis jointing section plane's height, slope and aspect, may know different section planes each item of data. This research are as follows: 1. Different sizes jointed section plane rock under residual condition, angle of friction and cohesive of value. size normal stress Shear displacement residual angle of friction cohesive (MPa) (mm) (°) (MPa) A(10cm×10cm×10cm) 0.5、1、2、4 200 34.8 0.100 B(20cm×10cm×10cm) 0.5、1、2、4 200 39.1 0.233 C(30cm×10cm×10cm) 0.5、1、2 240 31.8 0.473 A(10cm×10cm×10cm) 0.4、0.6、0.8 200 39.7 0 D(20cm×20cm×10cm) 0.4、0.6、0.8 200 42.8 0 Because the non-homogeneous of the artificial joint surfaces of the specimens, the profile fluctuations of the joint surfaces affect the shear strengths of the specimens. Meanwhile, the residual friction angle has no obvious variation as the size of the specimen varies. 2. Higher the normal stress, higher the shear displacement for the specimen gets into the residual condition. When the normal stress is 0.5MPa and 1MPa, specimens present shear dilation and the shear strength originates from the friction as the specimen moves along the joint profile. When the normal stress is 2MPa and 4MPa, specimens present shear compaction and the joints of the specimen are cut off and broken to pieces. Higher normal stress indicates larger shear compaction and the joints of the specimen are cut off and broken more violent. 3. After the cyclic shear test, the JRC of the specimen with the same specimen size reduces more violent as the normal stress increases gradually. Meanwhile, under the same normal stress, the JRC of the specimen reduces more violent as the specimen size enlarges gradually. 4. The length of the specimen would affect the JRC of the specimen. In size A and size B specimens, as the JRC calculation length of the specimen closes to about 10cm, the JRC of the specimen becomes stable. In size C specimens, as the JRC calculation length of the specimen closes to about 15cm, the JRC of the specimen also becomes stable. 5. This study uses the Barton empirical formula to forecast the shear stress of the joint in the specimen. When the JRC of the specimen is higher than 18, which means the joint surface is rougher, the shear stress prediction error is getting higher. When the normal stress is lower than 0.5Mpa, the shear stress prediction is not stable and the prediction error is huge. However, the shear stress prediction error would reduce as the normal stress increases. 6. The joint of the specimen would be cut off and leads to the shear stress decreasing as the normal stress is over the normal stress threshold during the shear test process. When the specimen size of the Chaolan formation sandstone is in size A, the normal stress threshold of the Chaolan formation sandstone is 1.386Mpa by applying the regression analysis on the cyclic shear test results. 7. Through the geographic information system, the height, slope, aspect of the 3D joint surface data can be calculated and may take advantage of understanding the joint surface roughness fluctuation in different specimen sizes. In the slope analysis of the joint surface, the proportion of the slope in each direction is quite different which reveals the slope distribution is dissimilar in different joint surfaces. 8. According to the slope and aspect analysis of the joint surface acquired by the geographic information system, the splitting rock specimen method utilized in this study would lead to the different joint surface and joint roughness. The non-homogeneous of the joint surfaces in different specimens result in the shear strength of the specimen would not be affected by the scale effect obviously.

Rock masses are hardly present in intact state in nature but are most commonly found in jointed form. In-situ test for determining the behaviour of jointed rock mass is costly and time consuming, hence attempts are being made by researchers to predict the strength and deformation behaviour of jointed rock masses under controlled laboratory conditions. Considering its implications experimental study has been undertaken for determining strength characteristics of jointed rock mass. Models have been prepared using plaster of paris and different degree of anisotropy have been induced by inducing joints in them at orientation (β) varying from 0° to 90°. The parameters studied are- i) Variation of compressive strength ratio (σcr= σcj/σci) of Plaster of Paris under unconfined conditions with joint factor. ii) Variation of jointed cohesion (Cj), friction angle Φj and roughness parameters r=tanΦj. where, σcj = Uniaxial compressive strength for intact mass. σcj = Uniaxial compressive strength for jointed mass. n = Inclination parameter r = Joint strength The values for cohesion Cj for jointed specimen of Plaster of Paris was found to be 0.16 MPa and the value of friction angle Φj was found to be 39°. Hence the roughness parameter ( r= tan Φj ) comes out to be. 809 for the specimen of Plaster of Paris tested. The optimum value of uniaxial compressive strength (σ ci ) evaluated from the above test was found to be 11.00 MPa. Comparison also has to be made between the observed experimental values and the empirical relations given by various researchers previously.

Several massive, complicated and difficult to design structure are under construction or planning stages under very complex geological condition in India and around the world. Even small variation in appraisal and design can cost millions. Hence initial development of understanding under control condition is very important and desirable for characteristic and prediction of behavior. It is essential to have a clear understanding of strength and deformation behavior of jointed mass for realistic analysis and rational designing of engineering structure .The most important factors which govern the strength of rock mass type are type of rocks, bedding planes, stress condition, presence of cracks and fissures and nature of joint surfaces, presence of minerals in bedding planes also play an important role in the strength and deformation behavior of jointed rock mass. As the in situ determinations of jointed rock mass is costly and time consuming attempts are being made to predict the strength and deformation of rock mass through model test under controlled laboratory conditions Considering the importance of this study the experimental study has been under taken to determine the strength and deformation behavior of jointed rock mass. Models will be prepared using Plaster of paris, cement mad mica and different degrees of anisotropy have been induced by making joints in them varying from 0 to 90 degree. The specimen will be tested under direct shear, uniaxial compression to determine the various parameters.

碩士
國立雲林科技大學
營建工程系
107
Pre-cut is important for preventing random crack of concrete especially for slab. However, the strength of the concrete around the cutting reduces due to the damage caused by the cutting. The weakened edges of the cutting break easily in its early service life. Strengthening the edges is the only way to prevent the early breakage. To prevent using a concrete specimen of real size, cylindrical concrete specimen is characterized. The decrease of the strength can be characterized by comparing with that of the undamaged one, and different curing process are applied to recover the strength partially. In this study, various curing processes are tested for quantifying their recovering capability.

Most rock masses encountered in civil and mining engineering projects contain pre-existing discontinuities. These discontinuities weaken the rock masses to an extent, which depends very much on the size of engineering structure relation to discontinuity spacing. The strength and deformability of rock mass is controlled not only by the intact portion of rock, but by the characteristic of the joints that break up the mass, particularly their pattern and their orientation with respect to the in-situ stresses. In considering the effect of joints, the discrete approach emerged as an efficient tool and advocated since 1970s (Cundall, 1971). However, the numerical approach with modelling the joints explicitly has the limitation of computational complexity for modelling large-scale problems with extremely large number of joints. As an alternative to this limitation, the equivalent continuum approach models the jointed rock masses as a continuum with the equivalent properties that represent implicitly the effects of the joints. Several numerical methods have been developed by various researchers to model jointed rock masses as equivalent continuum, using various techniques. However, the existing equivalent continuum models are complicated and need more input data from experimental or field testing in order to carry out the analysis. Present approach attempts to use statistical relations, which are simple and obtained after analyzing a large data from the literature on laboratory test results of jointed rock masses. Systematic investigations were done including laboratory experiments to develop the methodologies to determine the equivalent material properties of rock mass and their stress-strain behaviour, using a hyperbolic approach (Duncan and Chang, 1970). Present study covers the development of equivalent continuum model for rock mass right from developing statistical correlations to find out equivalent material properties based on experimental results, to the implementation of the model in FLAC3D for 3-dimensional applications and subsequently verification leading to real field application involving jointed rocks. Experimental work carried out to study the strength and deformation characteristics of jointed rock by using standard laboratory tests on cylindrical specimens of plaster of Paris by introducing artificial joints. The objective was to derive the compressive strength and elastic modulus of rock mass as a function of intact rock strength/modulus and joint factor. The obtained experimental results and developed relations were compared with the previous experimental data on jointed rocks. Further, a failure criterion as proposed by Ramamurthy (1993) has been validated from these experimental results of intact and jointed rock specimens. Empirical relationships similar to Ramamurthy’s relations are established for the prediction of rock mass strength and were compared with proposed equation by Ramamurthy (1993) and are found comparable. However, the equations by Ramamurthy were based on different variety of rocks and therefore recommended for further use and were used in numerical models. For efficient application to the field problems the equivalent continuum model is implemented in the program Fast Lagrangian analysis of continua (FLAC3D). The model was rigorously validated by simulating jointed rock specimens. Element tests were conducted for both uniaxial and triaxial cases and then compared with the respective experimental results. The numerical test program includes laboratory tested cylindrical rock specimens of different rock types, from plaster of Paris representing soft rock to granite representing very hard rock. The results of the equivalent continuum modelling were also compared with explicit modelling results where joints were incorporated in the model as interfaces. To represent highly discontinuous system, the laboratory investigation on block jointed specimens of gypsum plaster (Brown and Trollope, 1970) was modelled numerically using equivalent continuum approach. To extend the applicability of the model to field applications, investigation were done by undertaking numerical modelling of two case studies underground caverns, one Nathpa Jhakri hydroelectric power cavern in Himachal Pradesh, India, and the other one Shiobara hydroelectric power cavern in Japan. This study verifies the efficiency of the present approach in estimating ground movement and stress distribution around the excavations in jointed rock masses. The modelling results were also compared with six other computation models as presented by Horii et al. (1999) for the Shiobara power house cavern. An attempt has also been made to numerically model the support system for the cavern and investigate the efficiency of reinforcements using FLAC3D. The model was also used for analyzing large scale slope in jointed rocks using the equivalent continuum model by undertaking numerical modelling of Anji bridge abutment slopes, in Jammu and Kashmir, India. Slope stability analysis is done using equivalent continuum approach for both, the original profiles as well as with the pier loads on cut profiles. Attempt was also made to exhibit the shear strength dependency of the strain though the hyperbolic stress- strain model. The shear strain developed in the slope increases with reducing the shear strength. The relationship between the shear strength reduction ratio ‘R’ and axial strain ‘ε’, for different values of failure ratio ‘Rf’ was studied and it was observed that, the value of ‘ε’ increases, as the value of ‘R’ increases especially it increases rapidly when the value ‘R’ approaches certain critical value, which varies with the value of ‘Rf’. This critical value of R is known as the critical shear strength reduction factor Rc and is highly sensitive to the confining stress. As the value of Rf increases, representing a transition from linear elastic nature to nonlinear nature, the value of critical shear strength reduction ratio also decreases. Relationship between the critical shear strength reduction ratio and the safety factor were examined to elucidate their physical meaning. It was observed that at critical value of the shear strength reduction ratio, a well defined failure shear zone developed from the toe to the crest of the slope. Intelligent models using ANNs were also developed to predict the elastic modulus of jointed rocks as an alternative to empirical equations and without predefining a mathematical model to correlate the properties.

Most rock masses encountered in civil and mining engineering projects contain pre-existing discontinuities. These discontinuities weaken the rock masses to an extent, which depends very much on the size of engineering structure relation to discontinuity spacing. The strength and deformability of rock mass is controlled not only by the intact portion of rock, but by the characteristic of the joints that break up the mass, particularly their pattern and their orientation with respect to the in-situ stresses. In considering the effect of joints, the discrete approach emerged as an efficient tool and advocated since 1970s (Cundall, 1971). However, the numerical approach with modelling the joints explicitly has the limitation of computational complexity for modelling large-scale problems with extremely large number of joints. As an alternative to this limitation, the equivalent continuum approach models the jointed rock masses as a continuum with the equivalent properties that represent implicitly the effects of the joints. Several numerical methods have been developed by various researchers to model jointed rock masses as equivalent continuum, using various techniques. However, the existing equivalent continuum models are complicated and need more input data from experimental or field testing in order to carry out the analysis. Present approach attempts to use statistical relations, which are simple and obtained after analyzing a large data from the literature on laboratory test results of jointed rock masses. Systematic investigations were done including laboratory experiments to develop the methodologies to determine the equivalent material properties of rock mass and their stress-strain behaviour, using a hyperbolic approach (Duncan and Chang, 1970). Present study covers the development of equivalent continuum model for rock mass right from developing statistical correlations to find out equivalent material properties based on experimental results, to the implementation of the model in FLAC3D for 3-dimensional applications and subsequently verification leading to real field application involving jointed rocks. Experimental work carried out to study the strength and deformation characteristics of jointed rock by using standard laboratory tests on cylindrical specimens of plaster of Paris by introducing artificial joints. The objective was to derive the compressive strength and elastic modulus of rock mass as a function of intact rock strength/modulus and joint factor. The obtained experimental results and developed relations were compared with the previous experimental data on jointed rocks. Further, a failure criterion as proposed by Ramamurthy (1993) has been validated from these experimental results of intact and jointed rock specimens. Empirical relationships similar to Ramamurthy’s relations are established for the prediction of rock mass strength and were compared with proposed equation by Ramamurthy (1993) and are found comparable. However, the equations by Ramamurthy were based on different variety of rocks and therefore recommended for further use and were used in numerical models. For efficient application to the field problems the equivalent continuum model is implemented in the program Fast Lagrangian analysis of continua (FLAC3D). The model was rigorously validated by simulating jointed rock specimens. Element tests were conducted for both uniaxial and triaxial cases and then compared with the respective experimental results. The numerical test program includes laboratory tested cylindrical rock specimens of different rock types, from plaster of Paris representing soft rock to granite representing very hard rock. The results of the equivalent continuum modelling were also compared with explicit modelling results where joints were incorporated in the model as interfaces. To represent highly discontinuous system, the laboratory investigation on block jointed specimens of gypsum plaster (Brown and Trollope, 1970) was modelled numerically using equivalent continuum approach. To extend the applicability of the model to field applications, investigation were done by undertaking numerical modelling of two case studies underground caverns, one Nathpa Jhakri hydroelectric power cavern in Himachal Pradesh, India, and the other one Shiobara hydroelectric power cavern in Japan. This study verifies the efficiency of the present approach in estimating ground movement and stress distribution around the excavations in jointed rock masses. The modelling results were also compared with six other computation models as presented by Horii et al. (1999) for the Shiobara power house cavern. An attempt has also been made to numerically model the support system for the cavern and investigate the efficiency of reinforcements using FLAC3D. The model was also used for analyzing large scale slope in jointed rocks using the equivalent continuum model by undertaking numerical modelling of Anji bridge abutment slopes, in Jammu and Kashmir, India. Slope stability analysis is done using equivalent continuum approach for both, the original profiles as well as with the pier loads on cut profiles. Attempt was also made to exhibit the shear strength dependency of the strain though the hyperbolic stress- strain model. The shear strain developed in the slope increases with reducing the shear strength. The relationship between the shear strength reduction ratio ‘R’ and axial strain ‘ε’, for different values of failure ratio ‘Rf’ was studied and it was observed that, the value of ‘ε’ increases, as the value of ‘R’ increases especially it increases rapidly when the value ‘R’ approaches certain critical value, which varies with the value of ‘Rf’. This critical value of R is known as the critical shear strength reduction factor Rc and is highly sensitive to the confining stress. As the value of Rf increases, representing a transition from linear elastic nature to nonlinear nature, the value of critical shear strength reduction ratio also decreases. Relationship between the critical shear strength reduction ratio and the safety factor were examined to elucidate their physical meaning. It was observed that at critical value of the shear strength reduction ratio, a well defined failure shear zone developed from the toe to the crest of the slope. Intelligent models using ANNs were also developed to predict the elastic modulus of jointed rocks as an alternative to empirical equations and without predefining a mathematical model to correlate the properties.

Rock, like soil, is sufficiently distinct from other engineering materials that the process of design in rock is very complex. In rock structures, the applied loads are often less significant than the forces deriving from redistribution of initial stresses. Hence, the determination of material strength requires as much judgement as measurement. A thorough review of literature on different aspects of jointed rock mass indicate that the behavior of jointed rock mass is influenced by many factors such as location of joints, joint frequency, joint orientation and joint strength. In the present study, an effort has been made to establish empirical relations to define the properties of jointed rock mass as a function of intact rock properties and joint factor. The effect of joints in the jointed rock is taken into account by the joint factor. The most important factors which govern the strength of rock mass are type of rocks, bedding planes, stress condition, presence of cracks and fissures, nature of joint surfaces and presence of minerals in bedding planes also play an important role in the strength and deformation behaviour of jointed rock mass. As the in situ determination of jointed rock mass is costly and time consuming, attempts are being made to predict the strength and deformation of rock mass through model test under controlled laboratory conditions.

Several massive, complicated and difficult to design structure are under construction or planning stages under very complex geological condition in India and around the world. Even small variation in appraisal and design can cost millions. Hence initial development of understanding under control condition is very important and desirable for characteristic and prediction of behavior. It is essential to have a clear understanding of strength and deformation behavior of jointed mass for realistic analysis and rational designing of engineering structure. Rock, like soil, is sufficiently distinct from other engineering materials that the process of design in rock is very complex. In rock structures, the applied loads are often less significant than the forces deriving from redistribution of initial stresses. Hence, the determination of material strength requires as much judgement as measurement. A thorough review of literature on different aspects of jointed rock mass indicate that the behavior of jointed rock mass is influenced by many factors such as location of joints, joint frequency, joint orientation and joint strength. In the present study, an effort has been made to find out the strength of jointed rock mass with different gouge material. The most important factors which govern the strength of rock mass are type of rocks, bedding planes, stress condition, presence of cracks and fissures, nature of joint surfaces and presence of minerals in bedding planes. As the in situ determination of jointed rock mass is costly and time consuming, attempts are being made to predict the strength of rock mass through model test under controlled laboratory condition.
Dr. A.K.SAHU (ASSOCIATE PROFESSOR) DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

碩士
淡江大學
土木工程學系
85
The strength and deformability of jointed masses are primarily dominated by the joint configuration, such as dip angle, spacing, persistence, and sets of joints. This paper aim at the post-peak behavior of jointed masses affected by the fracture of rock bridge and sliding of joints. First, the model proposed by Shen and Stephansson is extended to suit for the mass with various persistence during destroy of rock bridge. Secondly, the analysis on the post-peak behavior of three- dimensional masses by 3DEC is also discussed. Some conclusions are drawn as follows. (1) Mathematical model : The post-peak behavior of jointed masses is strongly dependent on dip angle and persistence of joints. It also affected by the shape and size of jointed masses. The existence of rock bridge can strengthen the deformation modulus, but the relatively distributed position of rock bridge is negligible. The scale effect of joint number on deformability vanishes rapidly on the case of mass with continuous joints. (2) 3DEC : The anisotropy of mass strength is deduced as the confining pressure increasing. The post-peak behavior of masses is more ductile while the dip angle and the thickness increases. The strength of masses is independent of the stiffness of joints. The mechanical behavior of masses with multiple sets of joint is predominated by the dipper and weaker one. The effect of strike of joints is observed under the true triaxial stress condition. The post-peak behavior of jointed mass is independent of the intermediate stress.

碩士
國立臺灣科技大學
營建工程系
90
Jet grouting and mechanical mixed grouting usually used to improve soft clay associated with deep excavation. The objective of this study is to investigate the characteristics of the shear strength and the anisotropic behavior of composite soil specimen of soft clay and grout column. A series of true triaxial tests of different loading pattern were conducted to study shear strength and anisotropy behavior of the composite soil specimen. Test results are then used to evaluate the equations that are commonly used in practice for the estimation of the equivalent shear strength of the improved soil mass. Results from the triaxial test of different stress path indicate that: the compressive strength of composite soil specimen increases significantly with the improvement ratio, the consolidation stress and the curing time; however, the increase of the extension strength of composite soil specimen is much less significant. Strength on the strength anisotropic characteristics of composite soil specimen shows that: degree of anisotropy will increase with the improvement ratio and the consolidation stress. However, the curing time will not influence the degree of anisotropy. The investigation on the equivalent stress strength equations shows that: commonly used equations that are based on the weighted average strength and grouted soil give reasonable estimation of the test results. However, the stress strength parameter for soil and grouted soil should be carefully selected according to the loading path.

碩士
國立臺灣科技大學
營建工程系
91
Jet grouting method is usually used to improve soft clay associated with deep excavation. The main purpose of this study is to investigate the characteristics of the strength and the anisotropic behavior of the composite soil specimen consisted of soft clay and treated material. A series of stress path tests has been performed on composite soil specimen with flexible boundary true triaxial apparatus to explore its strength characteristic and mechanical anisotropy behavior. The test results are used to evaluate the empirical formulas that are commonly used to estimate the equivalence strength of the composite soil. Results from the true triaxial test indicate that (1) the strength of composite soil specimen decreases progressively with wave pattern as the stress path angle (θ) decreases from 0°to 180° (2) If the improvement ratio enhance, the degree of anisotropy of the composite soil specimen will also increase. When the stress path angle (θ) varies from 0 to 120°, the strength of the composite soil specimen increase significantly with the increase of the improvement ration. But when the stress path angle (θ) is from 120°to 180°, rising improvement ratio exhibits less effect on the strength. (3) When evaluating the equivalence strength using the formula：Su,eq= Su,p×Ir+ Su,c×(1- Ir), the strength parameter for clay and treated material should be carefully selected according to the loading pattern. When the formula “Su,eq= α×Su,p×Ir+ Su,c×(1- Ir)” is used, test results indicate that the appropriate strength reduction coefficient α is about 0.25.

The compressive strength test, split tensile strength test, bending strength test, standard normal consistency test and setting time test of plaster of Paris specimens are found out by present case studies. These strengths are governed by the shape and size. For each of the rectangular, cube and cylindrical specimen load versus deflection curve was measured.

Stability analysis of a rock mass is an important and complicated problem related to the safety of engineering buildings. One of the major tasks of engineering geomechanics is to evaluate the rock mass stability both qualitatively and quantitatively. The ultimate strength and deformation of jointed rock mass are important parameters that designers look for in selecting sites for foundations of civil structures in rocks. In nature rock is exists as a rock mass. It is a discontinuous medium with fissures, fractures, joints, bedding planes, and faults. These discontinuities may exist with or without gouge material. The strength of rock masses depends on the behaviour of these discontinuities or planes of weakness. The frequency of joints, their orientation with respect to the engineering structures, and the roughness of the joint have a significant importance from the stability point of view. Reliable characterization of the strength and deformation behaviour of jointed rocks is very important for safe design of various types of civil structures such as arch dams, bridge piers, and tunnels.

碩士
國立成功大學
材料科學及工程學系
102
This study is focused on the properties of eyeglass type austempered ductile iron (ADI) specimen. The eyeglass type specimen is used in transmission systems, and the essential properties are good hardness and tensile strength. But the notch effect would cause the mechanical performance of eyeglass type specimen becoming worse. The base of ADI is bainite, which is good combination of hardness, strength and ductility. In this study, the ductile iron casting was shaped into eyeglass type dimension. The ductile iron also processed into thin standard specimen, in order to be a contrast. The specimens were austenized at 930°C for 30 minutes, followed by a quench to salt bath, which the austempering temperature is 250°C, 300°C, 350°C, 400°C, and holding for 30 minutes. The results showed that the best tensile strength of eyeglass specimen was austempered at 350°C, but the best austemperig temperature for standard specimen was 300°C. The reason is that the factor which affected the standard specimen was the base strength. In eyeglass type specimen, the factors were not only the base strength but also the amount of retained austenite. When austempered at 350°C, lower bainite structure supplied good strength, and enough amount of retained austenite to reduce the notch effect. In this study, austempering temperature at 350°C is the best temperature parameter for eyeglass type specimen.

碩士
國立雲林科技大學
營建工程系
106
Pre-cutting is important for preventing random crack of concrete especially for slab. However, the strength of the concrete around the cutting reduces due to the damage caused by the cutting. The weakened edges of the cutting break easily in its early service life. Strengthening the edges is the only way to prevent the early breakage. To prevent using a real size concrete specimen, cylindrical concrete specimen is used in this study. Pre-cutting is applied, and the strength of the cut specimen is characterized. The decrease of the strength can be characterized by compared with that of the undamaged one. It is found that curing of the cut specimen may recover part of the strength.

Research Doctorate - Doctor of Philosophy (PhD)
The shearing behaviour of current and planned coal mine spoil dumps up to 400m in height is studied using large-specimen-high-stress direct shear tests performed on a range of materials that are commonly encountered in the Hunter and Bowen Basin coalfields. The motivation for this research is to address industry concerns that some current spoil dump heights (>350m) are surpassing the scale (≤120m) for which reliable design information exists, and because standard geotechnical laboratory equipment is not able to test representative spoil specimens at field-scale stresses. A Large Direct Shear Machine (LDSM) with specimen size 720mm x 720mm x 600mm, and a normal stress capacity of 4.6MPa was custom designed and constructed to generate the data presented in this thesis. Bulk samples comprising 120 x 200L drums of five spoil types from the Bowen Basin and Hunter Coalfields were collected and tested. Detailed geotechnical characterisation of these materials was carried out. LDSM data validation involved comparisons with direct shear strength tests carried out, using 100mm and 300mm Direct Shear Machines (DSMs), on a previously well-studied, uniformly-graded sand and one of the spoils. The LDSM testing program consisted of thirteen sand tests and fifty-two spoil tests. The DSM and LDSM results were critically analysed to provide insights into a range of prior uncertainties regarding the shear strength of coal mine spoil: (i) shear strength and behaviour for a wide range of spoils compressed under normal stresses between 500kPa- 4600kPa; (ii) the significance of moisture content for shear strength; (iii) the potential for mechanical (compression-induced) saturation to occur at high stress; (iv) the significance of scale effects for spoil dump design; (v) applicability of the previously widely-used BMA Coal (BMAC) shear strength framework to higher stress situations and widely varying spoil types. A fundamental distinction between “rock-like” and “soil-like” spoils is identified on the basis of simple, visual-tactile observations, and evaluation of the uncertainties described above is made with respect to these two types of spoils. The shearing behaviour for “rock-like” spoils prepared to unsaturated (air-dried) and “saturated” (inundated under load until no further deformation) moisture conditions can be described using trilinear or linear envelopes, depending on clast strength. Trilinear envelopes are appropriate for stronger “rock-like” spoils (clast strength ≥5MPa). Within each normal stress zone of the trilinear envelope there is a prevailing shearing mechanism that is an artefact of the structure of the spoil fabric and its response to the level of compression applied. Clast strength is found to determine the transition stresses that separate these trilinear zones. For weaker “rock-like” spoils (clast strength 1-5MPa), the trilinear lines converge to a sigmoidal curve to indicate more gradual changes in the shearing mechanism, and as such, a linear failure envelope is equally appropriate. A curvilinear failure envelope (power-law trendline) is found to be suitable for characterising the shearing behaviour for “soil-like” spoil. The shear strength of “rock-like” and “soil-like” spoils is found to be discernible by clast strength, particularly at medium-high normal stress (>1500kPa). For unsaturated conditions, the corresponding BMAC failure envelope can be notionally related to strength of the most abundant clasts within a specimen. Shear strength and horizontal strain at peak strength are found to be sensitive to moisture content for all spoil types. Lower shear strengths and smaller horizontal strains at peak strength are associated with the saturated moisture condition. The effect of moisture content on strength for a commonly-encountered “rock-like” BMAC-Category 2 spoil, was accounted for by a “moisture content correction factor”. This correction factor accounts for the rate of strength change with respect to water content, and it is normal stress dependent. For the Category 2 material studied, shear strength increases by (25σ’n) kPa for every percentage decrease in water content below saturation, where σ’n is the numerical value of the normal stress in MPa, under which the shear strength was measured in the saturated condition. Mechanical (compression-induced) saturation (Tarantino, 2009) is not achieved for any of the “rock-like” spoils that were air-dried and then compressed up to stresses representative of “very-high” dumps (500kPa- 4600kPa). For the “soil-like” spoil, a high degree of saturation (>90%) is achieved when compressed at very-high normal stress (4200kPa), and a further increase in overall (average) degree of saturation occurs when shear failure is then mobilised (approached 100%). This finding implies that, since shear deformations are concentrated in the shear zone, shearing of highly-loaded “soil-like” spoils could lead to localised mechanical saturation of the shear zone, whilst the rest of the spoil pile remains unsaturated. For “rock-like” spoils, shear strength (as defined by the secant friction angle) is found to be scale-dependent in terms of both specimen size and the magnitude of normal stress. These scale effects are significant for dump design of current-built and planned heights because they imply that the adoption of shear strength parameters measured from standard-sized DSMs (100mm and 300mm) will overestimate the shear strength for dumps with height-equivalent stresses ranging between 450kPa-4600kPa. The largest values of bulk unit weight are associated with the saturated moisture condition for all spoil types. The LDSM data suggests that linear depth-based equations are appropriate for estimating the bulk unit weight profile for spoils exposed to increasing depths of burial. This finding is important because it controverts the current approach by industry, whereby a constant value for bulk unit weight is adopted, irrespective of the dump height. For some materials tested, the shear strength measured by the LDSM was different from the BMAC framework strengths, both within the BMAC-applicable stress range, and when extrapolated to higher stress levels. This is fundamentally important because it identifies several non-compliant spoils for which correct application of the BMAC categorisation process will not provide reliable shear strength parameters. The research outcomes suggest that the BMAC framework can be used for reliable estimation of shear strength for spoil dumps of current and planned heights under the following conditions: (i) CAT2 or CAT3 materials which contain clasts with UCS ≥ 5MPa; (ii) the fine fraction of the spoil has a liquid limit ≤ 35%; (iii) Clasts have low slake and swell potentials, and low or moderate dispersion potential; and (iv) CAT1 strengths are only adopted within the BMAC-intended stress range (i.e. for dumps up to 120m in height).

Dreiaxiale Druckprüfungen können als Einstufenversuche, als Mehrstufenversuche oder als Versuche mit kontinuierlichen Bruchzuständen ausgeführt werden. Bei der Anwendung der Mehrstufentechnik ergeben sich insbesondere Fragestellungen hinsichtlich der richtigen Wahl des Umschaltpunktes und des optimalen Verlaufs des Spannungspfades zwischen den einzelnen Versuchsstufen. Fraglich beim Versuch mit kontinuierlichen Bruchzuständen bleibt, ob im Versuchsverlauf tatsächlich Spannungszustände erfasst werden, welche die Höchstfestigkeit des untersuchten Materials repräsentieren. Die Dissertation greift diese Fragestellungen auf, ermöglicht den Einstieg in die beschriebene Thematik und schafft die Voraussetzungen, die zur Lösung der aufgeführten Problemstellungen notwendig sind. Auf der Grundlage einer umfangreichen Datenbasis gesteinsmechanischer und petrophysikalischer Kennwerte wurde ein numerisches Modell entwickelt, welches das Spannungs-Verformungs-, Festigkeits- und Bruchverhalten eines Sandsteins im direkten Zug- und im einaxialen Druckversuch sowie in dreiaxialen Druckprüfungen zufriedenstellend wiedergibt. Das Festigkeitsverhalten des entwickelten Modells wurde in Mehrstufentests mit unterschiedlichen Spannungspfaden analysiert und mit den entsprechenden Laborbefunden verglichen.