Дисертації з теми "Reinforced Soil Slopes"

The application of geosynthetic reinforcements in civil/geotechnical engineering projects (retaining walls, foundations, pavements, dams, slopes, etc.) has gained much popularity during the past few decades due to several benefits, including cost-effectiveness, environmentally friendly and sustainability. A detailed literature review as presented in this thesis has indicated that when a slope is reinforced with the geosynthetic layer(s), it improves the overall stability of the slope with or without loaded footing on the slope crest. However, studies on the performance of strip footings embedded in the slopes are very limited, and, especially for the geosynthetic-reinforced slopes, there is no work when the slope is reinforced with geosynthetic layers with or without wraparound ends. Also, there is no available literature on the design charts for low-height slopes, without footing/surcharge loads on the crest, which are usually constructed for the landscape developments in many countries. Furthermore, the literature has no information on the stability charts for reinforced sand slopes carrying embedded strip footing subjected to loads. This thesis work is based on the laboratory experiments and numerical simulations. The laboratory model tests were conducted on a sand slope supporting an embedded strip footing (width B = 75 mm ) in a rigid test tank (internal dimensions of 1250 mm × 445 mm in plan and 800 mm in height). The slope was reinforced with a single and multilayer geotextile with and without wraparound ends as different test trials. The model tests were conducted to evaluate the effect of the footing embedment depth D, footing edge distance e , number of geotextile layers N , and wraparound end of geotextile on the behaviour of the embedded footing. The footing was subjected to incremental loads to observe the corresponding stabilised settlements until it failed. The slope angle and relative density of the sand were maintained at constant values, β = 35 and Dr = 70%, respectively, throughout the laboratory experiments. For the case of the single geotextile layer with no wraparound ends, the geotextile was installed at the depth ratio u / B = 0.5 below the base of the footing which was first fixed at the edge distance ratio e / B = 1, while the depth ratio (D/ B)was varied from 0 to 1.5. After that, the footing was maintained at a constant depth ratio D/ B = 1 while the edge distance ratio (e / B) was varied from 0 to 3. In the case of the multilayer geotextile (N = 2, 3) , with no wraparound ends and single layer geotextile with wraparound ends, the top geotextile layer was placed at the depth ratio u / H = 0.5 below the base of the footing and the subsequent layers were positioned at a constant vertical spacing(h) to footing width ratio h / B = 0.5 from the top layer. The footing edge distance ratio was kept constant as e / B = 1 while depth ratio (D/ B) was varied from 0 to 1. The numerical models for the laboratory experiments were developed using the Plaxis 2D, a finite element package. The numerical analysis utilised the Mohr-Coulomb criterion to model the slope soil, the geogrid option to model the geotextile layer(s), the gravity force to simulate the initial stress condition within the slope and prescribed footing load option to simulate the applied footing loads accompanied by iterative analysis until failure occurred. The developed numerical after validation has been used for a detailed parametric study in order develop design charts for the stability of slopes with embedded footing. Additionally, the stability (factor of safety) analysis of a geotextile-reinforced low-height sandy slope, without footing or surcharge loads, was carried out using the limit equilibrium method available in Slope/W package. The experimental results indicate that the bearing capacity of the footing increases with increasing D/ B , e / B and N . The benefits derived from reinforcing the slope with geotextile layers have been evaluated using a non-dimensional parameter, called the ultimate bearing capacity ratio BCRu , defined as the ratio of ultimate bearing capacity of the reinforced case to that of unreinforced case. In the case of the single layer geotextile without wraparound ends, the maximum value of BCRu ≈ 2.5 − 3 is observed for D/ B = 0 and e / B = 0 , while the minimum value of BCRu ≈1.5 has been obtained for D/ B =1and e / B = 3 . The BCRu for the multilayer geotextile with no wraparound ends improves with an increase in N but reduces with an increase in D/ B . The minimum BCRu , BCRu (min) ≈ 2 , is observed for N =1 and D/ B =1, while the maximum BCRu , BCRu (max) ≈ 6 is attained when the footing is placed at D/ B = 0 and N = 3 . The installation of the single layer geotextile with wraparound ends brings an additional improvement in the bearing capacity of the footing compared to the case of no wraparound ends. The results obtained from the numerical simulations, on the load-settlement analysis of the embedded footing, closely agree with the experimental data, particularly for low settlements. The results from the numerical slope analysis show that the factor of safety (F) of the unreinforced sandy slope with an embedded footing increases with an increase in the footing edge distance ratio (e / B) , footing depth ratio (D/ B) and soil relative density(Dr ) , but it decreases with an increase in the slope angle (β ) and applied pressure on the footing(q) . For the surface footing (D/ B = 0) , F increases to a critical value at e / B = 3 then remains constant for e / B > 3. Though in the experimental study, only Dr = 70% was used, in the numerical simulations, = 50% r D and = 90% r D have also been considered. The study shows that with respect to increase in Dr , F significantly improves until Dr = 70%; after that, further increase in reduces the rate of increase in F . For the low-height sandy slopes, placing a single geosynthetic reinforcement layer at the depth ratio u / H = 0.5 in the 40° slope results in a stable slope with a maximum factor of safety Fr (max) = 1.61 , but this depth is not appropriate to stabilize the 50° and 60° slopes. The study shows that three geosynthetic layers are generally not be required as the two-reinforcement layers are adequate to attain the minimum factor of safety as usually recommended in most standards on stability of slopes. This thesis has many graphical presentations, which can be used as the design charts by the practising engineers.

The main purpose of this thesis is on one hand to enhance the current predictive capabilities of the stability of soil slopes and on the other hand, to improve the design practice to stabilise natural slopes showing signs of distress and make the design of engineered slopes more affordable. To achieve the first objective an analytical method achieved by the upper bound theorem of limit analysis and the pseudo-static approach is derived for the assessment of the stability of slopes manifesting vertical cracks and subject to seismic action. The method is validated by numerical limit analyses and displacement-based finite-element analyses with strength reduction technique. Employing this method slope stability charts to assess the stability factor for fissured slopes subject to both horizontal and vertical accelerations for any combination of c, φ, and slope inclination are produced. To achieve the second objective limit analysis was employed to derive a semi-analytical method to extend the applicability of current method to design the slope reinforcement for frictional backfills to cohesive frictional backfills. Design charts providing the amount of reinforcement needed as a function of cohesion, tensile strength, angle of shearing resistance and slope inclination are obtained. From the results, it emerges that accounting for the presence of cohesion allows significant savings to be made, and that cracks are often significantly detrimental to slope stability so they cannot be overlooked in the design calculations of the reinforcement. Also, a new numerical method to determine multi-linear profiles of optimal shapes for reinforced slopes in frictional backfills is presented. The method is based on the limit analysis upper bound method together with genetic algorithms and provides an optimal profile for a prescribed average slope inclination, backfill strength properties and desired number of layers to be used. Several stability charts illustrating the savings on the required amount of reinforcement are provided for the benefit of designers.

Thesis (Ph. D.)--University of Missouri-Columbia, 2005.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (November 7, 2006) Vita. Includes bibliographical references.

Apesar das vantagens relacionadas ao uso de estruturas de contenção em solo reforçado, a maioria das obras em nosso país ainda é executada por soluções convencionais. A ausência de um conhecimento mais profundo sobre o real comportamento das estruturas em solo reforçado, principalmente em termos de deslocamentos, certamente impede uma utilização mais intensa desse tipo de obra no Brasil. Com isso, para contribuir para um melhor entendimento do desempenho de estruturas em solo reforçado, foram construídos oito protótipos de estrutura de contenção em solo reforçado com geotêxtil, com 4,0 m de altura cada. Todas as estruturas foram instrumentadas, principalmente visando os deslocamentos, para avaliar o comportamento de campo. Adicionalmente, foi realizada a análise, em longo prazo, de um talude íngreme com 15,3 m de altura, construído no estado americano de Idaho, em que foram realizadas leituras até cinco anos após o fim da construção. Esse trabalho apresenta os resultados de cada protótipo construído, juntamente com os resultados do talude íngreme em Idaho, tanto em curto, quanto em longo prazo. As análises desenvolvidas compreendem, além da avaliação dos resultados individuais de cada estrutura, uma análise paramétrica entre todos os protótipos, investigando entre outros fatores, o tipo de solo, tipo de geossintético e geometria interna das estruturas. Além disso, foi realizada uma abordagem especial sobre a análise em longo prazo do protótipo 7. Dentre as conclusões mais importantes obtidas nesta pesquisa, podem-se citar as grandes deformações de fluência registradas no protótipo 7, a tendência de formação de uma superfície potencial de ruptura linear para os protótipos construídos com solo granular e de espiral logarítmica para os protótipos construídos com solos coesivos, a importância da coesão no bom comportamento das estruturas e a redução das movimentações verticais das estruturas com o acréscimo do teor de areia na granulometria do solo
Despite the important advantages associated with the use of geotextiles as reinforcement, most retaining walls in Brazil still use more conventional. The lack of field monitoring data regarding the internal and face displacements of these structures has certainly prevented broader use of this reinforced soil technology. This study addresses several aspects related to the behavior of geotextile-reinforced soil structures, such as the deformability of reinforcement materials under the confinement of soil, and quantification of the actual failure mechanisms. To achieve these goals, eight 4.0 m high geotextile-reinforced soil retaining wall prototypes were built and instrumented in order to quantify their behavior under ambient atmospheric conditions. Granular and poorly draining backfills were used in this study. Innovative construction methods and instrumentation were developed specifically for this research program. A significant laboratory testing program was conducted to quantify the stress-strain properties of the soils and geosynthetics involved in the construction of the walls. As a reference, the behaviors of these prototype structures were compared with that of a long term analysis of a steep slope in Idaho, USA. This wall is 15.3 m high, with displacement measurements carried out until five years after the end of the construction. A parametric analysis was conducted for the prototypes, in order to investigate the effects of soil type, reinforcement type and internal geometry of the structures. Among the most important conclusions obtained in this research, it is the large creep strains observed in prototype 7, the tendency of a linear potential slip surface observed for the walls constructed with granular backfills, and a log spiral slip surface for the prototypes constructed with cohesive backfills, the importance of the apparent cohesion in the behavior of the structures, and the reduction of the vertical movements of the structures with the increase of the amount of sand in the grain size distribution of the soil

Experiences from recent earthquake records all over the world suggest that reinforced soil slopes provide better resistance to the seismic forces and possess higher yield accelerations compared to unreinforced slopes. While the design and practice of geosynthetic reinforced soil slopes has reached a level where the basics are well established and the procedures are standardized, the seismic designs still lack complete understanding of concepts and principles that alter the performance of the slope during seismic episodes. This thesis presents results from shaking table tests on geosynthetic reinforced soil slopes subjected to cyclic base shaking to understand the influence of various parameters that govern the performance of these slopes during seismic events. A uniaxial shaking table was used in the study and reduced scale model slopes were built in a laminar box and were subjected to sinusoidal base shaking, varying the frequency and acceleration of base shaking in different tests. Various series of shaking table tests were carried out to study the effects of shaking acceleration, frequency of shaking, fines content in soil, type and quantity of reinforcement and slope inclination on the response of model slopes in terms of acceleration amplifications and horizontal displacements. Acceleration of shaking was varied between 0.1g - 0.3g and frequency was varied between 1Hz - 16Hz in different tests. The frequency of testing was much below the natural frequency of the slopes. Two soils, a clayey sand with 44% fines content and a poorly graded sand with no fines were used to study the effect of fines content on the slope response. A geotextile and a biaxial geogrid were used to study the effect of type of reinforcement and reinforcement was placed in single, two and three layers in different tests to study the effect of quantity of reinforcement. Slope inclination was varied as 45, 60 and 75. While understanding the influence of reinforcement parameters, soil gradation and slope angle, tests were carried out at different accelerations and frequencies, to investigate the influence of these parameters under different ground shaking conditions. Results from shaking table tests revealed that among all the parameters studied, soil gradation has greater influence on the seismic response of the unreinforced as well as reinforced soil slopes. Slopes made of sand without fines showed highest acceleration amplifications and displacements. While the slopes made of clayey sand showed higher displacements at higher frequency levels, exhibiting progressive failure, slopes built with cohesionless sand showed higher seismic response at low-frequency high-amplitude motions, exhibiting sudden flowslide type of failure. Inclusion of reinforcement did not have significant influence on the acceleration amplifications, but the displacements were drastically reduced by reinforcing the slopes, the beneficial effect more pronounced in case of slopes made of sand without fines. Among the two types of geosynthetics used in the study, both were equally effective in reducing the deformations, the different being not significant. Results showed that reinforcement saturation occurred in the models at 2 layers, beyond which further increase in reinforcement did not influence the response of the slope. The catastrophic flowslide occurred in unreinforced slope at low frequency shaking in case of sand without fines is completely arrested by reinforcing the slope with three layers of geotextile and the deformations were reduced by about 92% for that case, indicating the importance of soil reinforcement in mitigating seismic hazards. Increase in slope angle resulted in increase in deformations but the acceleration amplifications remained unaffected. Steeper slopes benefitted more by the inclusion of reinforcing layers. Displacements computed using Newmark’s sliding block method agreed reasonably well with the experimental measurements.

博士
國立臺灣科技大學
營建工程系
105
Assessment of rainfall-induced slope failures is important in reducing damage to infrastructures as well as guarantee safety of people living close to hazardous areas. This study presents case studies and numerical investigations of three unstable unsaturated slopes. The studied slopes are two natural slopes (Slopes T16 and T2) along the Taipei Maokong Gondola (Cable Transit) system and one unstable 26 m high multi-tier geosynthetic-reinforced soil (GRS) slope with marginal backfill in Taichung County, Taiwan. Slope T16 collapsed during torrential rainfall during Typhoon Jangmi in September 2008, and another nearby slope (T2) developed excessive deformation under consecutive wetting and drying cycles. The GRS slope first experienced excessive deformation after seasons of typhoon and heavy rainfall from 2010-2012. The measured settlement and horizontal deflection at slope crest were 140 and 80 cm respectively from June to December 2012. Although an immediate remediation had been conducted for the slope excessive deformation, the slope final collapse was caused by two sequential typhoon events with total accumulated rainfall over 600 mm in August 2013. Recorded rainfall, measured soil parameters, site geology, and slope geometry were used in coupled hydro-mechanical finite element analyses to investigate the failure and deformation mechanisms of these three slopes. The numerical results demonstrated that the coupled hydro-mechanical analysis based on the framework of unsaturated soil mechanics satisfactorily predicted deformation characteristics and failure timing of unsaturated soil slopes during rainfall. The slopes’ failure was attributed to a decrease in soil shear strength when the matric suction gradually decreased as rainfall progressed. Examination of the relationships between the slope factor of safety and the corresponding hydrological data (i.e., rainfall and soil PWP) revealed that coupled hydro-mechanical analysis combined with detailed site investigation could be performed to establish factor of safety (FS) versus accumulated rainfall relationship for slopes to act as reference in disaster mitigation (forecasting) strategies. Findings of this study implies that continuous assessment of slope stability during wetting and drying cycles is significant in order to circumvent catastrophic slope failures. In addition, it is crucial to pay special attention to unstable rock or soil layers (such as weathered sandstone interbedded with shale layers) prior to design or construction of the GRS slope as well as to drainage installations to ensure that they remain intact and efficient if slope deforms. Lessons learned from this study are discussed, and remedial measures to improve the slope stability are proposed and evaluated. The significance of this study is to provide means for assessing and predicting slope stability (deformation and failure timing) using recorded rainfall, measured soil parameters, site geology, and slope geometry in order to mitigate the catastrophic damage and failure caused by natural and reinforced slopes failure during heavy rainfall.

碩士
淡江大學
土木工程學系
92
Soil nailing has been used successfully in temporary and permanent geotechnical applications in recent years. Soil nail not only improves the stability of slope greatly but also has advantages with economic benefit and fast construction. Nailed soil improves shear strength of soil body through development of tension in the nail when diversity of strains occurs between soil mass and the nail. Because the applications of nailed soil in permanent structures have been increased rapidly, behavior of nailed slope under seismic loading becomes an important issue and attracts attention. This study revises the assumption of a single rigid block sliding along the failure plane by two-blocks. Results of the present study are compared with those obtained from shaking table tests and conventional Newmark method. Analytical results reveal that prediction of block displacement obtained from the present study and those of shaking table test have good agreement when the nailed slope subjected to mild or moderate seismic loading. However, as nailed slope subjected to strong seismic loading, the present study underestimates displacement of sliding block as compared to shacking table test.

碩士
國立宜蘭大學
土木工程學系碩士班
103
Taiwan is located in the circum-Pacific seismic belt, thus the earthquakes occur frequently in this area and destructive earthquakes occasionally take place. With the booming development of Taiwan's economy, civil engineering projects, such as high-rise structures, bridges, and engineering facilities, need to be considered for earthquake effects. The disaster of earthquake therefore became design considerations. However, during the 921 Chi-Chi Earthquake, many buildings and structures in Taiwan, including a few geosynthetic reinforced soil retaining structures (GRSRS), have been damaged. In order to understand the performance of the seismic behavior of the GRSRS influenced by the earthquake, this study uses actual record seismic data from an earthquake monitoring system to understand the dynamic behavior of GRSRS in FoGuang University and follows by computer simulation used the finite element program PLAXIS dynamic analysis. In this study, we use the finite element program PLAXIS to analyze actual record seismic data from earthquake monitoring system. The seismic parameters of dynamic simulation use the accurate seismic data directly from seismic monitoring system. The results of the real seismic data and the PLAXIS finite element program analysis are compared. The agreeable comparison results give us the confidence to explore the variation relationship of top maximum acceleration and bottom maximum acceleration. The dynamic simulation results from the numerical simulation analysis of geosynthetic reinforced slope are quite reliable. Finally, we explore the distribution of tensile axis forces for the reinforcement material during the maximum acceleration. The results of seismic analysis show that the tensile axis forces occur obvious diversification located the junction of two stairs. Besides, it is also found that the distribution of tensile axis forces have the tendency of outward movement situation. Hopefully, it can be take into account for designing the geosynthetic reinforced soil retaining structures in earthquake condition, as a result we can have the ability to consider the extra tensile axis force position on the geosynthetic reinforcements.

碩士
國立臺灣科技大學
營建工程系
90
For different sites condition, the bentonite were added into I-Lan sands to obtain different friction angles. The dynamic parameters were also produced with performing a series of dynamic pullout tests. A numerical program by Lee and Hsu (2001), named NERVES, was then used to examine the dynamic behavior of Mechanical Stabilized Earth Wall and Reinforced Soil Slopes. According to the result of the numerical analysis, the reinforcement length suggested by this study were compared with the one suggested by FHWA depending upon the lateral deformation of wall. The factor of safety was also reviewed with STABL to check the rationality of the recommendation of this study. To present the real-time dynamic deformation of Mechanical Stabilized Earth Wall and Reinforced Soil Slopes, we employed the “movie” function in FLAC into the NERVES programs. Finally, a design chart regarding the reinforcement length under seismic conditions was recommended for the design practice.

碩士
國立臺灣科技大學
營建工程系
106
A series of numerical analyses based on the framework of transient seepage and unsaturated soil mechanics was performed to investigate the impact of rainfall on the design of geosynthetic-reinforced soil (GRS) slopes. To consider the regional hydrology, the antecedent and major rainfall were input using the rainfall intensity-duration-frequency (I-D-F) curves from Taipei as an example. The numerical simulations consider backfill fine contents (i.e., 0, 6, 19, 30 and 60%), soil initial matric suctions (i.e., as compacted, after plum rain, and after typhoon), and major rainfall conditions (i.e., 7-day extremely heavy rainfall and 1-day torrential rainfall). The hydraulic responses and stability of the GRS slopes including porewater pressure development, factor of safety (FS), and required reinforcement strength (Treq) are evaluated and compared. The numerical results reveal that under the combined effects of plume rainfall and 7-day extremely heavy rainfall the GRS slopes with high backfill fine contents (≥ 19%) could develop high porewater pressure which consequently leads to the slope failure. To satisfy FS ≥ 1.1 under the prescribed rainfall conditions, the Treq values in the GRS slopes with backfill fine contents of 30% and 60% should be increased by 2.65 and 2.06 times, respectively, of the original design values in which the effect of rainfall is not included: the corresponding FS values are 1.48 and 1.64, respectively, when the increased Treq values are used in the original design. The rainfall thresholds for the GRS slopes with various backfill fine contents and antecedent rainfall conditions were established. The calculated rainfall thresholds as well as those determined from failure cases of GRS structures were compared with the regional rainfall I-D-F curves to facilitate the assessment of selecting backfill type for the GRS structure in the region of interest.

碩士
國立臺灣科技大學
營建工程系
104
This study presents a numerical study to investigate the hydraulic response and stability of GRS slopes subject to rainfalls, considering the combined effect of backfill (i.e., sand silt, and clay), reinforcement types (i.e., geogrid or nonwoven geotextile) and rainfall intensity (350 and 800 mm/day). The backfills were modeled using three soil-water characteristic curves (SWCCs) representing the general suction range associated with sand, silt and clay. The numerical models were first validated for their accuracy and suitability for stability analyses considering the effect of matric suction on soil shear strength using the experimental results of an unsaturated reinforced embankment. Thereafter, a series of numerical simulations of unsaturated slopes with various backfill–reinforcement systems subject to rainfall infiltration were performed. The effect of sand cushion thickness (0 - 35 cm) on improving the stability of reinforced slopes with marginal backfills was also assessed. The numerical results reveal the loss of matric suction and development of capillary barrier effect within clay backfills could have negative impacts on both the global and local stabilities of reinforced-clay slopes. The contribution of matric suction in enhancing slope stability is high initially for reinforced clay slopes; however, the global stability of the reinforced clay slope decreases substantially due to the loss of matric suction as the rainfall infiltration proceeds. The local instability of geotextile-reinforced slope with clay backfill occurred due to the capillary barrier effect at the geotextile-clay interface. Both the global and local factors of safety (FS) of reinforced sand slope shows little influence by the loss of matric suction induced by the rainfall infiltration and by the geosynthetic type (with and without drainage function). The required reinforcement tensile strengths for silt-geogrid and clay geogrid system to maintain FS = 1.3 are approximately 3 and 4 times respectively larger than that for sand-geogrid system. Numerical results also indicated that the inclusion of sand cushions can effectively enhance the slope stability and the increase in the thickness of the sand layer leads to less decrease in both the global and local factors of safety. Even with a thin layer of sand cushion inclusion (5 cm), the stabilities of reinforced clay slopes are significantly improved. The contribution of sand cushions to the stability improvement resulted from their strength and drainage functions; in particular, the strength function is more effective in the global stability improvement, whereas the drainage function become more dominant in the local stability improvement. Findings of this study provide improved methodologies for the analysis and design of reinforced soil structures constructed with marginal soils and provide a suitable guidance of selecting an appropriate backfill-reinforcement-drainage system.

Yes
This paper provides results of a comprehensive investigation into the use of waste carpet fibres for reinforcement of clay soil slopes. The interaction between laboratory scale model slopes made of fibre reinforced clay soil and surface strip footing load was examined. Results for the influence of two variables namely fibre content and distance between the footing edge and the crest of the slope are presented and discussed. Particle Image Velocimetry (PIV) technique was employed to study the deformation of the slope under the surface loading. The front side of the tank was made of a thick Perspex glass to facilitate taking accurate images during the loading stage. To study the stress induced in the slope under footing pressure, excess pore-water pressure and total stress increase were measured at predetermined locations within the slope. The results showed that fibre reinforcement increased the bearing resistance of the model slope significantly. For instance, inclusion of 5% waste carpet fibre increased the bearing pressure by 145% at 10% settlement ratio.
The post-print of this article will be released for public view when the version of record has been published by ASCE.

碩士
國立臺灣大學
土木工程學研究所
107
The mudstones in southwestern Taiwan belong to the ancient pavilion of the western Laoshan belt in geology. The formation time of mudstone formation was between the Pliocene and the Pleistocene. The mechanical properties of mudstone have some special characteristic. When mudstones transfer the water content form dry state into wet state, the shear strength would decrease significantly. This is related to the diagenetic bond dissolution chemical reaction of mudstone. When the bond is dissolved, the inter-mineral beam-forming ability is reduced. Inflated, the unsaturated soil mechanics will be used to simulate the swelling behavior of mudstone. In addition, the climatic characteristics of southwestern Taiwan experienced long-term dryness during the dry season and high intensity rainfall during the flood season. In this study, the accumulated rainfall reached 3,000 mm in June to August. The surface soil of mudstone slope water cracked due to reaching the shrinkage limit. The crack would develop because of the high intensity rainfall. In the end, the slope would develop the erosion pipe when the crack pass through the crust and the toe of slope. The erosion pipe cannot provide the shear strength for stability. Therefore, as the erosion pipes develops continuously, the shear strength of the slope will be weakened to less than or equal to the driving shear stress and cause failure. Therefore, the top priority of mudstone slope protection is the prevention of rainfall infiltration. The most traditional method is shotcreting, but with the rising of environmental protection consciousness, it is rarely used nowadays. Therefore, the way to improve the mudstone slope protection is hanged-net with spraying seed. However, the characteristics of mudstone slope when undergoing high intensity rainfall is surface erosion, that make the method invalid to protecting. This paper will discuss whether the use of mechanically stabilized earth slope protection method can effectively protect the mudstone slope. Because the self-weight of the MSES can provide the confining pressure required to resist the swelling of mudstone. When design the MSES, the prevention of backfill material loss must be fully considered. The method of installation the soil bag and the geotextile returned-facing will be used to effectively prevent the erosion of mudstone slope surface. This paper will focus on whether the drainage system function will influence on the stability of the slope. The issue of surface erosion prevention will be discussed, concentrating on the difference of fully protecting MSES and the partially protecting MSES. In the end, to do the numerical analysis, the fully coupled analysis of seepage and stress and the strength reduction analysis would be executed.

碩士
國立宜蘭大學
土木工程學系碩士班
100
In this research, the most popular employed geotechnical computer programs in the field of domestic geotechnical engineering, namely SLOPE/W stability program, SIGMA/W finite element program, STABL Slope stability program, and PLAXIS finite element program, are used to simulate the geosynthetic reinforced soil retaining structure built in Fo-Guang University. First, this study introduces the theoretical analysis of the program SLOPE/W and the method of calculation of the reinforcements. Even though the applications of the STABL limit equilibrium theory and PLAXIS the finite element method theory have been discussed in the past, this study also gives a brief description for them. After that, the SLOPE/W program, the STABL program, and PLAXIS program, are used to explore the mechanic behavior of the geosynthetic reinforced soil retaining structure. Finally, interactive application of the SIGMA/W program SLOPE/W program is presented. Using the SLOPE/W program for geosynthetic reinforced soil retaining structure analysis, each layer of reinforcement is considered by the identical tensile stress on the sliding surface on the same slice. In addition, when reinforcement committed pull-out failure, it suffered different tensile stresses. While the reinforcement committed break-off failure, the tensile stresses are the same. The unique part is the neat consideration for making the different required length of reinforcement. Under the circumstance of the failure surface not cutting through the reinforcement, it does not provide any resistance stress. Comparing the analysis results of the SLOPE/W and STABL, factor of safety obtained by SLOPE/W is generally small than that by STABL. The main reason is that the SLOPE/W analysis consider the reinforcement with friction reduction. As a result, the SLOPE/W computer program can predict the factor of safety of slope stability more rigorous and conservative than the STABL computer program. Comparing the predicted results from the PLAXIS program and SLOPE/W program, it is found that the factor of safety predicted by PLAXIS program analysis considers the soil stress-strain relationship but not so by the SLOPE/W program. Thus, the analysis results from two programs do show some slight difference. The interactive application of SIGMA/W program and SLOPE/W program provides a higher value of safety factor for the slope stability analysis compared to that obtained directly from the SLOPE/W program. It can be proved by the fact that the limit equilibrium method is more conservative than the finite element method for the stability analysis.

碩士
雲林科技大學
營建工程系碩士班
98
In this study, a series of model test on geogrid-reinforced soil (GRS) retaining wall with wrapped-around facing and with granular backfill was performed. The mean particle sizes of the used backfills, namely sand and gravel, were respectively equal to 0.4 mm and 5.23 mm. Three types of geogrids having different nomial strengths were independently adopted for each wall with the granular backfill. The dimensions of the model wall with were 250 cm (width) × 80 cm (depth) × 112 cm (height). A footing of 30 cm wide was located on the surface of backfill to resist the applied vertical load during model test. The lateral deformation of facing, the vertical displacement of footing and the tensile strain of the first layer of geogrid were measured during the test. Besides, a photogrammetric analysis procedure was used to distinguish the deformed pattern of marked gird on the membrane and to define the thickness of shear zone. The above results indicate that the larger particle size of backfill the thicker thickness of the shear zone. The bearing capacity became higher in the model wall with larger particle size and higher stiffness of geogrid. The tensile strain of greogrid at the vircinity of shear zone is the largest. The mobilized strain profile was strongly affected by the stiffness of geogrid and the particle size of backfill. A back analysis of stabililty analysis using the measured tensile force was performed for each model wall. The analysis results showed that using peak strength for gravel case can induce a higher safety factor than that of sand case. A similar result was found in the analysis using residual strength but with a less extent. The analysed location of shear zone coincided with the measured deeper shear zone in the model wall.

碩士
國立臺灣科技大學
營建工程系
105
This paper presents a failure case investigation of a multi-tier geosynthetic-reinforced soil slope with marginal backfill subjects to rainfall infiltration. The considered slope is 26 m high, 4 tier geogrid-reinforced structure constructed for traffic demands in mountain area in Taichung, Taiwan. Contrary to the backfill recommendations in design guidelines, low permeability sandy silt (CL-ML) with over 60% of fines was used as backfill in the reinforced zone. The shear strength of this kind of soil would decrease according to the increasing pore water pressure triggered by the low permeability. This GRS structure first experienced excessive deformation after seasons of typhoon and heavy rainfall from 2010-2012, and the measured settlement at wall crest were 140 cm from June to December 2012. Although an immediate remediation had been conducted for the excessive deformation, the slope finally collapsed caused by two sequential typhoon events in August 2013. A series of soil mechanic laboratory test will be used in this study, including mineral components, physical and engineering properties of the soil. However, not only those properties mentioned above will be done, but also unsaturated one, such like pressure plate test to determine soil-water characteristic curve (SWCC). After soil laboratory tests have been done, a numerical finite element study using hydro-mechanical coupling analysis will be used to investigate the failure mechanisms of this GRS structure. According to the analysis, this study will propose design and construction implication for GRS structures with marginal backfill subject to heavy rainfall.

碩士
國立中興大學
水土保持學系所
95
Due to situating at the circum-Pacific belt, earthquake is very active and frequent in Taiwan. The Chi-Chi earthquake (921 Quake) possesses a Richarter Magnitude of 7.3 triggered at the central part of Taiwan on 21, September, 1999 and caused large scale and extensive slope failure at the mountain region. As a consequence, the earthquake induced slope failure becomes one of the most critical issues in the relevant research of natural disaster prevention in Taiwan. Besides, because of the increasing reclamation of slope land the slope stabilization also comes to be an important work in the engineering construction. This study investigates the reinforced mechanism of soil nail in steep slope and the resistance capability of slope reinforced by soil nail with various installation configurations during the earthquake. To verify the validity of numerical analysis, a numerical modeling was performed to simulate the lateral displacement of a soil nail reinforced model slope subjected to the vibration loading on a shaking table. The calculated lateral displacement profiles of the slope surface at each vibration step were then compared with those from the measurements. The comparisons indicate that the calculations are approximately two times larger than the measurements. The deviations between the calculation and measurement can be resulted from the inherent limitation of the function of numerical tool in dynamic aspect such as soil constitutive model or the incapability of simulation processes which unable to reflect the actual configuration of shaking table test such as boundary conditions. Nevertheless, the predicted tendency of lateral displacement under vibration loading is still coincident with the measurement to a certain extent. Subsequently, a series of two-dimensional finite element dynamic analyses were performed to simulate the dynamic behaviors of the fictitious slope reinforced by soil nail and subjected to earthquake loadings. In the analysis, the earthquake loadings were applied by the input of various acceleration time series. To investigate the influence of various installation parameters of soil nail on the resistance behavior of reinforced slope subjected to earthquake loading, the length, the inclination angle and the spacing of soil nail were varied in the calculation. In addition, the finite element reduction method (or FEM method) and the limit equilibrium sliced method (or LEM method) were also adopted to analyze the static stability of the reinforced slope. As to the length of soil nail L, for the steep slope with slope height H=15 m and slope angle=80∘,the maximum horizontal displacement ratio induced from earthquake loading can be apparently reduced for 15% when the L value is increased from 7 m (0.47H) to 12 m (0.8H). However, for the milder and lower slopes with H= 5 m, 10 m and the influence of length variation of soil nail on the horizontal displacement is insignificant. Regarding the inclination angle of soil nail for the steep slope with slope height H=15 m and slope angle=80∘,the magnitude of value merely displays slight influence on the stability of reinforced slope as 15∘. This can be due to the fact that the soil nail can penetrate orthogonally through the potential sliding surface of the slope and provide an optimum resistance against the sliding of the slope. On the contrary, as 15∘ the maximum horizontal displacement ratio induced from earthquake is increasing instead of decreasing with the ascending value. This can be due to the intersection angle between soil nail and potential sliding surface has greatly deviated from 90∘ and is unable to give the best resistance to potential sliding surface during earthquake loading. Concerning the ratio of inclination angle of soil nail to slope angle (α/β), for the slope with slope height H=10 m and slope angle β=60∘, the stability of reinforced slope increasing with the increase of α angle remains. Meanwhile for the maximumαvalue of 20∘used in the analysis, one can obtain the corresponding value of the ratio of inclination angle (α/β)=0.33. On the other hand, for the steep slope with slope height H=15 m and slope angleβ=80∘, the maximum horizontal displacement ratio (δhmax/H) induced from earthquake loading is greatly increased once the angleα>15∘, namely, the ratio of (α/β)>0.19. It is therefore suggested that the ratio of inclination angle of soil nail (α/β) value should be maintained at the range of 0 ~ 0.19 for the soil nail installed at the relatively steep slope. Considering the spacing of soil nail Sv, in general the reduction of maximum horizontal displacement ratio (δhmax /H) induced from earthquake loading for the case of Sv descending from 2 m to 1 m (1 m reduction) is approximately twice of that from 1.5 m to 1 m (0.5 m reduction). This implies that the stability of reinforced slope is significantly influenced by the installation spacing of soil nail. About the earthquake intensity, the maximum horizontal displacement ratios (δhmax/H) generated by the intensities of level-5 (acceleration time series E5) and level-6 (acceleration time series E6) are approximately equivalent. However, the (δhmax/H) value generated by the intensities of level-7 is nearly 1.5 and 1.75 times of those generated by the intensities level-5 and level-6 respectively. For the forces of soil nail, the analyses indicate that the mobilization of axial tensile force in soil nail during earthquake is much more predominant than those of shear force and bending moment. Base on the analysis result, it can be concluded that the stabilization force of reinforced slope is mainly obtained from the mobilization of axial tensile force of soil nail. Consequently, in the resistance design of soil nail to earthquake loading, the tensile strength of soil nail should be emphasized to achieve a most efficient design of reinforcement in earth slope. Keywords: soil nail, finite element dynamic analysis, limit equilibrium method, maximum horizontal displacement ratio, axial tensile force

碩士
國立臺灣科技大學
營建工程系
105
The research presents a failure case study on a geosynthetic-reinforced soil wall with marginal backfill subject to rainfall infiltration. The considered wall is a 26 m high, 4 tier geogrid-reinforced structures constructed for traffic demands in mountain area in Taichung, Taiwan. Contrary to the backfill recommendations in design guidelines, low plasticity silty clay (CL) with over 60% of fines was used as backfill in the reinforced zone. This could have been as a result of attempting to reduce cost and environmental impact associated with transportation of recommended backfills to construction site and disposal of excavated in-situ soils. The backfill material is a locally available residual soil from weathered mudstone and shale and the soil shear strength are found can be significantly reduced when soil become wet. The GRS slope first experienced excessive deformation after seasons of typhoon and heavy rainfall from 2010-2012. The measured settlement and horizontal deflection at wall crest were 140 and 80 cm from June to December 2012. Although an immediate remediation had been conducted for the wall excessive deformation, the wall finally collapsed caused by two sequential typhoon events with total accumulated rainfall over 600 mm in August 2013. A series of numerical and physical investigation were performed to examine the failure mechanism and causes contributing to the failure. Using recorded rainfall, measured shear strength parameters and site geology, transient slope stability analyses were conducted to reconstruct the failure event. Lessons learned from this case history are discussed.