Academic literature on the topic 'Swell-shrink/consolidation'

Current research main aim is to study the effect of adding polypropylene fiber (PPF) on the behavior of expansive soil to reduce the swelling as percentage (0.5, 1 and 2%) of the weight of dry soil. Expansive soil used in this research was prepared artificially by mixing Ca-based bentonite from geological survey and mining company with sandy soil brought from Karbala city as percentage 80% bentonite to 20% sand of dry weight. Multiple laboratory tests have been carried are (Unconfined Compression Test, One-Dimensional Consolidation Test, Swelling Test, Sieve Analysis and Cycle Swell Shrink Test). A conventional odometer cell was modified to allow the study of swell- shrink cycle test to be carried out under controlled temperatures and surcharge pressure. The results showed that the increase in percentage of (PPF) led to decrease the swelling and to increase the unconfined compression strength. The wetting and drying results of (PPF) showed that with continuous cycles the effect of (PPF) keeps on reducing the swelling and the 2% of (PPF) produces less ratio of swell - shrink, which has obtained higher than 57 % in the improvement factor of swell and shrink.

Expansive soil has the characteristics of strong swell-shrink, developing fissures and over consolidation. This kind of soil soaking into water, which leads to its volume expansion, strength reduction but compressibility decreasing make its engineering geology properties worsen. The distribution of expansive soil in Hefei is very wide, there are more pit accidents in Hefei district in recent years. Causing the accident is mainly due to the ignorance of the characteristics and damage of expansive soil. According to many years engaged in related working experience, this paper analyses two common types of damage in foundation pit accidents. Finally, throughout the analysis of several accidents, corresponding prevention measures and construction improvement scheme have been put forward.

The mainly white-yellow marly soils studied present medium degree of consolidation and induration. The predominant grain size of the non - carbonate constituents is that of silt varying from 34 to 64%. According to the textural classification of soils of the SSDS the samples are mainly silty-clay loams with moisture capacity 30-40%. In the untreated samples in decreasing abundance the following minerals predominate: calcite (31-59%), clay minerals (20-34%) and quartz (12-20%). In the clay fraction (<2μπι) in decreasing abundance the following clay minerals (in discrete and interstratified phases) predominate: illite, smectite and vermiculite. Chlorite and kaolinite are missing. Mineralogically the marly soils are immature, because of the extended presence of Fe-Mg minerals (i.e. amphiboles, pyroxenes and clay minerals). According to the Unified Soil Classification System of the ASTM the studied marly soils mainly belong to the groups MH and CH (inorganic silts and inorganic clays respectively with high plasticity and liquid limit >50%), as well as to the group CL (inorganic clays with low plasticity and liquid limit <50%). The degree of consolidation and induration, as well as of compaction of these soils is medium. They contain significant amounts of discrete or interstratified smectite and mainly present high to very high swelling potential and activity between 0.5 and 2.0. It is concluded that specific precautions must be taken into account, when it is unavoidable the foundation of various constructions on these marly soils, because they swell and shrink extensively.

Abstract. Evaluating the possibility of leakage through low permeability geological strata is critically important for sustainable water supplies, the extraction of fuels from strata such as coal beds, and the confinement of waste within the earth. The current work demonstrates that relatively rapid and reliable hydraulic conductivity (K) measurement of aquitard cores using accelerated gravity can inform and constrain larger scale assessments of hydraulic connectivity. Steady state fluid velocity through a low K porous sample is linearly related to accelerated gravity (g-level) in a centrifuge permeameter (CP) unless consolidation or geochemical reactions occur. The CP module was custom designed to fit a standard 2 m diameter geotechnical centrifuge (550 g maximum) with a capacity for sample dimensions of 30 to 100 mm diameter and 30 to 200 mm in length, and a maximum total stress of ~2 MPa at the base of the core. Formation fluids were used as influent to limit any shrink–swell phenomena which may alter the permeability. Vertical hydraulic conductivity (Kv) results from CP testing of cores from three sites within the same regional clayey silt formation varied (10−7 to 10−9 m s−1, n = 14). Results at one of these sites (1.1 × 10−10 to 3.5 × 10−9 m s−1, n = 5) that were obtained in < 24 h were similar to in situ Kv values (3 × 10−9 m s−1) from pore pressure responses over several weeks within a 30 m clayey sequence. Core scale and in situ Kv results were compared with vertical connectivity within a regional flow model, and considered in the context of heterogeneity and preferential flow paths at site and formation scale. More reliable assessments of leakage and solute transport though aquitards over multi-decadal timescales can be achieved by accelerated core testing together with advanced geostatistical and numerical methods.

Expansive/swell-shrink soils exhibit high plasticity and low strength, which lead to settlement and instability of lightly loaded structures. These problematic soils contain various swelling clay minerals that are unsuitable for engineering requirements. In an attempt to counter the treacherous damage of such soils in modern geotechnical engineering, efforts are underway to utilize environmentally friendly and sustainable waste materials as stabilizers. This study evaluates the strength and consolidation characteristics of expansive soils treated with marble dust (MD) and rice husk ash (RHA) through a multitude of laboratory tests, including consistency limits, compaction, uniaxial compression strength (UCS), and consolidation tests. By using X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, the effect of curing on UCS after 3, 7, 14, 28, 56, and 112 days was studied from the standpoint of microstructural changes. Also, the long-term strength development of treated soils was analyzed in terms of the interactive response of impacting factors with the assistance of a series of ANN-based sensitivity analyses. It is found from the results that the addition of MD and RHA lowered down the water holding capacity, thereby causing a reduction in soil plasticity (by 21% for MD and 14.5% for RHA) and optimum water content (by 2% for MD and increased by 6% for RHA) along with an increase in the UCS (for 8% MD from 97 kPa to 471 kPa and for 10% RHA from 211 kPa to 665 kPa, after 3 days and 112 days of curing, respectively). Moreover, from the oedometer test results, m v initially increased up to 6% dosage and then dropped with further increase in the preconsolidation pressure. Furthermore, the compression index dropped with an increase in the preconsolidation pressure and addition of MD/RHA, while the coefficient of permeability (k) of RHA stabilized soil was higher than that of MD-treated samples for almost all dosage levels. The formation of the fibrous cementitious compounds (C-S-H; C-A-H) increased at optimum additive dosage after 7 days and at higher curing periods. Hence, the use of 10% RHA and 12% MD as replacement of the expansive soil is recommended for higher efficacy. This research would be helpful in reducing the impacts created by the disposal of both expansive soil and industrial and agricultural waste materials.

Time domain reflectometry (TDR) measures the apparent relative dielectric permittivity (ARDP) of a soil and is commonly used to determine the volumetric water content (VWC) of the soil. ARDP is affected by several factors in addition to water content, such as the soil’s electrical conductivity, temperature, and density. These relationships vary with soil type and are very soil-dependent, and despite previous research, they are still not fully understood. A multivariate statistical approach (principal component analysis, PCA) is used to describe a range of soils from two separate sites in the UK (clay and silty sand – sandy silt). The advantage of a PCA is that it considers several variables at a time, giving an immediate picture of their underlying relationships. It was found that for the studied soils, ARDP was positively correlated with VWC and bulk electrical conductivity, but did not show any dependence on some other geotechnical parameters. TDR has recently been used in geotechnical engineering for measuring the gravimetric water content (GWC) and dry density. However, the current approaches require a custom-made TDR probe and an extensive site specific empirical laboratory calibration. To extend the potential use of TDR in the geotechnical industry, three relatively simple methods are proposed to estimate the GWC from VWC (derived from the measured ARDP values) and dry density depending on the amount of information known about the soil. Examples of possible applications of these methods include continuous monitoring of consolidation adjacent to a structure, the effect of seasonal weather and climate change on ageing earthwork assets, and the shrink–swell potential adjacent to trees. All three methods performed well, with between 83% and 98% of the data lying within a ±5% GWC envelope, with the data for clay soils performing better than those for silty sands – sandy silts. This is partly due to the fact that the applied relationship converting ARDP to VWC performs better for clays than silty sands – sandy silts, as well as less variation of the estimated bulk density that is needed to derive the dry density.

Abstract. The ploughing of soils in autumn drastically loosens the soil structure and, at the same time, reduces its stability against external stresses. A fragmentation of these artificially produced soil clods during wintertime is often observed in areas with air temperatures fluctuating around the freezing point. From the pore perspective, it is still unclear (i) under which conditions frost action has a measurable effect on soil structure, (ii) what the impact on soil hydraulic properties is, and (iii) how many freeze–thaw cycles (FTCs) are necessary to induce soil structure changes. The aim of this study was to analyse the cumulative effects of multiple FTC on soil structure and soil hydraulic properties for two different textures and two different initial structures. A silt clay with a substantial amount of swelling clay minerals and a silty loam with fewer swell/shrink dynamics were either kept intact in undisturbed soil cores taken from the topsoil from a grassland or repacked with soil clods taken from a ploughed field nearby. FTCs were simulated under controlled conditions and changes in pore structure ≥ 48 µm were regularly recorded using X-ray µCT. After 19 FTCs, the impact on hydraulic properties were measured, and the resolution of structural characteristics were enhanced towards narrow macropores with subsamples scanned at 10 µm. The impact of FTC on soil structure was dependent on the initial structure, soil texture, and the number of FTCs. Frost action induced a consolidation of repacked soil clods, resulting in a systematic reduction in pore sizes and macropore connectivity. In contrast, the macropore systems of the undisturbed soils were only slightly affected. Independent of the initial structure, a fragmentation of soil clods and macro-aggregates larger than 0.8 to 1.2 mm increased the connectivity of pores smaller than 0.5 to 0.8 mm. The fragmentation increased the unsaturated hydraulic conductivity of all treatments by a factor of 3 in by a factor of 3 in a matrix potential range of −100 to −350 hPa, while water retention was only slightly affected for the silt clay soil. Already 2 to 5 FTCs enforced a well-connected pore system of narrow macropores in all treatments, but it was steadily improved by further FTCs. The implications of fewer FTCs during milder winters caused by global warming are twofold. In ploughed soils, the beneficial seedbed consolidation will be less intense. In grassland soils, which have reached a soil structure in dynamic equilibrium that has experienced many FTCs in the making, there is still a beneficial increase in water supply through increasing unsaturated hydraulic conductivity by continued FTCs that might also be less efficient in the future.

Abstract. Evaluating the possibility of leakage through low-permeability geological strata is critically important for sustainable water supplies, the extraction of fuels from coal and other strata, and the confinement of waste within the earth. The current work demonstrates that relatively rapid and realistic vertical hydraulic conductivity (Kv) measurements of aquitard cores using accelerated gravity can constrain and compliment larger-scale assessments of hydraulic connectivity. Steady-state fluid velocity through a low-K porous sample is linearly related to accelerated gravity (g level) in a centrifuge permeameter (CP) unless consolidation or geochemical reactions occur. A CP module was custom designed to fit a standard 2 m diameter geotechnical centrifuge (550 g maximum) with a capacity for sample dimensions up to 100 mm diameter and 200 mm length, and a total stress of ∼ 2 MPa at the base of the core. Formation fluids were used as influent to limit any shrink–swell phenomena, which may alter the permeability. Kv results from CP testing of minimally disturbed cores from three sites within a clayey-silt formation varied from 10−10 to 10−7 m s−1 (number of samples, n = 18). Additional tests were focussed on the Cattle Lane (CL) site, where Kv within the 99 % confidence interval (n = 9) was 1.1 × 10−9 to 2.0 × 10−9 m s−1. These Kv results were very similar to an independent in situ Kv method based on pore pressure propagation though the sequence. However, there was less certainty at two other core sites due to limited and variable Kv data. Blind standard 1 g column tests underestimated Kv compared to CP and in situ Kv data, possibly due to deionised water interactions with clay, and were more time-consuming than CP tests. Our Kv results were compared with the set-up of a flow model for the region, and considered in the context of heterogeneity and preferential flow paths at site and formation scale. Reasonable assessments of leakage and solute transport through aquitards over multi-decadal timescales can be achieved by accelerated core testing together with complimentary hydrogeological monitoring, analysis, and modelling.

Expansive soils are amongst the most significant, widespread, costly, and least publicized geologic hazards. Where exposed to seasonal environments, such soils exhibit significant volume changes as well as desiccation–induced cracking, thereby bringing forth instability concerns to the overlying structures and hence incurring large amounts of maintenance costs. Consequently, expansive soils demand engineering solutions to alleviate the associated socio–economic impacts on human life. Common solutions to counteract the adversities associated with problematic soils include soil replacement and/or soil stabilization. The latter refers to any chemical, mechanical or combined chemical–mechanical practice of altering the soil fabric to meet the intended engineering criteria. Though proven effective, conventional stabilization schemes often suffer from sustainability issues related to high manufacturing and/or transportation costs, and environmental concerns due to greenhouse gas emissions. The transition towards sustainable stabilization necessitates reusing solid wastes and/or industrial by–products as part of the infrastructure system, and more specifically as replacements for conventional stabilization agents such as cement, lime, geogrids and synthetic fibers. Among others, discarded tires constitute for one of the largest volumes of disposals throughout the world, and as such, demand further attention. Given the high–volume generation (and disposal) of waste tire rubbers every year throughout the world, a major concern hitherto has been the space required for storing and transporting such waste materials, and the resulting health hazards and costs. Those characteristics which make waste tire rubbers such a problem while being landfilled, make them one of the most reusable waste materials for engineering applications such as soil stabilization, as the rubber is resilient, lightweight and skin–resistive. Beneficial reuse of recycled tire rubbers for stabilization of expansive soils would not only address the geotechnical–related issue, but would also encourage recycling, mitigate the burden on the environment and assist with waste management. The present study intends to examine the rubber’s capacity of ameliorating the inferior engineering characteristics of expansive soils, thereby solving two widespread hazards with one solution. Two rubber types of fine and coarse categories, i.e. rubber crumbs/powder and rubber buffings, were each examined at various rubber contents (by weight). The experimental program consisted of consistency limits, standard Proctor compaction, oedometer swell– shrink/consolidation, soil reactivity (or shrink–swell index), cyclic wetting–drying, cracking intensity, unconfined compression (UC), split tensile (ST), direct shear (DS) and scanning electron microscopy (SEM) tests. Improvement in the swell–shrink/consolidation capacity, cracking intensity and shear strength (DS test) were all in favor of both a higher rubber content and a larger rubber size. However, rubber contents greater than 10% (by weight) often raised failure concerns when subjected to compression (UC test) and/or tension (ST test), which was attributed to the clustering of rubber particles under non–confinement testing conditions. Although the rubber of coarser category slightly outperformed the finer rubber, the effect of larger rubber size was mainly translated into higher ductility, lower stiffness and higher energy adsorption capacity rather than peak strength improvements. The volume change properties were cross–checked with the strength–related characteristics to arrive at the optimum rubber content. A rubber inclusion of 10%, preferably the rubber of coarser category, satisfied a notable decrease in the swell–shrink/consolidation capacity as well as improving the strength–related features, and thus was deemed as the optimum choice. Based on the experimental results, along with the SEM findings, the soil–rubber amending mechanisms were discussed in three aspects: i) increase in non–expansive fraction; ii) frictional resistance generated as a result of soil–rubber contact; and iii) mechanical interlocking of rubber particles and soil grains. A series of empirical models were suggested to quantify the compaction characteristics of soil–rubber mixtures as a function of their consistency limits. Moreover, the dimensional analysis concept was extended to the soil–rubber shear strength problem, thereby leading to the development of a series of practical dimensional models capable of simulating the shear stress–horizontal displacement response as a function of normal stress (or confinement) and the composite’s basic index properties, i.e. rubber content, specific surface area and initial placement (or compaction) condition. The predictive capacity of the proposed empirical and dimensional models was examined and further validated by statistical techniques. The proposed empirical and dimensional models contain a limited number of fitting/model parameters, which can be calibrated by minimal experimental effort as well as simple explicit calculations, and thus implemented for preliminary assessments (or predictive purposes). To justify the use of higher rubber contents in practice, a sustainable polymer agent, namely Polyacrylamide (PAM) of anionic character, was introduced as the binder. A series of additional tests were then carried out to examine the combined capacity of rubber inclusion and PAM treatment in solving the swelling problem of South Australian expansive soils. As a result of PAM treatment, the connection interface between the rubber particles and the clay matrices were markedly improved, which in turn led to lower swelling/shrinkage properties, higher resistance to cyclic wetting–drying, and reduced tendency for cracking compared to that of the conventional soil–rubber blend. A rubber inclusion of 20%, paired with 0.2 g/l PAM, was suggested to effectively stabilize South Australian expansive soils.
Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2018