Stress-strain Behavior Of Soil Research Articles

Collapse potential and ultrasonic pulse velocity of loess soils after treatment with expanded perlite and metakaolin

Collapsible soils, including loess, can support heavy loads at their natural humidity but then collapse rapidly and lose a substantial volume when the humidity increases. Soil collapse potential at different immersion stresses was investigated according to ASTM D5333. Different immersion stresses, including 100, 200, 300, 400, and 500 kPa, were used to evaluate the stress-strain behavior of soils before and after saturation. The results indicated that soil collapse potential rose with a raising of immersion stress, resulting in the highest soil collapse potential at 500 kPa immersion stress. Furthermore, the effectiveness of expanded perlite and metakaolin in treating loess soils was examined. The results revealed that the soil collapse potential reduced with an increase in perlite and metakaolin up to 8 %. Also, perlite had a more significant impact on the soil collapse potential than metakaolin. The interlocking force between soil particles was enhanced as the perlite quantity rose, and perlite prohibited soil particles from slipping on each other. Metakaolin decreased the soil collapsibility due to the pozzolanic and chemical reactions which increased particle bonding. The ultrasonic pulse velocity of soils decreased as the percentage of perlite increased. Because the perlite was not spread homogeneously, and the waves can be stuck in the heterogeneities, Metakaolin acted as a filler and increased the ultrasonic pulse velocity of the soils.

PREDICTION OF SOIL SETTLEMENT ON SOFT CLAY SOIL USING NORMALIZED ROTATIONAL MULTIPLE YIELD SURFACE FRAMEWORK (NRMYSF)

Soft clays are highly compressible, high-water content, low shear strength, and have poor permeability, which result in significant settlement under long-term loads. Therefore, one of the most challenging geotechnical engineering problems is to predict the settlement from soft clay soil. Normalized Rotational Multiple Yield Surface Framework (NRMYSF) is developed from the soil stress-strain behaviour and shear strength characteristic. It is able to estimate the stress-strain curve for shear strength in triaxial tests. The consolidated drained (CD) triaxial tests and conventional 1-dimensional consolidation of oedometer has been conducted on soft clay soil. The settlement soil prediction was compared between the NRMYSF and conventional 1-dimensional consolidation under Terzaghi’s principle. The NRMYSF prediction model was smaller than the conventional oedometer by 0.1459m to 0.1431m for Sample A, and by 0.1890m to 0.1398m for Sample B. Therefore, this method has the potential to predict the settlement of soft clay soils.

Factors Influencing Post-Construction Responses of Underlying Tunnel below Excavation Base in Gravelly Clay

This paper investigates the response mechanism behind an existing tunnel subjected to a long and deep collinear excavation in Shenzhen granite residual strata. The maximum excavation depth was 18.0 m and the minimum residual soil depth above the tunnel crown was only 6.3 m, causing appreciable tunnel heave and transverse deformation. Two-dimensional parametric numerical study is adopted to examine the impacts of influential factors (excavation dimensions, ground permeability coefficient, and exposure time of the excavation base) on the tunnel responses. The hardening soil model with small strain (HS-Small) is used to model the soil stress–strain behavior. It is found that the long-term deformation of the tunnel after excavation and unloading cannot be ignored. The soil will continue to consolidate and deform, and the tunnel will continue to heave with soil due to the dissipation of the negative excess pore water pressure. The long-term deformation of the tunnel after excavation and unloading is significantly affected by the excavation geometry. With the increase in excavation width B, the final tunnel heave after excavation and unloading increases first and then tends to be stable. Furthermore, the relative position of the tunnel and the excavation base is also one of the major contributors to the long-term deformation of the tunnel. The growth of tunnel deformation Δf and the exposure time T are exponentially negatively correlated with Ly. The change in the permeability coefficient k has no effect on the final stable tunnel heave and the growth of tunnel deformation Δf, which is exponentially negatively correlated with the exposure time T.

Effect of elevated temperature on geotechnical properties of soils – A review

Land used for construction purposes should have large bearing capability and less squeezability. Soft soils such as clayey soil have low bearing capacity and high compressibility which must be converted or treated before the construction process to meet the requirements. The presence of oil and gas pipe lines, buried high voltage cables, fire accidents, storage of high-level waste could limit the use of conventional methods such as deep cement mixing. Hence, alternate methods are required, heat treatment has been considered to be the efficient technique, if the need of enhancement in characteristics are required. This paper discusses the literature available on thermal treatment. The effect of temperature on various properties of soil like Atterberg limits, free swell, porewater pressure, swelling, shear strength, stress strain behavior of soil and mineralogy is included in this paper. This review paper summarizes the effectiveness of thermal treatment on soft soil.

Calibration of discrete element parameters and experimental verification for modelling subsurface soils

The discrete element method (DEM) has shown considerable advantages for the simulation of soil-tool interaction simulation. To develop reliable DEM simulations, the selection of an appropriate contact model and its parameter calibration are critical. A DEM model of cohesive subsurface soils was established to predict the draught of sweep cultivation by using the Edinburgh elasto-plastic adhesion (EEPA) contact model. Firstly, the DEM parameters were used for calibration, which were significant for the results of the uniaxial confined compression test and the unconfined compressive strength test. Then, the mapping relationship between other DEM parameters and the soil stress–strain behaviour was calculated to obtain a solution matching the stress–strain measurement results. Finally, cone penetration resistance (penetration rate of 8 mm s−1) and the draught of sweep tillage (depth of 200 mm and speed of 1.67 m s−1) were used to evaluate the accuracy of the parameters. The results showed that the penetration resistance in the elastic phase of the simulation was in close agreement (R2 = 0.9964) with the measurements, and the total relative error and the average relative error between the predicted sweep draft and the measurement were 9.4% and 4.77%, respectively. Thus, it was shown that the developed calibration method can effectively predict the development of the sweeping draught and the penetration stress.

Behavior of Residual Soil with High Silt Content Under Low Frequency Cyclic Loading Using Modified Direct Simple Shear Apparatus

This paper presents the experimental work on typical Malaysian silty residual soils in order to evaluate fundamental soil properties in particular its stiffness under low frequency cyclic loading. There has been very little information on local silty residual soils which is very important for local geotechnical design purposes. Lack of such information contributes to the dependency of foreign soil data which might not be representative of local silty residual soils. This study departs from the basis of there have been verified evidences that we are not spared from seismic activity in Malaysia. Hence, it would be misleading if we were to exclude soil properties under cyclic loading for design purposes in Malaysia. This research revolves around the development of simplified device to evaluate the stress-strain behaviour of soils under simple shear strain conditions. The cyclic loading test results on Malaysian sedimentary residual soil sample exhibit increase of drained shear stiffness, GSTIF and gained strength after 30 cycles indicating cyclic hardening behaviour. It is evident that magnitudes of cyclic load and cyclic displacement influences the rate of soil volume change. Nevertheless, the densification of soil samples due to increment of cycles caused reduction in volume change. It is foreseen that the obtained parameters could assist in the practical geotechnical engineering problems related to cyclic conditions.

A Simplified Method for Analysis of Laterally Loaded Piles considering Cyclic Soil Degradation

This paper proposes a simplified method to analyze the bearing behavior of pile undergoing cyclic lateral load. Firstly, a modified strain model is proposed by utilizing the Duncan–Chang model to describe the stress-strain behavior of soils in the strain wedge. Then, a cyclic degradation model of soft clay considering the accumulation of plastic strain and pore water pressure is presented based on the cyclic triaxial test. Combining with the modified strain wedge model and degradation model of soil, a simplified method is established for the cyclic laterally loaded pile. The accuracy of the present method is verified by comparing it with existing model tests. The results show that the pile lateral displacement and strain wedge depth increase with the number of cycles and cyclic load amplitude. It is necessary to consider the effect of cumulative pore water pressure during the analysis of cyclic laterally loaded pile embedded in soft clay.

A review on modelling of the stress-strain behaviour of soil.

Soil has been used as a construction material since antiquity with both success and failure. As the earth material is widely available and relatively economical, it has been found very useful in the construction of foundations, subgrades, embankments and as backfill. The collapsibility of soil is mainly due to the decrease of shear strength and macro-deformation with the increase of moisture content. This can result in some serious problems, such as the differential settlement of the foundation, landslides, and slope instability, resulting in a series of damages of infrastructures and loss of human lives to some degree. In civil engineering, it is very important to make realistic predictions of the behaviour of soil under various conditions. Triaxial tests are to be carried out to study soil behaviour. The results will indicate the shear damage characteristics during the test. The relation of stress and strain of soils can be expressed using constitutive models. It can provide a brief idea about how soil will behave under different conditions. Application of Neural Network can be used to develop a data-driven constitutive modelling of the soil.
 Keywords- Shear strength, Triaxial test, moisture content, constitutive model

Revisiting Hardin’s parameters for the quantification of particle breakage – A statistical entropy approach

It is well recognised that particle breakage in granular materials is affected by stress level, stress path, initial density, and particle size distribution (PSD), amongst others. Furthermore, it has been shown that breakage has a significant influence on the stress-strain behaviour of soils. This paper compares a commonly used breakage parameter with grading entropy coordinates. Such coordinates enable for the representation of any PSD as a single point in a Cartesian coordinate plane. Hence, the evolution of PSD changes may be easily tracked. This paper aims to demonstrate that grading entropy coordinates are as (or more) effective than other breakage parameters, whilst providing additional insight. On the basis of limited data it is shown that grading entropy coordinates are able to capture the dependence of breakage on stress level, stress path and initial PSD.

A sphere packing model for shear bands in dense soils

The rhombic sphere packing can be used to model the biaxial test on granular soils in a very simple way. According to the angle of assemblage, the packing is dilatant or contractive. Correspondingly, overall stresses are transmitted as chains of forces or oblique forces of contact. The connection of the soil stress-strain behaviour and the packing void ratio is achieved by mapping both of the plots. The mapping shows that dense soils are dilatant and loose soils are contractive, separated by the critical state. It also shows that the bifurcation point and the peak strength are features only of dense soils. The band of strain localization is analysed in the elastic regime, and its inclination is found maximizing the intensity of the mobilized stress ratio. The stresses within the shear band are obtained by assuming a partially coaxial packing rotated to reach the full plastic state. The equilibrium of the overall stress at the line of discontinuity reveals a relationship between the peak friction angle and the coefficient of lateral pressure at rest. As long as these parameters are obtained independently of each other, they allow the validation of the theory.

One-step analytical method for required reinforcement stiffness of vertical reinforced soil wall with given factor of safety on backfill soil

The selection of geosynthetic reinforcements in the design of geosynthetic-reinforced soil (GRS) retaining walls has been based on the requirement on the long-term strength. However, the mobilized loads in the reinforcements are related to both the reinforcement stiffness and soil deformation, and the desired factor of safety may not exist in the earth structure if they are not properly considered. Therefore, it is also important to take into account the long-term reinforcement stiffness when designing GRS retaining walls. In this study, a simplistic analytical method is proposed to determine the required reinforcement stiffness with given factor of safety on the backfill soil. The method takes into account soil-reinforcement interaction, nonlinear stress-strain behavior of soil, and soil dilatancy. The reinforcement strains predicted by the proposed method were compared to those analyzed by validated nonlinear Finite Element analyses, and close agreement was obtained.

Application of LSTM approach for modelling stress–strain behaviour of soil

This paper presents a new trial to reproduce soil stress–strain behaviour by adapting a long short-term memory (LSTM) deep learning method. LSTM is an approach that employs time sequence data to predict future occurrences, and it can be used to consider the stress history of soil behaviour. The proposed LSTM method includes the following three steps: data preparation, architecture determination, and optimisation. The capacity of the adapted LSTM method is compared with that of feedforward and feedback neural networks using a new numerical benchmark dataset. The performance of the proposed LSTM method is verified through a dataset collected from laboratory tests. The results indicate that the LSTM deep-learning method outperforms the feed forward and feedback neural networks based on both accuracy and the convergence rate when reproducing the soil’s stress–strain behaviour. One new phenomenon referred to as “bias at low stress levels”, which was not noticed before, is first discovered and discussed for all neural network-based methods.

Fly-by-Pi: Open source closed-loop control for geotechnical centrifuge testing applications

Geotechnical centrifuges are valuable instruments for physical modelling of complex geotechnical problems in a controlled laboratory setting. In comparison to full-scale testing, scaled models are cost effective to construct and instrument and, when tested in a geotechnical centrifuge at increased centrifugal accelerations, are capable of replicating full-scale stress–strain soil behaviour. Centrifuge modellers require specialised hardware and instruments capable of functioning under high accelerations. Such hardware is costly, nearly always purpose built, and often rely on commercial, closed-source data acquisition systems, hardware and control systems.This paper demonstrates a novel and versatile, low cost, open source logger and control system that works in parallel alongside existing centrifuge hardware. This solution, termed Fly-by-Pi, was developed using the Raspberry Pi microcomputer. The system provides closed-loop control of linear actuators with the ability to operate in either cyclic, monotonic, or static load- or displacement-control. The control mechanism can be reprogrammed according to experimental requirements, even during flight in the centrifuge. Three independent experiments are described which included the Fly-by-Pi controller as a key component in their operation. Based on the experience gained during these experiments, the authors encourage wide-spread adoption of open-sourced hardware solutions in extreme testing environments.

Proposed Methods on Enhancement of Dynamic Response of RC Frames and Soil Structure Interaction

In this paper, proposed methods on enhancement of a nonlinear behavior of reinforced concrete frames subjected to cyclic load. A fully nonlinear dynamic analysis is adapted using three-dimensional finite element analysis by means of ANSYS 16.0 code. All structural elements such as footings, columns and girder are simulated in the numerical model. The concrete is assumed to be nonlinear and isotropic. In addition, some proposed methods are investigated to enhance the performance of RC frames under cyclic loading such as, cross bracing steel at the connections and at girder region as well as additional bent bars at the ends of girder. The results of analyses are presented in terms of envelope capacity, load-displacement relationship, stresses and cracks distribution. The results indicated that the provision of additional reinforcement increased the ultimate lateral capacity, ductility and introduce an additional mechanism for shear stresses for RC frame under cyclic loading. The best performance is observed when the cross-bracing is used at the top and bottom column connections whereas, the lateral capacity and displacement is increased by 12.9 % and 27.63% respectively of that computed for Control Frame. In case of cross-bracing steel at beam column connections and case of cross-bracing at beam region, the lateral capacity of RC frames is about 1.09 and 1.04 times that of control frame respectively. Furthermore, the dynamic analysis is carried out under considering the foundation soil whereas the Drucker-Prager model is used to define the stress strain behavior of soil. Besides, some significant observations on the performance of RC frames with change of the values of parametric study are presented in this paper.

Evaluation of the coefficient of earth pressure at rest (K0) of a saturated-unsaturated colluvium soil

To predict the stress-strain behaviour of soils under loading it is relevant the knowledge of its natural stress state, expressed by the coefficient of earth pressure at rest (K0). There are correlations in theliterature for K0determination that comes from researches developed considering sedimentary soils,typically from temperate or cold regions. In dealing with residual and colluvium soils, typical of tropical regions, it is not appropriate to use these correlations, since K0is affected by factors such as degree of weathering, laterization processes and suction, among others that also affect saturated sedimentary soils. This work analysed samples of a colluvium soil from a natural slope at the Pontifical Catholic University of Rio de Janeiro. For the determination of the coefficient of earth pressure at rest of the unsaturated colluvium soil, a flexible wall equipment, with a system of suction control was used. The influence of the net stress level on the value of the coefficient of earth pressure at rest was investigated under a constant suction of 10 kPa, following a loading and unloading cycle of applied vertical stress. The coefficient of earth pressure at rest of the saturated colluvium (null suction) was also determined using a stress-path, Bishop and Wesley type, servo-controlled triaxial equipment. The obtained results are presented and discussed.

Foundation and Pile Interaction with Swelling Soil

The paper provides the results of experimental studies pilot studies of the moisture transfer and clay soil swelling characteristics and their mathematical description. An analytical solution is suggested to determine a stress-strain behavior within a body of soil with non-uniform moisture content interacting with underground structures (foundation, pile, etc.). It is shown that the swelling pressure depends on the type of the stress-strain behavior of soil, and under the compression conditions, exceeds the corresponding swelling pressure under the finite-width foundation base by several times. It was found that the pull-out force of the pile greatly depends on the modulus of deformation of the swelling soil, influence zone and pile diameter.

Immediate and long term effects of compaction on the stress-strain behaviour of soil

This paper explores whether delay in construction after compaction can benefit from the gain in soil’s strength and stability point of view. An experimental investigation has been carried out to examine the gradual development of soil’s shear strength by ageing of mechanically compacted soil at three relative densities. In order to separate the gain in strength due to ageing from that occurring from the reduction in soil moisture, the soil samples prepared in moulds were kept in desiccators for different periods of time (1, 9 and 17 days) before testing unconfined compressive strength test. The soil in densely compacted state is found to gain in strength due to ageing faster than that in medium compacted state. Only due to ageing of 9 days or more, unconfined compressive strength of compacted soil is found about 1.7 to 2.4 times of that attained in day 1 after compaction.

Evaluation of One-Dimensional Multi-Directional Site Response Analyses Using Geotechnical Downhole Array Data in California and Japan

This study presents a comprehensive investigation of one-dimensional (1-D) site response analysis (SRA) to predict the dynamic response of soil deposits under earthquake loading utilizing the recordings at selected borehole arrays. Seven instrumented downhole arrays in California and Japan were studied using 41 recorded ground motions that cover a broad range of intensities. The arrays were initially assessed in terms of effectiveness of 1-D SRA using taxonomy screening. Furthermore, LS-DYNA, an advanced Finite Element (FE) program, was employed to develop the 1-D soil column models for the SRA of these arrays. The soil stress-strain behavior was characterized with three different models including one linear elastic and two nonlinear backbone curve formulations. All predictions were compared to the measured ground motions to quantify the model biases and uncertainties. Lastly, the practical limitations of 1-D SRA models considered herein are identified, and recommendations are provided to assess the usefulness of the predictions in engineering practice.

Stress-Dilatancy of Cambria Sand for Triaxial Tests at High Pressures

In this paper, the stress-dilatancy relationship of Cambria sand for drained triaxial compression and extension tests at high stress level is investigated. The stress dilatancy relationship is obtained by use of frictional state theory and experimental tests data published in literature. It is shown that stress-dilatancy relationship is bilinear, described by three parameters of frictional state theory: critical frictional angle and two other parameters. It is accepted that critical friction angle is independent of confining pressure. The two additional parameters are strongly dependent on confining pressure and different for initial and advanced stages. The point at which the values of these parameters change is termed as Transformation Shear Point. This point is not simply visible either in stress ratio-strain or the volume strain-shear strain relationship which are traditionally shown in soil mechanics papers. Transformation Shear Point is very characteristic in stress ratio-plastic dilatancy plane. Thus, stress ratio- plastic dilatancy is very important for describing stress-strain behaviour of soils. The relationship shown in the paper can be used in soil modelling in the future.

TBM soft ground interaction: Experimental study on a 1 g reduced-scale EPBS model

This paper brings new elements of understanding on the stress–strain behaviour of soils during tunnel excavation using earth pressure balance shields (EPBS), thanks to laboratory tests carried out with an original reduced-scale physical model. Typical experiment results obtained during tunnelling with different soil types (purely frictional, cohesive-frictional) and different geometries (homogeneous or stratified grounds) are presented and discussed. These results mainly concern the soil stress–strain behaviour around the tunnel boring machine (TBM) and the soil-machine interaction at ideal rates of excavation. Firstly, results concerning the identification of pertinent control parameters to guarantee the safe advancement of the machine and the ground-supporting function of the cutting wheel are analysed. Surface settlements, stresses and displacements around the tunnel and behind the tunnel face, as well as arching effects around the shield are then presented and discussed.