In this paper, a finite element model is developed for the fully hydro-mechanical analysis of hydraulic fracturing in partially saturated porous media. The model is derived from the framework of generalized Biot theory. The fracture propagation is governed by a cohesive fracture model. The flow within the fracture zone is modeled by the lubrication equation. The displacement of solid phase, and the pressure of wetting and non-wetting phases are considered as the main unknown parameters. Other variables are incorporated into the model using empirical relationships between saturation, permeability and capillary pressure. Zero-thickness element and conventional bulk element are used for propagating fracture and the surrounding media, respectively. The model is validated with respect to analytical solution of hydraulic fracture propagation problem in saturated media and then the problem is solved in semi-saturated media, considering the wetting and non-wetting pore fluid. 

Fly ash is one of the most plentiful and versatile of the industrial by-products. At present, nearly 150 million tonnes of fly ash is being generated annually in India posing dual problem of environmental pollution and difficulty in disposal. This calls for establishing strategies to use the same effectively and efficiently. However, it is only in geotechnical engineering applications such as the construction of embankments/dykes, as back fill material, as a sub-base material etc., its large-scale utilization is possible either alone or with soil. Soil stabilization can be achieved by various means such as compaction, soil replacement, chemical improvement, earth reinforcement etc. Usually, in the case of clay soils, chemical improvement is commonly most effective since it can strengthen the soil, to remove its sensitivity both to water and its subsequent stress history. Among chemical means or additives, fly ash/lime provides an economic and powerful means of improvement, as demonstrated by the significant transformation that is evident on mixing with heavy clay. In the present investigation, different percent fly ashes (10%, 20%, 40%, 60% & 80%) were added to a highly expansive soil from India by dry weight of the natural soil, and subjected to various tests. The important properties that are necessary for using fly ash in many geotechnical applications are index properties, compaction characteristics, compressibility characteristics, permeability and strength. Based on test results, it has been found that using fly ash for improvement of soils has a two-fold advantage. First, to avoid the tremendous environmental problems caused by large scale dumping of fly ash and second, to reduce the cost of stabilization of problematic/marginal soils and improving their engineering properties for safe construction of Engineering Structures. 

ABSTRACT The influence of the sand placement method above geotextile layer on interface shear strength behavior was investigated. Seven different types of woven and non woven geotextile were used with only poorly graded sand. The investigation involved placement of sand layer through inclined horizontal plane with different angles. This step constitutes a fundamental step for assessing soil to be deposited in different plane and therefore with different internal soil fabric. The interface shear strength was evaluated by using direct shear test. Although the investigated soil is uniform poorly graded sand, the influence of the deposit plane was significant especially for nonwoven geotextile. Differences in soil interface shear strength associated with the tested geotextiles samples shows that samples with higher mass per unit area and same opening sizes had the higher interface friction angle regardless the bedding plane. Influence of bedding plane on interface modulus of elasticity which used in most of interface modeling was investigated using Janbu’s formula. It is noted that the use of secant interface modulus of elasticity at 1% strain and at 50% of peak stresses gave a consistent prediction of n and Ku constant appear in Janbu’s formula for all types of geotextile. The above results were reflected in the prediction for interface molded such as Chen and Juran as shown. Therefore, the existing interface modeled is needed to be modified to account for the method that the sand is being placed above the geotextile layer.

This paper investigates the time dependent behaviour of Sunshine embankment on soft clay deposit with and without prefabricated vertical drains. An elasto visco-plastic model was used to investigate the influence of anisotropy and creep effect on the settlement behaviour of the embankment. The constitutive model, namely ACM accounts for combined effects of plastic anisotropy and creep. For comparison, the problem is also analysed with isotropic Modified Cam Clay model which does not consider creep effect. To analyse the PVD-improved subsoil, axisymmetric vertical drains were converted into equivalent plane strain conditions using two different mapping approaches. The results of the numerical analyses are compared with the field measurements. The numerical simulations suggest that the anisotropic creep model is able to give a better representation of soft clay response under an embankment loading. The isotropic model which neglects effects of anisotropy and creep may lead to inaccurate predictions of soft clay response. Additionally, the numerical results show that the mapping method used for PVD improved soft clays can accurately predict the consolidation behaviour of the embankment and provide a useful tool for engineering practice.

A study has been conducted on the bearing capacity of strip footings over sandy layered soils using the stress characteristic lines method. Traditional bearing capacity theories for specifying the ultimate bearing capacity of shallow foundations are based on the idea that the bearing layer is homogenous and infinite. However layered soils are mainly happening in practice. The stress characteristic lines method is a powerful numerical tool in order to solve stability problems in geotechnical engineering. In the present paper, an appropriate algorithm is derived for estimating the static bearing capacity of strip footing located on two layered soils using the stress characteristic lines method. Some numerical and experimental examples are presented in order to validate the proposed algorithm. Some graphs and equation are presented for initial estimating the effective depth of strip footings located on two layered soils.

Lateral earth pressure on retaining walls is a widely researched classical problem in geotechnical engineering. This study investigates the active lateral earth pressure on a circular retaining wall using the stress characteristics method in the presence of soil-wall adhesion and friction. A computer code was developed for determining the lateral pressure of soil on the wall as well as the lateral pressure coefficients upon receiving the required input parameters. The principle of superposition was implemented to determine the lateral earth pressure coefficients. The effects of the soil-wall adhesion and friction angle on the lateral earth pressure were studied under active conditions. Moreover, the effects of these parameters on the characteristics network and failure region were demonstrated. The results showed that the coefficient of lateral earth pressure due to cohesion increased with increasing adhesion at the soil-wall boundary.

The paper present the results of various experimental and numerical studies on slopes, small scale physical modeling of slope under surcharge load were performed in loose sand environment. Digital images were captured during the incremental loading from side of model simultaneously. The Particle Image Velocimetry (PIV) and 3D numerical model was applied to investigate the slope under surcharge loading and some of the other important factors that control the performance of piles are investigated. The factors of safety and location of critical failure surfaces of reinforced and unreinforced slopes obtained and compared for various slopes. For homogenous slope, it is found for stabilized slope with piles, the 3D failure surface shape in front of piles is triangle, unlike its conical shape in laterally loaded piles. The paper also studies numerically the effect of soft bound effect, soil properties, pile spacing, pile position and surcharge distance effects on stabilized and none stabilized slopes. The results indicate that the depth of soft soil layer from ground surface and its angles with horizontal direction has importance effect on optimum location of stabilized pile. Studies on pile space effects shows with increasing pile space, arching phenomenon didn’t developed and partial pressure of supported portion transferred to un supported soil portion and the potential failure volume of the slope becomes large.

Abstract To meet construction demands, reinforcement and stabilization methods have been widely used to improve properties and mechanical behavior of clays. Although cement stabilization increases soil strength, at the same time reduces ductility which is of paramount importance in roads, landfill covers, etc. In current study, kaolinite was stabilized with 1, 3 and 5% cement and mixed with 0.05, 0.15, 0.25 and 0.35% polypropylene fibers to increase ductility. Samples were cured at 35°C for 1, 7 and 28 days and subjected to unconfined compression tests. Results showed that inclusion of discrete fibers to uncemented and cemented kaolinite reduced stiffness and the loss of post-peak strength and changed brittle behavior of cemented samples to a more ductile behavior. Cement and fiber contents as well as curing period were found to be the most influential factors and fiber – soil interaction was influenced by binding materials.

The main purpose of this study is to investigate the influence of urban solid waste leachate on the mechanical properties of the soil. Order to provide a more accurate identification of the contaminated soils, Cylindrical specimens of the soil, according to the density curves with different initial conditions (different initial contamination levels) were prepared, then the soil specimens were loaded at different load levels using a direct shear testing equipment and a universal testing machine to apply axial compression on the specimens. By analyzing the results, the stress-strain and failure behavior of the soil specimens containing different percentages of the solid waste leachate was evaluated. The most important result was reducing the mechanical properties of the soil contaminated with different percentages of solid waste. The results of adding lower quantities of leachate, is far more significant compared to the received results from adding higher amounts of leachate.

The main objective of present study is to possible use of plastic waste materials for reinforcing clayey soils. An experimental study was planned to investigate compressibility and undrained shear behavior of clayey soil mixed with plastic waste. The mixtures were prepared with various amount of plastic waste (i.e. 0%, 0. 5%, 1.0%, 1.5% and 3.0% in dry weight) and interactive effect of plastic waste, plastic flexibility, confining pressure and initial density on the behavior of clayey soil was studied by performing compaction, consolidated undrained triaxial and oedometer consolidation test. The results show that plastic wastes do not affect compaction characteristics of clayey soil considerably and adding them to the clay more than a specific value (i.e. 1.0% in this research) causes to change undrained behavior of samples from contractive to dilative. In addition, beyond this specific value, it improves shear strength and reduces compressibility of clay. The rate of increase in shear strength and decrease in compressibility depends on the confining pressure, flexibility of plastic and initial density of samples. It is more noticeable when plastic waste in mixtures is relatively rigid and density and confining pressure are high. Moreover, plastic waste has a negative effect on the free swelling, swelling pressure and swelling index of samples, so that these parameters for plastic waste mixed clay are higher than the associated values of plain clay.

In the present research, an analytical method is applied to determine the bearing capacity of strip footing on two layers of the soil. Bearing capacity of the footing is calculated according to soil resistance beneath the foundation and virtual retaining wall method. In the said method, the active and passive force on the retaining wall are considered equal on the edge in order to determine the bearing capacity of the footing. Regarding two layers of soil, the active and passive forces of each layer is found and their resultant is applied to calculate footing bearing capacity. This method has many advantages including the possibility to determine the depth of rupture surface of the soil beneath the footing, and to study the effect of the soil second layer on footing bearing capacity. Moreover, the effect of soil improvement beneath the footing as well as the depth and width of compacted area on bearing capacity of footing are also studied here in this research. In general, the studied parameters in this project consist of soil layers thickness, soil cohesion and friction angle, footing depth and width, the width of compacted soil beneath the footing, and the depth of underground water. By programming in MATLAB, the calculation and deduction was fulfilled. The results were compared with the bearing capacity of the footing on one layer of the soil in various situations in order to study the effect of various parameters in two layers of the soil. Finally, this bearing capacity of the footing was compared with the previous experimental methods and reliable results were obtained.

Pile penetration and rebound amount measurements during pile driving are important in analysis of penetration and bearing characteristics of piles and for assurance of pile installation quality. Traditional manual measurement of penetration and rebound of piles exposes engineers under unfavorable environment of injury risk and significant vibration and noise. To improve accuracy of pile penetration and rebound measurements and to ensure safety of engineers during pile driving, the close-range photogrammetry approach was implemented. For the track of three-dimensional spatial information of one point on the pile during driving, a series of stereo pair images of the point attached on a pile is required using more than two camera systems at different locations. In this study, two charge coupled device cameras were used to obtain stereo images. Robust measurements and reliable results can be guaranteed by the constrained geometry of close-range photogrammetry. From the field implementation, it was found that the newly developed pile penetration and rebound measurement system is accurate and safe.

Considerable strains appear in the structures during accumulation of the irreversible strains of the subgrade under the effect of the cyclic loads. If the number of cycles is very large, even a small strain after accumulation becomes significant and sometimes harmful. In this study, a simple numerical modeling of the behavior of sand under cyclic loading is proposed. The suggested approach consists, in drained condition, in determining the parameters characterizing the average cyclic path of the soil under the effect of the number of cycles duly characterized and translating the cyclic effect by a volumetric strain cumulated by a variation of the module of the soil. In this study, we are interested in cyclic triaxial compression tests simulated by a finite element calculation. While proposing an analogy between the cyclic pseudo creep and the soft soil creep model (SSCM), on the first hand we propose an equivalence between the cyclic parameters and the parameters of SSCM, and on the other an equivalence time number of cycles will be established. The application of the formulation suggested on a shallow foundation under cyclic loading confirms the good adaptation of the model suggested to this type of problem.

Climate change and global warming have led to severe typhoons and sea level rise (SLR) which may threat the stability of coastal structures. However, countermeasures to enhance coastal protection against SLR and severe typhoons have not appropriately considered. The Hai Hau coast with 33.3 km of sea dikes is located in the Red River delta of Vietnam. Herein, coastal dikes have collapsed twice over the last 30 years, which lead to about 1.5 km of coastline retreat. This paper aims to assess quantitative impacts of SLR on sea dike stability. Change in pore water pressure (PWP) in the dikes was monitored by piezometers. Distribution of PWP at different tide levels was then used to calculate factors of safety (Fs) of inner and outer slopes. Projected SLR until 2100 will reduce Fs of the outer slopes, but sea dikes have no problem with sliding stability. The main threats of SLR to sea dike stability are indirect impacts such as accelerated erosion, scouring, and wave overtopping-induced soil erosion on the inner slopes. Troughs of sea dikes in Hai Hau coast could fail in 6–10 years due to accelerated coastal erosion. A solution of multiple protections to adapt to SLR in Hai Hau coast was proposed which includes conventional structures (i.e. dike, revetment, groins, and mangrove) together with geotubes as submerged breakwaters and vetiver grass.

Most of the proposed methods for obtaining the free vibration natural frequency of the retaining wall have been presented, assuming the behavior of the wall in two-dimensional domain, and they are not able to express the three-dimensional behavior of these structures in a satisfying manner. In this paper, the plate theory is employed to analyze the free vibration of wall-soil system in three-dimensional domain. So the retaining wall is modeled as a clamped-free plate and the stiffness of the soil existing behind the wall is modeled as a set of springs. Using the approximate Rayleigh method, new analytical expression for obtaining the free vibration natural frequencies for the three first modes of the wall is represented. The results of the proposed model are compared with both the results of the other researchers and the ones from finite element method (FEM). They are also compared with the results of a full-scale experiment and it shows a good agreement. The comparison shows that modeling the wall in two-dimensional form is not accurate enough to calculate all the natural frequencies of the wall. The results of this paper show that there is a considerable difference between two- and three-dimensional behavior of the walls. The proposed method also gives the free vibration natural frequencies of the wall extensional modes with an acceptable accuracy. Finally, the effect of tensile and compressive behavior of the soil on the fundamental frequency is studied. This research can be considered as a new field in three-dimensional calculation of the retaining walls.

To study and predict the behavior of flexible pavement over expansive soils, a pavement structure was subjected to different laboratory and fieldwork experiments. The existing pavement was replaced and designed based on California Bearing Ratio (CBR) method, with a new one, and subjected to the traffic from various number of load cycles from 12.1 up to 155.52 kcycles of standard axle load (80 kN) through dual wheel assembly over a 6-month period. As the preliminary step, the deflection measurements were taken at the asphalt surface layer, using a Total station at different distances as function of truckload applications. The numerical analysis is carried out with the Finite Element software package PLAXIS version 2012. In the new model, the calculation of the transferred pressure to the pavement through contact area of tires is 3D it was turned into a 2D problem, and the pavement was subjected to a static loading using a ratio factor of dynamic additional charge. The materials’ behavior was simulated with nonlinear models: Mohr–Coulomb (MC) for pavement layers and soft-soil model (SSM) for the expansive subgrade, in saturated drained and undrained conditions. The results indicate that displacements under static loading in saturated drained conditions and when non-linear materials are present are the closest to field measured deflections.

Soils with poor engineering properties have been a concern to construction engineers because of the need to strike a balance between safety and economy during earthworks construction. This research work investigates the effects of treating a soil having poor geotechnical properties with a bio-enzyme to determine its suitability for use as road pavement layer material. The elemental composition and microstructure of the soil was determined using energy dispersive X-ray spectroscopy and scanning electron microscopy, respectively. The specific gravity, Atterberg limits, compaction, strength and permeability characteristics of the soil was determined for various dosages of the bio-enzyme. The mountain soil is classified as clayey sand and A-2–4, according to unified soil classification and AASHTO classification systems, respectively. With increasing dosage of the bio-enzyme, the plasticity index, maximum dry unit weight and permeability of the soil decreased, while its 28-day California bearing ratio value, unconfined compressive strength and shear strength increased. Consequently, the application of bio-enzyme to the soil improved its plasticity and strength, and reduced its permeability. It, therefore, became more workable and its subgrade quality was improved for use as a road pavement layer material. The stabilized soil can be suitably used for constructing pavement layers of light-trafficked rural (earth) roads, pedestrian walkways and bicycle tracks.

The effects of effective stress and void ratio on the secondary compressibility of the sandy and clayey soils were investigated in this study. The coefficient of secondary compression of Ottawa sand in single stage and stepwise loading tests increases with effective vertical stress while that of saturated kaolinite decreases with effective vertical stress. Multi-staged loading tests showed that at a given effective stress, the higher the void ratios of the soils, the higher the coefficients of secondary compression of the soils are. It was concluded that the secondary compressibility of a soil depends on not only the effective stress, but also the void ratio of the soil. A general relationship between the coefficient of secondary compression, and effective stress and void ratio was proposed for soil. The discrepancy of the dependency of secondary compressibility on effective stress for different soils was well explained using this relationship, moreover, the quasi-overconsolidated state of clayed soil induced by time effect and the effect of surcharge preloading on the secondary compressibility of soft ground were discussed in light of the general relationship.

The correlations and relationships between electrical resistivity and geotechnical parameters of soils have become very important for site investigation. However, there is a lack of understanding about the relationships between electrical resistivity and geotechnical parameter values. The resistivity piezocone penetration tests and laboratory tests have been conducted for geotechnical investigations of marine clay in Jiangsu province of China to establish quantitative relationships between electrical and geotechnical data. The geotechnical investigation reveals that electrical resistivity values are very low for marine clay in Jiangsu, ranging from 5 to 10 Ω m. The correlations between electrical resistivity and geotechnical parameters are examined using Spearman’s rank correlation test that is a rank-based test for correlation between two variables without any assumption about the data distribution. It was shown that the electrical resistivity has strong bonds with the moisture content, void ratio, salt content and plasticity index. In terms of quantitative relationships, good fitting relationships between electrical resistivity and selected geotechnical parameters are observed. The statistical analysis indicates that the electrical resistivity is a good indirect predictor of selected geotechnical parameters. The data studied demonstrates the usefulness of the in situ resistivity method in geotechnical investigations, which have an advantage over other geotechnical methods in cost performance.

Abstract: Rainfall is an important triggering factor influencing the stability of soil slope. Study on some influences of the rainfall on the instability characteristics of unsaturated soil embankment slope has been conducted in this paper. Firstly, based on the effective stress theory of unsaturated soil for single variable, fluid-solid coupling constitutive equations were established. Then, a segment of red clay embankment slope, along a railway from Dazhou to Chengdu, damaged by rainfall, was theoretical and numerical-simulating researched by considering both the runoff-underground seepage and the fluid-solid coupling. The failure characteristics of the embankment slope and the numerical simulation results were in excellent agreement. In the end, a sensitivity analysis of the key factors influencing the slope stability subjected to rainfall was performed with emphasis on damage depth as well as infiltration rainfall depth. From the analysis in this paper, it was concluded that the intensity of rainfall, rainfall duration and long-term strength of soil have most effect on slope stability when subjected to rainfall. These results suggest that the numerical simulation can be used for practical applications.