Soil Shear Strength Parameters Research Articles

Influence of biochar in the calcite precipitation of sandy soil using sporosarcina ureae

The microbially induced calcium carbonate precipitation (MICP) technology is an emerging novel and sustainable technique for soil stabilization and remediation. MICP, a microorganism-mediated biomineralization process, has attracted interest for its potential to enhance soil characteristics. The inclusion of biochar, a carbon-rich substance formed by biomass pyrolysis, adds another degree of intricacy to this process. The study highlights the impact of the combination of biochar and MICP together, using a bacterium, Sporosarcina ureae, on soil improvement. This blend of MICP and biochar improved the soil in terms of its geotechnical properties and also enabled the sequestering of carbon safely. It was observed that addition of 4% biochar significantly increased the soil's shear strength parameters (c and φ) as well as its stiffness after 21 treatment cycles. This improvement was because the calcium carbonate precipitate, which acts as a crucial binding agent, increased significantly due to microbial action in the soil-biochar mixture compared to the pure soil sample. The excess carbonate precipitation on account of biochar addition was verified through SEM-EDAX analysis where the images showed noteworthy carbonate precipitation on the surface of particles and increment in the calcium mass at the same treatment cycles when compared with untreated sand. The collaboration between MICP and biochar effectively increased the carbon sequestration within the sand sample. It was observed that at 21 cycles of treatment, the carbon storage within the sand sample increased by almost 3 times at 4% biochar compared to sand without any biochar. The statistical analysis further affirmed that strength depends on both biochar and the number of treatment cycles, whereas carbon sequestration potential is primarily influenced by the biochar content alone. This strategy, as a sustainable and environmentally friendly approach, has the potential to reform soil improvement practices and contribute to both soil strength enhancement and climate change mitigation, supporting the maintenance of ecological balance.

Experimental Study of Cationic-Modified Biopolymer for Increasing the Shear Strength of Sand

Experimental Study of Cationic-Modified Biopolymer for Increasing the Shear Strength of Sand

Effects of Bio-enzyme on the strength properties of soil

Engineers regularly attribute the complexity of constructing parts on or by soils, those do not have sufficient strength to sustain the loads required leading them either all over construction or in the study life of the structure. The more areas of India shows of CH (Inorganic Clay of High Plasticity) clay soil characterized by more small portion, lower shear strength and lesser bearing capability. The unfortunate engineering performances of these soils has enforced Engineers to instrument charge competent and eco-friendly processes for increasing the engineering properties of these soils. As the conservative soil stabilizers like gravel, sand, etc. Are declining and suitable expensive day by day at an extremely quick rate, it becomes necessary to emerge for possible ecological stabilizers as their substitute. In current scenario the various Bio-enzymes have emerged as lesser cost stabilizers for soil stabilization. Bio-enzyme is a common, harmless, non-flammable, noncorrosive liquid enzyme formulation fermented from vegetable forms that creates the engineering behavior of soil, generates more soil compaction densities and more stability. One such Bio-enzyme, Terrazyme, has been applied in the current occupation to study its consequence on Atterberg Limits, Unconfined Compressive strength, and shear strength parameters of a CH soil. It has been confirmed that Terrazyme purifications of CH soil outcome in main development in Unconfined Compressive strength and Shear Strength parameters separately from Index characteristics. The entire characteristics are reliant on remedial time also. There is a specific best concentration for each characteristic in concern and it ranges from 0.2 ​ml/kg and 0.4 ​ml/kg of soil. Although, the more plastic clay soil is get to be addition responsive to Terrazyme purifications.

Study on the mechanical characteristics of sand pebble surrounding rock considering the disturbance effect of tunnel excavation

When conducting tunnel construction in sandy gravel strata, disturbance to the sandy gravel soil is inevitable, resulting in alterations to the properties of the surrounding rock. This paper investigates the relationship between the relative density (Dr) and shear strength parameters under different disturbance states through the implementation of indoor triaxial tests. Utilizing Dr as a disturbance parameter, a unified disturbance function that reflects the weakening and strengthening of sandy gravel soil is proposed. Furthermore, a revised constitutive model based on this unified disturbance function is established for the first time. The study results indicated that the results calculated by traditional models, which do not take into account disturbance effects, deviate from the experimental results by more than 20%. However, the error rate of the results computed by the modified model can be reduced to within 8%. The new model establishes a dynamic relationship between relative compactness and shear strength parameters of sand and pebble soils, which can take into account both the effects of negative and positive perturbations. The results can more accurately characterise the strength and deformation properties of the surrounding rock under the influence of construction disturbances in sand and pebble ground tunnels.

Investigation on shear strength parameters of soil and soft rock material in the low stress range

ABSTRACT The use of the Mohr-Coulomb shear parameters, friction angle (φʹ) and cohesion (cʹ), to define the expected shear strength of the soil is a widespread approach in the verification of the stability of a wide variety of structures. Due to technical limitations, these parameters are generally determined in the lab at excessively higher stress levels compared to field stress levels. The aim of this work is to investigate material behaviour in the lower stress range in the laboratory and to illustrate the development of the failure surface in these areas. For this purpose, special tests were carried out in which, by increasing the pore water pressure, a reduction in the effective stresses in the specimen could be achieved. The effective stresses were reduced until the specimen failed. By performing this test - starting from a normal consolidation stress the shear strength can be investigated in the low stress level.

Diatom-induced impact on shear strength characteristics of fine-grained soils

Diatomaceous soils, composed of diatom microfossils with biological origins, have geotechnical properties that are fundamentally different from those of conventional non-diatomaceous fine-grained soils. Despite their high fines content, diatomaceous soils typically exhibit remarkably high shear resistance, approaching that of sandy soils. However, the exact role that diatoms play in controlling the mechanical properties of fine-grained soils and the underlying mechanisms remain unclear. In light of this, the shear strength response of diatomaceous soils was systematically investigated using consolidated undrained triaxial compression tests on diatom–kaolin mixtures (DKMs) with various diatom contents and overconsolidation ratios. The micro- and nano-scale structures of the soil samples were characterized in detail using scanning electron microscope (SEM) and atomic force microscope (AFM) to interpret the abnormal shear strength parameters of diatomaceous soils. The results indicated that the presence of diatoms could contribute to significantly higher strength, e.g. the friction angle of DKMs was improved by 72.7% to 37° and the value of undrained shear strength tripled with diatom content increasing from 20% to 100%. Such significant improvement in soil strength with diatom inclusion could be attribute to the hard siliceous skeleton of diatoms and the interlocking between particles with rough surfaces, which were quantitatively analyzed by the surface roughness parameters with AFM. Furthermore, a conceptual model established based on the macro-mechanical tests and microscopic observations portrays a microstructural evolution of soils with increasing diatoms. The microstructure of soils was gradually transformed from the matrix-type to the skeletal one, resulting in a continual augmentation in shear strength through mutual interactions between diatom microfossils. This paper provides new insights into the multi-scale structural properties of diatoms and significantly advances our understanding of the mechanical behavior of diatomaceous soils.

Digital tools used on the teaching-learning process in geotechnical engineering

This article presents the incorporation of information and communication technologies on the teaching-learning process of geotechnical engineering to improve the quality of education and provide practical knowledge to civil engineering students. The content of this paper is divided into three main modules, which are: Treatment of laboratory tests results, Slope stability and Rock mass stability. For this, some software were used, including 2D limit equilibrium stability analysis, stability analysis of rock wedges and a dynamic mathematics, to obtain and analyze soil shear strength parameters, among others. Furthermore, a digital tool was developed to analyze the results gathered in compaction, one-dimensional consolidation, and direct soil shear tests, in order to clarify the relationship between theoretical concepts and practical results of the tests and analyses and to help students on doubts, in addition to increase their interest and motivation to perform the complete interpretation of the collected data. The activities were conducted in classes of geotechnical disciplines of the undergraduate course in Civil Engineering at the Federal University of Viçosa, aiming to promote active learning and improve teaching quality. Based on the results of an applied feedback questionnaire, it was observed that most students were satisfied with the resources used in the classroom, demonstrating that the implemented digital tools work as a didactic instrument that facilitates learning and comprehension of practical problems, in addition to enabling the resolution of several geotechnical engineering problems much more quickly and efficiently.

Advanced prediction of soil shear strength parameters using index properties and artificial neural network approach

This study embarks on developing predictive models for soil shear strength parameters, cohesion (c) and angle of internal friction (ϕ), in Bishoftu town, employing Artificial Neural Networks (ANN). It aims at offering a cost-effective and time-saving alternative to traditional, often expensive, and labor-intensive laboratory methods. The research utilizes soil index properties such as Sand %, Fines %, Liquid Limit, Plastic Limit, and Plasticity Index to construct separate ANN models for c and ϕ. These models use a multi-layer perceptron network with feed-forward back propagation, varying the number of hidden layers to optimize performance. The study's dataset comprises 316 soil test results, encompassing both primary and secondary data, conforming to ASTM Standards. Soil cohesion and internal friction angle were determined using the direct shear box method. The models demonstrated remarkable success in predicting shear strength parameters, evidenced by correlation values of approximately 0.99 for cohesion and 0.98 for internal friction angle, surpassing the capabilities of existing empirical methods. Further examination of the models included comparison with existing correlation techniques and cross-validation using primary soil test data. This validation process confirmed the ANN method's superior accuracy and fit for predicting shear strength parameters over selected empirical methods. This research substantiates the efficiency of ANN in geotechnical engineering, particularly for areas with limited resources for extensive soil testing. It establishes ANN as a powerful, efficient tool for estimating soil shear strength parameters, with significant implications for future planning, design, and construction projects in similar environments.

Optimasi Geometri Lereng dengan Evaluasi Nilai Faktor Keamanan Menggunakan Software Geostudio

The slopes of the Widas watershed in Kutorejo Village, Bagor District, Nganjuk Regency were hit by a landslide, damaging a 50-meter-long road. This damage has an impact on the activities and mobility of residents. The impact of landslides caused enormous losses, both infrastructure damage and loss of life. Several studies have been carried out, in determining slope stability it is necessary to observe at the research location and determine the type of soil, soil consistency, and soil shear strength parameters. This research aims to determine the value of the safety factor (FK) on the slopes of the Widas River. This research began by conducting a case study, including interviews, collecting field survey data, taking soil samples, and laboratory testing. Slope stability analysis was carried out using Geostudio software. The research results show that the soil type is classified as Poorly Graded Sand (SP), and the soil consistency is classified as Non-Plastic soil with a liquid limit of 26.093 and a shear angle of 20° - 30°. Slope improvements were carried out by changing the slope geometry until a slope ratio of 1V:2H was obtained by creating two slope core models. The FK value increased from 1.007 to 1.107 and 1.437 to 1.585 under pore water pressure conditions. Thus, the slope modeling obtained can be used to overcome landslide problems.

Effect of copula dependence structure on the failure modes of slopes in spatially variable soils

The copula dependence structure underlying the correlated shear strength parameters of soils can significantly affect the results of slope reliability analysis and risk assessment of slope failure. Currently, how do copula dependence structures affect the failure modes of slopes in spatially variable soils still remains an open question. This study systematically investigates the effect of copula dependence structures on the failure modes of a cohesive-frictional slope in spatially variable soils via an adapted random finite difference method (RFDM) that incorporates the copula-based random fields. The proposed RFDM proceeds with the simulation of cross-correlated random fields considering the copula dependence between the shear strength parameters of the slope. The strength reduction analyses are then performed within the framework of Monte Carlo simulation to obtain the stability analysis results, including the critical slip surface (CSS) and associated factor of safety (FS) and sliding volume. Finally, various statistical analyses on the number and distribution of CSS, FS and sliding volume as well as the failure modes versus different statistics of soil properties are analyzed considering different dependence structures. The results show that the overall distribution range of CSS obtained by the commonly used Gaussian copula is more concentrated, whereas the result by the No. 16 copula is the widest. The differences in the overall distribution range of CSS among different copulas decrease with the increase of the scale of fluctuation, coefficient of variation, and cross-correlation coefficient of the strength parameters. The proportions of different failure modes are comparable for the Gaussian, Plackett and Fran copulas, whereas the No.16 copula has the smallest proportion for the shallow failure and largest proportions for the deep and multi-slip failures. The influence of copula dependence structure on the slope failure mode is more significant than the statistical parameters of soil properties. The results provide useful references for copula selection when the underlying dependence structure is difficult to be determined.

A novel framework for ascertaining the safety factor and critical slip surface of 3D slopes reinforced with piles

The pile is a widely used reinforcement device in geotechnical engineering. For the present paper, we propose a new solution for calculating the safety factor (SF) of the 3D slope reinforced with piles and determining the critical slip surface (CSS) in the framework of minimum potential energy method. In particular, the mobilized shear stress on failure surface is determined by the equilibrium equation of forces operating on slip body. Meanwhile, the moving direction of 3D slope is equivalent to the direction of combined force acting on slip body. Additionally, the present method is combined with the genetic algorithm to identify CSS, and a novel criterion is proposed to locate the shape and position of CSS of a 3D slope using the total potential energy of landslide system as the objective function. The validation and comparison of results indicate that the SF obtained by the introduced method are close to reference solutions, and SF shows an obvious negative correlation with sliding direction (SD). It is also found that the support effect of pile is related to the pile location and the pile density. Meanwhile, the optimal pile position depends on the shape of failure surface and shear strength parameter of soil. Moreover, the effects of some parameters on SD of 3D slopes reinforced with piles are also studied.

Hazard Curves for Reliability Assessment of Strip Footings on Spatially Varying Cohesive Soils

The present study aimed to create a series of hazard curves against maximum total settlement and angular rotation of strip footings for probabilistic shallow foundation design on clays. Random field finite element method (RFEM) was adopted with elasto-plastic clay-like soil behavior, deformation modulus (Ed) and shear strength parameters (c and ) were employed as random field inputs. Parameters were defined and assigned to the analysis models with varying correlation lengths (h, v). Models have been iteratively solved one thousand times, and output distributions of maximum settlement and angular rotations were recorded. Probability density functions (PDF) were fitted to the outputs, and probability of failure (Pf) for footing deformation limits was subsequently estimated. Proposed hazard curves for two anisotropy and three variability categories were developed employing the estimated Pfs. The method proposed has been validated using an independent database of in-situ results, and a worked example was provided to illustrate the implementation of the process. The key contribution of the research is to form hazard curves for shallow foundations considering elasto-plastic soil behavior with the impact of all influencing parameters, respecting the limit values for foundation deformation in the design codes. The proposed technique offers a probabilistic evaluation of strip footings with spatial variation of clayey soils and a valid method for the reliability-based design of foundations in the serviceability limit state.

Estimation of Shear Strength Parameters from Easily-Collected Soil Physical Properties Using Bagging Learning Technique

Shear strength parameters, including cohesion and friction angle, are among the most crucial factors in soil mechanics, playing a pivotal role in the design and construction of engineering projects. This paper aims to estimate these essential soil shear strength parameters using an ensemble learning model. To achieve this, the current study employs the Random Forest (RF) model incorporating various physical parameters of soil, such as density (?), saturation degree (Sr), liquid limit (LL), silt content (SC), clay content (CC) to predict cohesion (c), and friction angle (?). In order to assess the predictive performance of the used model, this research used various metrics, including the mean absolute error (MAE), root mean square error (RMSE), and correlation coefficient (R2), to evaluate the model’s accuracy. The results reveal that RF performs superior predictive capabilities. Furthermore, the proposed model prediction ability was compared to the previous empirical equations. The comparison results indicated that the prediction capability of RF outperforms the previously developed equations.

Temperature Effects on Atterberg Limits

This study aims to investigate the effects of temperature on Atterberg limits of fine-grained soils with different mineralogies using fall cone tests. It is found in the literature that Atterberg limits are dependent on the clay mineralogy [1, 2] and are subjected to change upon an increase in temperature [3-5]. Measurements of liquid limit at different temperatures reveal sodium smectite is more sensitive to temperature than kaolinite. This observation is justified by relating the evolution of liquid limit to the initial changes of total specific surface areas associated with the physicochemical activity and inter-particle contacts [6]. Measurement of Atterberg limits using the conventional methods of Casagrande’s cup and threading is not very practical when the impact of temperature on these parameters is investigated. The trial and error associated with this method and the time they take may hinder a robust estimation of the liquid and plastic limit. Various studies have shown that Atterberg limits measured using Cone Penetration Test are less subjective and more consistent compared to traditional ways [7-9]. For these reasons, utilizing a Fall Cone Test apparatus and a temperature control unit facilitates the investigation of the impact of temperature on Atterberg limits. In this study, first, the liquid limits measured at room temperature by Fall Cone and Casagrande’s method are compared, and then Cone Penetration is utilized to investigate the evolution of liquid limit with temperature.
 Rhassoul Clay (29.4% Illite, 0.10% Kaolinite, 70.5% montmorillonite) and Illite Clay are considered in this study. The measured penetration values of the cone against moisture content at room temperature for these two clays are plotted in Figure 1. The liquid limit is the water content at which the cone penetrates 20mm into the soil in the cup [10]. Accordingly, Table 1 lists the determined liquid fall cone test and their deviation for the measured Atterberg limits using Casagrande’s cup. This comparison was performed to ensure that the difference between these two methods is not significant and the utilized device was accurate enough.
 To determine the Atterberg limits at higher temperatures (40 °C and 50 °C) and lower temperatures (10 °C), a temperature control unit is used to maintain the temperature of the soil sample during fall cone testing. For this purpose, first, the cup was filled with soil and then wrapped to avoid moisture migration in and out of the sample. The sample was then placed inside the temperature controller for an hour at the desired temperature. After one hour, the sample was swiftly unwrapped, and Cone Penetration test was performed. After the penetration a thermometer was used to measure the temperature at the center of the cup. This measurement showed that the alteration of temperature during the whole process is less than 1°C. Next, more water was added to the batch and then the same steps were followed until enough data points were obtained to estimate the liquid limit. The result of these tests allows for an assessment of temperature effects on Atterberg limits, which would be helpful in the understanding of the influence of temperature on different shear strength parameters of fine-grained soil with regards to their mineralogy.
 Table 2 lists the measured liquid limit values for Rhassoul Clay and Illite clay at different temperatures. The results suggest that the liquid limit of Illite is temperature independent. On the other hand, Rhassoul clay liquid limits was more sensitive to elevated temperatures and did not change with cooling. As mentioned earlier, the liquid limit is directly associated with clay mineralogy and the thermal alteration of soil characteristics [11, 12]. Therefore, the observed thermally-induced change in liquid limit should be discussed with respect to mineralogy. According to Table 1, the Illite liquid limit is temperature independent. Furthermore, Rhassoul clay comprises 70.5% montmorillonite minerals and 29.4% Illite. Providing this and the observed sensitivity of Rhassoul clay to temperature change can be attributed to the montmorillonite constituent. This argument can be further supported by testing more clays with different percentages of montmorillonite and illite.
  

Mechanical Behavior of Fiber-Reinforced Soils under Undrained Triaxial Loading Conditions

The design of fiber-reinforced soil structures, such as embankments and pavements, can be carried out using the results of unconsolidated, undrained triaxial compression tests conducted on specimens at their “as-compacted” water content and analyzed in terms of total stresses. The effects of soil and fiber type on the mechanical behavior of fiber-reinforced soils have not been methodically or adequately examined in the past under these conditions, and the effects of fiber length and content on the shear strength parameters of fiber-reinforced soils need further experimental documentation. Accordingly, five soils ranging from “excellent” to “poor” materials for use in earthwork structures were tested in the present study, in combination with five types of polypropylene fibers having lengths ranging from 9 to 50 mm. Unconsolidated undrained triaxial compression tests were conducted on specimens at their “as-compacted” water content, with fiber contents ranging from 0.5 to 2% by weight of dry soil. Fiber reinforcement reduces the stiffness and increases the deformability of the soil. The fiber-reinforced soils exhibit a more ductile behavior in comparison with the unreinforced soils. A Mohr–Coulomb type linear failure criterion satisfactorily describes the shear strength behavior of fiber-reinforced soils in total stress terms. The cohesion values of the fiber-reinforced soils range between 61 kPa and 301 kPa and increase up to seven times in comparison with the cohesion values of the unreinforced soils. The variations of the angle of internal friction of soils due to fiber reinforcement are generally limited to ±25%. The cohesion improvement due to fiber reinforcement is increased with increasing fiber content and fiber length up to 30 mm and is inversely proportional to the fine-grained fraction and the cohesion of the unreinforced soil.

Non-Probabilistic Reliability Analysis of Slopes Based on a Multidimensional Parallelepiped Model

Aiming at the problem that the non-probabilistic reliability analysis method of slope engineering, which is based on an interval model, cannot consider the cross-correlation of geotechnical parameters, a non-probabilistic reliability analysis method of slopes based on a multidimensional parallelepiped model is proposed. This method can effectively alleviate the problem of difficult data survey in the field of geotechnical engineering. Using the limited sample data of soil parameters, the multidimensional parallelepiped model is constructed. The performance function of the slope is constructed based on Latin hypercube sampling and the quadratic response surface method. Then, the limit state equation of the slope can be standardized using the multidimensional parallelepiped model. The non-probabilistic reliability indexes of the slope are calculated based on the global optimal solution to judge the stability state of the slope. The example analysis verifies the feasibility of the proposed method. The results show that the correlation of shear strength parameters of soil has a great influence on the non-probabilistic reliability indexes of the slope. When the correlation coefficients of the shear strength parameters are between −1.0 and 0, the smaller the correlation coefficient is, the greater the non-probabilistic reliability index of the slope is; when the correlation coefficients of the shear strength parameters are between 0 and 1.0, the non-probabilistic reliability index of the slope does not change with the correlation coefficient. The non-probabilistic reliability indexes of the slope obtained using the multidimensional parallelepiped model are between the results obtained using an ellipsoid model and those obtained using an interval model, which are validated by Monte Carlo method and relatively more reasonable. In the absence of a large number of geotechnical sample data, this method provides a new way for slope stability analysis and expands the application field of calculation methods based on non-probabilistic theory.

Probabilistic analysis of tunnel face stability in spatially variable soil

the limit analysis incorporated with the random field theorem is an effective approach for the probabilistic analysis of tunnel face stability. However, the existing incorporation procedure is not sufficiently efficient and accurate. A modified random field model, which is directly superimposed onto the rotational failure mechanism, is proposed to address this issue. In comparison with previous methods, the proposed approach avoids the generation of redundant random field elements and evades the inaccurate matching procedure of the elements, thereby enabling efficient and accurate estimation of the failure probability of a tunnel face. Moreover, cross-correlated random fields with the rotated anisotropy are readily generated with the proposed approach. Parametric sensitivity analysis is performed with Monte Carlo simulations to investigate the effects of the coefficient of variation, the scale of fluctuation, cross-correlation coefficient, and rotated anisotropy on the failure probability of a tunnel face. It is found that: (1) the failure probability is more sensitive to the scale of fluctuation in the vertical direction than that in the horizontal direction; (2) neglecting the cross-correlation of soil shear strength parameters leads to a slightly conservative design for tunnel face stability; (3) the influence of rotated anisotropy on the failure probability of a tunnel face is limited unless the soil exhibits high levels of uncertainty in its friction angle. Application of the proposed approach to multi-layered soil demonstrates its superiority in the probabilistic analysis of tunnel face stability in spatially variable soil.

Effect of the foundation soil properties on the optimum design of reinforced concrete retaining walls and defining critical boundary lines

The optimum design of reinforced concrete retaining wall (RCRW) is among the common optimization problems in civil engineering as it is affected by many different failure modes and input parameters. The properties of the foundation soil are one of the most critical input parameters in the optimum design of the retaining wall, just as in other civil engineering structures. While the existing foundation soil conditions on the site may sometimes be sufficient for an optimum design or it is necessary to consider alternative solutions such as ground improvement or foundation type change. This paper aims to determine the effects of the shear strength parameters of the foundation soil on the optimum wall cost using the modified artificial bee colony algorithm. For this purpose, optimum designs were performed separately for a total of 9246 different shear strength parameter combinations for a wide range, where the cohesion parameter was also considered in addition to the internal friction angle only used in the literature. The analysis results showed that the shear strength parameters of the foundation soil are highly influential in wall costs under weak soil conditions but not under strong soil conditions. In order to make this distinction easier, three important cost regions and two boundary lines separating these regions were defined depending on the shear strength parameters of the foundation soil, and an approach was proposed to determine the positions of these boundary lines. Moreover, the 125 wall models were investigated under 9246 different foundation soil conditions to reveal the effects of important parameters such as wall height, surcharge load, and backfill internal friction angle on the critical boundary lines. Knowing the boundary lines separating weak and strong soil conditions depending on the wall input parameters will significantly contribute to the truly optimum design of retaining walls.

Determination of Drained Residual Shear Strength Parameters of C Soil Using Ring Shear Apparatus

bstract: Shear strength parameters such as cohesion and angle of internal friction of soil are very important for the design of foundation of the structures and soil structures. Many tests such as direct shear, Tri-axial, UCC are available to determine the shear strength parameters of soil. Specifically, Residual Shear strength plays a major role in slope stability analysis and Earthquake analysis. The Residual Cohesion (Cr) and Residual angle of internal friction (Φr) are used for slope analysis. In this study, the soil used is c-Φ soil collected from Anaikatti, Coimbatore district and the residual shear strength was determined using Ring shear apparatus. In Ring shear test, the sample undergoes different stages such as consolidation and shearing for varying applied pressures of 100kPa, 200kPa and 300kPa. A plot drawn between normal stress and residual shear stress gives the residual shear parameters and the values of Cr and Φr are respectively 6kPa and 180

Anchor conditions for estimated unsaturated shear strength functions

Since the mid-1990s, several empirical unsaturated shear strength equations have been proposed for use in geotechnical engineering practice. Most of the equations have been based on information associated with the measured drying soil-water characteristic curve (SWCC) in combination with the effective shear strength parameters of the saturated soil. There have been few studies, however, undertaken on verifying and comparing the suitability of the proposed unsaturated shear strength equations. This study involves consideration of a wide range of possible drying SWCCs plotted as a relationship between the degree of saturation and suction (saturation soil-water characteristic curve ( S-SWCC)). The study forms the basis for comparing five methodologies that have been proposed for the estimation of the shear strength of unsaturated soils. The SWCCs are defined by the fitting parameters for the Fredlund and Xing (1994) sigmoidal equation. This study supports the use of unsaturated soil shear strength empirical estimation methods using the S-SWCC anchor points of air-entry value and residual suction of the soil.