Soil Strength Parameters Research Articles

Impact of Isothermal Layering on the Stability of Saline Soil Subgrade in Cold Regions

In order to determine the influence of heat on the stability of the saline soil subgrade slope in cold regions. Firstly, four typical representative saline soils were selected as subgrade fillers, and geotextiles were added at the bottom of the subgrade as a study subject. A two-dimensional numerical model for the temperature field of subgrade soil was established based on COMSOL Multiphysics. Secondly, combined with the main strength parameters of subgrade soil at different temperatures, an isothermal stratification-strength parameter function calculation model was proposed. Then, the SLOPE/W module in GeoStudio is used to stratify the established subgrade model according to isotherms and calculate the stability safety factor of saline soil subgrades in cold regions under different months, slopes, and subgrade heights, respectively. Finally, the influence of submergence at the foot of the slope on the stability of the subgrade slope is discussed. The results show: After the cold season coming, with the decreasing of temperature, the stability of HC-1 and HC-2 saline soil subgrade slope increased to different extents when the ground temperature dropped to -10°C. When the local temperature dropped below -10°C, the stability has slight decline; CS-1 and CS-2 saline soil subgrade in the ground temperature dropped to 10°C (HC-1 and HC-2 denote two groups of saline soil with high chloride-salt content (≥15%) and low sulfate salt content (≤0.5%), whereas CS-1 and CS-2 denote two groups of saline soil with low chloride-salt (≤5%)), the slope stability was significantly improved, and the stability of CS-1 increases slightly with further decrease in temperature.

Prediction of Shear Strength Parameters of Gypseous Soil using Artificial Neural Networks

The shear strength of soil is one of the most important soil properties that should be identified before any foundation design. The presence of gypseous soil exacerbates foundation problems. In this research, an approach to forecasting shear strength parameters of gypseous soils based on basic soil properties was created using Artificial Neural Networks. Two models were built to forecast the cohesion and the angle of internal friction. Nine basic soil properties were used as inputs to both models for they were considered to have the most significant impact on soil shear strength, namely: depth, gypsum content, passing sieve no.200, liquid limit, plastic limit, plasticity index, water content, dry unit weight, and initial voids ratio. Multi-layer perceptron training by the backpropagation algorithm was used in creating the network. It was found that both models can predict shear strength parameters for gypseous soils with good reliability. Sensitivity analysis of the first model indicated that dry unit weight and plasticity index have the most significant effect on the predicted cohesion. While in the second model, the results indicated that the gypsum content and plasticity index have the most significant effect on the predicted angle of internal friction.

Parametric study of glass fiber reinforced fine-grained soil with emphasis on microstructural analysis

ABSTRACT A comprehensive experimental programme was undertaken to study the parametric effect on mechanical behaviour of fine-grained soils by inclusion of glass fibres. The behaviour of both unreinforced and reinforced soil specimens under uni-axial compression was systematically investigated corresponding to fibre length, fibre content, soil density, moisture content and loading rate. The unconfined compression strength test (UCS) results confirmed the reliance of UCS improvement index () on the selected parameters. For 18 mm fibre length and 0.9% fibre content, UCS improvement index of 71.68% was observed. The interface morphologies were studied by analysing the failure patterns and microstructural mechanisms through scanning electron microscopy. Artificial neural network (ANN) was used to develop an estimation model of the relationship between soil strength and different reinforcement parameters. This study is expected to help in better understanding of mechanical behaviour of FRS and its subsequent application in the field.

DEVELOPMENT OF A SIMPLE DESIGN CHART AS AN EVALUATION OF SLOPE STABILITY

Landslides can damage public facilities and also have a negative impact on the community. This impact will be able to minimize when knowing the slope stability by carrying out the analysis to determine the factor of safety against landslide. The most accurate results usually get from calculation through computer software, but sometime it will take time and also not all of the designer have the sophisticated software. Another method in predicting the slope stability is using design chart as carried out in this study. The aim of this study is as a sustainable development of a simple chart to help the designer in predicting the landslide possibility. The graph will consist of the relationship between the slope height and the factor of safety for several soil strength parameter and slope angles. The slope stability analysis method will be based on LEM (Limit Equilibrium Method) through Bishop’s equation. The result is then being tested through case study and comparing with the other existing design chart and show a satisfactory result.

The Interaction Effect of Particle Composition and Matric Suction on the Shear Strength Parameters of Unsaturated Granite Residual Soil

The Interaction Effect of Particle Composition and Matric Suction on the Shear Strength Parameters of Unsaturated Granite Residual Soil

The Chemical and Mineralogical Composition and Their Effects on Strength Parameters of Cohesive Soil Developed over Enugu Shale

The results of chemical and mineralogical composition of cohesive soils developed over Enugu Shale, as well as the effects on the strength parameters are presented in this paper. The strength parameters were determined in the cohesive soil specimens in the study area, while the chemical and mineralogical tests were done on the representative soil types from the study area. Some correlations between chemical composition and strength parameters of cohesion and angle of internal friction as well as other physical parameters such as liquid limit, plastic limit, plasticity index and activity of soil were obtained. The effects of chemical and mineralogical composition on strength parameters, based on the correlation between chemical composition and strength parameters (cohesion and angle of internal friction) were examined. The results show that chemical and mineralogical compositions significantly affect the angle of internal friction and cohesion thereby impacting on the strength of cohesive soils developed over Enugu Shale.

Comprensión de la sensibilidad a las propiedades del suelo y condiciones de lluvia de dos modelos de estabilidad de taludes basados en la física

Physically-based models have been used to assess landslide susceptibility, hazard, and risk in many regions worldwide. They have also been regarded as valuable tools for landslide prediction and the development or improvement of landslide early warning systems. They are usually validated to demonstrate their predictive capacity, but they are not deeply studied regularly to understand the sensitivity of the input variables and the behavior of the models under many different rainfall scenarios. In this research paper, we studied two distributed physically-based models for shallow landslides: SLIP and Iverson. For this, the first-order second-moment (FOSM) method was used to calculate the contribution of random input variables (soil strength, unit weight, and permeability parameters) to the variance of the factor of safety. Different intensity and duration rainfall events were simulated to assess the response of the models to those rainfall conditions in terms of the factor of safety and failure probability. The results showed that the shear strength (cohesion and friction angle, in order of significance) parameters have the largest contribution to the variance in both models, but they vary depending on geological, geotechnical, and topographic conditions. The Iverson and SLIP models respond in different ways to the variation of rainfall conditions: for shorter durations (e.g. ≤ 8 h), increasing the intensity caused more unstable areas in the SLIP model, while for longer durations the unstable areas were considerably higher for the Iverson model. Understanding those behaviors can be useful for practical and appropriate implementation of the models in landslide assessment projects.

The behaviour of stress variation in sandy soil

Abstract This research article represents the recompacted dense sand sample behaviour and stress distribution in the direct shear box. In Lithuania, sand is quite common on a construction site, in general about 32%. To reduce the influence of the shear box design on the experimentally determined values of the soil strength parameters, it is necessary to know the regularities of the change of the normal load acting in the shear plane. Three different normal stresses of 50, 100, and 200 kPa were applied to the dense sand in the direct shear boxes during experimental and numerical simulation. The results showed an obvious evidence of non-uniformity of stress for standard and raised specimens. The numerical analysis exhibited that when the sample is loaded only with a vertical load, approximately 75% of that load is transferred to the sample bottom, 84% to the shear plane, and 95% to the top. At the end of the shear test, the vertical force in the shear plane reaches maximum, the normal stress is higher by 13.5% than applied on the sample top. The shear strength of sandy soils were influenced by box size and sample height too. The improved shear box apparatus allows to estimate the vertical load at shear plane.

Soil Hydraulic and Strength Parameters as influenced by various Mechanized Rainwater Conservation Practices in Rainfed Groundnut Crop

In India, rain fed agriculture constitutes to 60% of the net cultivated area and accounts for nearly 44% of the National food basket. 54.6% of the total workforce is engaged in agricultural and allied sector activities (Census, 2011) and accounts for 17.8% of the country’s Gross Value Added (GVA) for the year 2019-20. Rain Water Harvesting (RWH) is a low-cost, easy-to-use, environmentally friendly way to recover a large part of this lost water. In India, the rainfed agriculture constitutes 60% of the total net sown area and Andhra Pradesh constitutes nearly 57% net sown area under rainfed agriculture. Groundnut (Arachis hypogea) occupies nearly 28.3% of the cultivated area under oil seed crops in India and the area under groundnut in the Country is 5.40 Mha with a total production of 6.57 Million Tonnes (MT) and with the productivity of 910 kg ha-1. The area of groundnut crop in Andhra Pradesh is 7.47 Lakh ha whereas Ananthapuramu District occupied 6.71 Lakh ha. The study was carried out under different surface and subsurface rainwater conservation practices with the objective to study the soil hydraulic and strength parameters viz., soil moisture content in frequent intervals at 10 cm, 20 cm, 30 cm depth and bulk density, particle density and porosity at 20 cm depth. From the study, it was observed that, highest soil moisture content was observed in subsoiling at 1 m distance + broad bed and furrow system treatment at three different soil sampling depths of 10 cm, 20 cm and 30 cm as 25.40%, 31.20% and 27.50%, respectively at 40 Days After Sowing (DAS) and 29.74%, 34.71% and 22.38%, respectively at 80 Days After Sowing (DAS). The lowest bulk density and highest soil porosity were observed as 1.52 g cm-3 and 32.7% in subsoiling at 1 m distance + broad bed and furrow treatment than other practices.

Reinforcement Effect of Polypropylene Sheet on Soil Strength with Cement

Following thorough soil investigation, the designs for the foundations and other structures are made. The foundations and structures are more reliable and safer when the right soil is used. In this study, cement-coated Polypropylene (PP) sheets were employed to strengthen the soil, enhancing its shear strength and other characteristics. Two (2) soil samples were taken to compare the average outcomes and minimize error. Before using PP sheets for soil reinforcement, various index and strength parameters, such as breaking tensile strength, elastic modulus, and breaking and fusion points, among others, were examined. Properties like liquid and plastic limit, specific gravity, Maximum Dry Density (MDD), and Optimum Moisture Content (OMC) were examined as discussed. Reinforcement of 0%, 0.05%, 0.15%, and 0.25% were applied and tested against shear strength evaluation with the help of a direct shear test. An increase in strength is observed in soil samples 1 and 2, i.e., 1.27, 2.25, 2.27 and 1.28, 1.42, 1.65, and 1.79 in kg/cm2, respectively. Similarly, unconfined compression strength was observed to increase from 0.0692 MPA to 0.0942 MPA, which is 11.68% and 35.94% increment in soil samples 1 and 2 at 0% and 0.05% reinforcement, respectively.

Evaluation and statistical description for the soil characteristics in Nasiriyah based on Eurocode 7

The reliability-based geotechnical design emerged with Eurocode 7 standards and is still popular. This paper studies the engineering properties of a model of Nasiriyah soil. It aims to calculate the distinctive value of Nasiriyah soil and describe the different identification methods for laboratory tests. Knowledge of the properties of engineering parameters is essential for accurate design, measurement methods, and geotechnical investigation, and the Eurocode 7 approach of the soil is essential for geotechnical design. Therefore data were collected, and the characteristic values were determined using statistical methods. Three project sites in Nasiriyah city were studied to determine the correlation of soil strength parameters and calculate the characteristic value based on Eurocode 7. The study results showed that the Marquez method and Schneider's equations give characteristic values with a 95% reliable and economical design within the measured data range, taking into account the average, coefficient of variation of the site, and the number of measured data. It is found that the most appropriate characteristic values of the soil of the studied sites are less than the mean by half a standard deviation.

Estimation of Critical Safety Thickness of the Base against Confined Water Inrush for a Rectangular Foundation Pit

Affected by confined aquifer, basal inrush accidents caused by excavation are common in foundation pits, and accurate estimation of the safety thickness of the base is a big concern of engineers. In this paper, a three‐dimensional failure mechanism of base inrush was constructed for a rectangular foundation pit. In this mechanism, the strength of the soil mass was assumed to be nonhomogeneous along the depth, and the soil‐mass failure satisfied the linear and nonlinear Mohr–Coulomb strength criteria. Then, based on the limit equilibrium theory, the prediction method for the safety thickness of the base against confined water inrush was deduced, and a comparison with existing research works was conducted. Furthermore, the influence laws of soil strength parameters, pit design parameters, and confined water pressure on the critical safety thickness were analyzed. The results show that the critical safety thickness of the base is positively correlated with nonlinear coefficient and confined water pressure but negatively correlated with cohesion, internal friction angle, nonhomogeneity coefficient, and unit weight. The soil strength is a key factor affecting the base safety thickness, which should be paid enough attention to in engineering design and construction. The research findings in this paper can provide a theoretical reference for the prevention and control of basal inrush accidents in confined water strata.

The Numerical Solutions of the Nonlimit-State Active Earth Pressure Under Back-Fill Wall Rotation Around the Bottom

The displacement pattern of wall footing rotation occurs for the backfill wall constrained at the bottom. The non-limit states of the soil layers at different depths are different in this pattern, and present difficulties for soil stress calculation. Based on the existing research, the functional relationship between soil strength parameters of the wall footing rotation pattern and wall displacements were detruded. Under the assumption that the backfill forms a circular arch and the slip surface is uncertain, the backfill was divided into long horizontal slices, the numerical iteration scheme for the nonlimit-state active earth pressure in the wall footing rotation pattern was constructed, and the numerical calculation method for the active earth pressure was given. The numerical method not only determines the slip surface shape, but calculates the intensity, the resultant force and the action point of the nonlimit-state active earth pressure. The backfill slip surface is a curved one and the new numerical solution is more consistent with the existing full-scale test results than the existing analytical results. This work provides more accurate numerical solutions of the nonlimit-state active earth pressure on the rigid retaining wall in the footing rotation pattern, and makes a practical guide to design of such retaining walls.

Study on gravel soil strength degradation and its influence on the slope stability in reservoir bank fluctuating zone

During the operation of the reservoir, due to the periodic fluctuation of the reservoir water level, a certain depth of fluctuation zone of the reservoir bank slope will be formed. The fine particles in the soil of the fluctuation zone will erode and migrate with the seepage of the reservoir water, resulting in the deterioration of soil strength parameters in different degrees, and even affecting the stability of the bank slope in severe cases. Because of the continuous particle size distribution and large porosity of gravel soil bank slope, under the periodic seepage of reservoir water, it is more likely to have serious particle loss, and the accumulated soil strength degradation caused by particle loss will further cause bank deformation, even instability. This paper carries out periodic pressure permeability tests on gravel soil samples to obtain the change law of particle loss rate and the degradation law of strength characteristics, and researches its influence on the slope stability. The research results show that the periodic seepage will degrade the strength of gravelly soil. With the increase of infiltration times, the deterioration range gradually decreases and the strength tends to be stable.

CHANGE IN STRENGTH PARAMETERS OF DISPERSED SOILS AFTER HIGH-FREQUENCY VIBRATION

The use of the technology of high-frequency sheet piles driving or extraction in conditions of weak, structurally unstable soils inevitably leads to a change in the structure of the soil. This is especially true for buildings which fall into the zone of influence. Often, foundation for historical buildings is water-saturated sands, spread by fluid and fluid-plastic clay soils. In the process of external dynamic action, the soil foundation is been destructing, so their strength and deformation parameters are reduced. In this case, the result of vibration effects on a dispersed water-saturated sample can be both compaction for sandy soil and decompaction of clay soils. These changes lead to additional deformations of buildings and structures of the surrounding area. Therefore, the issue of assessing the limits of applicability of vibration technology in certain conditions is relevant. The object of the study is the changes in the properties of clay soils of various consistencies after exposure to vibration. The results of laboratory studies to determine the strength parameters of dispersed soils after high-frequency vibration are presented. The results of field measurements by CPT "before", "after" vibration immersion and vibration extraction of sheet piles are considered. Comparison of the results of field and laboratory studies is carried out to identify patterns of change in the strength characteristics of weak soils under the influence of vibration loads. A tendency towards a decrease in the strength parameters of dispersed soils is shown. Currently, due to the insufficient number of laboratory and field studies to study the effect of high-frequency vibration on the change in the strength parameters of weak water-saturated clay soils, it is not possible to identify a clear dependence of the change in parameters on the time and frequency of vibration.

COMPARATIVE ANALYSIS OF NATM CONSTRUCTION TECHNOLOGIES OF DNIPRO METRO ESCALATOR TUNNEL

Purpose. On the basis of the comparative analysis to carry out a substantiation of the most expedient and rational way of strengthening of a weak massif during a construction of Dnipro metro escalator tunnels by NATM. Methodology. To achieve this goal, an analysis of construction technologies in weak soils was conducted. The most used technologies are Forepoling Umbrella System (FUS), artificial ground freezing and chemical cementation. The peculiarities of carrying out each of the technologies for the conditions of inclined production were analyzed. It is determined how each of the technologies is applied to escalator tunnels and implements the strengthening of weak soil. Findings. The advantages and disadvantages of three technologies for fixing weak soil around the escalator tunnel are identified. Based on comparative analysis, it was found that the only technology that provides increased strength parameters of loamy soils, characteristic for the upper part of the escalator tunnel of the Dnipro metro, is the technology of chemical strengthening (cementation). In some cases, if necessary, short sections of sloping course, characterized by particularly weak soil, can be supported by several pipes, without creating a continuous leading mount. The results of the analysis are the basis for further substantiation of cementation, which creates a multilayer system "reinforced soil massif – temporary fastening – permanent lining". Originality. Based on the results of comparative analysis of three technologies for escalator tunnel construction by NATM, it is proved that the use of cementation not only increases the strength of the soil during drilling, but also further in operation serves as an additional element of the multilayer system "reinforced soil massif – temporary fastening – permanent lining". Practical value. In the course of research, the substantiation of cementation as the most rational and effective technology of strengthening of the surrounding weak massif at construction of the Dnipro metro was carried out.

Stabilization of Kaolin Clay Soil Reinforced with Single Encapsulated 20mm Diameter Bottom Ash Column

Ground improvement methods are used to reduce the weakness of soft clay, which is low strength and high compressibility. The stone column technique involves replacing any of the soil with crushed stone such as broken rocks or sand which is an efficient method of improving the strength parameters of soil. Bottom ash usage in materials of building will effectively decrease the buildup of the waste and hence protect the environment. This study is to determine the shear strength of kaolin soft clay reinforced with a 20 mm diameter single encapsulated bottom ash column with various lengths. The research will look into the physicomechanical qualities of the materials used, including subsoil and bottom ash. Three (3) batches of samples with each batch consists of five (5) samples were prepared by using compaction method. All kaolin samples with a diameter of 50mm and height of 100mm with single encapsulated bottom ash columns with various lengths which are 60mm, 80mm, and 100mm were tested under Unconfined Compression Test (UCT). The result illustrated that the strength of samples increases as the height and volume of encapsulated bottom ash column increases.

Influence of shear rate on the soil's shear strength

One of the most important mechanical properties is shear strength. It is conditioned by the value of the maximum shear stress that the soil can withstand before failure. Exceeding the shear strength causes one particle to slide next to another, causing the failure of soil. The shear strength of the soil for effective stresses is1 a combination of drained strength parameters: internal friction angle (φ) and cohesion (c) defined by the Mohr-Coulomb failure criterion. It is determined “in situ” and by laboratory experiments. Direct shear is the oldest and the simplest laboratory experiment to determine the shear strength of the soil. The first phase of experiment is specimen consolidation under specific vertical stress, and in the second phase specimens are sheared at a given shear rate, depending on the consolidation properties of the soil. Cohesionless soils are sheared at up to 100 times higher shear rate compared to cohesive soils. Shear rate and drainage conditions affect the magnitude of soil strength parameters. The paper is based on the comparison and demonstration of the influence of different shear rates on the peak and residual shear strength in the direct shear device. The tests were performed on two samples of low plasticity clay (CL) and one sample of high plasticity clay (CH).

An optimization procedure for the soil behavior identification using pressuremeter results

The soil parameters identification procedure is usually a trade-off between sophisticated soil model behaviour and the large number of parameters to identify. Such procedure that can accomplish both of these objectives is highly desirable, but also difficult. This paper presents a methodology for identifying soil parameters that takes into account different constitutive equations. For identifying the generalized Prager model parameters, associated to the Drucker and Prager failure criterion, using an in-situ pressuremeter curve, we have proposed a procedure that is based on an approach of inverse analysis. This approach involves the minimizing the function representing the area between the experimental curve and the simulated curve, obtained by fit in the model along the in-situ loading path. A comparative study between two optimization processes is proposed. The first is based on the technique of the simplex by Nelder and Mead, while the second is based on the decomposition of the pressuremeter curve in three distinct areas. After a brief description of an existing computer program called Press-Sim, which has been written in Fortran for analyzing a cavity expansion using the finite element method, a short explanation is given about the two optimization procedures considered in this article. Then, for a chosen site where soil strength parameters are measured, the comparative study has been performed for both methods at four different depths. For the determination of the angle of friction, the two procedures yield very close values and are in a good agreement with that given by the triaxial test, while for the cohesion, they both diverge from each other on both sides of the value measured by the trial test.

Towards an improved analytical framework to estimate active earth pressure in narrow c – ϕ soils behind rotating walls about the base

Retaining walls are sometimes unavoidably constructed near existing stabilized structures to maintain stability of narrow retained c-ϕ soils. Although some analytical approaches have been presented to estimate active earth pressure on the wall undergoing rotation about the base (RB), the contributions of soil cohesion and horizontal shearing forces in c-ϕ soils are typically neglected for brevity. Hence it is always expected to be improved, and to seek a more economical design framework used in the retaining wall with narrow c-ϕ soils. This paper first uses finite element limit analysis (FELA) to study the developed failure mechanisms under RB mode, which provides a basis to establish a calculation model. An analytical framework using arched differential element method is further presented with overall considerations of soil cohesion, soil arching effect, shearing forces between adjacent elements and the studied failure mechanism. The calculation flowchart is mapped and executed under C++ environment. The results from centrifuge test, existing analytical approaches and FELA are compared for validation in both purely-frictional and cohesive-frictional soils. A parametric study considering the effects of sensitive variables (e.g. aspect ratio, soil strength parameters and wall-soil interface friction angle) on the design is carried out. For the use of proposed analytical framework in practice, two simplified design equations are provided to correlate standard Coulomb’s solutions.