Strength Of Expansive Soil Research Articles

Numerical simulation of the uplift bearing behavior of pile foundations for transmission towers in expansive soil area

Piles are commonly used as foundations for power transmission towers located in expansive soil areas. The strength of expansive soil is highly sensitive to the changing water content, which complicates the pile–soil interaction. In this study, a 3D elastoplastic finite element analysis of a typical pile foundation for a transmission tower in an expansive soil area was conducted to understand the effect of water content in expansive soil on the uplift bearing capacity of the pile foundation. The results that the failure mode of the pile foundation is almost unaffected by the water content. Shear failure was observed at the pile–soil interface, and, when the pile was pulled out, it lost its uplift bearing capacity. With the increasing water content of the soil, the ultimate uplift bearing capacity of the pile foundation exhibited a significant decreasing trend, whereas the displacement of soil around the pile became remarkable. The distribution of pile axial force and lateral frictional resistance during the uplift process was also evaluated. The pile axial force decreased gradually and at a higher rate with increasing depth. Once the pile reached the ultimate uplift bearing state, the pile lateral friction increased almost linearly with depth.

Laboratory modeling of thermal and temporal cracking in swelling clays

Crack development in a changing environment is the controlling factor for the stability and strength of expansive soils. Expansive soils exhibit large volumetric changes with changes in their moisture conditions that may occasionally lead to reduced bearing capacity and foundation failures. This study purports to model crack initiation and its spatial progression in relation to the moisture content and drying period, respectively. Volumetric soil shrinkage is determined using high-definition digital camera imaging and Vernier scale methods, while the soil settlement under vertical shrinkage deformation could be captured through a tensile stress model for soils. It was revealed that a small change in suction could trigger crack initiation, which would propagate further under different environmental conditions. Furthermore, it was observed that the crack volume increased rapidly at specific moisture content and could penetrate as deep as 1 m after nearly 1.5 months that is fully consistent with the current model predictions. A comparison between the performance of the model proposed in this study and that of two existing models shows that the former predicts the vertical shrinkage strain values in closer agreement with those observed experimentally and is less conservative than those predicted by both models. Nevertheless, the findings from this study could be used to quantify the detrimental behavior of expansive soil present in pavement subgrades and shallow foundations for lightweight structures.

The Effects of Salt-Lake Salt Solution on the Strength of Expansive Soil

Expansive soils are widely distributed and often cause serious damage to structures. Hanzhong expansive soil and Yulin salt-lake solution were adopted to investigate the effect of salt-lake salt solution on the strength of expansive soil. Expansive soils modified with salt-lake salt solutions with different concentrations (0.1, 0.5, and 1.0 mol/L) were evaluated by X-ray diffraction (XRD), Atterberg limit, free swelling, no load swelling ratio, and triaxial compression tests. The improved expansive soil research using salt-lake salt solution was carried out based on the macroscopic mechanical characteristics. Test results showed that the addition of salt-lake solution effectively inhibited the expansibility of soil. With the increase of the concentration of salt-lake solution, liquid limit, plastic limit, plastic index, free expansion rate, no load swelling, cohesion, and internal friction angle of expansive soil were decreased in varying degrees, and stress-strain relationship curve gradually showed strain softening trend. The reason for the above results was believed to be that salt-lake salt solution reduced the force between particles on shear surface and reduced mutual hindrance.

Study on Mechanical Properties of the Expansive Soil Treated with Iron Tailings Sand

Aiming at researching shear strength parameters of expansive soil modified by industrial waste iron tailings sand, the enhancement of expansive soil is explored from macroscopic and microscopic aspects. After characterization and testing by various means, the results show that expansive soil modified by iron tailings sand will increase the maximum dry density of the improved soil and reduce its optimal moisture content, which is beneficial in tuning the moisture content at the construction site. In addition, iron tailings sand can improve the shear strength of expansive soils. The influence of iron tailings sand on cohesion increases first, then decreases, and reaches the peak value at 30%, while the effect on internal friction angle exhibits a continuously increasing trend. Furthermore, according to mercury intrusion tests and microangle analysis, the addition of iron tailings sand can reduce the tiny pores and enhance the occlusal force of the soil. Simultaneously, it increases the number of large pores, maximizing the macroscopic strengthening of iron tailings sand towards the expansive soil.

Physical and Mechanical Characteristics of Shallow Expansive Soil due to Freeze-Thaw Effect with Water Supplement

Shear strength of shallow expansive soil varies along with the depth under the freeze-thaw effect. This work investigates shear strength characteristics of shallow expansive soil by simulating the actual freeze boundary conditions of seasonal frozen areas with water supplement. An integrated approach incorporating the freeze-thaw test and direct shear test was adopted. Firstly, unidirectional freezing tests for expansive soil columns under three different freezing temperature gradients were carried out. Secondly, direct shear tests under low vertical stress were performed on the standard samples, which were prepared by using cutting rings cut the thawed expansive soil columns into nine segments along with the depth. Temperature, water content, and dry density at different depths were also investigated after the freeze-thaw process. The test results showed that, after the freeze-thaw process, the shear strength of expansive soil columns showed significant differences along with the depth and highly correlated with water content, specifically the higher water content and the lower shear strength. The minimum shear strength in the expansive soil columns occurred at the soil layer below the frozen and unfrozen zones interface. The expansive soil column’s shear strength changed most under the moderate freezing temperature gradient corresponding to the most considerable shear strength reduction. Moreover, the significant decrease in cohesion was the main reason for the shear strength reduction of expansive soil after the freeze-thaw process. These results indicate significant depth variability in shear strength of expansive soil under the freeze-thaw effect.

Experimental study on unconfined compressive strength of expansive soil improved by lignin and cement

Aiming at the question of improvement expansive soil in Nanyang area, the composite improvement method of lignin and cement was adopted. Based on the unconfined compressive strength test, the variation law of unconfined compressive strength of improved expansive soil with different lignin content, different compaction degree and different curing age was studied. The test results show that the composite of lignin and cement can effectively improve the unconfined compressive strength of expansive soil. The unconfined compressive strength of L-C (lignin and cement) improved expansive soil reaches the maximum when the cement content is fixed at 4% and the lignin content is 1%. The unconfined compressive strength of L-C improved soil increases with the increase of compaction degree and curing age, and the strength growth mainly concentrated in the first 7 days of curing age. From the point of improvement mechanism, the hydration and gelation reaction of cement occur in expansive soil, and gel material with higher strength is formed to enhance the strength of expansive soil. The appropriate amount of lignin can fill the pores between soil particles and make the connection between soil particles more closely, so as to improve the strength of expansive soil.

Exploratory study on argo-industrial wastes for improving geotechnical properties of expansive soil – As sustainable material

The suitability of using Mango Kernel Ash (MKA) as fruit processing industrial waste is a cheap and satisfactory stabilizing agent for pavements laid on expansive soils in low rural roads. A research facility test program comprising an arrangement of Atterberg's limit, standard Proctor test, Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), Free Swell Index (FSI), and Swell Pressure tests was conducted on the untreated and treated soil samples with MKA (0%, 5%, 10%, 15%, 20%), CCR (2%, 4%, 6%) and lime (2%, 4%, 6%) by weight of soil. The application of MKA with Calcium Carbide Residue (CCR) and Lime to the soil significantly changed its properties by decreasing its plasticity and making it more workable by improving its CBR and UCS values. With the increase in MKA, and its mix combinations the increment is seen in the strength of expansive soil, and higher strength was obtained with 20%MKA and 6%CCR; which were later compared with lime instead of CCR. The results of swell pressure decrease by 1/6th of virgin soil value and the Free Swell Index also decreases. To know the microstructural orientation Scanning Electron Microscopy (SEM) analysis was done.

Using Fine Silica Sand and Granite Powder Waste to Control Free Swelling Behavior of High Expansive Soil

Many researchers have been interested in studying the effect of adding local natural materials or construction waste on the properties of poor subgrade soil. However, changes in size and strength of expansive soils can cause extensive damage to the geotechnical infrastructure. This damage is often repeatable and latent in the long term, and is a critical issue in highway subgrade engineering. This paper examines the effect of adding both Fine Silica Sand (FSS) and Granite Cutting Powder Waste (GPW) materials on the welling characteristics of expansive soils. Atterberg limits, free swell index, and rate of swell of the mixtures were used as a key to assess properties of a group of expansive soil samples after adding different percentages of the mentioned materials. The rates of additions were 10%, 20%, 30%, 40%, 50%, 60 and 70% of the weight of the soil samples. The test results showed that FSS and GPW significantly affect the expansive soil properties. However, adding 70% of both FSS and GPW reduced the swelling index from 58.3% to 6.6% and from 58.3% to 11% after 7 days of curing, respectively. This study suggests that the Fine Silica Sand and Granite Powder Waste can be used as stabilizers for expansive highly plastic soils.

Effect of fly ash-limestone dust stabilization on volume change and strength of expansive soil

The expansive soils in semi-arid and arid regions are affected by swelling-shrinking due to climatic effects, causing damage to lightweight structures. Various methods and materials have been employed to improve the engineering properties of these soils. This paper includes the findings of experimental work conducted studying the effectiveness of use of fly ash (FA) and limestone dust (LS) in the enhancement of the engineering properties of expansive soil sampled from Haspolat, Nicosia. Limestone quarry dust is a by-product produced in quarries as a result of the process of crushing and grinding. Laboratory experiments were conducted on the expansive soil with additive proportions of 5% LS, 10% FA, and 5% LS+ 10% FA by dry mass of the soil at curing periods of 1, 14 and 28 days. The 5% limestone dust and 10% fly ash mixed samples have shown significant increment of up to 220% in CBR value, 82% in volumetric shrinkage, and 100% in swell potential. The study has concluded that the introduction of admixtures to expansive soil generally enhanced the geotechnical properties, exhibiting greater durability and stability compared to the untreated soil. Hence limestone dust and fly ash can be regarded as effective expansive soil stabilizers, also providing cheap solutions to the disposal issue.

Improving Strength of Expansive Soil using Coffee Husk Ash for Subgrade Soil Formation: A Case Study in Jimma Town

Improving Strength of Expansive Soil using Coffee Husk Ash for Subgrade Soil Formation: A Case Study in Jimma Town

Numerical Simulation of Geogrid-Reinforced Flexible Support for Treating Expansive Soil Cut Slopes

The influence of various interface strength parameters, different reinforcement spacing, and type of slope (enveloped or not) with a geogrid on flexible-support-reinforced expansive soil cut slopes was investigated by numerical simulation. The simulation considered the attenuation of the shear strength of expansive soil due to rainfall, evaporation, and other long-term atmospheric weathering actions in combination with shear strength parameters determined by a laboratory-measured expansive soil nonlinear strength envelope. Results showed that the geogrid can effectively restrain horizontal slope displacement and decrease the soil expansion softening effect to a certain extent, such that the sliding surface of the slope became deep. The change in maximum axial force was small due to a change in interface strength parameters between the geogrid and soil, but the safety factor increased with the increase in maximum axial force. The changes in maximum axial force along the height for different geogrid reinforcement spacing values were basically similar; the values increased initially and then decreased. Small reinforcement spacing equated to a small maximum value. The stability of the expansive soil slope was significantly influenced by reinforcement spacing; small spacing meant good slope stability. The enveloped geogrid indirectly improved the safety, resistance to erosion, and integrity of the slope.

The effect of freeze-thaw cycling on the mechanical properties of expansive soils

Expansive soils, which contain the clay mineral montmorillonite, are extensively distributed throughout many regions of the world and represent a source of risk to civil engineering structures. For example, some cutting slopes on the Jilin-Tumen-Hunchun high-speed railway in Northeast China consist of expansive soils. These soils, when exposed to freeze-thaw (F-T) cycles, can cause heavy economic losses, as well as present risk to the earth retaining system. In this study, consolidated-undrained (CU) triaxial tests were performed to investigate the effect of F-T cycles on the strength of expansive soils. The stress-strain relationship, elastic modulus, failure strength, effective stress paths, and effective shear strength parameters (i.e., effective cohesion and internal friction angle) were measured for expansive soils after a maximum of 9 F-T cycles. The test results indicate that expansive soils tend to exhibit strain-hardening behavior as the confining pressure is increased. By increasing the number of freeze-thaw cycles (NFT), the elastic modulus, failure strength, and effective shear strength parameters (i.e., effective cohesion and internal friction angle) of expansive soils decrease significantly. However, when the NFT exceeds a threshold value, the effect of F-T cycles on the strength behaviors of expansive soils is not significant. With the increase in the number of F-T cycles, the curvature of the effective stress paths also increases. In addition, based on the experimental results, a unified stress-strain relationship considering the effect of F-T cycles on the mechanical behavior of expansive soils was formulated in a disturbed state concept (DSC) framework. A state function based on the DSC was employed to characterize the gradual change in state of the expansive soils under the influence of F-T cycles.

The Impact of Initial Placement Conditions on the Shear Strength of Expansive Soil

The Impact of Initial Placement Conditions on the Shear Strength of Expansive Soil

Study on Shear Strength of Expansive Soil Considered Softening by Triaxial Tests

Swell-shrinking, crack development and over-consolidation are the characteristics of expansive soil, and it is an over-consolidation soil undergone dry-wet cycles. So there may be some faults to analyze expansive soil slope stability adopting the traditional strength criterion and calculation methods. In this paper, triaxial tests were carried out to obtain the relations between the parameters of shear strength and generalized plastic shear strain. The soil shear strength increases and then decreases along with the increasing of shear deformation due to soil over-consolidation. Moreover, the residual strength is achieved finally. The functions are applied in simulating the relations between the parameters and generalized plastic shear strain in order to analyze expansive soil slope stability.

Research on the Shear Strength Properties of Expansive Soils

The shear strength of expansive soils is now a key geotechnical problem. The water content and dry density of expansive soils have deep effect on its shear strength. For analyzing the detail relationship of the water content, dry density and shear strength of this special soil, direct shear test was carried out with the samples from Xinxiang in middle line of South to North water diversion project. The results indicate that both of the cohesion and friction angle grow with dry density and decrease with initial water content. Applying the linear regression calculation, we obtained mathematical expressions which reveal the variation of shear strength with the dry density and initial water content of Xinxiang expansive soils.

Study on Three-Dimensional Reconstruction of Macro/Meso-Structure Evolution of Expansive Soils with CT-Triaxial Apparatus

A program is used to reconstruct the computerized tomography (CT) images of expansive soils in the manuscript. The physical and mechanical properties of expansive soils can be researched accurately and visually. In the experiment, the CT-triaxial apparatus is used to research the shearing strength of expansive soils with artificial holes in different conditions of suctions and net pressures. The three-dimensional reconstruction is successful and considerable. The principle of program is easy and convenient, and it can be learned fast and directly by those who are not major in computer. This technique will have a better prospect in geotechnical engineering.

Research on Fatigue Accumulative Damage of Expansive Soil in the Alternation of Wetting-Drying Environment

The shear strength of expansive soil has the obvious varying property with the changing of seasonal climatic. Based on Palmgrem-Miner linear accumulative damage theory, laboratory experiments on the strength of expansive soil combining with different wetting-drying cycle amplitudes were performed to discuss on the fatigue accumulative damage of expansive soil in the alternation of wetting-drying environment. The results show that：(1)The applying sequence of high (low) cycle amplitudes have significant effect upon the fatigue accumulative damage of expansive soil, and the strength attenuation of expansive soil is mainly controlled by the high circulate amplitude. (2) The Palmgrem-Miner linear accumulative damage criterion can basically reflect the fatigue accumulative damage process of expansive soil in the alternation wetting-drying environment, and the value of damage score “D” is close to 1 when the strength of expansive soil is stabled.

A novel methodology for measuring the tensile strength of expansive clays

Several experimental techniques (viz., triaxial tests, direct tensile tests or suction measurements) have been developed and employed by earlier researchers to measure the tensile strength of fine-grained soils. However, these studies yield results that are soil specific and dependent on the methodology adopted. Apart from this, due to the bulk form of the sample, the sample heterogeneity (i.e., both in terms of the density and the moisture content) influences test results to a great extent. Under this situation, and in the absence of guidelines regarding sample thickness, determination of the tensile strength of expansive clays by employing their thin samples (1 mm to 5 mm) appears to be an excellent alternative. With this in view, efforts were made to determine the tensile strength of expansive clays by resorting to techniques that deal with measurement of (a) the deflection undergone by a silicon wafer, due to air-drying of a thin film of these clays, with the help of a laser beam and (b) the suction by employing a dewpoint potentiameter, WP4. Results obtained from these techniques were critically evaluated vis-à-vis those obtained from triaxial tests and empirical relationships reported in the literature. It has been observed that there is a unique relationship between the results of the thin and thick samples and hence thin samples of expansive clays can be employed for determining their tensile strength. This shows the usefulness of the proposed techniques for measuring the tensile strength of expansive soils.