Strength Of Residual Soil Research Articles

Effect of Shear Rate on the Residual Strength of Clayey Soils

The residual strength of soils in the shear zones at different shear rates can correspond to the movement of landslides. However, the rate-dependency of residual strength has not been quantified. A laboratory study on the residual strength of clay soils at shear velocities is present in this paper. The samples were extracted from the shear zone of a deep-seated landslide experiencing reactivation movement. The residual strength of samples at step-up shear rates from 0.5mm/min to 10000mm/min was obtained. Test results indicate that the samples at increasing shear rate tend to exhibit positive rate effect. At 10000mm/min the residual strength shows a gain of 2.21~2.68 times above the slow residual value. A model for predicting the residual strength correlating the shear rate is introduced. The different features in the slow and fast residual strength are attributed to soil fabric modifications within the shear zones. This is of practical significance to the stability and kinematic analysis of landslides.

Effect of pore water chemistry on the ring shear behavior and the rate dependency of residual strength

The rate dependency of residual strength plays an important role in the selection of residual strength parameters to design the remediation works for reactivated landslides. In the literature, it is shown that the rate dependency of residual strength depends on some factors such as types of soil, range of shear rates, range of effective normal stresses, and pore water chemistry. Recently, the effect of pore water chemistry on the rate dependency of residual strength soil has been examined. However, the ring shear behavior and the rate dependency of residual strength of soil having different pore fluids should be more evaluated. In this study, the effect of the pore fluids of distilled water and 1 M NaCl on the rate dependency of residual strength of kaolin clay was investigated in the Bishop ring shear apparatus. The ring shear tests were conducted at different shearing rates from 0.02 mm/min to 20 mm/min under the effective normal stress of 98 kPa. The research results showed that the pore fluid chemistry affected the shear displacement required to reach the peak strength, the vertical displacement, and the peak strength of kaolin clay. These parameters also exhibited rate dependency, especially at the fast shear rates. The research also indicated that the pore fluid chemistry had a significant effect on the rate dependency of residual strength. Accordingly, the rate dependency of residual strength of kaolin mixed with distilled water showed a positive tendency while that of kaolin with 1 M NaCl as the pore fluid was the neutral tendency.

Short-Time Effects on Compressive Strength of Residual Soils Due to Rainwater

Abstract: The short-term effects of acid rain on the geotechnical properties of residual soil were investigated. Artificial acid rain (AAR) of pH values 2, 4 and 6 was created with an infiltration setup to replicate the interaction between acid rain and soil. The soil specimens were infiltrated with AAR for durations of 30mins and 60mins for each pH level of 2, 4 and 6 and a control sample using deionised water of pH 7.5. Unconfined compression test (UCS) and Atterberg limits test were performed on the treated samples to study the mechanical behaviour and the characteristics of the soil once contaminated with AAR. The results revealed that reducing the pH value of AAR led to a reduction in compressive strength and Young’s modulus and an increment in liquid limit while the plastic limit remained unchanged. The reduction in compressive strength due to acid rain was observed to be almost halved when the bulk unit weight of the soil was increased for the same infiltration period.

Effect of principal stress direction during consolidation on the shear strength properties of natural granite residual soil

In numerous real-life civil engineering practices, including multi-stage embankment construction and foundation pit excavation, the direction of the major principal stress σ1 becomes rotated. In these cases, the granite residual soil may be subjected to inclined consolidation (IC) with σ1 being inclined, because of the relatively high permeability as a result of the fissures formed during weathering. While the effect of the σ1 direction during the shear on the strength of granite residual soil (inherent strength anisotropy) has been primarily established, little is known about how the soil strength is affected by the direction of σ1 during consolidation. This paper presents the effects of IC on the shear strength properties of natural granite residual soil through undrained hollow cylinder torsional shear tests. The effect of the soil structure is also considered by testing remolded soil specimens. The results reveal that while IC changes neither the shape of stress–strain curve nor the specimen features at failure, it leads to an increased ultimate shear strength in terms of both the undrained strength and stress ratio, with the remolded soil being more affected. The presented data provide new insights into the understanding of residual soil strength behaviors.

A novel seepage device and ring-shear test on slip zone soils of landslide in the Three Gorges Reservoir area

For the deformation and evaluation of reservoir accumulative landslide, it is of great significance to study the strength characteristics of slip zone soils under rainfall and reservoir operation. In this paper, slip zone soils from Tongjiaping landslide in the Three Gorges Reservoir area is taken as the research case, and the self-developed seepage device matching with the ring-shear test is designed and manufactured. Then, the shear strength of slip zone soils under different seepage-shear conditions is studied to reveal the strength evolution law of riverside landslide. Eventually, the creep characteristics of slip zone soils are described by the Burger model. The experimental results indicate that: (1) the weakening effect of slip zone soils will be induced by the increase of seepage cycles, change amount of seepage pressure, initial and constant seepage pressure, which decrease the residual strength of slip zone soils. (2) When the seepage cycles are <15, the weakening of residual strength of slip zone soils is not obvious. While when the cycles reach 20, the residual strength of soil samples decreases rapidly. (3) The Burger model, which connected the Maxwell model and Kelvin model in series can appropriately reflect the creep characteristics of slip zone soils of Tongjiaping landslide. The research results reveal the weakening law of mechanical strength of slip zone soils under seepage cycles, which provides a basis for the mechanism of accumulative landslide under the fluctuation of reservoir level.

Shear Strength Deterioration of Compacted Residual Soils under a Wind Turbine due to Drying-Wetting Cycles and Vibrations

The soil beneath a wind turbine withstands not only environmental impacts but also continuous vibrations transmitted from the superstructure. This paper presents an experimental study of the deterioration characteristics of shear strengths of residual soils affected by drying-wetting cycles and continuous vibrations. A series of triaxial tests were performed on compacted residual soil specimens after various drying-wetting cycles and vibrations. The influences of drying-wetting cycles and vibrations on the shear strengths of residual soils with different compaction degrees were analyzed. The results demonstrate that the shear strength and cohesion of compacted residual soils decreased as the number of drying-wetting cycles increased, and they tended to be stable after three drying-wetting cycles. The angle of internal friction decreased linearly with the reduction of compaction degree but was generally not affected by drying-wetting cycles. The shear strength of compacted residual soils also decreased because of continuous vibrations. After 10000 vibrations, the strength was stabilized gradually. Both the cohesion and angle of internal friction showed dynamic attenuation phenomenon. Finally, a modified Mohr–Coulomb strength equation considering the effects of drying-wetting cycles and vibrations was established. This equation could be used to predict the shear strength of compacted residual soils and further estimate the embedded depth of wind turbine foundations.

Shear strength assessments of residual soil for Ia Pet wind power project in Vietnam

The geotechnical parameters are of great importance in wind turbine foundation design. As a case study, laboratory test results of Ia Pet wind power project in Vietnam were analysed to accurately estimate the strength of residual soil, which is classified as high plasticity silt (MH). Due to sample disturbance, the undrained shear strength s u from triaxial unconsolidated undrained shear test (UU) is absolutely underestimated, while su from direct quick shear tests (DSq) and triaxial consolidated undrained shear test (CU) are more representative. Good linear correlations have been found between soil depth and strength obtained from DSq and CU tests. The normalised undrained shear strengths s u/σ v0’ indicate that the residual soil at 0m to 8m is heavily overconsolidated, where s u/σ v0’ is larger than 0.4. Furthermore, the normalised undrained shear strengths s u/σ v0’ presented negative linear correlation of liquidity index, which can be used to quick and cautious estimate the strength of Ia pet residual soil in the future by using liquidity index. The undrained shear strength evaluation using liquidity index is in good agreement with DSq and CU test results, which preliminarily verifies the applicability of expression between s u/σ v0’ and I L.

Effect of Biocementation via Enzymatic Induced Calcium Carbonate Precipitation (EICP) on the Shear Strength of Compacted Clay Liner

The strength of residual soil treated via biocementation means by employing enzymatic induced calcium carbonate precipitation (EICP) was assessed based on the standard recommended for compacted clay liner. EICP treated samples were prepared at four different concentrations of cementation solution (urea-CaCl 2) (0.25, 0.50, 0.75 and 1.00 M) and at various moulding water content (-2, 0, +2 and +4% OMC) using reduced British standard light compaction effort (RBSL). The result obtained has shown UCS values of untreated natural soil at the four molding water contents were less 200 kPa, the minimum standard recommended for compacted clay liner. Upon EICP treatment, it was determined that the UCS values increase with the increase in the concentration of cementation solution. The treated soils at all the cementation solutions and molding water contents have UCS values greater than 200 kPa. The lowest strength of the treated soils was 468.5 kPa determined at 0.25 M cementation solution and +2% OMC molding water content. The maximum UCS (643.5 kPa) value was determined at 1.00 M urea-CaCl 2 and -2% OMC. The results also reveal that calcium carbonate content in the treated soil increases with the increase in the concentration of cementation solution. Microstructural analysis on the treated soil indicated the presence of white precipitation within the pore space of the soil, and the mineral was confirmed to be calcite through XRD analysis.

Effect of wet-dry cycles on shear strength of residual soil

In order to investigate the relationship between the shear strength of residual soil and the number of repeated wet-dry cycles it underwent, the direct shear for different water content, different numbers of wet-dry cycles and different vertical stresses were examined. Based on the comprehensive structural potential theory, a comprehensive structural potential model considering the water content, the number of wet-dry cycles and the vertical stress was constructed. Then, the internal relationship between microstructure characteristics and structural strength attenuation of residual soil under alternate wet-dry conditions was emphatically discussed. As the number of wet-dry cycles and water content increased, the structural variability provided by the soil particle arrangement increased, while the structural stability provided by the soil particle cohesion decreased, causing the shear strength and structural potential of the soil to show a downward trend. As vertical stress increased, the variation range of structural stability was greater than that of structural variability. This asynchronous change caused decreased soil structural potential mτ. Under the same levels of vertical stress and the same water content, the model we constructed well represented the exponentially decreasing trend between the structural potential and the increased number of wet-dry cycles. Scanning electron microscope (SEM) images of the sample after five wet-dry cycles showed that the surface layer had lifted and the overhead structure between aggregates was clear, suggesting that unit cell connections had changed from face-to-face contact to edge-to-surface contact. That is, the overall orientation of the unit cell was diminished. As the successive wet-dry progressed, the overhead structure provided a more open water migration channel. The nuclear magnetic resonance (NMR) test showed that the content of micropores in soil samples decreased, and the proportion of mesopores and macropores increased, resulting in a decrease in soil strength. With the further development of wet-dry cycles (>5), the peak and residual strength of the soil gradually decreased to be stable. This is related to the decrease in soil saturation after multiple wet-dry cycles, and the stronger the stabilizing effect provided by soil–water meniscus.

Experimental Study and Numerical Simulation Analysis of Geosynthetics Reinforced Bond Performance

The test of bond performance of civil composite reinforcement is usually carried out by consolidation drainage triaxial shear test, which involves three aspects: the stress, strength and volume change of cohesive soil. If we want to increase the volume stability of the high-pressure compaction soil, we need to increase the way of reinforcement, but through the way of reinforcement, the shear swelling body of the soil will be reduced, while the shear shrinkage body of the soil will not be reduced or increased. The test pieces used in the experiment are reinforced specimen and plain soil specimen. The biggest difference between them is the axial strain. When the axial strain is low, the reinforced specimen is lower than the strength of plain soil specimen, and the plain soil specimen is slowly higher than the reinforced specimen, which requires the axial strain to increase to a certain extent, which also has the phenomenon that the reinforcement delays the soil strength, which also depends on the number of reinforcement layers and tension of the reinforcement materials with the increase of modulus of elongation, the phenomenon of delay will be more obvious. The peak strength of the soil is controlled by changing the number of layers of reinforcement and the tensile modulus of reinforcement. It shows that with the increase of the number of layers of reinforcement, the peak strength of the soil is increased in a certain range, but once the peak value is exceeded, the peak strength of the soil will not be greatly changed by changing the number of layers of reinforcement, except through by changing the number of reinforcement layers, the residual strength of soil can be controlled by changing the reinforcement material of tensile modulus, so that the stress-strain characteristics of soil will be greatly changed.

Strength Enhancement of Geotextile-Reinforced Fly-Ash-Based Geopolymer Stabilized Residual Soil

Soils in their natural form are often deemed unsatisfactory to be directly used as a construction material for their respective applications. Under such circumtances, employment of ground improvement techniques to better suit the soil for its function is typically the most economical approach. Consequently, the present research investigated into the beneficial effect of modernized soil treatment techniques, i.e., geopolymer stabilization using fly ash as the precursor and geotextile reinforcement, on the strength enhancement of natural residual soil. A series of unconsolidated undrained (UU) triaxial compression tests were carried out to assess variation of geopolymer stabilized residual soil strength based on the varying number of geotextile layers, geotextile arrangement, and confining pressures. It was found that the increase in the number of geotextile layers resulted in a corresponding rise in soil strength and stiffness. It was also discovered that placement of geotextile layers at sample regions which suffered the maximum tensile stress–strain during loading was more effective compared to random placement. Soil strength was observed to reduce with increasing confining pressure which demonstrated the effectiveness of utilizing geotextile reinforcement at greater depths below the ground to be less. Failure patterns showed that while unreinforced soil resulted in failure along a shear plane at an approximate angle of 45 + φ/2 (φ: angle of internal friction), reinforced samples demonstrated a bulging failure where the soil between adjacent layers of geotextiles appeared to bulge. The findings deemed the employment of geopolymer stabilization and geotextile reinforcement on natural residual soil very effective with regards to the enhancement of soil strength and stiffness.

Hydrothermal clays and their influence on slope stability in residual soils of Southern Brazil

Clayey veins may develop in areas of hydrothermal activity by seepage of hot water through the soil and rock. In a slope located in Southern Brazil, such veins occur along the slip surface of some landslides. This paper aims to characterize this kind of clay and investigate its influence over the stability of that slope. An electro resistivity survey had been conducted to characterize the soil profile, and SPT boreholes were used to confirm geophysical data. An experimental laboratory campaign included the investigation of chemical, mineralogical, and geotechnical properties of these clay veins and the embedding residual soil. Drained shear strength of residual soil was measured through triaxial tests, and residual strength was measured for both materials using a ring shear apparatus. A series of limit equilibrium analyses were conducted to assess the role of clay veins on the slope stability. The geometrical discretization of veins is a difficult task, and an approach based on the assumption of overall shear strength is required to establish the operational shear strength parameters for this slope. A series of back analyses showed that failure surfaces consistent with those observed in the field were only reproduced when the adopted shear strength parameters of the soil mass were c’ = 5 kPa and φ’ = 20°. Considering the measured shear strength parameters of the hydrothermal clay c’ = (0 and φ’ = 8.5°) and the pattern in which the clay veins occur, it seems that they do not fully control the slope stability, but they significantly reduce the global cohesion and the average mass friction angle.

Evaluating the performance of human hair impregnated with cement slurry in remediation of the Caspian coastal silty sand

Construction of various civil structures on problematic soils with weak or soft density is associated with many hazards. Such soils are prone to asymmetric subsidence caused by poor shear strength and high compressibility. Silica sand in the Caspian coast are mainly exposed to river sediments or absorbent sewage leachate of the urban and residential areas, and the presence of these materials in the soil environment weakens their strength parameters. Generally in the remediation of problematic soils, a variety of methods have been developed, including the use of bearing elements or remediation and modification of soil physical characteristics. In this study, for remediation of this type of sandy soils, the Human Hair Fibers (HHF) are used, which have considerable advantages in terms of tensile strength and compatibility with environmental conditions compared to other natural and synthetic fibers. The effect of adding different contents of natural human hair fibers as impregnated and non-impregnated fibers to cement slurry at different soil relative densities shows that the addition of this type of natural fibers in both cases has improved the soil undrain compressive strength, increased the failure strain and initial Young’s modulus, and also reduced the post-failure strength loss and increased the residual soil strength.

Experimental Study and Numerical Simulation Analysis of Geosynthetics Reinforced Bond Performance

In the laboratory, the test of bond performance of civil composite reinforcement is usually carried out by consolidation drainage triaxial shear test, which involves three aspects: the stress, strength and volume change of cohesive soil. From the experimental results, it is not difficult to find that if researcher want to increase the volume stability of the high-pressure compaction soil, researcher need to increase the way of reinforcement, but through the way of reinforcement, the shear swelling body of the soil will be reduced, while the shear shrinkage body of the soil will not be reduced or increased. The test pieces used in the experiment are reinforced specimen and plain soil specimen. The biggest difference between them is the axial strain. When the axial strain is low, the reinforced specimen is lower than the strength of plain soil specimen, and the plain soil specimen is slowly higher than the reinforced specimen, which requires the axial strain to increase to a certain extent, which also has the phenomenon that the reinforcement delays the soil strength, which also depends on the number of reinforcement layers and tension of the reinforcement materials. With the increase of modulus of elongation, the phenomenon of delay will be more obvious. In the experiment, the peak strength of the soil is controlled by changing the number of layers of reinforcement and the tensile modulus of reinforcement. The experiment shows that with the increase of the number of layers of reinforcement, the peak strength of the soil is increased in a certain range, but once the peak value is exceeded, the peak strength of the soil will not be greatly changed by changing the number of layers of reinforcement, except by changing the number of reinforcement layers, the residual strength of soil can be controlled by changing the reinforcement material of tensile modulus, so that the stress-strain characteristics of soil will be greatly changed.

Variation in Shearing Rate Effect on Residual Strength of Slip Zone Soils Due to Test Conditions

Shearing rate effect on the residual strength of slip zone soils is considerable for sliding or reactivated landslides. It is complicated and variably affected by external inducing factors, and its variation has not attracted much attention. Using drained ring shear tests on the slip zone soils from two selected landslides with the shearing rates of 0.1–20 mm/min, this study investigated the variation in the shearing rate effect on the residual strength under the influences of the clay fraction, water content, and normal stress. In addition, the shear zone structures were analysed using microscopic observations. The results show that the residual strength decreases with increasing shearing rate (i.e., negative rate effect) and exists a good linear relationship with the logarithmic shearing rates. The slope of the fitting lines of the residual stress ratios versus shearing rates is proposed to assess the shearing rate effects. Furthermore, the effect is significantly affected by the clay fraction, water content, and normal stress. The samples with the low clay fraction exhibit a more significant negative rate effect, and the effect weakens with decreasing water content and normal stress, which are associated with the variations in the shear zone structures due to particle breakage. Additionally, increasing shearing rates and shear displacement change the shear zone structures and thus induce a negative rate effect on the residual strength of the soils.

Determination of Residual Strength of Soils for Slope Stability Analysis: State of the Art Review

Determination of Residual Strength of Soils for Slope Stability Analysis: State of the Art Review

INFLUENCE OF CLAY CONTENTS ON DRAINED SHEAR STRENGTH PARAMETERS OF RESIDUAL SOIL FOR SLOPE STABILITY EVALUATION

Consolidated drained triaxial compression tests (CD) were conducted to determine the compression properties of remolded samples collected from hillslope in residual soil. The test results showed that the effective drained shear strength of residual soil was primarily affected by the degree of weathering according to depth, parent rock material, and clay contents and also influenced by initial moisture content. These samples were classified as silt soils of high to low plasticity. CD tests were performed on samples prepared under 100 and 200 kPa remolding pressure with three different confining pressures of about 50, 100 and 150 kPa. Predicted results showed that the soil strength increased with increasing samples’ density for those who prepared with a higher remolding pressure. According to the soil composition, a clear decrease in soil cohesion was observed for samples collected at a deeper depth, while a further increase in the effective internal friction angle was observed for samples collected with a lower depth. However, this explains the significant influence of clay contents that can be represented as a relevant relation. Therefore, the results indicated that the studied residual soils have physical and geotechnical properties that are highly dependent on the clay and initial water contents. Then, the concept of long-term stability analysis of hillslope of Balai Cerap area (in UTM/ Malaysia) was presented in the form of factors of safety as discussed later in this study by employing Geo-Studio program (SLOPE/W application) with Limit Equilibrium Method.

Influence of Blended Lime-GGBS Slag on the strength of Laterite

Residual soils are referred to soils that formed through process of physical and chemical weathering of in-situ rocks. Reactions of various physical and chemical weathering agents had resulted in physical and chemical variability of residual soil and site dependent. The structure and minerals of in-situ rock were degraded physically and chemically and thus making its less resistance to load compared to un-weathered parent rock. Hence, it is important to stabilize the residual soil. Different ratios of blended hydrated lime and Ground Granulated Blast Furnace Slag (GGBS) namely 10:0, 9:1, 8:2 and 5:5 were utilized in this study. The percentage of admixtures was set at 10% with respect to its dry mass of soil. Unconfined compressive strength of treated soil specimens were determined after 7 days, 14 days and 28 days of humid curing. The water contents of the specimens were found to decrease slightly with an increment of curing periods while the strengths of the stabilized specimens were increased with curing periods. The highest unconfined shear strength at 28 days was recorded as 321.74 kPa with 8.18% axial strain. Thus, it showed that the use of blended lime and slag can improve the strength of residual soil. However, the treated samples failed to achieve the minimum strength increment of 345 kPa to be considered as an effective stabilization as stated in ASTM D4609. Some other factors namely curing temperature and Initial Consumption of Lime (ICL) should be considered to optimize the strength of the stabilized materials.

Model applicability for prediction of residual soil apparent cohesion

Abstract The focus of this paper is on the measurement and prediction of unsaturated shear strength of residual soil as a function of matric suction by utilizing basic soil properties. A total of 19 unsaturated triaxial tests were performed on four groups of undisturbed residual soil specimens with different classifications and compositions. Six compacted specimens were tested and showed lower strength values than those of undisturbed specimens. The cohesion intercept due to matric suction was used to represent the strength contribution of the matric suction, thus accounting for the effect of confining pressure and effective cohesion. The feasibility of three existing models in predicting the apparent cohesion is investigated through comparing computed results to measured data from this paper and literature. A proposed regression equation, developed based on four data sets from the current research and six from the literature, shows an improved ability to predict measured apparent cohesion utilizing basic soil properties. The data set developed herein represent a significant addition to the literature on the unsaturated strength properties of natural residual soil, as sampled from the field.

Rate and acceleration effects on residual strength of kaolin and kaolin–bentonite mixtures in ring shearing

Rate effects on residual strength play an important role in predicting and evaluating the behaviour of reactivated landslides and in the application of test results and procedures. Although the rate dependency of residual strength has been investigated extensively, there is a lack of consistency in the experimental results. In particular, the effect of the shear rate on the residual strength of high-plasticity, low-permeability soils is not well understood. Additionally, field observations suggest that the sliding velocity of a soil block in the residual state is not constant and that its acceleration may affect the residual strength of the soil. However, the effect of acceleration changes on the residual strength of soil has not yet been investigated. The main objectives of this study are to elucidate the rate dependency of the residual strength of high-plasticity soils and investigate the effect of acceleration. In addition, the effect of the test procedure on the rate effect is also examined. A number of kaolin and kaolin–bentonite samples were tested using the Bishop-type ring shear device. The single-stage procedure which the shear rate was not changed during shearing, was conducted on individual specimens with shear rates from 0.02 to 20 mm/min to investigate the rate effect. The accelerations of 0.028 and 0.014 mm/min2 were applied in multi-stage procedure with shear rates increasing gradually from 0.002 to 20 mm/min to examine the acceleration effect. The test results show that the bentonite content significantly affects the rate effect on the residual strength of kaolin–bentonite mixtures. For instance, in the single-stage procedure, the presence of just 10% bentonite changes the rate effect from positive to negative. This may be due to the generation of unknown excess pore water pressure under fast shearing. Furthermore, the test results also show that the type of rate effect observed depends on the test procedure. For mixture samples of 90% kaolin and 10% bentonite, the rate effect is negative in the single-stage procedure but positive in the multi-stage procedure. The analysis of the experimental results suggests that the effect of acceleration can be neglected in determining the residual strength.