Residual Shear Strength Research Articles

Experimental study on the monotonic shear strength of GM/CCL composite liner interface

The interface shear strength between a geomembrane (GM) and a compacted clay liner (CCL) or a geosynthetic clay liner (GCL) is of great importance for landfill stability analysis. An experimental study of the interface shear behaviour between a smooth GM (GMS) or a textured GM (GMX) and a CCL is presented in this paper. A series of monotonic shear tests was conducted using a large direct-shear apparatus. Peak and residual shear strength parameters were obtained by linear fitting of the experimental data. The shear strength of both GMS/CCL and GMX/CCL interfaces was mainly driven by the normal stress level, while the displacement rate had very little influence on the interface shear strength. The residual shear strength of the GMX/CCL interface was even higher than the peak shear strength of the GMS/CCL interface at all normal stress levels. The GM/CCL interface showed considerably higher shear strength over the GM/GCL interface; the residual strength of the GM/CCL interface was even higher than the peak strength of the GM/GCL interface at all normal stress levels. The results presented in this paper are useful for the preliminary design of landfill composite liner systems.

Application of Residual Shear Strength Predicted by Artificial Neural Network Model for Evaluating Liquefaction‐Induced Lateral Spreading

The residual shear strength of liquefied soil is critical to estimating the displacement of lateral spreading. In the paper, an Artificial Neural Network model was trained to predict the residual shear strength ratio based on the case histories of lateral spreading. High‐quality case histories were analyzed with Newmark sliding block method. The Artificial Neural Network model was used to predict the residual shear strength of liquefied soil, and the post‐liquefaction yield acceleration corresponding with the residual shear strength was obtained by conducting limit equilibrium analysis. Comparing the predicted residual shear strength ratios to the recorded values for different case histories, the correlation coefficient, R, was 0.92 and the mean squared error (MSE) was 0.001 for the predictions by the Artificial Neural Network model. Comparison between the predicted and reported lateral spreading for each high‐quality case history was made. The results showed that the probability of the lateral spreading calculated with the Newmark sliding block method using the residual shear strength was 98% if a lateral spreading ratio of 2.0 was expected and a truncated distribution was used. An exponential relationship was proposed to correlate the residual shear strength ratio to the equivalent clean sand corrected SPT blow count of the liquefied soil.

Unsaturated Shear Strength of Compacted Clayey Soil via Suction-controlled Ring Shear Testing

An experimental program has been undertaken to assess both peak and residual shear strength parameters of statically compacted, moderate plasticity clayey soil under suction-controlled conditions, resulting in a defined set of suction-dependent peak and residual failure envelopes over a relatively wide range of suction states, from 0 to 300 kPa. The experimental program was accomplished in a servo/suction-controlled ring shear apparatus, which is suitable for testing unsaturated soils under large deformations via the axis-translation technique. Test results substantiate the crucial role that has been observed to be played by the imposed matric suction on the residual shear strength of compacted clayey soils. For the range of net normal stress (0-200 kPa) and matric suction (0-300 kPa) states investigated, the increase in either peak or residual shear strength, with increasing matric suction, was found to be manifestly nonlinear. Furthermore, a distinct correspondence was observed between the nonlinearity of the peak shear strength envelope, with respect to increasing matric suction, and the soil-water retention properties of the clayey soil. Results, in general, suggest that a conceptual residual shear strength framework for unsaturated soils, similar to that postulated for peak shear strength, can eventually be formulated as more experimental evidence of this kind is made available.

Investigation of the effect of shearing rate on residual strength of high plastic clay

The residual shear strength on failure plane is a crucial parameter to be estimated for analysis of an active landslide. This strength must be determined precisely to build a reliable theoretical model for calculations. The multi-reversal direct-shear test is a practical method to determine this shear strength in laboratory due to wider availability of apparatus. The shearing rate is among the factors that significantly affect the precision of test results for clay specimens. However, limits for this rate are yet to be clarified to shorten the duration of multi-reversal direct-shear tests. In this study, two tests series at different shearing rates were performed to investigate the effect of shearing rate on the residual strength of highly plastic clay sample recovered from a landslide area in Northern Turkey. The shearing rates were set to 0.024 mm/min which was decreased to 0.001 mm/min during the last forward shearing phase for the first test series, whereas the rate was fixed to 0.0007 mm/min for the second test series. The residual friction angle determined by these tests was interpreted by using a theoretical analysis of the landslide, and they were compared with the estimations due to empirical relationships given in the literature. It is concluded that, although the rate of 0.024 mm/min is consistent with the recommendations in literature, this rate can yield overestimation of residual shear strength determined in multi-reversal direct-shear tests.

Effect of one cycle of heating-cooling on the clay-concrete pile interface behavior

This study investigated the effect of applying one heating-cooling cycle on the interface strength parameters of saturated clay soil-concrete, and the potential use of the heating process to improve the side capacity of piles driven in clayey soil. A large direct shear test device with inner dimensions of 300 mm, 300 mm, and 200 mm for width, length, and height, respectively was modified to perform the interface soil-concrete tests. A concrete block (300 mm × 300 mm × 100 mm) was built and placed at the bottom section of the shear device. Watlaw heating fire rods system was used to heat the circulating water that heat the specimens. The experimental tests were conducted on Low Plasticity Index soil with PI=12. The specimens were first consolidated to a target normal stress prior to shearing. Two specimens at different testing temperature (room temperature = 20 °C, 70 °C) were tested for each of the four different normal stresses (30, 69, 110, and 150 kPa). The temperature for the heated specimens was increased gradually during the heating process from the room temperature (20 °C ± 2 °C) to 70 °C ± 2 °C in 3 hours. The specimens were then cooled back to room temperature. The test results showed significant increase in both peak and residual interface shear strength parameters by 13.6% and 15.6% increase in friction angle, respectively. Also, volumetric strain under shearing decreased after the heating and cooling cycle by 30.0%, 24.4%, 11.3%, and 24.2% under 30 kPa, 69 kPa, 110 kPa, and 150 kPa, respectively.

Research on residual shear strength of surrounding rock base on elastic-plastic softening model

With the rapid development of infrastructure construction, the edge shape analysis of underground chamber excavation in water conservancy and hydropower projects has received more and more attention. This paper takes an underground chamber of a hydropower project as the research object and uses an ideal elastoplastic stress-strain softening model to study the relationship between deformation, stress, plastic zone and strength parameters. The results show that the value of each shear strength parameter has a significant effect on the distance of the plastic zone, and the calculation result may provide a basis for the design.

Evaluating Lateral Spreading Using Newmark Method Based on Liquefaction Triggering

The prediction of liquefaction‐induced lateral spreading is an important geotechnical engineering problem. In this paper, a simplified prediction method based upon Newmark sliding block analysis was proposed to predict the liquefaction‐induced lateral spreading. The acceleration time history beneath the liquefied soil (starting from the triggering time of liquefaction) and the postliquefaction yield acceleration corresponding with the residual shear strength of liquefiable soil were used in the Newmark sliding block analysis. One‐dimensional effective stress analysis was conducted to obtain the motion beneath the liquefied soil and the liquefaction time. Limit equilibrium analysis was employed to determine the postliquefaction yield acceleration using the residual shear strength of liquefied soil, which correlated with the equivalent clean sand SPT blow count of the liquefied sand. This method was evaluated against five well‐documented case histories and the predicted displacements of lateral spreading were subsequently compared with the observed displacements. In addition, the lateral spreading predicted by the rigorous Newmark sliding block method and numerical difference analysis was presented. Based on the statistical analysis of the displacement ratios, it suggested that the method proposed in this paper identified the triggering time of liquefaction and provided a reasonable prediction of the liquefaction‐induced lateral spreading with an RMSE (root mean square error) of 0.63, a standard deviation of 0.40, and a CV (coefficient of variance) of 0.60, respectively.

Residual shear strength of a weathered graphitic-quartz-mica schist in humid tropical Peninsular Malaysia

Residual shear strength of a weathered graphitic-quartz-mica schist in humid tropical Peninsular Malaysia

Brittle failure of rockslides linked to the rock bridge length effect

A rock bridge along the potential sliding surface of a rockslide has a relatively large bearing capacity and governs the stability of the rock slope. The physical and mechanical properties of specimens representing four rock bridge lengths were researched by direct shear experimentation. The micromechanism associated with the change in shear strength parameters was analyzed by PFC2D numerical simulations that corresponded to the experiments. The results revealed a rock bridge length effect, through which the peak shear strength increases with rock bridge shortening, accompanied by an increase in cohesion and a decrease in internal friction angle and main fracture surface roughness. Rock bridge shortening decreased the density of the microcracks at the shear stress peak point, changing the cohesive strength and frictional strength. The decrease in the internal friction angle could change the critical stress intensity factors to make shear cracks preferentially initiate over tensile cracks. Fracture roughness therefore decreased, inducing a lower residual shear strength. As a result, the difference in the peak and residual strengths increased with rock bridge shortening, which would promote brittle failure of the corresponding rock slope.

Study on the Water Sensitivity Analysis of Red Clay Shear Strength Based on Culon-morper Rule

In this paper, the changing law of the peak and residual cohesive force and internal friction angle for undisturbed soil from three different sampling sites in Bijie area were obtained through the indoor experiment. In the case of natural undisturbed water content, the peak and residual cohesive force decrease with the exponential relationship of water content, while the peak and residual internal friction Angle decrease linearly with the water content range. Based on the traditional Culon-morper shear strength criterion the changes of peak and residual shear strength with water content were obtained. The research in this paper is helpful to understand the change of shear strength with water content in Bijie area and to guide engineering practice.

Effects of net normal stress on hydro-mechanical behaviour of a kaolinite clay soil under different suction paths

Hydro-mechanical behaviour of unsaturated soils has been extensively reported in the literature. However, the effects of net normal stress on soil behaviour under different suction paths have not been addressed. Therefore, in this study, the shear behaviour of a kaolinite clay soil subjected to drying or wetting prior to shearing was investigated by suction-controlled direct shear tests. It was found out that net normal stress suppresses both irreversible volume contraction and decrease in degree of saturation. The magnitude of irreversible volume contraction and the size of hydraulic hysteresis after drying–wetting decreased with the net normal stress. Soil specimens experiencing drying–wetting had lower degree of saturation, and thus generally exhibited lower residual shear strength due to the lower average skeleton stress as compared with those specimens experiencing only drying. It was also found out that, at (σv − σa) = 50 kPa, peak shear strength of specimens experiencing drying–wetting was generally higher than that experiencing only drying, since the contribution to peak shear strength made by lower void ratio might be dominant over the reduction of peak shear strength caused by lower degree of saturation. However, the contrary effect of suction path on peak shear strength was observed at (σv − σa) = 100 and 200 kPa. The peak shear strength of soil specimens experiencing drying–wetting was generally lower, because they had lower degree of saturation and hence lower average skeleton stress at the same net normal stress and the same suction as compared with those experiencing only drying. Furthermore, as compared with those experiencing only drying, soil specimens experiencing drying–wetting exhibited smaller stronger strain-softening and stiffer stress–strain relations, larger shear-induced volume dilation (or less contraction), and more obvious trend of water absorption during shearing at various net normal stresses. Regarding peak shear strength parameters, soil specimens experiencing drying–wetting showed higher cohesion, but lower friction angle than those experiencing only drying.

Оценка прочности массива горных пород при разработке месторождений открытым способом

The paper presents results of an experimental study on strength characteristics of the rock mass as applied to the assessment of open-pit slope stability. Formulas have been obtained that describe a correlation between ultimate and residual strength of rock samples and residual shear strength along the weakening surface. A new method has been developed to calculate residual interface strength of the rock mass basing on data from the examination of small-scale monolith samples with opposing spherical indentors. A method has been proposed to estimate strength characteristics (structural weakening coefficients and internal friction angles) of the fractured near-slope rock mass. The method relies on test data from shattering small-scale monolith samples with spherical indentors, taking into ac- count contact conditions along the weakening surface, and can be applied in the field conditions. It is acceptable to use irregular-shaped samples in thetests.

Unloading-induced rock fracture activation and maximum seismic moment prediction

Hundreds of anthropogenic earthquakes have recently occurred worldwide due to underground space creation and energy extraction. The mechanism behind the human-induced geohazards is most likely associated with the reduction of normal stress on pre-existing fractures and faults. This study reports a series of laboratory experiments to investigate the mechanism of unloading-induced fracture activation, and proposes a simple approach to predict the maximum seismic moment for a critically stressed fracture. The unloading-driven shear test results exhibit that the unloading process induces the stress states of the sawcut and natural fractures to approach the Mohr-Coulomb failure envelope, and the normal stress unloading rate influences the peak slip rate. The fracture instability is dependent on the relationship between the stiffness of the system and the slip weakening rate of the fracture, and the shear dilation mainly occurs after the fracture activation. The test results also show that the critical shear stress of the sawcut fracture during the unloading-driven shear test is approximately equal to the residual shear strength after the displacement-driven fracture slip. This relationship inspires us to develop a new approach to estimate the maximum seismic moment. Our data demonstrate that the maximum seismic moments for both the fractures obtained from the unloading-driven shear tests are all below the upper limit lines, indicating that the proposed approach is reasonable. The uncertainty analysis shows that the accurate estimation of fault size can improve the maximum seismic moment prediction.

Laboratory Investigation on Shear Behaviors of Bolt–Grout Interface Subjected to Constant Normal Stiffness

Shear behavior of the bolt–grout interface basically depends on site-specific boundary conditions, i.e., initial normal stress and normal stiffness of the borehole wall. Few studies have been conducted to investigate the shear behaviors between the bolt and grout material under different boundary conditions. To better understand the effect of boundary conditions on the shear behaviors of the bolt–grout interface, simplified two-dimensional (2D) bolt–grout interface specimens are prepared and tested using direct shear tests at various initial normal stresses and normal stiffnesses in this context. The testing results showed that both initial normal stress and normal stiffness significantly influence the bolt–grout interface shearing behaviors. Increasing the normal stiffness or initial normal stress would increase the peak and residual shear strength. However, the degree of the brittleness after the peak, normal displacement, and peak friction coefficient was reduced. It is noted that the peak and residual shear strength points under the constant normal stiffness conditions located near the peak and residual strength envelopes for the constant normal load tests, respectively. Besides, the shear failure process of the bolt–grout interface was captured by PAC acoustic emission (AE) monitoring and digital camera technology, a good correlation between the evolution of AE parameters and the shear stress curves was obtained.

Shear Resistance Prediction of Post-fire Reinforced Concrete Beams Using Artificial Neural Network

In this paper, a prediction method based on artificial neural network was developed to rapidly determine the residual shear resistance of reinforced concrete (RC) beams after fire. Firstly, the temperature distribution along the beam section was determined through finite element analysis using software ABAQUS. A residual shear strength calculation model was developed and validated using the test data. Using this model, 384 data entries were derived for training and testing. The input layer of neural network involved parameters of beam height, beam width, fire exposure time, cross-sectional area of stirrup, stirrup spacing, concrete strength, and concrete cover thickness. The output was the shear resistance of RC beams. It was found that use of BP neural network could precisely predict the post-fire shear resistance of RC beams. The predicted data were highly consistent with the target data. Thus, this is a novel method for computing post-fire shear resistance of RC beams. Using this new method, further investigation was also made on the effects of different parameters on the shear resistance of the beams.

The shear strength of Opalinus Clay shale in the remoulded state

The Opalinus Clay shale formation is considered as a potential host geomaterial for the Swiss deep geological repository for radioactive waste. It presents different facies and it is characterised by a multi-scale heterogeneous composition, by a typical fissile structure with well-defined bedding planes and by anisotropic hydro-mechanical behaviour. This peculiar complexity makes it difficult to assign a unique set of geomechanical parameters to the material. This paper presents an experimental study aimed at characterising the lowest values of the shear strength parameters. In this sense, the shear behaviour was investigated on remoulded samples where the fabric and the diagenetic bonds of the intact material were eliminated. The results of a triaxial test campaign belonging to different facies of Opalinus Clay shale (“shaly” and “sandy” facies) are presented. Furthermore, with the aim to study the mechanical properties of fault zones in Opalinus Clay, the effect of large cumulated shear displacements on shear strength was also investigated. Ring shear tests were performed to determine the residual shear strength. The main geotechnical property which discriminates the different facies of Opalinus Clay is the grain-size distribution; in this sense, well-defined correlations between this intrinsic characteristic and shear strength angles of the remoulded material are presented.

Effects of high temperature on residual punching strength of slab-column connections after cooling and enhanced post-punching load resistance

Large-scale experiments were conducted on six isolated slab-column connection specimens. Each specimen contained a 300 mm square center column and a 150 mm thick slab. The objectives of the experiments were to study the effects of fire-induced high temperatures on the residual punching shear strength of reinforced concrete flat-plate structures after cooling and to examine the effectiveness of a detailing approach for enhancing the post-punching load-carrying capacity. Ceramic fiber heating panels were used to apply high temperatures to slab shear-critical regions at the compressive face. The test results indicate that the high temperatures up to 800 °C did not seriously impact connection punching shear strength. Moreover, the use of crossties can effectively engage slab tensile reinforcement in resisting post-punching loads with a loading capacity close to or even greater than the punching failure load. Complementary to experiments, finite element simulations were conducted. The numerical simulations predicted the punching failure load of slab-column connections at room temperature with a good accuracy; however, the simulations underestimated the post-heating punching strength of the cooled slab-column connections by up to 11%.

Modeling of Landslide–Tunnel Interaction: the Varco d’Izzo Case Study

This paper reports a case study of the interaction between a slow-moving landslide in clay soil and a railway tunnel protected by sheet pile walls, that crosses the landslide accumulation. The earthflow, that develops in the Southern Apennines, Italy, has been long studied and monitored by different organizations, such as the national railway company and the University of Basilicata. Since the investigated landslide and construction typologies are quite diffused in mountainous areas, the case study can be considered representative of a large number of other similar cases. Differently from other approaches proposed in the literature, the role of the landslide slip surface depth, changing in the directions longitudinal and transversal to the tunnel, and of structural connections, affecting the pile–tunnel system response, are accounted for in detail. Several numerical models are used to simulate the interaction between the sliding soil and tunnel. Different 2D and 3D geotechnical and structural models are adopted to reproduce stress–strain scenarios compatible with the experimental evidence. The modeling results indicate that the interaction varies considerably along the tunnel length because of the 3D geometry of the landslide, and is conditioned by the residual shear strength available on the slip surface. The expansion joints in the tunnel lining only marginally influence the stress in the structure because of the presence of the adjacent sheet pile walls, which enable considerable collaboration between the tunnel sectors.

Drained Peak and Residual Interface Shear Strengths of Fine-Grained Soils for Pipeline Geotechnics

AbstractThis study presents the results of interface torsional ring shear tests conducted at intermediate normal stress levels that are usually prevalent at soil–pipeline interfaces under near-shor...

Shear Characteristics of Cement-Stabilized Sand Reinforced with Waste Polyester Fiber Fabric Blocks

The present paper is devoted to investigate the effects of waste polyester fiber fabric blocks on the strength and mechanical behavior of cemented sand. In the investigation, samples were prepared at four different percentages of waste polyester fiber fabric block content (0.0%, 0.5%, 1.0%, and 1.5% by weight of soil) and two different aspect ratios (2 : 1 and 3 : 1), and conventional triaxial compression tests were carried out after the curing period. The test results indicated that the addition of fibers increased peak and residual shear strengths of cemented sand and changed its brittle behavior to a more ductile one. As the fabric block content increased, the brittleness index and initial stiffness decreased, and the peak strain and internal friction angle increased. The optimal combination of the content and aspect ratio was determined to be 0.5% and 3 : 1. The integration of the fabric blocks with the cemented sand matrix was analyzed by using the scanning electron microscopy (SEM). It is found that the reinforcement effect is related to the bond strength and friction at the interface. The micromechanical properties of the fiber/matrix interface were influenced by the undulations between the fabric block components. In summary, this study presented a low-cost and environment-friendly method for reinforcing cement-stabilized sand.