Quasi-static analysis of soft rock failure characteristics targeted to cyclic direct shear test

Earthquake response of submerged gravity foundation on soft rock

Experimental investigation on the monotonic, cyclic and post cyclic interfacial behavior of non-water reacted polymer and concrete

Coupling effects of particle shape and cyclic shear history on shear properties of coarse-grained soil–geogrid interface

Among the constitutive models for rock fractures developed over the years, Barton's empirical model has been widely used. Although Barton's failure criterion predicts peak shear strength of rock fractures with acceptable precision, it has some limitations in estimating the peak shear displacement, post‐peak shear strength, dilation, and surface degradation. The first author modified Barton's original model in order to address these limitations.Barton proposed his model for degradation of fracture asperities in unloading, reloading, and shear displacement reversal based on just one cyclic direct shear test. In this study, a database of results of 18 cyclic direct shear tests available in the literature was collected and analyzed. Modifications were made to Barton's original model (in terms of fracture cyclic shearing) to make it consistent with the modified model proposed by the first author. Copyright © 2010 John Wiley & Sons, Ltd.

Saravan landfill, located in northern Iran, has been an environmental cause of concern through its entire time of operation. As part of a project aimed at bringing the landfill conditions closer to standards, large-scale cyclic direct shear and bender element tests were carried out on reconstituted waste samples, obtained from different locations and depths at the landfill. Samples obtained at greater depths were found to have a higher fibre content which mostly consisted of nondegradable plastics that accumulated while a large part of the rest of the waste succumbed to biodegradation. Bender element tests showed an increase in the shear wave velocity and maximum shear modulus of the waste with ageing. This increase coincided with an increase in the sample unit weight. Normalized shear modulus reduction and damping ratio curves were obtained from the cyclic direct shear tests which were consistent with data available in literature. In addition, ageing was observed to shift the modulus reduction and damping curves to the left, decreasing the former while increasing the latter and resulting in a reduction in the shear strain corresponding to the onset of plastic behaviour. Ten cycles of direct shear loading at a 3.33% strain caused shear modulus and damping ratio to decrease by about 50% and 40%, respectively, most of which occurred within the first three or four cycles. Secant friction angle obtained from post-cyclic shear strength tests were found to vary between 32° and 55°, which was consistent with previous research.

Water sorption is one of the most important causes for rock deformation and failure. Liquid and gaseous water adsorption experiments were carried out on shale, conglomerate and soft rock samples. First, water absorption experiments under different water pressures were carried out on a series of shale samples collected from a deep coal mine in China. The experimental results showed that the absorbed water increases with time while the water absorption rate decreases with time. Comparison between the water absorption capacities of the shale samples under different water pressures suggested that water pressure significantly increases the water absorptivity. Second, water vapor sorption experiment was carried out on clay-bearing conglomerate rock samples collected from northeast China to investigate dynamics of water vapor sorption and vapor-induced strength softening effect. The experimental results have shown that the amount of water vapor sorbed by each conglomerate sample kept increasing with time until finally reached to a plateau, generally following an exponential law. Negative correlations between water content and uniaxial compressive strength (UCS) as well as modulus of elasticity suggested that with increasing water content induced by vapor sorption conglomerate rock strength tended to decrease, and meanwhile it was more prone to deformation. Furthermore, microstructure images of scanning electron microscope (SEM) analyses for conglomerate rocks before and after water vapor sorption showed that after vapor sorption conglomerate rocks have undergone significant changes in microscopic morphology which may be an important cause for rock softening and deterioration. Third, X-ray diffraction analysis (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry experiments were carried out to investigate the mineral compositions, microstructure and porosity characteristics of the 13 clay-bearing soft rock samples collected from a deep coal mine in China. Water vapor absorption and uniaxial compressive experiments were also performed to examine water absorption characteristics and water-induced strength degradation effect of the investigated deep soft rock samples. Water vapor absorption processes of all the soft rock samples follow an exponential law. Correlation analyses also suggested that there were good positive correlation relationships between water absorptivity and clay minerals for both mudstone and sandstone samples.

Effect of the self-healing properties of asphalt mixture on the interlayer shear performance of bridge deck pavement

The cyclic shear stiffness and damping ratio of angular and round particle geogrid interfaces is of much concern in reinforcement structure seismic analysis. In this study, various component percentages of crushed limestone and spherical granular medium mixtures were used to investigate the role of particle regularity in static and cyclic direct shear tests. The test results revealed that an increase in the proportion of round particles decreased cyclic shear strength and volume change. The phenomenon of shear softening was observed with a high amplitude of shear displacement when the proportion of round particles was increased in the mixture. As the percentage of round particles increased, the maximum interface shear stiffness decreased significantly from, 39.69 to 28.28 MPa/m, but a reverse trend in the maximum damping ratio was observed, from 0.308 to 0.37. The effect of cyclic shear history and proportion of round particles on interface strength parameters was also analyzed. A linear regression model was fitted to the data for quantifying the relationship between the proportion of round particles and friction angle. The results suggest that different percentages of round and angular particles can produce varying degrees of particle interlock between aggregate and geogrid, influencing the macro-mechanical behavior of the reinforced soil interface.

The determination of strength parameters for stability analysis is the most important job in evaluation of landslide slope stability. Mitachi et al (1999) proposed a method for determining strength parameters for stability calculation rationally, and also proposed a practical method in which the strength parameters for design purpose are given by combining the conventional reverse calculation method with the strength parameters obtained by laboratory shear test. Calculation of landslide slope stability by using this method requires a shear test apparatus by which the strength parameters corresponding to peak, fully softened and residual states can be evaluated.Residual strength parameters can be obtained from a series of cyclic direct shear test. However, the shear mechanism of the soil specimen which is subjected reciprocal shear forces in cyclic direct shear test is different from that occurring along the shear surfaces. This paper describes the effect of reciprocal shear forces on the clay particle orientation along the shear surface based on the observation by using scanning electron microscope. For this purpose, three series of cyclic direct shear test were conducted by using reconstituted kaolin clay. The tests are conducted under consolidated constant pressure condition using normal type and precut specimen, and consolidated constant volume condition. Based on the test results, completely oriented clay particle structures were observed after two cycles of cyclic shear under the condition of consolidated con-stant pressure test using normal type and pre-cut specimen.

Particle size effects on coarse soil-geogrid interface response in cyclic and post-cyclic direct shear tests

Recycled concrete aggregate (RCA) has been widely used as a resource in reinforced soil structures, especially as a substitute for natural aggregate. Direct shear tests were conducted using a dynamic direct shear apparatus to study the effects of particle-size gradation (0.06–37.5 mm) on the shear properties of RCA-geogrid interface, in which geogrid was used to enhance the shear strength of RCA. The results exhibited that the geogrid significantly improved the interface peak strength of the RCA-geogrid interface. The inclusion of geogrid reduced the vertical displacement of RCA. The shear strength of the RCA-geogrid interface with different gradations increased with an increase in the relative density (RD) in the monotonic direct shear test. In the cyclic direct shear tests, the shear stiffness of the well-graded RCA(R2)-geogrid interface was the largest and the damping ratio of the discontinuous-graded RCA(R3)-geogrid interface was the smallest. In post-cyclic monotonic direct shear, the RCA-geogrid interface shear strength increased significantly, from 26.5% to 48.3%. After the cyclic shearing, the interface apparent adhesion and friction angle increased and the R2-geogrid interface demonstrated superior shear properties.

Strength of various sands in triaxial and cyclic direct shear tests

Geosynthetics are being widely used as a reinforcement material in the construction of mechanically stabilized earth (MSE) walls. The strength and stability of these walls are depending upon the interface behavior between soil and reinforcement material. It is understood from the literature review that the dynamic interface properties of soil and geosynthetics are not well explored yet, as in the case of static loading conditions. The present study investigates the cyclic behavior of the interface between sand and non-woven geotextile material. The objective was achieved by simulating the cyclic direct shear test using finite element-based package PLAXIS2D. The behavior of interface shear stiffness, and damping ratio were studied with increase in number of cycles and displacement amplitude. In addition, the interface behavior of geotextile with the sand having different fines content was also studied. The results revealed that the increase in the fines content causes the reduction in the interface shear stiffness. The interface shear strength properties obtained from the cyclic direct shear test were compared with the static shear test. The friction angle obtained from the cyclic shear test was 6% higher than that obtained from the static direct shear test.

Evaluation of disturbance function for geosynthetic–soil interface considering chemical reactions based on cyclic direct shear tests

ABSTRACT: For the design and performance analyses of geosynthetic-reinforced soil structures under repeated loading, such as those induced by compaction, traffic and earthquakes, the understanding of cyclic soil–geosynthetic interface behaviour is of great interest. Nevertheless, experimental data concerning this type of behaviour are very scarce. A laboratory study was carried out and is described in this paper. This paper presents the behaviour of an interface between a silica sand and a high-strength geotextile under monotonic and cyclic loading conditions. A large-scale direct shear test device able to perform load- or displacement-controlled cyclic tests was used. The results obtained are presented and discussed, especially in terms of interface shear stiffness and damping ratio. Monotonic direct shear tests indicated that the coefficients of interaction for the sand–geotextile interface depend on the confining pressure. Cyclic direct shear tests indicated that the interface stiffness tends to increase during the first loading cycles, exhibiting slight variation after 10 cycles. Slightly higher values of shear stiffness and damping ratio were reached with displacement-controlled cyclic direct shear tests. The cyclic loading of the interface did not lead to the degradation of the post-cyclic peak shear strength; however, the post-cyclic shear strength for large displacements exhibited an important decrease.