Variation Of Shear Strength Research Articles

The unsaturated characteristics of natural loess in slopes, New Zealand

Loess and loess-derived soils in the Akaroa harbour area of New Zealand are typically unsaturated and vulnerable to shallow landsliding during rainfall events. In this paper, the water retention properties and unsaturated shear strength of these materials are characterised using laboratory testing and long-term field instrumentation. Because the pore size distribution of the loess is fractal, the laboratory-derived soil-water characteristic curve is described mathematically using a series of power-law relationships. The same soil-water characteristic curve applies to both recompacted and intact loess when suction is normalised by the air entry value. Stress–strain behaviours of the recompacted and intact loess exhibit significant differences, however. The unique microstructure of the intact loess contributes to its larger shear strength. Long-term field instrumentation data, including suction and volumetric water content, indicate that the hydraulic state of in situ loess remained on a scanning curve for the duration of the monitoring period, despite the occurrence of significant wetting events. This, in combination with triaxial test results, allows the contribution of suction to unsaturated shear strength to be quantified. Temporal variations in suction's contribution to strength confirms seasonal variability in unsaturated shear strength and thus slope stability.

Effects of the reinforcement content and reinforcement scale on the shear strength characteristics of mechanically biologically treated waste.

Mechanical and biological treatment (MBT), which can be used for waste reduction and for the burning of methane from biological treatments to generate electricity and heating, has become a popular research topic in environmental geotechnical engineering. This study investigated the mechanical behaviour of MBT waste and the effects of different reinforcement contents and reinforcement scales on its shear strength characteristics, and 68 groups of MBT waste samples from the Hangzhou Tianziling landfill were tested in the laboratory with a direct shear test apparatus. The samples exhibited displacement hardening behaviour in their mechanical response. The results show that the content and scale of the reinforced materials in MBT waste play an important role in the strength characteristics of MBT waste, and graphs showing the variation of the MBT waste shear strength and shear strength parameters with different reinforcement contents and reinforcement scales are shown. The range of cohesion c is 6.0-12.0kPa, and the internal friction angle φ is 15.6-26.6°, respectively. The results of this study provide a reference for the assessment of slope stability at MBT landfills.

Calibration of Undrained Shear Strength Partial Factor Using Probability Theory

Design in accordance with Eurocode 7 applies the partial factors of geotechnical parameters to take into account uncertainties of various sources. The prescribed values of partial factors are unique, even though the degree of uncertainty can vary significantly. This can lead to an unequal reliability level of structures designed using the same procedures and methods. This paper analyses the influence of undrained shear strength variability on the reliability index (β), using reliability theory and statistical methods. Analyses were performed in the case of a shallow footing designed in accordance with Eurocode 7, design approach 3. It is shown that reliability indexes of a shallow footing could be lower than the target values prescribed in Eurocode. To meet these values, additional elaboration and calibration of undrained shear strength partial factor (γcu) was proposed.

Investigating the Basal Shear Zone of the Submarine Tuaheni Landslide Complex, New Zealand: A Core‐Log‐Seismic Integration Study

AbstractAlthough submarine landslides have been studied for decades, a persistent challenge is the integration of diverse geoscientific datasets to characterize failure processes. We present a core‐log‐seismic integration study of the Tuaheni Landslide Complex to investigate intact sediments beneath the undeformed seafloor as well as post‐failure landslide deposits. Beneath the undeformed seafloor are coherent reflections underlain by a weakly‐reflective and chaotic seismic unit. This chaotic unit is characterized by variable shear strength that correlates with density fluctuations. The basal shear zone of the Tuaheni landslide likely exploited one (or more) of the low shear strength intervals. Within the landslide deposits is a widespread “Intra‐debris Reflector”, previously interpreted as the landslide's basal shear zone. This reflector is a subtle impedance drop around the boundary between upper and lower landslide units. However, there is no pronounced shear strength change across this horizon. Rather, there is a pronounced reduction in shear strength ∼10–15 m above the Intra‐debris Reflector that presumably represents an induced weak layer that developed during failure. Free gas accumulates beneath some regions of the landslide and is widespread deeper in the sedimentary sequence, suggesting that free gas may have played a role in pre‐conditioning the slope to failure. Additional pre‐conditioning or failure triggers could have been seismic shaking and associated transient fluid pressure. Our study underscores the importance of detailed core‐log‐seismic integration approaches for investigating basal shear zone development in submarine landslides.

Effects of spatial autocorrelation structure for friction angle on the runout distance in heterogeneous sand collapse

This paper proposes a stochastic method for analyzing the runout distance of sand collapse considering the spatial variability of shear strength, in which random field theory and generalized interpolation material point method are integrated into a Monte-Carlo simulation basis. The random field is generated by Cholesky matrix decomposition method and implemented into the material point level, hence heterogeneity and large deformations are simultaneously considered in the modeling process. A sand collapse case is simulated with both homogeneous and heterogeneous condition assumptions by the proposed method. The effect of five theoretical autocorrelation functions (ACFs) on the runout distance of the collapse is highlighted since the ACFs are commonly adopted to characterize the spatial variability of soil properties due to sparse site observation data. It is shown that the deterministic analysis may underestimate the runout distance, while the heterogeneous model provides realistic results. Moreover, five ACFs and different coefficients of variation of friction angle (COVφ) are compared to investigate their influences on the runout distance modeling. The results show that the uncertainty of runout distance increases with the increase in COVφ. Meanwhile, the variances of the runout distance also become larger with COVφ increasing. Based on the proportion of the runout distance which exceeds the deterministic value, the results indicate that the deterministic analysis notably underestimates the risk induced by large runout distances in real heterogeneous granular flows (e.g., landslide, debris-avalanches).

Influence of non-persistent joint aperture and inclination angle on the shear behavior and fracture mode of solid rock and concrete material

Non-persistent joints or cracks are ubiquitous in both solid rock and concrete material. Numerous experimental and numerical studies have been conducted to study the influence of geometric properties (e.g., location, connectivity, number and length) of non-persistent joint on the mechanical characteristics of rock, but few focus on the effect of joint or crack aperture. In this study, PFC 2D numerical simulation is performed to study the influence of embedded joint aperture, joint inclination angle and normal stress on the shear behavior and fracturing modes of solid rock and concrete material. The results show that the aperture has a great impact on the mechanical behavior and fracturing process of rock and concrete, and the influence varies with the joint inclination angle and normal stress. There are usually two peaks on the shear stress curves, and the peak shear strength, the damage zone width and the total crack number all decrease with increasing joint apertures. For the specimen with the same joint aperture but of different inclination angles (−30°, 0° and 30°), the peak shear strength and shear modulus are the largest at an inclination angle of 30°, and the smallest at −30°. The damage extent and degree of the intact rock bridges is closely associated with the variation of the peak shear strength for the specimens with different joint inclination angles, which are caused by the different relative positions between the embedded joint and the shear direction. Furthermore, a higher normal stress leads to a larger width of the shear damage zone for all the joints and an earlier mobilization of the second peak shear strength for the joints with −30° inclination angle.

Random failure mechanism method for assessment of working platform bearing capacity with a linear trend in undrained shear strength

A bearing capacity evaluation for the surface strip foundation on a working platform modelled on a two-layered substrate is considered in the study. The upper layer is assumed as man-made and well-controlled and thus non-variable. The lower layer modelling natural cohesive soil is subjected to spatial variability of undrained shear strength. The random failure mechanism method (RFMM) is used to evaluate the bearing capacity. This approach employs a kinematic assessment of the critical load and incorporates the averaging of three-dimensional (3D) random field along dissipation surfaces that result from the failure mechanism geometry. A novel version of the approach considering an additional linear trend of undrained shear strength in the spatially variable layer is proposed. The high efficiency of the RFMM algorithm is preserved. The influences of foundation length, trend slope in the spatially variable layer, fluctuation scales, and thickness of the homogenous sand layer on the resulting bearing capacity evaluations are analysed. Moreover, for selected cases, verification of the RFMM based assessment obtained using random finite difference method (RFDM) based on 3D analysis is provided. Two types of analyses are performed using RFDM based on associated and non-associated flow rules. For associated flow rule which corresponds to RFMM, the RFMM is conservative and efficient and thus it seems preferable. However, if RFDM employs non-associated flow rule (much lower dilation angle for sand layer), the efficient RFMM is no longer conservative. For this situation, a combined approach that improves the efficiency of the numerical method is suggested.

Seismic Behavior of Stone Masonry Joints with ECC as a Filling Material.

This paper investigates the seismic behavior of novel stone masonry joints using ductile engineered cementitious composite (ECC) as a substitute for ordinary mortar. Ten stone masonry joints with different types of mortar/ECC were tested under axial and cyclic loads. The filling materials of mortar joints tested included ordinary mortar, polymer mortar, ECC, and composite mortar with two combination proportions of ECC and ordinary mortar. The test results indicated that ECC specimens exhibited a more stable hysteretic response as well as an improvement in strength, deformation, energy dissipation, and strength degradation. The ECC mortar joints maintained integrity during the entire loading process due to the “self-confinement” effect of ECC. A partial substitution of mortar with ECC could provide effective reinforcement and confinement to prevent mortar failure and peeling, thereby allowing such specimens to approach the seismic performance of ECC specimens. Based on the trend of shear strength variations, a corresponding failure process is defined for ECC/mortar joints under cyclic and axial compressive loads, including four distinct stages: linear elastic, crack-developing stage, interface debonding, and friction sliding. New equations are proposed for predicting the shear strength and residual shear strength of the ECC/mortar joints on the basis of the test results, which are validated in the composite mortar specimens.

Effect of Bedding Orientation and Spatial Variability of Stratification Shear Strength on Stability of Transversely Isotropic Rock Slope

The spatial variability of soil properties is inherent. A series of direct shear tests were carried out on strongly weathered slates samples with weak bedding planes, the result of which indicates the existence of variability of shear strength parameters. Based on the testing results, several numerical simulations of slopes were conducted considering such a variability of shear strength. The results had shown that the weak bedding planes affect the shape of sliding arc as well as the factor of safety of slopes. As the dip angle of bedding planes increases, the shape of the sliding surface changes from circular to a mixed form of circular and planner. When incorporating the spatial variability of weak planes’ shear strength into the stability analysis, the safety factors of slopes would reduce, in which the sliding arc exhibited a sliding band comprising multiple sets of sliding arcs.

Post-Cyclic Mechanical Behaviors of Undisturbed Soft Clay with Different Degrees of Reconsolidation

Soft soil is often subjected to cyclic loading such as that imposed during storms, under traffic, or in an earthquake. Furthermore, the cyclic-loading-induced excess pore water pressure can be partially dissipated after cyclic loading. Thus, different reconsolidation processes should be considered. A series of static and dynamic triaxial tests were conducted on undisturbed soft soil to determine the post-cyclic mechanical behavior thereof, such as the variation of undrained shear strength, the development of excess pore water pressure, and the evolution of effective stress path. The effects of consolidated confining pressure, cyclic stress ratio, and degree of reconsolidation were analyzed. Results show that the trend of all stress–strain curves is similar under different conditions. The effect of the degree of reconsolidation is such that, with increasing the degree of reconsolidation, the shear strength is enhanced. Meanwhile, compared with undrained shear strength without cyclic loading, the shear strength after cyclic loading with full reconsolidation is increased. These factors also have a significant effect on the undrained shear strength: the greater both the confining pressure and cyclic stress ratio are, the higher the undrained shear strength. A positive excess pore water pressure is always observed during post-cyclic shearing process, irrespective of different factors. The S-shaped effective stress paths under different test conditions are observed and cross the critical state line. The microstructures of undisturbed soil and post-cyclic specimens with different degrees of reconsolidation were quantitatively investigated. Besides that, the degree of influence of different factors on the post-cyclic undrained strength was analyzed. Based on the test results, the undrained shear strength with cyclic load-history was well predicted by existing models.

Effect of soil spatial variability on failure mechanisms and undrained capacities of strip foundations under uniaxial loading

This paper mainly investigates the effect of soil spatial variability on failure mechanisms and capacities of strip foundations under uniaxial loading on marine clay deposits with linearly increasing undrained shear strength using random finite element analysis. The soil spatially variable feature is characterised by a non-stationary random field where the ratio of the standard deviation and mean of undrained shear strength is maintained. The effect of soil parameters, including the dimensionless soil heterogeneity index, the coefficient of variation of shear strength and the dimensionless autocorrelation distance, on the uniaxial capacities are discussed. In addition, shapes of failure envelopes for combined loading in the probabilistic analysis are compared to those shapes in deterministic analysis. Results demonstrate that the difference in shapes of failure envelopes between deterministic and probabilistic cases is minimal and can be neglected for practical purposes. Probabilistic uniaxial capacities derived in this study can be employed to scale probabilistic failure envelopes, which represent sizes of probabilistic failure envelopes. The obtained results offer insights into how soil spatial variability can be comprehensively considered in the design of an offshore shallow foundation.

The effect of loading rate on the interfacial behavior of overmolded hybrid fiber reinforced polypropylene composites

AbstractIn the present work, the interfacial behavior of overmolded hybrid fiber reinforced polypropylene composites (hybrid composites) under the loading rate of 1, 10, and 100 mm/min are studied by experimental methods. The interfacial mechanical properties of hybrid composites are determined by monotonic and cycle loading‐unloading single‐lap‐shear tests. The experimental results reveal that interfacial shear strength increases with loading rate, while the shear stiffness shows insensitive to loading rate. A regression function is built to describe the variation of interfacial shear strength with loading rate. The cyclic loading‐unloading curves of hybrid composites samples indicate that loading rate effects on the interfacial nonlinear behavior of hybrid composites are considered by affecting plastic deformation. In addition, scanning electron microscopy and digital image correlation observations reveal the failure mechanisms of overmolded hybrid composites. The failure behavior of overmolded hybrid composites is mainly CFRT laminate failure for all cases. The evolution of non‐uniform strain fields indicates that the fracture of overmolded thermoplastic composites may initiate at the edges and spread out to the far fields.

Interfacial characterization and mechanical properties of reactive air brazed ZrO2 ceramic joints with Ag–CuO–Al2TiO5 composite filler metal

The Al2TiO5 particles reinforced Ag–CuO–Al2TiO5 composite filler metal prepared by mechanical milling was applied to reactive air braze ZrO2 ceramic to itself. The effect of Al2TiO5 particle content and brazing parameters on the interfacial microstructure and mechanical properties of the joints was systematically analyzed. Moreover, the stability of joint microstructure and the variation of bonding properties were investigated by subjecting them to prolonged heat treatment at 800 °C. The results show that the shear strength of the reactive air brazed joints at 1050 °C for 30 min with 10 wt % Al2TiO5 additives reached 104 MPa, which was 112% higher than that of the joints brazed with single Ag–CuO filler metal. The added Al2TiO5 particles were decomposed into TiO2, which was further reacted with ZrO2 ceramic to form ZrTiO4 phase and blocky Al2O3 phase in the Ag matrix and thus generating the particle-reinforced brazing seam. The variation of joint shear strength caused by brazing parameters and Al2TiO5 contents was analyzed from the viewpoints of the wettability of composite filler, microstructural evolution of joint and formation of void defect. When the ZrO2 ceramic was brazed with Ag–CuO-10 wt % Al2TiO5 at an optimized parameter of 1050 °C for 30 min, the joint shear strength did not decrease obviously after oxidation at 800 °C for 100 h because of the good high-temperature stability of the joint microstructure.

Prediction of Shear Strength of Fully Weathered Coastal Red Sandstone: Influence of Water Content, Fine Content, and Relative Compaction

Xu, H.; Cai, L.; Shao, Z.; Wang, Z.; Li, Z., and Huang, C., 2021. Prediction of shear strength of fully weathered coastal red sandstone: Influence of water content, fine content, and relative compaction. Journal of Coastal Research, 37(4), 827–841. Coconut Creek (Florida), ISSN 0749-0208.Shear strength of coastal rock mass can be characterized by parameters such as cohesion and internal friction angle, which are relatively difficult to measure with accuracy on coastal engineering sites. This paper aims to predict shear strength of fully weathered coastal red sandstone with physical property parameters—water content, fine content, and relative compaction—that are easily measured on site. The variation of shear strength parameters with physical property parameters was obtained with indoor direct shear tests, and the real-time prediction of shear strength of fully weathered coastal red sandstone was realized by employing a decision tree model. The results show that the variation of shear strength parameters with physical properties can be accurately characterized by cubic polynomials and that the cohesion and internal friction angle can be well predicted by a 10-layer decision tree model with high accuracy. This study sheds light on the variation of shear strength of fully weathered coastal red sandstone and similar rock mass with physical properties and has practical significance for engineering conducted in such strata, which require in-time monitoring of shear strength of rock mass.

Strength and structural variations in dredger fill subjected to vacuum dynamic consolidation

Laboratory vacuum dynamic consolidation tests were performed to study the effect of dynamic impact loads on the shear strength characteristics of dredger fill. The results revealed that the shear strength increased with the increase in the number of blows. The relationship between the increase in the shear strength and the soil structure was analyzed through scanning electron microscopy and mercury intrusion porosimetry. The structure collapsed progressively and the larger inter-aggregate pores were affected the most. Considering pore evolution, the pore size distribution was primarily unimodal, and the variations in porosity and shear strength with the blow count were the same. Thus, the shear strength of dredger fill is influenced by its structure. On average, five blows ensure high compaction efficiency.

System failure probability analysis of cohesive slope considering the spatial variability of undrained shear strength

System failure probability analysis of cohesive slope considering the spatial variability of undrained shear strength

Random field model of soil parameters and the application in reliability analysis of laterally loaded pile

The bearing capacity of pile under horizontal load is not only related to pile size and pile material, but also closely related to soil parameters. In this paper, based on the probability analysis method of random field theory, a non-stationary random field model is firstly proposed for the undrained shear strength Su of soil. In this model, the uncertainty of the increase trend of Su along the direction of depth is taken into account, and the mean value and standard deviation of random field increase linearly along the depth. Then, by comparing with other random field models, the applicability of the non-stationary random field model for undrained shear strength proposed in this paper is verified. Finally, the random field model is applied to the reliability evaluation of horizontally loaded pile, and the influence of the spatial variability of undrained shear strength on the failure probability of horizontally loaded pile is discussed. The results show that the coefficient of variation and correlation length of undrained shear strength have obvious influence on the failure probability of pile foundation. The uncertainty of increase rate b of undrained shear strength with depth also has influence on the failure probability of pile foundation. If the spatial variability of the soil parameters is not considered in the evaluation and design of pile foundation, the failure probability of pile foundation will be large, which will make the design results of pile biased toward conservative.

Shear strength measurements and hydrostatic compression of rhenium diboride under high pressures

Shear strength measurements have been carried out on rhenium diboride, ReB2, to a pressure of 74 GPa using a Radial X-ray Diffraction (R-XRD) technique in a diamond anvil cell using platinum as an internal x-ray pressure standard. The R-XRD result has provided a unique insight into the deformation of hexagonal crystal lattice under non-hydrostatic compression and variation of shear strength with increasing pressure. From R-XRD data, we have estimated hydrostatic component of compression to determine an equation of state of rhenium diboride yielding a bulk modulus of K0 = 366 ± 25 GPa with a pressure derivative K0′ = 4.3 ± 0.5 in good agreement with hydrostatic density functional theory calculations. The average lower bound of shear strength (τ) from various diffraction planes was then calculated using the measured interplanar d-spacing (dm) and hydrostatic component of d-spacing (dp) to be shown to approach 6.7 ± 0.4 GPa at 70 GPa. Our results show that the anisotropic compression effects observed in ReB2 under hydrostatic compression are correlated to electronic structure changes under compression as predicted by theoretical calculations.

Review of Recent Developments and Understanding of Atterberg Limits Determinations

Among the most commonly specified tests in the geotechnical engineering industry, the liquid limit and plastic limit tests are principally used for (i) deducing useful design parameter values from existing correlations with these consistency limits and (ii) for classifying fine-grained soils, typically employing the Casagrande-style plasticity chart. This updated state-of-the-art review paper gives a comprehensive presentation of salient latest research and understanding of soil consistency limits determinations/measurement, elaborating concisely on the many standardized and proposed experimental testing approaches, their various fundamental aspects and possibly pitfalls, as well as some very recent alternative proposals for consistency limits determinations. Specific attention is given to fall cone testing methods advocated (but totally unsuitable) for plastic limit determination; that is, the water content at the plastic–brittle transition point, as defined using the hand rolling of threads method. A framework (utilizing strength-based fall cone-derived parameters) appropriate for correlating shear strength variation with water content over the conventional plastic range is presented. This paper then describes two new fine-grained soil classification system advancements (charts) that do not rely on the thread-rolling plastic limit test, known to have high operator variability, and concludes by discussing alternative and emerging proposals for consistency limits determinations and fine-grained soil classification.

Study on shear behavior of coral reef limestone–concrete interface

To examine the coral reef limestone–concrete shear failure characteristics, we conducted large-scale direct shear tests to study five types of interfaces: planar, sloped, arc shaped, stepped, and triangular. Furthermore, the shear failure characteristics and shear strength variations were examined under three interface connection types: smooth, mud filled, and cemented. The results show that the shear phenomena at the smooth and mud-filled interfaces between the coral reef limestone and concrete were characterized by the interface slip failure mode. The mud at the interface acted as a good lubricant and greatly reduced the shear strength. For the cemented connection between the coral reef limestone and concrete, the shear strength increased rapidly with the shear displacement. When the shear strength reached a certain value, it abruptly decreased and then tended to level off, and shear failure occurred at the coral reef limestone side of the interface. Among the studied specimens, the maximum shear strengths were in the following order from highest to lowest: stepped interface, triangular interface, arc-shaped interface, sloped interface, and planar interface, while the corresponding shear displacements increased in that order. The results of this study can serve as a reference for the construction of pile foundations on coral reef limestone strata.