Shear Stress Displacement Research Articles

Surface Effect in Nano-Scale Fretting Contact Problems

Abstract The fretting contact behavior of nanostructured materials is significantly influenced by the surface effect. A model of fretting contact between a nano-sized rigid cylindrical indenter and an elastic half-plane is established based on Gurtin–Murdoch (G–M) surface elasticity theory, with which the surface effects on the stress and displacement distributions and the size of stick region (no-slip region) in the contact zone are systematically studied. It is found that the surface effect induces an additional traction besides the external force applied by punch, which could help to smoothen the stress and displacement distributions. The normal surface-induced traction related to the residual surface stress is opposite to the externally applied compression, which results in a material stiffening in the contact zone so that the contact radius, normal displacement, and normal stress decrease compared with their classical counterparts. The tangential surface-induced traction is also opposite to the externally applied frictional stress, consequently leading to reductions of the shear stress and tangential displacement induced by friction in the contact zone. More interestingly, the surface effect leads to three possible states in the contact zone, including complete slip, partial slip, and complete stick, instead of the solely partial slip state in classical fretting contact models without surface effect. Among them, the complete stick due to the action of surface residual stress is more beneficial for inhibiting the wear of contact devices, which can be realized by reducing the indenter size. The present research does not only help one to better understand the physical mechanism in nano-scale fretting contact problems, but should also guide the anti-wear design in nano-electro-mechanical (NEMs) systems.

Airflow Field and Shelter Effect Around Flexible Plants Using Fluid‐Structure Interaction (FSI)‐Large‐Eddy‐Simulation (LES) Simulations

AbstractVegetative windbreaks have a significant advantage in regulating microclimates and improving soil conditions. Some studies highlight the importance of turbulence and plant flexibility, but few has investigated the relationship between flexibility and the shelter effect of windbreaks. Therefore, we perform a series of 3D fluid‐structure interaction (FSI)‐large‐eddy‐simulation (LES) simulations to study the airflow passing through flexible single‐plant windbreaks. We first model the plants with branches according to their geometric features in the field, present a FSI solver to strongly couple the airflow velocity field and windbreak vibration, and then use a LES turbulent model to resolve the turbulent flows. Based on the simulations, the airflow fields around the plants (Plant #1 and Plant #2) with different flexibilities, evaluated by Young's modulus, were analyzed and compared. Afterward, the shelter effect of flexible plants is analyzed based on three indices, including turbulence intensity, surface shear stress and plant swing displacement. The peak turbulence intensity of the three plants follows the order Plant #1 > Plant #2 > rigid plant. Regardless of wind speed, the surface shear stress around the plants follows the order Plant #1 < Plant #2 < rigid plant. The swing displacement increases as the velocity and flexibility increase. It is concluded that the flexible plant has a better shelter effect than the rigid plant, and within a certain range, the stronger the flexibility of the plant is, the better its shelter effect. This study not only investigates the interaction mechanism between flexible plants and airflow, but also provides a theoretical reference for the application of flexible plants in wind protection engineering.

Mechanical properties and soil failure process of interface between grouser of tracked mining vehicle and deep-sea sediment

Tracked mining vehicles (TMVs) are key equipment in deep-sea mining systems and can easily slip when walking on soft sediments on the seabed. Thus, it is important to investigate the effect of track parameters and grounding-specific pressure on the shear interaction between mining vehicles and sediment. The sediment was simulated using a mixture of bentonite and water, and a shear test of the track with a single grouser and sediment was conducted. A numerical model of the track–sediment shear test was established, and the shear strength and failure mode of the sediment soil under the track action were examined. The results demonstrate that the peak shear strength of the track–sediment interface increases with an increase in the grounding-specific pressure, gradually increases with an increase in grouser height, and tends to stabilize at a given level of grouser height. Owing to the presence of the grouser, the deep-sea sediment transitions from the elastic state to the plastic state faster than the typical clay during the shear test. The variation law of peak shear strength at the track-sediment interface with the height of track grouser under different grounding-specific pressures was analyzed, and a modified shear stress-displacement relationship model was proposed. Wedge failure is the predominant method of failure for a single-grouser shear sediment soil at various heights. The primary factor affecting the horizontal disturbance range is the grouser height, and the range increases as the grouser height increases; the primary element affecting the vertical disturbance range is the grounding-specific pressure, and the range increases as the grounding-specific pressure increases. The relationship of the grouser height and cohesiveness with the interfacial shear strength was examined and a new shear stress–displacement relationship model that can accurately capture the shear mechanical behavior between the track and sediment under various grouser heights was proposed. In conclusion, the study findings could serve as a guide for the engineering design of a TMV walking system.

Development of Cyclic Interface Shear Test Device and Testing Procedure to Measure the Response of Cohesive Soil-Structure Interface

Abstract Cyclic loading acting on foundations supporting renewable energy systems affects the soil-structure interface properties and shear resistance. The cyclic shear stress and cyclic displacement applied to the cohesive soil-structure interface may cause volume changes and pore pressure build up in the surrounding soil. This article focuses on the development of a new testing device named the cyclic interface shear test (CIST). The CIST is a fully automated device developed to directly measure the response of cohesive soil-structure interface for foundations subjected to long-term cyclic axial loading. This article describes the newly developed testing device, including the design of the shear head and the three-dimensional (3D) printed interface elements, as well as the control system and data acquisition system. Furthermore, the article presents the sample preparation for clayey soil and the recommended testing procedure for conducting static or cyclic interface shear tests, or both. The developed CIST device is capable of applying one-way, two-way, or combined one- and two-way cycles. Furthermore, the CIST is capable of applying different amplitudes, a range of loading frequencies, and a large number of cycles. To demonstrate the capabilities of the CIST device and to finalize the testing procedure, a series of preliminary CISTs and a static baseline test on cohesive soil-3D printed interface were performed.

Experimental study on the effects of triangular groove inclination angles on the mechanical behavior of sand–concrete interfaces

The mechanical properties of pile–soil interfaces directly affect the bearing capacity of pile foundations. In this study, the effects of triangular groove inclination angles on the mechanical properties of sand–concrete interfaces were investigated. Random rough concrete surfaces were obtained through slurry intrusion testing, and the roughness of concrete surfaces was evaluated based on the sand cone method. According to the roughness of random concrete surfaces, five regular concrete surfaces with different triangular groove inclination angles were constructed. A series of direct shear tests between (i) sand and random concrete surface, (ii) sand and regular concrete surface, as well as (iii) sand and smooth concrete surface were performed. Moreover, a direct shear test of natural sand was conducted. Lastly, a shear strength model considering the triangular groove inclination angle of sand–concrete interfaces was established, and the shear failure mechanism of interfaces was discussed. The results firstly indicated that the shear stress-displacement curves of random rough concrete surfaces were ideal elastic-plastic curves; and the regular rough concrete surfaces were found to incur strain softening under a normal stress of 300 kPa. Secondly, the shear strength of sand–concrete interfaces increased with the increase in groove inclination angle of concrete interfaces. Thirdly, sand was found to achieve the highest shear strength, while sand–smooth concrete interfaces proved to attain the lowest. Lastly, the internal friction angle value of random concrete interfaces was shown to range between the values of concrete surfaces with triangular groove inclination angles of 70° and 90°.

Effects of freeze–thaw cycles on the shear stress induced on the cemented sand–structure interface

Freeze–thaw alternation and freeze–thaw cycle erosion are the main reasons for the failure of the cemented soil–structure interface in cold regions. In this study, the direct shear and cyclic direct shear tests of cemented sand–structure interface were conducted in the frozen state (−10 °C) and thawed state (25 °C) at a 300 kPa normal stress under different freeze–thaw cycles (i.e., 0, 1, 5, 10, 15, 20, 25, 30). The experimental results for the shear stresses of the cemented sand–structure interface are presented, and the mechanism of shear stress formation and change was examined through mesoscopic analysis. Variations in shear stress with different freeze–thaw cycles were consistent. Typically, 10 was identified as the critical freeze–thaw cycle number for adfreeze strength, and the hyperbolic model of shear stress–displacement curve in the thawed state was obtained. The peak shear stresses of different freeze–thaw cycles gradually decreased as the shearing cycle number increased until entering a stable stage in frozen state and were close to each other in the thawed state. The internal damage of cemented sand and the formation of ice crystals on the surface increased with the increase in freeze–thaw cycle number. Hence, internal change in cemented sand under freeze–thaw cycles is the fundamental reason for alterations in shear stress. The results of this study shed light on shear stress complexity at the cemented sand–structure interface under freeze–thaw cycles and provide references for practical engineering.

Experimental and theoretical investigation on compression-shear properties of high-strength engineered cementitious composites (HS-ECC)

High-strength engineered cementitious composites (HS-ECC) has broad application prospects due to its excellent mechanical performance and durability. Construction materials in structural members are susceptible to combined compression-shear stress. Therefore, the mechanical properties of HS-ECC under the combined stress are experimentally investigated by a servo-controlled biaxial testing machine. The effects of normal stress ratio on the compression-shear properties are systematically studied, and mortar specimens serve as control group. The experimental results show that the shear stress versus shear displacement curves of HS-ECC are able to be divided into four stages, namely linear ascending, non-linear ascending, rapid descending and stable stages. Compared with mortar specimens, the shear strength and residual shear strength of HS-ECC increase by 5–21% and decrease by 33–42% respectively. HS-ECC has a friction coefficient of 0.53, which is smaller than that of mortar specimens and concrete. When the normal stress ratio increases, the dilation angle of HS-ECC decreases at first and then remains basically unchanged. The damage evolution of HS-ECC is delayed when compared with that of the mortar specimen. Finally, a damage constitutive model is proposed to describe the compression-shear properties of HS-ECC. It is found that the predicted results agree well with the experimental results. This study is of great significance to understand the compression-shear properties of HS-ECC and promote its structural applications.

Shear strength of soil-root system under different vegetation restoration modes on the Loess Plateau of China

The soil-root system shear strength (SRSS) is a useful dynamic parameter for evaluating soil detachment capacity by flowing water and slope stability. The changes in soil properties and root traits induced by vegetation restoration likely affect SRSS considerably. Nevertheless, few in-situ shear tests have been conducted to quantify the effects of restoration mode on SRSS in semi-arid region. This study was conducted to quantify the impact of restoration mode on SRSS of 0–50 cm soil layer at sites of one slope farmland (maize) and five vegetation restored lands (abandoned farmland, korshinsk peashrub, black locust, Chinese pine, and the mixed forest of amorpha and Chinese pine) and further to identify the related dominant contributing factors on the Loess Plateau. SRSS was reflected by the strain energy calibrated to 15% soil water content (SEc), peak shear stress (PSS) and the displacement of PSS (DPS) determined from the measured shear stress-displacement curves. The results showed that SEc decreased with soil depth (0–50 cm) for all vegetation restored lands. PSS increased with soil depth, except for slope farmland and abandoned farmland. DPS also decreased with soil depth as a whole. The mean SEc of 0–50 cm soil layer of different vegetation restored lands were 2.29–2.67 times greater than that of slope farmland. Chinese pine with a mean SEc of 138.3 J·m−2 was the best restoration mode to enhance soil erodibility. Soil water content significantly impacted SRSS and it decreased logarithmically with soil moisture. Plant roots could improve the ductility of soil, making shear failure with a great displacement. Root surface area density was the most sensitive parameter to reflect the effect of root system on soil strain energy. These results are helpful for understanding the mechanical mechanism of vegetation restored soils to mitigate erosion and to enhance slope stability in semi-arid region.

Dynamic Traction of Deep-Sea Polymetallic Nodule Collector

The ocean is extremely rich in mineral resources. To cope with the shortage of land mineral resources, countries are focusing on the development of deep-sea mineral mining technology. Owing to its superior traction performance, the deep-sea polymetallic nodule collector (DPNC) has become the preferred solution for ocean mining. This paper proposes a dynamic traction calculation model to address the shortcomings in the classical static traction calculation model with consideration of the dynamic variation rule of grouser–soil interaction in the DPNC process. Lab tests were conducted to formulate materials similar to deep-sea soil, and the corresponding shear stress–displacement models were established using the discrete element method (DEM) and Magic Formula to describe the “shear stress–displacement” relationship more accurately. Considering Kunlong 500, which is a Chinese DPNC, as an example, the periodicity and dynamics of the dynamic traction force were analyzed and compared with the numerical simulation results. The dynamic traction force was smaller than the static traction force and fluctuated significantly when considering the dynamic grousers–soil interaction. The magnitude and fluctuation of the dynamic traction force were influenced by the ratio of the grouser height to the spacing. In the DPNC design, the ratio of the grouser height to the spacing should be optimized according to the properties of the deep-sea subsoil to improve the traction performance and stability of the DPNC.

Experimental Study on the Shear Properties of Soil around Piles with Permeation Grouting

While post-grouting is frequently reported to improve the engineering performance of piles, the shear strength of the soil around piles is not well understood. To investigate the strengthening mechanism of soil around piles with permeation grouting, laboratory tests were carried out on homemade cement soil from the aspects of shear strength and microstructure characteristics. The evolution rule of the shear stress–shear displacement curve of grouting soil with different cement contents was analyzed, and the influence of grouting parameters on shear strength was explained. A composite exponential model describing the shear stress and shear displacement of permeation grouting silty clay was established. Furthermore, the influence of different cement content on changes in the microstructural characteristic parameters of the soil around piles was studied. The results show that penetration grouting has a positive effect on improving the shear strength of the soil around piles, and the failure mode of silty clay changed from elastic–plastic failure to brittle failure after grouting. Permeation grouting makes the particle structure denser, which limits the changes in pore arrangement and distribution. The shear failure of the soil around piles under permeation grouting obeys the Mohr–Coulomb criterion of failure. It is recommended to increase the grout diffusion radius during construction, considering the reinforcement effect of permeation grouting on the soil around piles.

Variation in shear strength of soil-root system under five typical land use types on the Loess Plateau of China

Shear strength of soil-root system (SRSS) is one of the most useful dynamic properties for evaluating soil erodibility and structural stability. The adjustment of land use may strongly affect SRSS by altering soil properties and plant root system. Few studies have been conducted to investigate the effect of land use on SRSS in semi-arid region. This study was performed to quantify the variation in SRSS with five typical land use types (cropland, orchard, grassland, shrub land and woodland) and identify the related dominant contributing factors on the Loess Plateau where land use has changed greatly in the past several decades. In-situ shear tests with large shear box (25 × 25 × 10 cm) were conducted to measure shear stress-displacement curves. The strain energy calibrated to 15 % soil water content (SEc), peak shear stress (PSS) and the displacement of peak shear stress (DPS) calculated from the curves were used to reflect SRSS. The results showed that woodland had the maximum SEc (124.4 J m−2) and PSS (1048.6 kPa), whereas cropland had the minimum SEc (65.6 J m−2) and DPS (7.2 mm). Woodland, especially coniferous species and its mixed forest, might be the most suitable land use type for vegetation restoration on the Loess Plateau to enhance soil erodibility or structural stability. The variation in SRSS with land use was closely related to the changes in soil properties and root traits. PSS increased with penetration resistance, while it decreased with soil water content. DPS was positive correlated to root biomass and morphological traits. SEc was mainly affected by the direct and indirect effects of root surface area density, penetration resistance, soil organic matter content and aggregate stability. The results are helpful for understanding the mechanical mechanism of vegetation restored soils to mitigate erosion and optimizing land use type in semi-arid region.

The development and application of an interfacial cohesive zone model of the pavement interlayer considering the characteristics of adhesive materials

The interlayer adhesive material is important to ensure the integrity of a pavement structure, but its influence on pavement performance as an actual material layer is usually ignored in pavement structure design and analysis. At present, the relationship between the shear stress and slip is usually expressed in the form of a coefficient. The interlayer adhesive material is a kind of heterogeneous composite material with rheological performance. Therefore, the relationship between a force and the displacement cannot be characterized by a simple linear relationship. In this paper, we develop a method for characterizing the properties of interlayer bonding materials using an interfacial cohesive zone model. First, we perform experimental tests, that is, a pull-out test and an oblique-shear test, to determine the optimal dosage of adhesive material, and then obtain the normal stress-displacement characteristic curve and shear stress-displacement characteristic curve for the optimal dosage of the adhesive material. Then, we divide the shear stress-displacement characteristic curve into four stages. Next, based on the characteristics of normal stress displacement curve and shear stress displacement curve, we develop a cohesive zone model based pavement interlayer simulation approach that can be used to characterize the stress displacement characteristics of interlayer adhesive materials. Finally, we present the performance of the interfacial cohesive zone model using finite element software to simulate the shear test and pull-out test, and find that the simulation results are basically consistent with the experimental results. Further, we apply the model to a special case, and the results are also consistent with the actual monitoring. It shows that the proposed method is reasonable.

Axial Wall Displacement at the Common Carotid Artery is Associated With the Lamb Waves

Abstract As compared with its radial wall displacement, axial wall displacement at the common carotid artery (CCA) carries independent clinical values, but its physical mechanisms are unclear. This study aims to investigate whether axial wall displacement at the CCA is solely from Young waves. A pulse wave propagation theory is utilized to identify two types of waves, Young waves, and Lamb waves, in an artery, and identifies two sources for axial wall displacement, wall shear stress and radial wall displacement gradient with a factor of the difference between axial and circumferential initial tension, which reveals the influence of axial initial tension on the waveform of axial wall displacement. Theoretical expressions are derived for calculating the waveforms of axial wall displacement and its two sources in the Young waves. With the measured pulsatile pressure and blood velocity at the CA of three healthy adults as the inputs, the waveforms of axial wall displacement in the Young waves are calculated at different values of axial initial tension and are found to greatly differ from their measured counterparts. As such, the Lamb waves may contribute to axial wall displacement at the CCA and the associated physical and physiological implications are discussed. Given the clinical values of axial wall displacement at the CCA, the Lamb waves may play a non-negligible role in determining arterial health and needs to be further studied for a comprehensive assessment of arterial wall mechanics.

Shear mechanical responses and cracking evolution mechanisms of flawed sandstone containing two circular holes

Shear tests on rectangular plate sandstone containing two pre-existing holes were performed to analyze the shear mechanical responses and cracking evolution mechanisms. With generation of the penetrating fracture surfaces, both shear stress and normal displacement show a dramatic drop. Then, during the shear slipping process, the shear stress increases once again due to wear and shear off of the surface asperities, and three different variation trends of the normal deformation including shear dilation, fluctuation, and shear contraction are respectively identified. The role of ligament length and normal stress on several key indices such as peak shear stress, peak normal displacement and residual shear stress was investigated. Violent AE (acoustic emission) responses occur along with penetration of the fracture surfaces, and in the shear slipping process, AE events continue to occur due to wear of surface asperities, while the increase rate of accumulative AE events declines. Cracks coalesced at the rock bridge and running through the rock matrix form the main failure planes of the samples. From the PFC2D simulation results, the crack clusters first initiate from hole-walls and coalesce at the rock bridge for a small ligament length, while first produce the main failure planes at the right/left rock matrix for a large ligament length. The total number of micro cracks shows a “calm → rapid increase → decreasing growth amplitude” variation during shearing, and the induced cracks become more concentrated for a larger normal stress, implying a cumulative damage of the failure surfaces.

Analysis of Cyclic Shear Stress–Displacement Mechanical Properties of Silt–Steel Interface in the Yellow River Delta

Pile foundations of offshore structures are often subjected to cyclic loads under storm loads, thus reducing their vertical bearing capacity. Therefore, studying the cyclic shear behavior of the soil–structure interface is important for maintaining the stability of offshore structures. A series of cyclic shear tests of the silt–steel interface were carried out using a large interface shear apparatus. The effects of various factors (i.e., normal stress, shear displacement amplitude, roughness, and water content) on the shear stress characteristics of the silt–steel interface were investigated. The stress–displacement model of the cyclic shear silt–steel interface was deduced. The results showed that the shear stress at the silt–steel interface was softened, and the type of bulk deformation was shear shrinkage under cyclic shear. With the increase in shear amplitude, the hysteresis curve gradually developed from “parallelogram” to “shuttle” and “hysteresis cake”. With the increase in normal stress and roughness and the decrease in water content, the interfacial shear strength, volume displacements growth rate, and growth rate increased. The stress–displacement mathematical model of the silt–steel interface based on the modified hyperbolic model was in good agreement with the test data.

A Study on the Interaction Behavior between an Earth-Rock Dam and a New-Typed Polymer Anti-Seepage Wall

Polymer anti-seepage wall has been gradually applied in earth-rock dam reinforcement projects as a new seepage control technique. However, due to all-pervasive properties of the new materials and root-like connection between the materials and soils, the interface characteristics between the polymer wall and the earth-rock dam, as well as the interaction behavior of both, are complex and still not clear, which obstruct studying coordination mechanism of dam and wall under earthquake. Therefore, the interface characteristics and interaction behavior of dam and wall were studied in the article. Firstly, the dynamic shear stress-displacement, shear stiffness and damping ratio of the interface between polymer and soil were investigated by ring shear test. In addition, the viscoelastic constitutive model of polymer materials were researched by dynamic mechanical analysis (DMA) test. Based on tests results, a finite element model of earth-rock dam with polymer wall was established, including a non-linear simulation interface element and viscoelastic polymer constitutive model. Next, the validity of the simulation model was verified based on dynamic centrifuge test results. Then, the interaction behavior and seismic response of the dam with polymer wall were explored by using the verified model. The research results provide a scientific basis for the development and application of new-typed polymer anti-seepage wall in reinforcement engineering.

Effect of particle regularity on the shear response of geogrid-granular material interface under cyclic normal loading

The investigation of shear behaviour on geogrid-granular material interface under cyclic normal loading (CNL) is significant in seismic design of reinforcement structure. The cyclic shear mechanism about the effect of particle overall regularity on reinforced soil interface was analysed using dynamic direct shear apparatus. Five mixtures of round spherical media and crushed limestone with different percentages were selected to obtain various particle overall regularity. By comparing the shear behaviour under various overall regularity, the interface shear stress and vertical displacement under the CNL condition were smaller than those under the static loading condition. The decrement in interface shear stress of lower overall regularity was smaller than that of higher overall regularity. The interface peak shear stress, final vertical displacement decreased with the increase of cyclic normal loading amplitude and overall regularity. The effect of initial normal loading on ratio of strength reduction and energy consumption was reverse to that of the overall regularity. Based on the constant relative phase shift of the peak normal stress and friction coefficient for various overall regularity, the prediction formula was proposed. The test results improve the understanding on how normal loading perturbations and particle overall regularity affect the shear behaviour of reinforced soil interface.

Analysis of interface mechanical properties between geotextiles and tailings during pull-out tests.

Considering the strain-softening characteristics of the pull-out interface between geotextiles and tailings; to determine the interface interaction characteristics, this paper proposes a trilinear shear stress displacement softening model of geotextile-reinforced tailings. The obtained nonlinear governing equations were dimensionless, which were expressed in finite difference form. The results indicated that an accurate numerical solution could be obtained within a reasonable calculation time by discretizing the reinforcement length into 300 units. Three new dimensionless interaction terms, namely, the relative stiffness α, relative displacement β, and relative interface shear stiffness η of the reinforcement-tailings interaction, were introduced. In addition, an estimation method based on the approximate value of the relative stiffness α of the reinforcement-soil interface in the low-tensile-force displacement range was proposed. The interface shear stress range according to parameters α, β, and η was parameterized, and the normalization relationship between the tensile force and pull-out end displacement was determined. The numerical values calculated by the model were compared with the pull-out test results, demonstrating that the proposed model can accurately predict the pull-out behavior of the extensible reinforcement.

Seismic Response of a Liquefiable Site-Underground Structure System

To study the dynamic response of a saturated sand-underground structure system subjected to earthquakes, a series of shaking table tests with a geometric scale ratio of 1/30 were conducted. Based on the experimental acceleration records of testing soil deposits, the relationship between dynamic shear stress and horizontal soil displacement was analyzed by the 1D shear beam inverse calculation method. Meanwhile, the development law of the equivalent dynamic horizontal subgrade reaction coefficient and the dynamic strain of the sidewall in the underground structure has also been discussed. The testing results indicate that the dynamic shear stress of the soil deposit under the bottom plate of the underground structure is larger than that of the soils surrounding the sidewall and above the roof plate; in addition, the soil displacement tends to decrease with the buried depth. The dynamic shear stress–displacement hysteretic loop of the soil deposits tends to be plump as the input amplitude increases. The spectral characteristics of ground motions obviously influence both the dynamic shear stress–displacement hysteretic curve and the excess pore water pressure ratio of saturated sand soil, especially under medium and strong excitations. The equivalent dynamic horizontal subgrade reaction coefficient decreases with the increase of soil depth, and the difference between the coefficient above and underneath the underground structure model can reach 7.589 MN/m3. On the contrary, the equivalent dynamic horizontal subgrade reaction coefficient decreases with the increase of the input amplitude of ground motions, and the maximum reduction ratios of the coefficient are 74.4%, 66.7%, and 47.3%, corresponding to the El-Centro, Kobe, and Wolong ground motions, respectively. The soil liquefaction has a certain effect on the equivalent dynamic horizontal subgrade reaction coefficient. In general, the dynamic strain at the top of the sidewall in the underground structure is higher than that at the bottom of the sidewall, which illustrates that the deformation of underground structures is in good agreement with the seismic deformation mode of soil deposits.

Effect of Water Content on Strength of Alluvial Silt in The Lower Yellow River

In order to study the strength characteristics of alluvial silt in the lower Yellow River Channel at Luokou, Jinan, by varying the moisture content five times, direct shear tests were conducted and soil–water characteristics curves were obtained to explore the relationships between moisture content and matric suction as well as the bishop coefficient and shear strength. The soil–water characteristics curve test shows that the water retention curve of silt samples in the lower Yellow River can be fitted by the VG (Van Genuchten) model with the appropriate fitting coefficients. The direct shear test reveals that the relationship between shear stress and shear displacement alters from the shear softening type to the hardening type with the increase in moisture content and normal stress. The cohesion has a nonlinear inverse relationship with moisture content while a small variation is reported in the internal friction angle. Finally, a simple shear strength equation for silt in the lower Yellow River is proposed in relation to moisture content, to define the relationship between the effective stress parameter and the matric suction for future engineering purposes.