Shear Stress Displacement Curves Research Articles

Study on Shear Strength of Soil–Root Systems of Different Vegetation Types

The root systems of vegetation significantly contribute to enhancing slope stability. The shear strength of soil–root systems is a crucial parameter for assessing slope stability. This study focuses on six types of vegetation in the Yellow River Basin of China (woodland: Populus przewalskii and Broussonetia papyrifera; shrubland: Periploca sepium and Ziziphus jujuba; grassland: Artemisia hedinii and Setaria viridis), employing in situ shear tests and the Wu–Waldron model (Wu model) to investigate the shear strength of soil–root systems. The results show that the shear stress–displacement curves for P. przewalskii, B. papyrifera, and Z. jujuba are higher and steeper, with clear inflection points. The tensile strength of the roots from the six vegetation types decreases as the root diameter increases. According to the Wu model, the additional root cohesion is ranked as follows: A. hedinii > B. papyrifera > P. przewalskii > Z. jujuba > P. sepium > S. viridis. Based on the in situ shear tests, the shear strength increments are ranked as follows: Z. jujuba > B. papyrifera > P. przewalskii > A. hedinii > P. sepium > S. viridis. Overall, the additional root cohesion obtained by the Wu model in each soil layer is greater than the shear strength increment measured from the in situ shear tests. In the 0–30 cm soil layers, the soil–root systems of Z. jujuba, B. papyrifera, P. przewalskii, and A. hedinii exhibit a better shear strength, whereas P. sepium and S. viridis perform poorly. A principal component analysis reveals that the shear strength of the soil–root systems of different vegetation types is primarily influenced by the soil moisture content and root mass density. Z. jujuba, B. papyrifera, P. przewalskii, and A. hedinii are recommended for ecological restoration projects in the Yellow River Basin of China.

Effect of Water Content and Degree of Compaction of Clay Subgrade Soil on the Interface Shear Strength Using Geogrid

Pavement performance in clay soil roads can be enhanced with the help of the geogrid concept by increasing lateral confinement, bearing capacity, and overall rigidity of the pavement. Also, geogrid is useful in minimizing vertical and lateral pavement deformations. In this study, 65 tests are performed without and with two types of geogrid, and the aim behind it is to investigate the effect of the moisture content and degree of compaction of clay soil on the interface shear strength. The number of materials used to conduct this study, included subbase granular (type B), clay subgrade soil, the Biaxial and SS2 geogrid which is used as a reinforcing material. Testing the direct shear is conducted by a large-scale direct shear manufactured device contains an upper box with side lengths of (20×20×10) cm, and a lower box with side lengths of (20×25×10) cm. Results show that for all tests the normal applied stresses are 25, 50, 75 and 100 kPa, the shear stress displacement curves for all cases follow similar trends and they are affected by normal stress, density and water content of subgrade soil and type of geogrid. Also, it is obvious that the shear stress increases by increasing the normal applied stress and degree of compaction of clay subgrade soil reaching its maximum value at 95% degree of compaction while it decreases by increasing the water content of subgrade soil. The maximum value of shear strength is observed when water content is equal to 8% (dry side) and finally, the Biaxial geogrid BX1100 (G1) is more efficient in reinforcing clay-subbase interface as compared with SS2 geogrid (G2).

Influences of the normal loading condition and surface texture on interface shear behavior between sand and suction caisson wall

The mechanical behavior of the interface between soil and the suction caisson wall determines the installation behavior and bearing capacity. A series of interfacial shear tests are conducted to study the effects of the normal loading condition and the interface texture on the sand-suction caisson interface shear characteristics. The relative density of the sand used in the test is 0.9. It is found that with the increase of shear displacement, the shear stress-displacement curve under a constant normal load condition (CNL) has an obvious strain-softening trend. On the contrary, the shear stress increases linearly with increasing the shear displacement under a variable normal load condition (VNL). The stress ratio between shear and normal stress, the broken zone thickness, and the shear deformation zone thickness for a convex suction caisson wall-sand interface are significantly larger than those of the grooved interface. However, when the roughness increases to a certain value, the stress ratio between shear and normal stress would decrease. Under large displacement shearing, the degree of sand particle breakage becomes significantly higher than that under small displacement shearing. These results help understand the shear characteristics of the sand-suction caisson wall and invent the new type of the suction caisson.

A novel statistical damage constitutive model of rock joints considering normal stress and joint roughness

The shear constitutive model of rock joints is of great significance to the stability analysis in rock engineering, and it is closely related to the normal stress ([Formula: see text]) and joint roughness coefficient ( JRC). However, the existing investigations seldom consider the influences of [Formula: see text] and JRC simultaneously. Therefore, a novel damage constitutive model considering the [Formula: see text] and JRC is developed in this work. In the presented model, it is assumed that the rock materials are composed of damaged and undamaged microunits, and the damage evolution law of the microunits conforms to the Weibull distribution in the shear process. Based on the proposed assumption, the constitutive relationship between shear stress and shear displacement is deduced. The evolutions of the mechanical parameters and damage variable versus [Formula: see text] and JRC are analyzed in detail. The proposed damage model that involves [Formula: see text] and JRC is verified by comparing theoretical values with the laboratory results. The results show that the damage constitutive model is in good agreement with the test results. Additionally, the influences of [Formula: see text] and JRC on the shear stress-displacement curves are studied. This work can provide a valuable theoretical method for analyzing the shear mechanical characteristics and damage evolution laws of rock joints.

Consideration of Different Soil Properties and Roughness in Shear Characteristics of Concrete–Soil Interface

To investigate the impact of diverse soil characteristics and surface irregularities on interfacial shear strength attributes, a large-scale straight shear apparatus and particle flow software were employed to conduct interfacial shear experiments with varying soil properties and surface irregularities. The results demonstrated that, under an identical R and normal stress conditions, the clay and silty clay shear stress–displacement curves exhibited strain softening, while the silt curve exhibited strain hardening. An increase in R can markedly enhance the peak shear strength at the interface, although a critical value exists beyond which this effect is no longer observed. The Rc is primarily contingent upon the soil properties. Numerical simulations demonstrate that the internal shear displacement and deformation resulting from the diverse soil properties are distinct. Clay particles are constituted of varying-sized particle aggregates that collectively resist shear. Silt particles resist shear through interfacial friction generated by shear. The practicality of Duncan and Clough’s constitutive model for interfacial shear with roughness influence is verified, and the constitutive model under strain hardening is modified.

Experimental investigation of permeability evolution and progressive damage of sandstone in the complete process of direct shear

Permeability evolution and damage behavior under shearing conditions are critical for reliable predictions of rock seepage characteristics during excavation and a correct assessment of their impacts on the occurrence of natural or induced hazards. However, publications concerned with this problem have been poorly issued so far. The primary objective of this study is to innovatively investigate permeability evolution and damage behaviors of sandstone in the complete process of direct shear. Several groups of red sandstone specimens are deformed in direct shearing using a newly modified servo-controlled direct shear apparatus to measure permeability evolution and monitor acoustic emission (AE) activities with damage under various normal stress conditions. The morphology of the rupture surfaces is scanned using a 3D laser scanner after tests. According to our experimental results, the locus of the shear stress-displacement curve is found to be closely associated with microcrack progressivity. The initial permeability in advance of shearing test and the peak permeability appearing after the peak shear stress decrease with the increasing normal stress. The minimal and maximum permeability values exhibit a lag-effect with respect to the turning and the peak points on the shear stress-displacement curve. Furthermore, a palpable surge is found in the interevent time function during shearing, which can be a potential indicator for early warning of catastrophic rupture of brittle rock materials under shearing or compression. The joint roughness coefficient (JRC) values in the direction of shearing deformation for each normal stress case are more significant than those in the direction perpendicular to the shear displacement. The impacts of our obtained results are potential ramifications for permeability control in rock engineering projects.

Shear behavior of cement-stabilized silty clay exposed to low-temperature curing

Cement-stabilized soils are widely used in civil engineering applications. However, they inevitably encounter low-temperature curing conditions, particularly in cold regions. In this study, shear experiments were conducted on cement-stabilized silty clays with different dry densities, cement contents, curing ages and temperatures. The factors influencing the shear performance of cement-stabilized soils were analyzed. The results showed that the peak value of the shear stress-displacement curve of the cement-stabilized silty clay increased with the vertical pressure, and the failure patterns for soils with and without cement significantly differed. Generally, the soils without cement underwent ductile failure, whereas the cement-stabilized soils experienced brittle failure. The shear strength and cohesion of the cement-stabilized soils increased with cement content, dry density, curing age and temperature. In addition, the ice and hydration products significantly influenced the internal friction angle of the cement-stabilized soils. An optimal cement content for silty clay was determined to obtain the largest internal friction angle, which ranged from 12% to 15%. Furthermore, at the curing temperature of −2 °C, the edge-face contact form accounted for the majority with a relatively high porosity, but the morphology of C-S-H changed from a sheet-like form to reticulate structure when the curing temperature increased to 22 °C. However, the contribution of the ice crystals to the shear strength was less significant than that of the hydration products. This study provides insights into the mechanical and microstructural properties of cement-stabilized soils in cold-region geotechnical construction.

Preliminary study on double-sided direct shear test of microbial mortar

A new method of strengthening masonry structures of ancient architecture has been proposed, which involves the use of microbial grouting to generate mineralized mortar. To study the shear mechanical properties of microbial mortar, a comparative experiment was designed with 9 groups of specimens, including acid washing method to test the amount of calcium carbonate, penetration method to test compressive strength of mortar, double-sided direct shear method to test shear strength of mortar and get shear stress-strain curve. According to the experimental results, when the brick joint is thick, more bubbles remain at the contact between the brick and the mortar, reducing the saturation of the grouting liquid and affecting the amount of calcium carbonate generated, thereby affecting the shear strength of the mortar. When the brick is placed vertically, the contact area between the brick and the mortar is on the side, and it is not easy for bubbles to remain, so the amount of calcium carbonate generated is high, and the corresponding shear strength of the mortar is high. Reducing the concentration of calcium solution and implementing bidirectional perfusion can slow down the deposition of calcium carbonate and blockage of perfusion pathways, thereby improving the homogeneity of the carbonate level. A well-graded filling of sand particles is an effective measure to improve the binding efficiency of calcium carbonate.These measures not only increase the production of calcium carbonate, but also result in higher compressive and shear strength.The shear stress-displacement curve of microbial mortar specimens with damagedmortar layer exhibits strain-softening behavior, while the specimens with inter facial damage show strain-hardening behavior.The shear strength of specimens with interface damage is lower than that of specimens with mortar layer damage, so measures should be taken to avoid interface damage.

Large-scale field test on the shear behavior of concrete pipe-silty soil interfaces in pipe jacking: A case study

With the rapid advancement of urbanization, research on the shear behavior of concrete pipe-silty soil interfaces in pipe jacking has a high engineering application value. In this study, a large-scale field direct shear test apparatus and the corresponding test method were designed and proposed to investigate the shear properties of the concrete-silty soil interfaces in pipe jacking. A series of in-situ direct shear tests were conducted at five normal stress levels under four interface contact conditions. The results show that the shear stress-displacement relationships of the interfaces conform to the typical elastic-plastic constitutive relations, the shear strength-normal stress relationships of the interfaces can be well fitted by the Mohr-Coulomb failure criterion, and the interface shear properties are influenced by soil properties, normal stress, lubrication conditions and stagnation time. Without lubrication, the concrete-silty soil interfaces have a shear stress-displacement curve shape similar to that of the test results obtained from indoor direct shear tests, but their ductility and shear strengths are lower. Under lubrication conditions, the paraffin wax and thixotropic slurry can both effectively diminish the interface friction angle, thereby reducing the concrete-silty clay interface friction coefficient by 62.8% and 72.2% and reducing the concrete-silty sand interface friction coefficient by 60.8% and 59.2%, respectively. Based on the macroscopic and microscopic images observed in the tests, the lubrication mechanisms of the lubricants were analysed. The research results can provide a reference for the prediction of jacking force and construction disturbance in adjacent pipe jacking projects.

Counterface soil type and loading condition effects on granular/cohesive soil – Geofoam interface shear behavior

Soil – geofoam interfaces have been studied through an extensive experimental program by performing multiple series of interface shear tests using two different granular soils (i.e. beach sand and construction material sand) and one cohesive soil (i.e. bentonite clay) as well as a soil mixture containing 75% sand and 25% clay by dry weight at distinct loading conditions (i.e. normal stresses (σ): 25, 100, 250; low, moderate, high loading conditions, respectively). Using the shear stress versus horizontal displacement curves obtained, some important engineering design parameters including peak shear stress, residual shear stress, interface sensitivity (i.e., peak/residual ratio) and displacement required to reach peak stress have been determined and the variations in those interface mechanical properties as a function of loading condition and counterface soil type have been investigated. It was shown that the peak as well as residual shear stresses increased with an increase in normal stress for all the interface systems tested. Further, the granular soil (sand) interfaces demonstrated relatively larger frictional strengths (both peak and residual) as compared to both the cohesive soil (clay) interface and the sand/clay admixture soil interface. Additionally, the higher the angularity of granular soil particles became, the larger the interface shear strengths (peak and residual), when sheared against geofoams, developed in light of experimental results attained as a result of interface shear tests on different material combinations. For comparison, the detected peak strength at average for the construction material sand, the beach sand, and the sand/clay admixture soil interfaces as compared to the bentonite clay interface were improved 59.8%, 43.4%, and 20.3%, respectively. Additionally, the detected residual strength at average for the construction material sand, the beach sand, and the sand/clay admixture soil interfaces as compared to the bentonite clay interface were improved 53.9%, 28.6%, and 15.4%, respectively.

Experimental investigation on shear strength deterioration at the interface between different rock types under cyclic loading

The shear strength deterioration of bedding planes between different rock types induced by cyclic loading is vital to reasonably evaluate the stability of soft and hard interbedded bedding rock slopes under earthquake; however, rare work has been devoted to this subject due to lack of attention. In this study, experimental investigations on shear strength weakening of discontinuities with different joint wall material (DDJM) under cyclic loading were conducted by taking the interface between siltstone and mudstone in the Shaba slope of Yunnan Province, China as research objects. A total of 99 pairs of similar material samples of DDJM (81 pairs) and discontinuities with identical joint wall material (DIJM) (18 pairs) were fabricated by inserting plates, engraved with typical surface morphology obtained by performing three-dimensional laser scanning on natural DDJMs sampled from field, into mold boxes. Cyclic shear tests were conducted on these samples to study their shear strength changes with the cyclic number considering the effects of normal stress, joint surface morphology, shear displacement amplitude and shear rate. The results indicate that the shear stress vs. shear displacement curves under each shear cycle and the peak shear strength vs. cyclic number curves of the studied DDJMs are between those of DIJMs with siltstone and mudstone, while closer to those of DIJMs with mudstone. The peak shear strengths of DDJMs exhibit an initial rapid decline followed by a gradual decrease with the cyclic number and the decrease rate varies from 6% to 55.9% for samples with varied surface morphology under different testing conditions. The normal stress, joint surface morphology, shear displacement amplitude and shear rate collectively influence the shear strength deterioration of DDJM under cyclic shear loading, with the degree of influence being greater for larger normal stress, rougher surface morphology, larger shear displacement amplitude and faster shear rate.

Mechanical properties and damage model of coral seawater sea sand concrete under compression-shear composite action

The present study investigates the mechanical properties of coral seawater sea sand concrete (CSSC) under compression-shear composite action. A total of 54 concrete specimens were designed for the shear test with varying parameters such as normal stress ratio, curing age and different aggregate types considered. The CSSC shear stress-displacement curve was obtained by observing the damage morphology of the specimen under a combination of compressive and shear stresses. The effects of different normal stress ratios on the shear strength, peak shear displacement, and damage evolution pattern of the CSSC specimen are analyzed. The results show that the width of the main cracks on the surface of the specimen gradually increases with the normal stress ratio, and the tiny oblique cracks gradually become denser. The peak shear displacement and shear strength also increase with normal stress, and the damage evolution of the concrete gradually slows down. When the curing age was increased from 7d to 14d and 28d, the shear strength of the CSSC specimens increased by 5.9% and 11.3%, respectively. In this paper, we propose two failure models that better reflect the shear strength of CSSC under the combined action of compression and shear. Finally, a compressive-shear damage constitutive model for CSSC at different normal stress ratios has been developed and the results are in good agreement with the experimental results.

Engineering properties and optimal design of foam lightweight soil composite fly ash: An eco-friendly subgrade material

Foam lightweight soil is used frequently in engineering construction for soft soil areas due to its superior lightness and economy, but its greater cement usage will result in cost increase, resource waste, and environmental pollution. This study modified foam lightweight soil with industrial solid waste (fly ash) in place of some cement to propose an eco-friendly and useful lightweight subgrade filling material. A series of macro-micro tests were conducted to investigate the engineering properties and micro-mechanisms of foam lightweight soil composite fly ash (FLS). The results showed that the axial stress-strain and shear stress-displacement curves of FLS showed softening types. The fluidity, compressive strength, toughness and shear strength of FLS first increased and then decreased with the increasing fly ash content. The mechanical strength of 20% FLS was the optimal value for meeting the application requirements of subgrade engineering. Due to the volcanic ash and micro-aggregation effects, fly ash consumed the calcium hydroxide to produce more calcium silicate hydrate for filling the pores of sample and improving its internal structure. According to the results of numerical simulation, the settlement deformation and lateral deformation of subgrade could be better controlled by using 20%FLS as filling material compared with ordinary soil. Consequently, it is feasible to apply FLS in subgrade engineering.

On the calibration of a shear stress criterion for rock joints to represent the full stress-strain profile

Conventional numerical solutions developed to describe the geomechanical behavior of rock interfaces subjected to differential load emphasize peak and residual shear strengths. The detailed analysis of pre- and post-peak shear stress-displacement behavior is central to various time-dependent and dynamic rock mechanic problems such as rockbursts and structural instabilities in highly stressed conditions. The complete stress-displacement surface (CSDS) model was developed to describe analytically the pre- and post-peak behavior of rock interfaces under differential loads. Original formulations of the CSDS model required extensive curve-fitting iterations which limited its practical applicability and transparent integration into engineering tools. The present work proposes modifications to the CSDS model aimed at developing a comprehensive and modern calibration protocol to describe the complete shear stress-displacement behavior of rock interfaces under differential loads. The proposed update to the CSDS model incorporates the concept of mobilized shear strength to enhance the post-peak formulations. Barton's concepts of joint roughness coefficient (JRC) and joint compressive strength (JCS) are incorporated to facilitate empirical estimations for peak shear stress and normal closure relations. Triaxial/uniaxial compression test and direct shear test results are used to validate the updated model and exemplify the proposed calibration method. The results illustrate that the revised model successfully predicts the post-peak and complete axial stress–strain and shear stress–displacement curves for rock joints.

Effect of Temperature on Interface Characteristics between Compacted Recycled Asphalt Pavement and Geogrid

This study presents an experimental investigation of the interface behaviors of recycled asphalt pavement (RAP) reinforced with biaxial geogrid. A series of direct shear tests were conducted on compacted RAP specimens with or without geogrid under different normal stresses (50, 75, and 100 kPa) and test temperatures (0, 20, and 35°C) using an improved temperature-controlled direct shear apparatus. The effect of test temperature on interface shear strength and strength parameters was systematically examined. Test results showed that shear stress versus shear displacement curves of RAP specimens with or without geogrid show strain-softening characteristics. Under the same normal stress, the curve of the reinforced RAP sample with a high temperature is always below that with a low temperature, which indicates the test temperature has an adverse effect on the strength of the reinforced RAP sample. The shear strength consistently increases linearly with the increase of applied normal stress for all RAP samples. The shear strength with geogrid is greater than pure RAP under a given test temperature and normal stress. The shear strength of RAP samples at lower test temperatures is higher than that at a higher temperature. Both apparent adhesion intercept of RAP-geogrid and cohesion of RAP show a decreasing trend with the increase of the test temperature and tend to be stable with increasing temperature. Both the interface friction angle of RAP-geogrid and the internal friction angle of RAP slightly decrease with the increase of test temperature. For RAP-geogrid, the value of the apparent adhesion intercept is higher than that for sand and gravel with geosynthetics. The interface friction angle is close to that of sand and gravel with geosynthetics. Therefore, RAP material can be well used as alternative backfill materials in lieu of natural aggregates such as gravel and sand in geotechnical applications.

Triaxial direct shear properties, cohesive damage behavior and shear constitutive model of sandstone under high confining pressure

The shear mechanical properties of rock under high confining stresses are required in deep underground construction projects for stability evaluation. This paper tested the sandstone shear properties under high confining pressures by a novel triaxial direct shear device with a self-balancing structure for both low and high confining pressure. The triaxial direct shear experiments on Zigong sandstone from a deep tunnel were carried out to evaluate its strength and deformability. Our experimental results suggested that the shear stress-displacement curves exhibited two distinct characteristics under different confining pressures. The damaging stage occurs initially and turns wider in the shear stress-displacement curve as the confining pressure exceeds the threshold stress. The confining pressure threshold of Zigong sandstone is observed to be 10–20 MPa. Meanwhile, a statistical damage model based on Beta distribution was proposed to describe the shear stress (cohesion contribution) during the whole shearing process, which demonstrates better prediction performance than previously existing models, especially under high confining pressures. This study provides important insights into the high-pressure induced rock shear properties and sheds light on the engineering stability assessment under high stress of tunnels.

Impact of Climate Change on the Performance of Permafrost Highway Subgrade Reinforced by Concrete Piles

Climate change has a detrimental impact on permafrost soil in cold regions, resulting in the thawing of permafrost and causing instability and security issues in infrastructure, as well as settlement problems in pavement engineering. To address these challenges, concrete pipe pile foundations have emerged as a viable solution for reinforcing the subgrade and mitigating settlement in isolated permafrost areas. However, the effectiveness of these foundations depends greatly on the mechanical properties of the interface between the permafrost soil and the pipe, which are strongly influenced by varying thawing conditions. While previous studies have primarily focused on the interface under frozen conditions, this paper specifically investigates the interface under thawing conditions. In this study, direct shear tests were conducted to examine the damage characteristics and shear mechanical properties of the soil-pile interface with a water content of 26% at temperatures of −3 °C, −2 °C, −1 °C, −0.5 °C, and 8 °C. The influence of different degrees of melting on the stress–strain characteristics of the soil-pile interface was also analyzed. The findings reveal that as the temperature increases, the shear strength of the interface decreases. The shear stress-displacement curve of the soil-pile interface in the thawing state exhibits a strain-softening trend and can be divided into three stages: the pre-peak shear stress growth stage, the post-peak shear stress steep drop stage, and the post-peak shear stress reconstruction stage. In contrast, the stress curve in the thawed state demonstrates a strain-hardening trend. The study further highlights that violent phase changes in the ice crystal structure have a significant impact on the peak freezing strength and residual freezing strength at the soil-pile interface, with these strengths decreasing as the temperature rises. Additionally, the cohesion and internal friction angle at the soil-pile interface decrease with increasing temperature. It can be concluded that the mechanical strength of the soil-pile interface, crucial for subgrade reinforcement in permafrost areas within transportation engineering, is greatly influenced by temperature-induced changes in the ice crystal structure.

Theoretical and experimental investigation of a shear failure model for anisotropic rocks using direct shear test

This study proposes a theoretical model for predicting the shear strength of anisotropic rocks in which failure is dependent on the inclination of the inherent structural weak planes. For this purpose, triaxial and direct shear tests were conducted on dried and saturated shale samples. Samples were cored at different orientations (β) to the inherent structural weak planes, i.e., bedding planes. To verify the anisotropic behavior of the samples, triaxial tests were performed on samples with various inclinations of the bedding planes. The experimental results demonstrated a U-shape relationship between the compressive strengths and the inclination of the bedding planes, which is in accordance with Jaeger's model of the plane of weakness (JPW). Accordingly, apparent strength and elastic properties, such as Young's modulus, Poisson's ratio, cohesion, and internal friction angle were all observed to be dependent on β, which verified the mechanical anisotropy of the shale samples. Many of the existing failure criteria consider the impact of bedding inclination on failure strength based on uniaxial and triaxial conditions. However, it is also important that the failure modes of anisotropic rocks are evaluated during shearing. For this purpose, a theoretical model was derived to relate shear strength to β following the Coulomb-Navier criterion. The relationship between shear strength and β was plotted and illustrated in an Inverted-U shape. Direct shear tests were conducted to validate the proposed criterion. Plotted experimental data confirmed the shape of the geometry determined by theoretical analysis. From the results, the maximum shear strength occurred when β was between 30° and 60° in direct shear tests. To obtain a more comprehensive understanding, changes in the shear stress-displacement curve and dependence of the friction angle, to the bedding plane orientation, β, were evaluated and indicated shear anisotropy behavior.

Analytical model of skin friction for bored pile socketed into weak rocks in ice-rich permafrost regions

Bored piles constructed in permafrost regions often need to be socketed into weak and weathered rock strata, such as marl stratum. When these strata are ice-rich, the meltwater caused by construction will form an ice film at the pile-rock interface during refreezing, leading to a reduction in pile bearing capacity. By analyzing the shear mechanism of pile-rock interface with ice film, an interface shear model was proposed in this paper. Based on this model, the load transfer analytical method of rock-socketed bored piles was improved. Finally, the effects of pile-rock interface roughness, ice filling degree, and residual friction angle on skin friction were analyzed. The results show that the shear stress-displacement curve of the ice-containing interface unit exhibits two peaks and can be divided into four stages: ice film shear stage, ice film extrusion stage, concrete-rock relative sliding stage, and interface residual sliding stage. Increasing either the dilation angle or half-wavelength can improve the interface's shear resistance when only one variable is altered. Furthermore, the peak shear strength of the interface decreases as the filling degree increases. The interface residual shear stress is positively correlated with both the residual friction angle of weak rock (ϕu−r) and ice (ϕi−r), and increasing the proportion of ice in the residual sliding surface will lead to the reduction of residual shear stress.

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°.