This study investigates the seismic response of a reinforced concrete (RC) tunnel using two-dimensional plane strain finite element models calibrated and validated against experimental results. A comprehensive parametric study is then conducted to explore the influence of tunnel-soil flexibility ratio, soil relative density, Arias intensity of the input motion, and ground motion components on the seismic soil-structure interaction (SSI). The results demonstrated that the flexibility ratio and racking coefficient increase with overburden height, while soil deformations decrease. Acceleration amplification factors rise from the bottom soil to the ground surface, with dense soil showing higher amplification especially in the regions at and near the tunnel field. The horizontal amplification factor exhibits greater variability with increasing seismic energy intensity, and the effect of the vertical motion becomes more pronounced near the structure. The vertical amplification factor is lowest for the horizontal component, while the vertical and combined components exhibit higher values influenced by the presence of the tunnel with lower earthquake intensity. Soil relative density significantly influences the vertical and lateral pressures on the tunnel, with dense sand causing maximum vertical pressures on the top slab and walls. The vertical earthquake component has a greater impact on the tunnel's top slab pressure distribution than the horizontal component. Seismic bending moments are influenced by earthquake components, with the vertical component leading to the greatest positive bending moment values in the middle of the roof slab. Vertical soil deformation is significantly affected by the horizontal input motion component, whereas the vertical component minimally affects lateral soil deformation. These findings underscore the importance of capturing stress-strain response under cyclic loading, particularly near the tunnel crown, where complex stress interactions lead to increased variability in behavior.

A self-designed water level control system was used to simulate the collapse of a red mud dam in a dry storage yard under varying water levels. The study unveiled the distribution patterns of seepage lines, pore water pressure, soil pressure, and crack evolution in red mud dams with varying slope ratios (1:2 and 1:1) under changing water levels. Experimental findings show that the rise of the infiltration line is initially rapid, then slows down, exhibiting a lag effect. The area with the highest pore water pressure beneath the infiltration line also experiences the highest horizontal soil pressure. Under different slope ratios, the reasons for the formation of main cracks are different. When the slope ratio is 1:2, under the combined action of gravity and hydraulic forces, slope cracks are generated due to the formation of a through channel extending from the interior of the red mud dam body to the slope surface. When the slope ratio is 1:1, cracks appear at the dam crest due to the traction effect of the sliding slope below the infiltration line on the upper slope. The stress and seepage fields of red mud dams with different slope ratios were analyzed using the finite element software ABAQUS, revealing the stress and displacement distribution patterns on the dam slope surface.

Understanding the mechanical response of Q2 loess subjected to dry-wet cycles (DWCs) is the premise for the rational design of a hydraulic tunnel. Taking the Hanjiang-to-Weihe south line project in China as the research background, the microstructure evolution, strength degradation and compression characteristics of Q2 loess under different DWCs were investigated, and the fluid-solid coupling analysis of the hydraulic tunnel was carried out using the FLAC3D software. The amplification effect of tunnel surrounding soil pressure (SSP) and its influence on the long-term stability of the tunnel under different DWCs were obtained. The results showed that the pore microstructure parameters of the undisturbed and remolded loess basically tend to be stable after the number of DWCs exceeds 3. The porosity of Q2 loess is increased by 26%. The internal friction angle and cohesion of Q2 loess are decreased by 35% and 31%, respectively. The vertical strain of Q2 loess is increased by 55% after considering the DWCs. After the DWCs stabilized, the SSP ratio is increased between 10% and 25%. With the increase in buried depth of the tunnel, the SSP ratio is increased by 8%-10%. The SSP is reduced from 8% to 16% by the rise in groundwater level. As the number of DWCs increases and the burial depth of the tunnel decreases, the distribution of SSP becomes progressively more non-uniform. Based on the amplification factor and the modified compressive arch theory, the SSP distribution model of loess tunnel was proposed, which can be preliminarily applied to the design of supporting structures considering DWCs. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

In the present study, centrifuge tests for small-scale specimens were performed to investigate the dynamic soil pressure of the basement of buildings subjected to seismic ground motions. To investigate the effect of the embedded depth of basement, a deep basement model fixed to rock (model 1) and a shallow basement model embedded in soil (model 2) were tested. The soil pressures acting at the front wall (Dynamic soil pressure, DSP) and back wall (Soil pressure at back wall, BSP) were measured. Under the Northridge earthquake (with PGA(b) = 0.33 g), DSP of Model 1 (fixed based model) reached 100 kPa showing an increasing linear distribution from bottom to top. The DSP profile was similar to the profile of relative displacement between the basement and soil. Interestingly, BSP decreased to 0 as a gap occurred between the soil and basement wall. On the other hand, in the case of model 2 with a smaller depth, the relative displacement between the basement and soil was smaller due to the influence of flexible base. As a result, DSP (<20 kPa) was smaller and BSP was greater than those of the deep basement model fixed to rock. The tested soil pressures were compared with the predictions of existing models.

The use of a micropile group is an effective method for small and medium-sized slope management. However, there is limited research on the pile-soil interaction mechanism of micropile groups. Based on transparent soil and PIV technology, a test platform for the lateral load testing of slopes was constructed, and eight groups of transparent soil slope model experiments were performed. The changes in soil pressure and pile top displacement at the top of the piles during lateral loading were obtained. We scanned and photographed the slope, and obtained the deformation characteristics of the soil interior based on particle image velocimetry. A three-dimensional reconstruction program was developed to generate the displacement isosurface behind the pile. The impacts of various arrangement patterns and connecting beams on the deformation attributes and pile-soil interaction mechanism were explored, and the pile-soil interaction model of group piles was summarized. The results show that the front piles in a staggered arrangement bore more lateral thrust, and the distribution of soil pressure on each row of piles was more uniform. The connecting beams enhanced the overall stiffness of the pile group, reduced pile displacement, facilitated coordinated deformation of the pile group, and enhanced the anti-sliding effect of the pile-soil composite structure.

Due to extensive sand mining, the depletion of traditional backfill materials is a significant concern globally. Unsustainable sand mining practices, driven by construction demand, result in environmental degradation and resource depletion. Alternative materials like coal-fired power plant bottom ash and plastic waste offer cost and eco-friendly advantages for backfilling. Reinforced soil walls, compared to traditional structures, accommodate more settlement and load, providing flexibility, resistance to static and dynamic stresses, and improved aesthetics. To mitigate lateral earth pressure on retaining walls, incorporating compressible inclusions between the backfill and the wall reduces stress, ensuring long-term stability. The current investigation examines the effectiveness of sand or geomaterial prepared from sand (S), bottom ash (10-50% by dry weight), and plastic strips (0.5-1.25% by dry weight) together as backfill, behind the wall to improve the deformation characteristics of the wall and reduce lateral soil pressure. At the interface between the wall and the backfill, geofoam with densities 11D, 16D, and 34D, where D is measured in kg/m3 was used as an absorber to reduce wall lateral movement, settlement, and lateral push acting on the wall. To determine the efficacy of geofoam inclusion, parametric studies were carried out with a range of factors, including geofoam density, backfill characteristics, and surcharge load on the backfill. The model retaining wall was backfilled with either sand or geomaterial under simple strain circumstances. Plaxis 2D numerical modeling was performed for similar conditions and backfill types showed test results from both approaches exhibit excellent agreement. Results from numerical analysis and experimental method gave an optimal mix of the geomaterial (Sand + 50% BA + 1% PS) and geofoam density (34D in case of settlement reduction and 11D in case of lateral movement reduction and earth pressure reduction) that can yield maximum reduction of earth pressure with minimal deformation characteristics was suggested. When 34D geofoam was laid behind the wall backfilled with S, 50% BA, and 1% PS resulted in 172% and 178% improvement in bearing capacities for tests conducted experimentally and numerically. The corresponding settlement reduction values were 73% and 75%. The wall deflection reduction at locations 300 mm (H1) and 500 mm (H2) from the base of wall and earth pressure reduction for 11 D as CI and same backfill were about 82%, 82%, and 43% respectively for both analyses. Conclusively, the provision of geofoam as CI at the interface of the wall and backfill manifests to be a feast alternative for improving the performance of the retaining wall in terms of increasing bearing capacity, reducing settlement, lateral deformation, and earth pressure.

The foundation of offshore wind turbines is an important factor that determines their bearing capacity and service life. A theoretical analysis and model test of the bucket foundation with and without bulkheads at a scale of 1:150 are conducted in this study. The frequency-domain impedances of the two models were obtained and compared via cyclic loading tests at different frequencies. When the loading frequency was low, the absolute values of the real and imaginary impedances of the foundation model without a bulkhead in the frequency domain were higher than those of the foundation model with a bulkhead. Based on the analysis of the variation in soil pressure at the top of the bucket, it was found that the variation in soil pressure almost alternated with the cyclic load. The adsorption force is beneficial for the bearing capacity of a composite bucket foundation, making the structure safer. The impedance matrix of the foundation is determined by the size and shape of the foundation, mechanical parameters of the foundation medium, and frequency of the forced vibration. Wolf's lumpedparameter model was evaluated for applicability to analyse the bucket foundations with bulkheads.

Drilling with prestressed concrete (DPC) pipe pile is a nonsqueezing pile sinking technology, employing drilling, simultaneous pile sinking, a pipe pile protection wall, and pile side grouting. The unloading induced by drilling, the pipe pile supporting effect, and the dissipation of the negative excess pore-water pressure after pile sinking, all of which have significant effects on the recovery of soil pressure on the pile side, are the main concerns of this study, which aim to establish a method to reasonably evaluate the timing selection of pile side grouting. The theoretical solutions for characterizing the unloading and dissipation of the negative excess pore-water pressure are presented based on the cylindrical cavity contraction model and the separated variable method. By inverse-analyzing the measured initial pore pressure change data from borehole unloading, initial soil pressures on the pile side of each soil layer are determined using the presented theoretical solutions. Then, the presented theoretical solutions were verified through a comparative analysis with the corresponding measured results. Moreover, by introducing time-dependent coefficients alpha(t1) and alpha(t2) to characterize the pore pressure dissipation and rheology effects, the effects of the negative excess pore-water pressure dissipation on the pile-side soil pressure recovery are discussed in detail.

Seepage damage is a significant factor leading to red mud tailings dam failures. Laboratory tests on seepage damage were conducted to investigate the damage characteristics and distribution laws of red mud tailings dams, including soil pressure, infiltration line, pore water pressure, dam displacement, and crack evolution. The findings revealed the seepage damage mechanisms of red mud slopes, offering insights for the safe operation and seepage damage prevention of red mud tailings dams. The results showed that the higher the water level is in the red mud tailings dam, the higher position the infiltration line is when it reaches the slope face. At the highest infiltration line point of the slope surface, the increase of pore water pressure is the highest and the change of horizontal soil pressure is the highest. Consequently, increased pore water pressure leads to decreased effective stress and shear strength, increasing the susceptibility to damage. Cracks resulting from seepage damage predominantly form below the infiltration line; the higher the infiltration lines is on the slope surface, the higher the position of the main crack formations is. The displacement of the dam body primarily occurs due to the continuous expansion of major cracks; the higher the infiltration lines are on the slope surface, the larger the displacement of the dam body is.

The tripod foundation (TF) is a prevalent foundation configuration in contemporary engineering practices. In comparison to a single pile, TF comprised interconnected individual piles, resulting in enhanced bearing capacity and stability. A physical model test was conducted within a sandy soil foundation, systematically varying the length-to-diameter ratio of the TF. The investigation aimed to comprehend the impact of altering the height of the central bucket on the historical horizontal bearing capacity of the foundation in saturated sand. Additionally, the study scrutinized the historical consequences of soil pressure and pore water pressure surrounding the bucket throughout the loading process. The historical findings revealed a significant enhancement in the horizontal bearing capacity of the TF under undrained conditions. When subjected to a historical horizontal loading angle of 0 degrees for a single pile, the multi-bucket foundation exhibited superior historical bearing capacity compared to a single-pile foundation experiencing a historical loading angle of 180 degrees under pulling conditions. With each historical increment in bucket height from 150 mm to 350 mm in 100 mm intervals, the historical horizontal bearing capacity of the TF exhibited an approximately 75% increase relative to the 150 mm bucket height, indicating a proportional relationship. Importantly, the historical internal pore water pressure within the bucket foundation remained unaffected by drainage conditions during loading. Conversely, undrained conditions led to a historical elevation in pore water pressure at the lower side of the pressure bucket. Consequently, in practical engineering applications, the optimization of the historical bearing efficacy of the TF necessitated the historical closure of the valve atop the foundation to sustain internal negative pressure within the bucket. This historical measure served to augment the historical horizontal bearing capacity. Simultaneously, historical external loads, such as wind, waves, and currents, were directed towards any individual bucket within the TF for optimal historical performance.