The excavation of the foundation pit impacts the safety, stability, and normal operational functionality of adjacent existing tunnels. With the increasing urban building density, it is becoming more common to conduct foundation pit excavation in close proximity to existing tunnels, which may result in deformation and damage to the tunnels. The impact of foundation pit excavation on adjacent existing tunnels was investigated using a transparent soil scale model and Particle Image Velocimetry technology. The horizontal and vertical distances between the foundation pit and tunnel, as well as the soil consolidation pressure, were individually examined to analyze their respective trends and magnitudes of impact on the maximum vertical deformation of adjacent existing tunnels. The findings suggest that as the excavation depth increases, the deformation of existing tunnels is increasingly impacted by the excavation of foundation pit. However, this impact decreases with greater horizontal or vertical distance between the foundation pit and tunnel. Furthermore, the impact of vertical distance between the tunnel and foundation pit on tunnel deformation is more significant. The pre-consolidation strength of the soil mass significantly impacts the deformation of the existing tunnel. In order to minimize tunnel deformation in practical engineering, constructive recommendations were proposed.

Shaking-table model experiments were conducted to study the dynamic response and damage mechanisms of pile-network composite high-speed railway foundations under seismic action. By inputting seismic waves of various types and acceleration amplitudes, the surface damage phenomena, acceleration response, and displacement response of the roadbed during vibration were analyzed. The time frequency information and energy distribution were examined using Hilbert marginal spectrum theory. Additionally, the damage mechanisms of the model were explored through transfer function analysis. The results indicated that the soil surface deformation measured using particle image velocimetry closely matched the observed macroscopic phenomena. The Peak Ground Acceleration amplification coefficients exhibited clear delamination before the structure showed signs of damage, indicating a significant energy-absorbing effect of the bedding. Spectral analysis revealed that as the vibration intensity increased, the nonlinear characteristics and damage effects of the model became more pronounced, and its ability to dissipate energy strengthened. Energy became more concentrated in the left half of the top of the model. Moreover, as the vibration intensity increased, the self-oscillation frequency of the roadbed decreased, the stiffness diminished, the damping ratio increased, and the seismic energy dissipation improved.

The present study aims to examine the behavior of sand reliquefaction phenomenon on gently inclined sloping ground subjected to repeated seismic events. The seismic sequence represents the combinations of foreshocks and aftershocks associated with mainshock events. Free field and pile group models were experimented with in a sloping ground with 5 degrees inclination using centrifuge modelling. A 2 x 2 pile group model was inserted in Toyoura sand, and results were compared with that with free field model ground. Tapered sinusoidal waveform was inputted at a constant 1 Hz shaking frequency, whereas the acceleration amplitude and shaking duration for the mainshocks were considered twice that of foreshocks and aftershocks. Two different seismic sequences with six shaking events were imparted to the model grounds to investigate the influence of slope and presence of pile group on sand reliquefaction behavior. The time history responses were recorded in the form of acceleration, excess pore pressure (EPP), bending moment, and lateral displacement and presented. The response indicates that sloping ground was stable under the action of foreshocks, whereas it collapsed during mainshocks, primarily due to liquefaction. The mainshock has transformed the gently inclined sloping ground to levelled ground model. This transformation has resulted in increased bending moment values in the pile group. Resistance to reliquefaction was smaller compared to first liquefaction, primarily due to change in soil state and increase in magnitude of anisotropy. Presence of slope has resulted in higher EPP response and bending moment values compared to levelled ground. GeoPIV analysis and visualization show the flow of sand particles from upside to downside due to lateral spreading at shallow depths that initiated the slope failure. The foreshocks and aftershocks are not very significant in increasing the resistance to reliquefaction. Meanwhile the presence of the pile group has reduced the EPP generation during repeated shaking events.

Commonly encountered problems, such as insufficient bearing capacity of the foundation and significant soil deformation, typically necessitate improvements to sandy soil. The excessive use of traditional soil improvement materials, such as cement and lime, causes irreversible damage to the ecological environment. As a sustainable soil reinforcement material, xanthan gum has broad application prospects with respect to its effects on the bearing capacity and deformation of sandy soil foundations. In this study, scanning electron microscope tests and cone penetration model tests based on particle image velocimetry technology were conducted to investigate the microstructure, mechanical behavior, and deformation characteristics around cones in sand treated with different xanthan gum rates. The test results show that the xanthan gum exerts cementation and filling effects between sand particles, enhanced the bearing capacity of sand. The displacement field around the cones in xanthan gum-treated sand during the penetration exhibits good symmetry. With increasing xanthan gum rate, the maximum displacement value and vertical influence range around the cone of xanthan gum-treated sand decrease, while the horizontal influence range increases. On the basis of the cone penetration test result, a predictive model for the vertical bearing capacity incorporating the xanthan gum rate is proposed using the Laboratoire Central des Ponts et Chauss & eacute;es (LCPC) model. The research results can provide a scientific basis for using xanthan gum when designing and constructing sandy soil foundations.

To study the crack evolution patterns in expansive soils under wetting-drying cycles, a series tests were conducted on the expansive soil from a canal side slope in the South-to-North Water Diversion Middle Route Project. Six indoor wet-dry cycle tests were performed on the samples with compaction degrees of 97%, 88%, and 79%. The crack image processing system by using Python was developed for quantitative analysis of crack ratios the expansive soil samples. Furthermore, PIV (particle image velocimetry) technology was also utilized to monitor the entire process of crack development. Results show that the evolution of crack ratios over time in the expansive soil samples can be divided into four stages, crack formation, crack development, crack closing, and crack stabilization stages. The higher the compaction degree of an expansive soil sample, the shorter its duration of the crack formation stage, and the shorter the time required for the crack ratio to reach its peak. The stress and displacement field nephograms of the samples can effectively reflect the crack evolution process on their surfaces. In addition, closing ratio was proposed to studied the crack closing capacity in expansive soil samples. The crack closing ratio decrease with the increase of the number of wet-dry cycles, as well as the compaction degree decreases. The primary cause of crack closing in compacted expansive soil is uneven shrinkage in the vertical direction, which arises from differing evaporation rates between the upper and lower parts of the sample.

In this study, the dynamic response and damage mode of a pile-geogrid composite reinforced high-speed railway subgrade under seismic action were investigated based on a unidirectional shaking table test. Various seismic waves were applied to the subgrade, allowing for an analysis of acceleration, dynamic soil pressure, displacement, and strain responses. The displacement field of the subgrade was visualized using particle image velocimetry (PIV). The study shows that changes in peak ground acceleration (PGA) amplification factors become evident with height due to the presence of geogrid layers. The increase in peak ground motion causes a redistribution of dynamic soil pressures inside the subgrade. The transverse and longitudinal ribs of the geogrids provide an anchoring effect. The peak strain of the piles in the center is greater than that of the piles on the sides. The direction of soil particle displacement is closely related to the damage patterns observed in the subgrade. Damage begins to occur once the peak ground motion exceeds 0.4 g, characterized by collapse at the bottom of the subgrade.

Nodular diaphragm wall (NDW) is a novel foundation type with favorable engineering characteristics. In contrast to traditional diaphragm walls, the vertical bearing capacity of NDW is significantly enhanced by the existence of nodular sections. Currently, the application and research of NDW are limited, and further clarification is needed regarding its deformation properties and failure modes. This study employs particle image velocimetry (PIV) technology to analyze the displacement and failure mechanisms of the foundation under vertical uplift. The findings indicate that positioning end and middle nodular sections extend the influence range to both deep and shallow soil layers, while multiple nodular sections facilitate in mobilizing broader spectrum of soil. The failure pattens of NDW involve interconnected sliding planes, including vertical sliding planes, inverted pyramid-shaped, or tangent curves, and vase-shaped curves (referred to as curve sliding planes). Overall, compared to pile foundations, the failure surfaces of the retaining wall exhibit complexity, influenced by the number and arrangement of sections, with certain sliding plane orientations correlated with the soil's internal friction angle.

Constitutive models in the literature for creep of frozen soil are based on the direct use of time counted from the onset of creep. An explicit time dependence in a constitutive equation violates the principles of rational mechanics. No change in stress or temperature is allowed for during creep, using the time-based formulations. Moreover, the existing descriptions need much verification and improvement on the experimental side as well. Creep behaviour of artificially frozen sand was evaluated experimentally. Novel testing methods were used, and new insights into the creep behaviour of frozen soil were gained. Creep rate under uniaxial compression was examined with different kinds of interruptions, like unloadings or overloadings. Experimental creep curves were presented as functions of creep strain. They were brought to a dimensionless form which describes the creep universally, despite changes in stress or temperature. Possible anisotropy of frozen soil was revealed in the creep tests on cubic samples with changes of the loading direction. Using the particle image velocimetry (PIV) technique, information on the lateral deformation and the uniformity of creep were obtained. Volumetric creep of unsaturated frozen soil under isotropic compression was demonstrated to be due to the presence of air bubbles only.

In this study, a visual medium-scale direct shear test is carried out on the sliding zone soil with different coarse particle strengths. The spatial information of the shear band is obtained by placing a vertical aluminum wire to observe its deformation after shearing, and the spatial surface equation of the shear band is established. Particle image velocimetry (PIV) technology is used to extract and compare the 2D shear band information at the visible surface with the boundary extrapolation value of the space surface equation obtained from the test, demonstrating that the spatial surface equation and PIV technology can describe the characteristics of shear band. Then, PIV technology is used to analyze the evolution rule of shear band under different total and specific displacements. Finally, the influence of prefabricated damage and coarse particle strength on shear band characteristics was analyzed. Results show that the thickness of shear band presents a distribution pattern of narrow ends and wide middle, and its shape can be fitted by Gaussian surface equation. The shear band undergoes four stages during its development: compaction, free damage, damage development, and penetration. Damage causes early development of shear bands at various stages. Furthermore, coarse particle strength exerts a greater effect on the deformation of local shear bands and a smaller effect on the overall shear band. These findings hold significant implications for elucidating the formation and evolution of landslide shear bands and designing a rational slope control plan,

为研究屋盖积雪对低矮平屋面风场特性的干扰影响，基于风吹雪风洞试验，通过3D打印获得平屋面的3D积雪形态，并以无积雪模型作为对照，系统地开展了PIV (particle image velocimetry)风洞试验，并结合LES(large eddy simulation)方法，研究了6组平屋面建筑有无积雪时的流场分布特性.试验研究表明：当无积雪时，来流在屋面前缘处分离后能形成典型的分离泡流动，分离泡内速度场存在明显逆流现象；当有积雪时，屋面上方的逆流减弱甚至消失，积雪显著地加快了流经屋面附近流场的速度，其最大速度增量约为0.6，同时，流线分布更贴合模型壁面，速度梯度增大，也相对增大了涡量值；积雪会使得屋面上方整体的时均湍动能和切应力均减小，但对屋面迎风区域的平均和脉动风压均有增大作用，其增大比值约为15%和20%.通过该研究可进一步对低矮建筑的风雪荷载作用机理展开分析，为屋盖结构的抗风雪设计提供参考.