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To investigate the influence of water film produced by the liquefaction of saturated sand with weak permeability on the distribution of sand strength and deformation index, the one-dimensional finite difference model of liquefied water film in saturated sand was established to simulate the formation mechanism, development and dissipation process of water film in the liquefaction process of saturated sand with weak permeability fine sand, and the relationship between the water film and the characteristic parameters of soil layer for especially the interlayer. The results show that there is obvious plateau stage in the process of excess pore water pressure dissipation, and the starting and ending points have good relationship with the formation of the maximum thickness and disappearance of the water film. The formation and development of water film is closely related to the duration of high pore pressure. In the case of weak permeability interlayer, the water film is produced under the interlayer, and the duration of high pore pressure application in saturated sand is significantly longer than that without interlayer, which has adverse effect on soil deformation. The rationality of the model is verified by comparing with the experimental results. [ABSTRACT FROM AUTHOR]

Reasonable assessment of free-field soil strain is fundamental to quantifying the hazards induced by normal faulting. Previous studies provided insights into the propagation mechanisms of fault rupture within the overlying soil. However, experimental and theoretical analysis of free-field soil response is particularly limited. In this study, four distributed optical fiber types were used to monitor the soil strains under normal faulting through full-scale experiments. A trapezoidal local shear zone was formed on the hanging wall side, within which multiple longitudinal tension cracks occurred. The required ratios of fault offset over bedding depth for the occurrence of local shear zone, primary cracks, and secondary cracks were 1.7%, 2.6%, and 5.2%, respectively. The measured soil strains exhibited a V-shaped pattern, with an approximately linearly increasing longitudinal propagation range with fault offset. The Φ2 mm optical fiber was identified as an appropriate fiber type to represent the free-field soil response, because it could capture the decreasing pattern of soil strains when the fault rupture propagated through the soil. An error function–based analytical method was proposed based on a linear fitting between length scale and burial depth, which demonstrated its effectiveness in reproducing the ground deformation profile and estimating the peak soil strain. [ABSTRACT FROM AUTHOR]

Desiccation cracking in clayey soils is a complex phenomenon investigated by researchers over many decades. Understanding and mitigating this issue will have a significant influence on the performance of raw earth construction materials and geotechnical engineering. In the current study, the digital image correlation technique was used to provide a thorough insight about the shrinkage anisotropy and the cracking mechanisms during drying. A series of free shrinkage tests were performed on an initially saturated slurries in order to assess the effects of the intrinsic characteristics of the material, the surface tension, the sample thickness and the geometric boundary conditions on the crack initiation and propagation in clays. The results show that increasing sample thickness prevents cracks formation in a non-swelling clay and delays it in a swelling clay. A vertical uplift was observed in the swelling clay due to a concave bending of the material during the desiccation shrinkage. An important anisotropy in the vertical shrinkage was observed compared to the horizontal shrinkage. The geometric boundary conditions indirectly influence the internal drying stress that becomes anisotropic. The intrinsic characteristics have a greater effect on the shrinkage behavior of the material than the hygrothermal and geometric boundary conditions. [ABSTRACT FROM AUTHOR]

Clay fine soils are characterised by an ability to change volume when subjected to suction. Soil cracking due to desiccation is a phenomenon of great importance in the environmental geotechnical engineering domain. Aiming to understand shrinkage mechanism, and conditions that lead to appearance of drying cracks, a new experimental testing coupled device digital image correlation‐ clay ring test (DIC‐CRT) was developed to investigate fine soils shrinkage and cracking. The new feature of this paper is to link both measurement techniques, based on 2D/3D‐DIC and an innovative CRT, in order to assess stress and strain in soils during desiccation. Tests were carried out on a kaolinite having a liquid limit of wL = 40%, and prepared as a slurry with w = 1.5 wL of water content. The results highlight the relevance in combining these two techniques, particularly to assess internal stresses developed in the material using CRT and link them to strains leading to cracking measured by DIC method. [ABSTRACT FROM AUTHOR]

Particle image velocimetry (PIV), or digital image correlation (DIC), is a widely used technique to measure soil displacements and strains in small‐scale geotechnical models. Arrays of single‐board computers (SBCs) produced by Raspberry Pi, and their associated 8‐MP cameras, are being used at the University of Cambridge to capture the images required for DIC analysis. This alternative to more expensive camera set‐ups has numerous advantages. A single expensive and large camera can be replaced—at low cost—by multiple cameras, adding flexibility and affordability to any experimental set‐up. Traditionally, the alignment of multiple cameras to each other and the referencing to a known coordinate system required painted or machined markers to be located on the observation windows through which the experiments are viewed. This can obstruct localised soil grain displacement measurements in those areas of the model where such markers are placed. To complement the Raspberry Pi camera system, a markerless calibration method was used during image acquisition. This paper outlines the set‐up of four of these small computers and associated cameras, provides an overview of the use of the markerless referencing system and reviews two different experimental apparatus used to measure soil displacement and strain. When the cost of additional cabling, connectors and mounting hardware is considered for this system, the total cost to implement was approximately $125 USD per camera plus one‐time costs of $175 USD for system peripherals, which represents outstanding value and enables practically all geotechnical laboratories to develop similar capabilities. [ABSTRACT FROM AUTHOR]

Urban vibrations are increasing due to urban developments all over the world. These vibrations are daily applied to all surrounding structures, while their effects are not mainly considered in regular geotechnical analyses. This research will focus on how much urban vibrations cause displacement and strain in soil in a tunnel surrounding. In fact, using a case study data and combination of numerical analyses, empirical equations, and geodetic monitoring, the displacements and strains of soil caused by urban vibrations were calculated, compared, and evaluated. A traffic tunnel in Tehran (Arash-Esfandiar tunnel) was studied, in which a section was monitored by geodetic tools (simple instruments that are glued to the tunnel roof and their displacements measured using a theodolite). To complete the required data, microtremor recording equipment was employed to record real urban vibrations in the site. Then, using numerical modeling, the strains and displacements were obtained by applying the recorded vibrations to the model. The obtained strain values were employed to calculate the constant parameters of two existing empirical equations of Li and Selig and Chai and Miura. The obtained parameters conformed to the results of the previous studies and were all in the ranges given in those studies. Thus, the obtained parameters are proposed for the soil of Tehran for the first time. These parameters could be used for future studies on the effect of urban vibrations on Tehran soil. Furthermore, the calculated displacements were compared with the results of geodetic monitoring, which were in good agreement. The amounts of measured strains and calculated displacements show the importance of studies on the effects of urban vibrations. [ABSTRACT FROM AUTHOR]

Intense groundwater exploitation and seasonal fluctuations of water level in phreatic aquifer cause land subsidence disasters. To better understand the land subsidence mechanism caused by groundwater withdrawal, a small-scale sand-clay interbedded model box was built to carry out consolidation and rebound tests during two drainage-recharge cycles. Distributed fiber optical sensing (DFOS) technologies were introduced for coupled monitoring of soil strain and water content to analyze response characteristics of each layer to water level changes. The results indicate that soil layers were compressed during drainage and rebound during recharge, with clay layer deformation more obvious than sand layer deformation. Deformation of the sand layer was synchronous with water content changes, while that of the clay layer lagged behind water content changes due to its lower permeability coefficient. The segmented compression clay layer curve shows that the water content rapidly decreased when it was lower than the liquid limit, while the clay layer compression rate obviously accelerated during drainage. When the water content was higher than that of the liquid limit during recharge, the rebound rate significantly increased. Under the condition of repeated drainage and recharge, the soil microstructure changed with decreasing porosity and permeability coefficient, leading to a longer consolidation time. With increasing cycling times, the soil gradually tended toward elastic deformation. The observations propose a novel technology, DFOS technology, for monitoring land subsidence caused by seasonal water level fluctuations and dewatering projects. The test results are of great significance to investigate land subsidence mechanisms and evaluate soil layer compression potential. [ABSTRACT FROM AUTHOR]

Abstract: The empirical Gaussian-based mathematical model of the soil displacement increment under a traveling wheel was extended to be applicable to any depth of soil layer under the ground contact surface of the wheel. The unknown coefficients were obtained by least mean-square fitting with the soil displacement curve measured through a sophisticated laboratory soil bin test. Those coefficients were then re-derived as a function of depth. The movement of soil particles at the ground contact surface was modeled by dividing movement into two kinds; first, the free movement of soil particles before contact with the wheel and the movement of the particles after they are separated from the wheel surface and, second, soil movement during attachment to the wheel surface. By combining the models for the ground contact surface of the wheel with that for all soil layers, an extended model that can describe soil displacement increment in both vertical and horizontal directions using one equation was established. The predicted results obtained using the extended model fitted quite well with the measured values. The predicted strain increment distributions also show the same trends as the measured distributions. [Copyright &y& Elsevier]