This paper presents a series of physical modelling tests of jacked-pile penetration into sand, combining the transparent soil and incremental reliability-guided particle image velocimetry, which provides a non-intrusively internal deformation measurement approach to monitor the internal movement of soil caused by jacked-pile penetration. The difference between the full-model test and the half-model test was analyzed quantitatively for the first time. This paper aims to provide some new insight into the penetration mechanisms of different shapes of pile tip. In addition, the phenomenon of meta-stable sand plug in the process of jacked-pile penetration was studied by means of the method of partial replacement with dyed particles. Experimental evidence has shown that the boundary and interaction effect causes the experimental phenomenon of the half-model test to be different from the true condition. The shape effect of pile tip on the governing penetration mechanisms was discussed, and the disturbance effect of different shapes of pile tip was evaluated and compared based on a large number of model tests and published literatures. The paper intuitively demonstrates that the different penetration mechanism of flat-ended pile and cone-ended pile is mainly due to the formation of the meta-stable sand plug beneath the pile tip.

Non-intrusive observation of the spatial deformation field of the soil has been a difficult problem for model test measurements. Based on the advantage that the visualization test method of transparent soil can observe the two-dimensional (2D) deformation inside the soil, this study proposes a new automatic tomographic scanning measuring device to observe the three-dimensional (3D) spatial soil deformation inside the transparent soil model. A series of 2D laser speckle images of different vertical cross sections before and after deformation were obtained, and an improved 3D reconstruction algorithm was used to reconstruct the 3D displacement field of soil after deformation. Different types of jacked-pile penetration model tests were carried out to investigate the spatial disturbance of the soil around the pile caused by the squeezing effect of the jacked-pile. The test results showed that the developed novel automatic tomographic scanning measuring device with the modified 3D reconstruction procedure could be an innovative tool in geotechnical physical model experiments. The model test results visually revealed the mechanism of the soil squeezing effect of jacked-piles with different pile head forms. Moreover, the spatial disturbance effect caused by different penetration stages was also discussed herein.

This study examined the effects of using bagasse ash in replacement of ordinary Portland cement (OPC) in the treatment of expansive soils. The study concentrated on the compaction characteristics, volume change, compressive strength, splitting tensile strength, microstructure, California bearing ratio (CBR) value, and shear wave velocity of expansive soils treated with cement. Different bagasse ash replacement ratios were used to create soil samples. At varying curing times of 7, 14, and 28 days, standard compaction tests, unconfined compressive strength tests, CBR tests, Brazilian split tensile testing, and bender element (BE) tests were carried out. According to X-ray diffraction (XRD) investigations, quartz and crystobalite make up the majority of the minerals in bagasse ash. Bagasse ash contains a variety of grain sizes, including numerous fiber-shaped particles, according to a scanning electronic microscope (SEM) test. For all of the treated specimens with various replacement ratios, the overall additive content has not changed. The results of the Brazilian split tensile tests demonstrate improved tensile strength for all specimens with various replacement proportions. A lower maximum dry density and a greater optimal water content would result from the substitution of bagasse ash. When the replacement ratio is not more than 20%, the CBR values of the parts replaced specimens are even higher than the cement treatments. The results of BE testing on the treated soils show that there is significant stiffness anisotropy but that it steadily diminishes with curing time and replacement ratio. According to the study, bagasse ash is a useful mineral additive, and the best replacement ratio (CBA20) is 20%.

To investigate the impact of localized failure in the support structure on the overall safety performance of the excavation pit and the mechanism of subsequent chain failure, model tests were conducted on the failure of internal bracing in an asymmetrically excavated pit. Unlike previous progressive-collapse model tests, which have addressed symmetric excavations only, the present test captures the cross-pit load-transfer mechanisms that arise when the two sides of a pit are excavated to different depths. The crown displacement of the retaining structure, the earth pressure, and the redistribution of internal forces caused by the failure of internal support members were measured. The results show that when an internal support fails, the lateral stiffness of the retaining plate decreases and the plate moves inward toward the pit, causing settlement of the surrounding soil. The horizontal displacement on the deep-excavation side is larger than that on the shallow side. Failure of one support increases the axial force in the adjacent support while reducing the force in supports farther away. The earth pressure increases in regions far from the failed support, owing to the soil arching effect, but decreases in the adjacent region because the large lateral movement of the plate unloads the soil. Within the failed-support region, the retaining piles are more prone to bending failure on the shallow-excavation side.