Research Of Two-dimensional Soil Deformation Caused By Single Piles With Caps Under Vertical Load Using The Transparent Soil Technology

Transparent soil technology with Particle Image Velocimetry (PIV) technology can be used to make non-contact and full-field measurement of the internal deformation of soil. Fused silica is similar to natural sand in geotechnical properties. When sectoral laser casted into the transparent soil, the laser speckle pattern changes with the internal texture deformation. This article uses the combination of a self-assembled vertical load tester, a self-designed sectoral laser system, industrial CCD camera to produce and record the speckle field. The acquired images are processed using the matlab program written upon the MatPIV toolbox to get the internal displacement field of soil. Fused quartz of different particle sizes (0.1-0.2 mm,0.2-0.5 mm,0.5-2 mm,2-5 mm) are used to make transparent soil to compare the induced speckle pattern and the measurement of the displacement field during translation model test. Two-dimensional soil deformation fields due to the interaction between soil and single piles with caps under vertical step loading are also investigated. The following are conclusions obtained:(1) Case-to-case testing strategy is used to control the refractive index of calcium bromide aqueous solution using refractometer and relative density of the transparent soil made of fused silica with larger density and smaller particle size through the non-vacuum stirring method. And the method shows good effect.(2) In order to ensure the accuracy of measurement and the ability of comparison when dealing with transparent soils made of quartz particles of different sizes, the window size used during the cross correlation calculation should be chosen carefully; Transparent soil model made of fused silica of larger particle size shows lower algorithm precision and stability of displacement field than the model of the small-sized fused silica.(3) Different pile lengths, pile parameter and dimensions of caps lead to different macro mechanical characteristics of the load-settlement curve. Existence of bigger pile cap(L/B is smaller, and B/d is larger.) can more greatly improve the bearing capacity of single pile, also more greatly influence the elastic-plastic performance in soil. The longer the pile, the ultimate bearing capacity gets larger.While the smaller the pile length, the length change will more obviously improve the ultimate bearing capacity. Pile length doesn’t influence the elastic-plastic performance in soil. Ultimate bearing capacity increase with increasing pile diameter. The smaller the pile diameter, pile diameter, the more obvious the effect is on ultimate bearing capacity. Pile diameter also affects the elastic-plastic performance of the soil, while not as great as the effect of the pile cap. Ultimate bearing capacity of the pile can be designed by adjusting the cap dimensions, pile length and pile diameter size. And adjustment shows better effect in changing the cap size.(4) Different pile lengths, pile parameter and dimensions of caps can differently affect soil deformation in the settlement process. With larger cap size, more load were transferred to the soil under the caps and this part of soil gets densified. And larger cap size also more heavily postpone the resistance capacity of the pile end. For large-sized cap, soil corruption happens with the slip between soil and pile model in the area around the cap. Upper load can be spread to deeper soil through the pile body, and thereby limiting the glide plane development around the cap. Wherever when pile length is too long, the limitation goes weaker. Change of pile diameter differently order the bearing capacity appearance around the model during the settlement progress. Increased pile diameter will make the pile side friction play in advance.