Expansive clays exhibit a high potential for the volume change behavior when the soil moisture changes. The estimated annual cost of the damage to the facilities built on expansive clay in the United States exceeds 9 billion dollars. Because of the physicochemical nature of the expansive clay, the use of chemical agents to improve their engineering properties is common. This research investigated the effects of chemical agents on an expansive soil from Texas through a laboratory injection method. The agents used in this study included lime, potassium based agents, and a group of ionic agents. Swelling tests, chemical tests, and soil suction tests were used to evaluate the stabilizing effects of those chemical agents. The testing results indicated that potassium based stabilizer, is an effective stabilizing agent to control the swelling potential of the expansive clay. It can also be injected in the field to build a moisture barrier. The chemical tests on the injected Texas clay showed that the stabilizing mechanism of the ionic agents is possibly through the cations’ exchange and the increase of the cations’ concentrations in the soil pore water.

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.

For the purpose of understanding the mechanism that results from treating expansive soil with lime, a series of tests were conducted on selected Nanyang expansive clay. X-ray diffraction tests indicated that the major clay minerals of Nanyang expansive clay are a mixture of illite and smectite with some kaolinite and chlorite. The scanning electron microscope images obtained at different curing times were used to interpret the change in the microstructure and the formation of new products from the lime treated samples. The atomic absorption method was adopted to test the concentration of ${\mathrm{Ca}}^{2+}$ and ${\mathrm{K}}^{+}$ in the pore water and exchange complex of lime treated Nanyang expansive clay. The results indicate that (1) cation exchange, ions crowding, formation of $\mathrm{Ca}{(\mathrm{OH})}_2·{\mathrm{nH}}_2\mathrm{O}$ , agglomeration, and breaking of clay particles in a high pH environment are the dominant reactions in the early stage of treating expansive clay with lime; and (2) the pozzolanic reaction and carbonation occurred at a late stage after lime treatment (90 days in this study).