Geological disasters often occur due to expansion and shrinkage properties of expansive soil. This paper presents a cementitious material combined with rice husk ash (RHA) obtained from biomass power plants and lime to stabilize expansive soil. Based on compressive and flexural strength of RHA-lime mortars, blending ratio of RHA/lime was adopted as 4 : 1 by weight for soil stabilization. When mix proportion of RHA-lime mixture varied from 0% to 20%, specific surface area of stabilized expansive soil decreased dramatically and medium particle size increased. The deformation and strength properties of stabilized expansive soil were investigated through swelling test, consolidation test, unconfined compression test, direct shear test, and so on. With increase in RHA-lime content and curing time, deformation properties including swelling potential, swelling pressure, compression index, crack quantity, and fineness of expansive soil lowered remarkably; meanwhile, strength properties involving unconfined compressive strength, cohesion, and internal friction angle improved significantly. Considering engineering performance and cost, mix proportion of 15% and initial water content of 1.2 times optimum moisture content were recommended for stabilizing expansive soil. In addition, effectiveness of RHA-lime to stabilize expansive soil was achieved by replacement efficiency, coagulation reaction, and ion exchange.

Expansive soil has harmful effect on engineering. Rice husk ash (RHA) has high pozzolanic activity, so it can form new cementing material with lime or cement to solidify soil. In this paper, the tests of free expansion rate, water ratio limit, and optimum moisture content (OMC) are carried out; then, RHA and lime were added to artificial soil in different proportions of 5, 10, 15, and 20% by weight, in which the ratio of RHA to lime is 80 : 20. The unconfined compressive strength (UCS) in different curing age is measured, and the improvement effect of RHA and lime to expansive soil can be obtained. Finally, the reason of improvement effect is explained by using the scanning electron microscope (SEM). The results of the study show that (1) for the best utilization effect, the optimum percentage of RHA is 12% and lime is 3%; (2) the UCS is 2.6 times of the pure soil after curing of 14 d under the optimum percentage; (3) the curing age has a significant effect on strength; (4) the main reason for the strength increase of the modified soil is that the crystal produced by the pozzolanic activity fills the pores of the soil.

Segment uplift is a frequent problem during the construction of shield tunnels. The phenomenon of segment uplift in Xuzhou Metro Line 1 is investigated. The segment uplift magnitude in the shale layer is quite smaller than that in the clay layer. A tunnel segment uplift calculation model based on the Pasternak foundation beam model is proposed, which considers the hardening process of the grouted body with time. The finite difference method is adopted to calculate the magnitude of segment uplift during different tunnel construction stages, and a numerical solution of segment uplift on the longitudinal direction is obtained. The applicability of the numerical solution is studied by comparing with the field test results and parametric analyses are also performed to investigate the effects of different factors on segment uplifting. The results show that the coefficient of subgrade modulus, shear stiffness of the shear layer, and grout pressure all influence the segment uplifting of the tunnel. The influence of the coefficient of subgrade modulus and grout pressure on segment uplift is more significant.