Grouting-Induced Soil Behavior in Structured Clay

Grouting below the tunnel invert is commonly used to remediate the settlement. Case histories demonstrate that the tunnel settlement still develops after the grouting is completed, especially in structured clay. The principal mechanism behind this is the grouting-induced soil disturbance, including the generation of excess-pore-water pressure (EPWP), degradation in soil structure, and changes in compressibility. To date, the mechanism behind the grouting-induced soil disturbance and responses of the ground heave is not yet fully understood. Toward this end, laboratory tests on grouting in mud with different sand content are carried out. Earth pressure, pore water pressure, shear stiffness, undrained shear strength, and ground heave are measured and analyzed. The results indicate that grouting causes increases in the lateral earth pressure and significant EPWP in the surrounding soil. Changes in undrained shear strength and shear stiffness are closely related to the comprehensive effects of increases in stress level and shear disturbance. The increased stress level leads to the growth in stiffness and strength, while shear disturbance causes degradation. The soils right nearby the grouting zone are subjected to significant shear disturbance and also increases in stress level. As a result, the soil stiffness and strength exhibit negligible change. In comparison, the soils above and below the grouting zone mainly experience an increase in stiffness and strength, because shear disturbance is comparatively smaller than the influence of the increases in stress level. Furthermore, the development of the vertical displacement of the ground surface demonstrates two stages of initial uplift during grouting and then settlement after the grouting is completed. In addition, stronger soil structure corresponds to larger settlement after the grouting is completed.