Compaction behavior of sand layer and its effect on diffusion process of fracture-compaction grouting mode

Fracture-compaction grouting mode is a kind of important mode in sand grouting projects. Com-pressibility of sand has a strong effect on fracture-compaction grouting process. As the clayey sand layer in Qingdao district is a typi- cal medium,a series of confined compression tests were conducted to clarify the characteristics of compressibility of sand. In compression tests,the grouting pressure was set at scope of 0 ~ 2 MPa,with the clay content at 10% to 50% and the initial water content at 12% to 28% . The effect of clay content and initial water content on the compression process of sand was analyzed,and the compression mechanism of sand layer was revealed in view of sand skeleton for- mation. The quadratic parabola model was used to fit the stress-strain data in the compression process. A mathematical model was developed to describe the nonlinear compression process of sand. Characteristic parameters in the model can be determined by initial compression modulus and strain value at 2 MPa. Finally,the compression process of sand layer on both sides of fracture channel was considered according to the confined compression condition approximately. Influ- ence of clay content on fracture-compaction grouting process was studied. Results show that that the main control factor for the compressibility of sand is clay content. When clay content is lower than 25% ,sand skeleton will form and the compressibility of sand will be poor. In a converse condition,sand skeleton will not form and compressibility will be good. There exists an optimum initial water content (about 20% ) in the compression process of sand. When the initial water content of sand becomes lower or higher than the optimum value,the compressed volume of sand layer at con- stant pressure will be smaller. Fitting curves of mathematical model of sand compression process have good consistency with test data. In the same condition of grouting time,the width of fracture is positively correlated with clay content, and grouting radius and grouting pressure is negatively correlated with clay content. In the same condition of grouting end pressure,grouting radius is positively correlated with clay content. In fracture-compaction grouting design engineer- ing projects of sand layer,the effect of compressibility of sand on grouting diffusion process should be fully considered.