Study on settlement deformation of unconsolidated strata during lowpressure water injection process of multi-borehole

To prevent the continuing settlement deformation of unconsolidated strata caused by groundwater dewatering,using the method of the long-term water injection of multi-borehole the settlement deformation of unconsolidated strata was controlled. The fiber Bragg grating sensors was used for the real-time strain monitoring of unconsolidated strata and a mathematical model for the compression settlement induced strain calculation was proposed which can assist understanding the effect of water injection on the ground settlement. Four water wells'( Z2,Z4,Z5,Z6) water injection process in the depth of 138. 80-171. 40 m,as well as water level monitoring system of four water injection well in the depth of 114. 00 to 176. 40 m and fiber Bragg grating monitoring system were introduced in this study. With the increase in water injection,unconsolidated strata compressed state is improved by the transition of the stress state from compressive stress to tensile stress. The wavelength change of fiber Bragg grating sensors and the trend of the water level at the same stratigraphic are synchronous. When water injection rate increase for each 1 000 m3,the unconsolidated strata increases 1. 715 micro-strain. Monitoring results show that it can control the development of the settlement of unconsolidated strata when the water injection quantity for each borehole reaches 3. 79-6. 00 m3/h and the annual water injection rate reaches 132 973. 23 m3.