Laboratory Investigation on the Influence of Cyclic Water Injection Pressure on Sands Hydraulic Conductivity

Hydraulic conductivity variations around the boreholes in uniformly graded sands for cyclic water injection pressure have been evaluated by laboratory tests. Prototype laboratory devices have been designed and constructed for this research. The cell has a capability to model the well, the boundary condition and to measure the hydraulic conductivity. While increasing water injection pressure, hydraulic conductivity suddenly increases in a special pressure value. Hydraulic conductivity is measured and compared with its initial value at the beginning of this cycle. Test procedures are conducted several times and results are compared and analyzed. In these sands with upper soil layers pressure up to 68.64 kPa, hydraulic conductivity at the end of the first cycle reaches to a 20% to 58% growth comparing to its initial amount at the beginning of the test. In the second cycle, this growth rate is up to 16% more than the first cycle. By decreasing the injection pressure at the end of each cycle, a part of the increased hydraulic conductivity due to the high injection pressure is dissipated.