Study On Analytical Theory For Consolidation Of Soft Soils Induced By The Changes Of Groundwater Level

The problem of land subsidence induced by groundwater withdrawal is more and more serious. Consolidation of aquitards is the dominant factor of land subsidence in China's coastal areas where deep soft clays are widespread. Therefore, it is meaningful to study the consolidation of aquitards for prediction of land subsidence. Moreover, analytical solutions for unsteady groundwater flow is also very important for the calculation of land subsidence. However, the existing solutions are more or less defective even wrong. For example, there are two problems about analytical solutions for unsteady groundwater flow in circular area with impervious boundary. One is that analytical solution under point-well assumption is wrong. The other is that analytical solution considering well diameter is approximate. Aiming at these problems, works were carried out as follows:1. Analytical solution was derived for one-dimensional consolidation of soft soil induced by instantaneous decline of groundwater level. Then, General analytical solution was obtained for one-dimensional consolidation of soft soil induced by arbitrary change of groundwater level. Furthermore, analytical solutions were given for common forms of groundwater level change. Comparing with Terzaghi one-dimensional consolidation theory, it is shown that when soft soil lies between aquifers, the amount of compression of soft soil induced by lm drawdown of single aquifer is equal to that induced by 5kPa uniformly distributed load on the top of the soil layer. When soft soil lies between an aquifer and an aquifuge, the amount of compression of soft soil induced by lm drawdown of the aquifer is equal to that induced by 10kPa uniformly distributed load on the top of the soil layer. Analytical solution for average degree of consolidation is the same with Terzaghi solution on condition that groundwater level drops instantaneously.2. Considering that initial water head is non-uniformly distributed along soil depth, analytical solution was derived for one-dimensional consolidation of soft soil induced by instantaneous decline of groundwater level. Then, study about analytical solution that considers groundwater level decline as well as soil's characteristics such as nonlinearity, rheological property and layered property was analyzed.