Land Subsidence and Earth Fissures Due to Groundwater Pumping

In this research, the fundamental mechanics for the changes in stresses and strains states due to groundwater pumping is formulated. This was accomplished by developing a 3D closed form solution. The results from this research are compared with results of finite element (FE) analyses and data obtained from interferometric synthetic aperture radar (InSAR). Land subsidence (LS) due to groundwater pumping from a single well for different geological profiles and the reason why LS continues after groundwater pumping cessation were investigated. FE analyses for four different scenarios were used to investigate the effects of cemented layers and non-cemented layers above the aquifer on EF initiation. A practical method which is based on the stiffness and cementation strength of the cemented layer and the gradient of the slope of the subsidence bowl (ɑ) was proposed to determine earth fissure (EF) initiation. Three-point bending beam test was conducted in the lab to determine the mode of failure and the modulus of rupture of a local cemented soil that occurs in areas where EFs were observed. The major findings are as follows. LS due to groundwater pumping consists of i) isotropic compression and ii) simple shear on vertical planes with rotation. For a parabolic distribution of groundwater level in a homogenous aquifer, simple shear on vertical planes will be dominant when the characteristic length of the aquifer is larger than √2 times the aquifer thickness. Fine-grained soils are responsible for LS occurring after the cessation of pumping and for sagging in LS profiles. Regardless of the stiffness and cementation strength of the top layer above the aquifer, EF will not initiate if ɑ is less than 8x10⁻⁵. When the stiffness of the top cemented layer increases, it becomes more prone to EF initiation. However if the layer is stiff enough to be classified as "rock" then a higher value of ɑ is needed to initiate an EF. The experiments show that the preferred mode of failure of a cemented soil is shear rather than bending and existing cracks significantly influence the results of EF formation