In the process of groundwater exploitation, the decrease
of groundwater head causes the dissipation of pore water
pressure, and the decrease part of pore water pressure
will be transformed directly into effective stress, and
the pore volume of soil will decrease continuously, resulting
in the compression deformation of soil. This process can be
summarized as follows:
Groundwater level drop-pore water pressure decrease-effective
stress increase-soil compression deformation.
Because of the local variation of aquifer thickness, such as
the abrupt change of the surface morphology of bedrock or the
obvious difference of the thickness distribution of compressed
soil, the differential compaction settlement of loose soil is
caused. Tensile stress concentration in the area with the
greatest difference in surface compaction settlement may
lead to cracking and deformation. In urban areas located on
the plain, subsidence basins are often produced by large-scale
concentrated exploitation of groundwater. The outer margin of
the basin is a tension stress zone, and a compressive stress
zone is formed in the center of the basin. The tension and
compression stress zone is formed between the two regions.
The concentration of tensile stress will lead to the cracking
and deformation of soil layer along the direction of tension.
As a result, ground fissures often occur At the outer edge of
the subsidence basin.