Abstract. Groundwater pumping can cause severe land subsidence, yet the mechanisms
have not been completely clear. A laboratory physical model test was done to
investigate the mechanism for pumping-induced land subsidence. In the model
test, a model well was installed and pumpage through the well was taken.
During and after pumping, the soil displacement and the pore water pressure
were documented. The pore water pressure within the pumped sand layer
decreased immediately after pumping and recovered immediately after stopping
pumping, while the pore water pressure in the neighboring silty clay layers
first increased and then decreased with pumping, and first decreased and
then increased after pumping was stopped and groundwater level in the sand layer recovered.
The duration within which the pore water pressure in the silty clay
increased when pumping was increasingly great with the distance from the
pumped sand layer. The compaction of the neighboring silty clay first
occurred near the interface between the silty and sand layers, and the silty
clay expanded vertically within some zones. The test results indicate that
the mechanism for land subsidence is complex. Due to their low permeability,
aquitard units may expand in a period when groundwater is withdrawn from the
neighboring aquifer units, and they may compact when groundwater is
recharged into the neighboring aquifer units. This is one of the reasons for
the lagging compaction of aquitard units.