The sinking issue is common in fragile geological regions, where rainwater infiltration, temperature variation creates freezing and thawing problem. Subsidence, sinking, and uneven settlement, which occur due to these combined effects lead to severe issues.
In many situations, it has also been noticed that the boulders, which are embedded and intermixed in loose sand deposits, after coming in contact with water creates pore pressure, and it gets released, which causes seepage through this strata; this seepage action results in the removal of fine from the strata, which give rise to sudden subsidence, sometimes creep condition.
Displacement of boulders and soil creep gives rise to local sinking.The above figure shows the sinking occurs post rainfall due to capillary action and temperature variations.
Scarp at the toe of slope having flowing river may also lead to movement of slope from toe, which ultimately creates sinking issues. The combined issues due to local sinking and deep sinking cumulates to major sinking issues.
In some situations, it has also been observed that jointed rocks, when subjected to temperature variations, give rise to expansion and contraction due to the presence of minerals creates a separation of joint planes.
Gravitational action creates detachment of rock masses from the rock body; thereby, sliding action gives rise to sinking issues also.