2. Large-area surcharge makes the soil around the pile compact, consolidate and sink.
3. In soft clay areas with normal consolidation or slight overconsolidation, the groundwater level is completely reduced due to pumping groundwater or precipitation during deep foundation pit excavation, which leads to the increase of effective stress of soil and large-scale land subsidence.
4. Self-weight collapsible loess will collapse after soaking in water: negative friction will also be generated on the pile foundation after sand liquefaction and frozen soil melting and sinking.
5. Saturated cohesive soil with high sensitivity is affected by construction disturbance (vibration, extrusion and displacement) such as piling, and the additional excess pore water pressure increases, so the thixotropy of soft soil increases, and then new consolidation settlement occurs.
6. Squeezed piles are driven into a large area of soft soil, which makes the original ground backwater high, and the total stress and pore water pressure in pile soil generally increase. Subsequently, the soil consolidation between these piles causes the soil to sink relative to the piles.
Extended data
Negative friction will inevitably increase the settlement of pile foundation. When the settlement of the soil around the piles of the building is uniform and the building is insensitive to uneven settlement, the settlement caused by negative friction will not endanger the normal use of the building, so it is not necessary to check the settlement.
However, uneven settlement will occur when uneven stacking load, uneven precipitation or uneven soil layer are applied around each pile foundation, and the pull-down load and settlement caused by negative friction of each pile gene will also be uneven, so it is necessary to consider negative friction to check the settlement of pile foundation.
Baidu encyclopedia-negative friction of piles
Baidu encyclopedia-negative friction