Design of Groundwater Extraction in Open Cut Foundation Pit and Simplified Calculation of Ground Subsidence due to Dewatering in Sandy Pebble Soil Strata

Abstract

In order to study the design of incomplete well point for groundwater extraction in open cut foundation pit in which the inner and outer aquifers are not completely isolated and the change mechanism of ground subsidence due to dewatering in the foundation pit, an open cut foundation pit for a subway station on Chengdu Metro Line 6 is taken as an example; meanwhile, the typical sandy pebble soil strata are also considered as a research object in this paper. Firstly, a new method for designing groundwater extraction in the open cut foundation pit is presented and applied to the practical project. The dewatering funnel curve is derived based on Dupuit’s assumption, and the ground subsidence around the foundation pit due to groundwater extraction is calculated using the stratification summation method as well as considering the effect of seepage force. The finite difference software FLAC3D is employed to simulate the groundwater extraction process in the foundation pit, and the simulation of groundwater extraction by single well point and group well points is also carried out and the unapparent effect of group well points is obtained. The comparison among on-site monitoring, theoretical calculation, and numerical simulation shows that these values have the same trend in indicating ground subsidence, and the conventional stratification summation method is conservative, and the algorithm considering the effect of seepage force is more accurate. Therefore, the ground subsidence curve caused by groundwater extraction in the foundation pit is presented. The above research methods and results can be applicable for practical engineering and be used to guide the design and construction of groundwater extraction in the foundation pit by using the open cut method in sandy pebble soil strata.

Investigation on Dewatering of a Deep Shaft in Strong Permeable Sandy Pebble Strata on the Bank of the Yellow River

“…Due to the high permeability coefficient and strong seepage, it is uncertain that the water level can be reduced to the safe level only by the pumping well and vertical waterproof curtain (2) In the thick and sandy pebble strata, the diaphragm wall is prone to defects which lead to leakage [8]. Therefore, groundwater flows into the excavation pit through the bottom of the diaphragm wall [8,11,20]. The principle of diaphragm wall that can be used for dewatering is its barrier effect on seepage.…”

“…Liu et al [10] proposed inflow prediction formulas for excavation pits with partial penetrating curtains in high-permeability aquifers. Other researchers [11][12][13] focused on the deformation mechanism of diaphragm wall and ground settlement induced by dewatering. Zeng et al [14] and Zeng et al [15] investigated ground settlement caused by preexcavation dewatering.…”

Dewatering System Control by MATLAB Software

“…The inflow of water Q2 is determined for a circular or rectangular excavation with a length-towidth ratio of less than 20, use the following equation [21].…”

Analysis of Deep Foundation Pit Pile-Anchor Supporting System Based on FLAC3D

“…Based on FLAC3D software, Zhibin et al [30] quantitatively analyzed the coupling effect of seepage and creep during the excavation of a soft soil foundation pit. Zhang et al [31] carried out a numerical simulation on the whole process of groundwater extraction in a deep foundation pit and studied a new groundwater mining method for the sandy cobble stratum. Wang et al [32] established a threedimensional foundation pit frost heaving model by using a numerical simulation method and discussed the functional relationship between soil frost heaving deformation and low temperature.…”