Standing water in foundation pit pile caps is a common problem on construction sites. If not pumped and drained promptly and effectively, it may cause soil collapse and other issues. A project department adopted embedded pipes to connect pile caps in series for pumping and drainage. Compared with the conventional method of pumping and draining each pile cap individually, this improves the rate, saves time and labor, and ensures the safety, quality, and progress of the project.

The basement foundation pit of this project is roughly rectangular, longer from north to south and shorter from east to west. The foundation type is such that every two pile caps are connected by ground beams, and the difference between the bottom elevation of the ground beam cushion and the bottom elevation of the pile caps is generally within 30 cm. The basement post-cast strips consist of one longitudinal and three transverse through post-cast strips, dividing the basement area into 6 blocks. During the period from the excavation of the pile caps to the completion of the bottom slab concrete pouring, under the influence of rainfall and groundwater, each pile cap in the basement forms a shallow water pit.

Standing water in pit-in-pit

The basement work of this project happened to be during the rainy season, and the soil is silty clay. If the standing water in the pit-in-pit cannot be removed well and quickly, it may cause soil collapse as well as pile head displacement and personnel construction safety issues. If the traditional method of pumping and draining each pile cap individually is adopted, it is time-consuming and labor-intensive, seriously affecting the subsequent pile head testing, brick formwork, cushion pouring, and the subsequent waterproofing works, up to the final bottom slab concrete pouring construction.

Pumping each pit individually is time-consuming and labor-intensive

The project department utilized the characteristic that pile caps and ground beams are connected in pairs, and adopted embedded pipes to connect the pile caps in series, which can maximize the requirements, improve construction efficiency, reduce costs, and achieve the effect of quickly removing standing water from the basement pit-in-pit.

The technical requirements of this scheme are simple; only one self-priming water pump is needed to meet the pumping requirements.

01. Equipment and Material Preparation

Selection of water pump: self-priming pump

Moderate suction strength, automatically starts when water is sensed. Moderate weight.

Selection of pipe material: PVC pipe

Moderate sealing performance and strength, low cost, and convenient connection.

Selection of filter head: stainless steel mesh filter head

Average filtration performance, with certain strength, not easily damaged, and durable.

Selection of pipe layout: parallel layout

Parallel layout arranged from one corner in one direction. When burying pipes, the level must be measured well; with a certain slope, water can converge in one direction.

Pipe layout method

02. Embedding PVC Pipes

Ensure that the pipes are embedded at the bottom of the cushion, with a certain slope so as not to affect drainage.

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03. Laying Waterproof Membrane

The laying of the waterproof membrane should not affect the normal drainage of the pipes.

By adopting this scheme to deal with the standing water problem in the pit-in-pit, the standing water in the pile caps can be collected in an organized manner, the pumping and drainage efficiency is improved, and there is almost no residual water in the pile caps. In the overall process, it was found that this method is easy to set up; the pipe network can be buried during the manual soil trimming stage of ground beam excavation, and the amount of excavation and backfill during the burying process is very small. It greatly speeds up the drainage rate of the foundation pit. Compared with the conventional method of pumping and draining each pile cap individually, this method only needs to install one water pump in the sump pit of one block to achieve the drainage effect, saving time and labor, minimizing adverse factors caused by standing water such as soil collapse, accelerating the follow-up of the next process, and ensuring the safety, quality, and progress of the project.