Foundation Pit Support Project for Plot No. {2020}31, Xiaozheng Churu

Project Overview

The project overview is as follows:

The proposed site is located on the southeast side of the intersection of Hengfeng Road and Mingxing Road, Xiaoshan District, Hangzhou. The project's ±0.000 corresponds to an absolute elevation of 6.550, and the natural ground absolute elevation is taken as +0.000 (i.e., the relative elevation is -0.550). For the two-story basement area of this project, the foundation pit excavation depth is 10.950 m; the excavation area is 8,841.6 m², and the pit perimeter is 376.4 m (along the pit bottom boundary line); the design service life is 2 years.

FCW Five-Axis Cement-Soil Mixing Pile Waterstop Support

Inside the foundation pit, 850 mm diameter five-axis mixing piles are used along the edges for skirt reinforcement and pier-type reinforcement.

Foundation pit support plan

Five-axis mixing pile skirt reinforcement diagram

Construction site photos

FCW construction method   

Basic technical principles

The non-replacement five-axis cement-soil mixing pile (wall) adopts an upper and lower grouting process to forcibly mix cement and soil in situ, improving mixing uniformity and preventing the reinforced soil from flowing up and down; during mixing and sinking, the lower grouting port injects grout, and during mixing and rising, the upper grouting port injects grout; during the mixing and sinking process, the original soil is removed in advance through the soil layer balance system according to the replacement rate, achieving balance of water and earth pressure in the reinforced soil; one down and one up (two mixing and two grouting synchronized) completes the construction of one pile wall panel; construction proceeds by successive overlapping or interlocking until all pile walls are completed.

Technical features

1. The arrangement of 5 parallel drill rods improves the efficiency of a single operation and effectively reduces the occurrence of overlapping cold joints;

2. The grouting method inside the drill rods allows mixing while sinking and excavating, improving mixing efficiency;

3. The grout supply system equipped with variable-frequency motors allows manual control of variable grouting at different depths and adjustment of grout volume at any time;

4. The pile frame has automatic walking functions of the walking type or crawler type, reducing labor intensity and improving operational efficiency;

5. The non-replacement pile-soil mode saves construction time compared with dual-axis mixing piles, costs less than triple-axis mixing piles, and causes little environmental pollution.

6. The drilling depth can reach 45 m (ordinary dual-axis mixing pile machines can only drill about 18 m).

Scope of application

It can be used for foundation treatment of water conservancy projects such as sluices and pump stations (normally consolidated mud and muddy soil, silt, saturated loess, plain fill, cohesive soil, and saturated loose sand without underground rivers, etc.). At scale, the technology can be applied to waterstop curtains for foundation pits in water conservancy projects, trench wall reinforcement for diaphragm walls, support walls (with inserted core materials), soft soil foundation reinforcement, etc.‍