What Is a Slurry Wall?

The underground continuous wall is a trenching machine used on the ground for the foundation project. Along the surrounding axis of the deep excavation project, under the condition of mud wall protection, a narrow deep trench is excavated. After the trench is cleared, it is suspended in the trench. Reinforced cages are then used to pipe the underwater concrete to form a unit slot section. This is done step by step to form a continuous reinforced concrete wall underground to serve as a water interception, seepage prevention, load bearing, and water retaining structure. ^[1]

China's slotting machinery has developed rapidly, and corresponding slotting methods have emerged endlessly; there are many new

(1) According to the method of forming a wall, it can be divided into: 1. pile row type; 2. trough plate type; 3. combined type.

(2) According to the purpose of the wall, it can be divided into: 1. Impervious wall; 2. Temporary retaining wall; 3. Permanent retaining (load bearing);

(3) According to the wall material, it can be divided into: 1, reinforced concrete wall;

(1) Retaining effect. When the trench of the underground continuous wall is excavated, the soil close to the surface is extremely unstable and easily collapses, and the mud cannot serve as a retaining wall. Therefore, the guide wall functions as a retaining wall before the unit trench section is dug.

(2) As a benchmark for measurement. It specifies the position of the groove, indicates the division of the unit slot section, and also serves as a benchmark for measuring the height, verticality and accuracy of the trench.

(3) as a support for heavy objects. It is not only the support of the trenching machinery track, but also the fulcrum of the shelving of steel cages, joint pipes, etc., and sometimes it also bears the load of other construction equipment.

(4) Storage of mud. The guide wall can store mud and stabilize the mud liquid level in the tank. The slurry liquid level should always be kept 20cm below the guide wall surface and 1.0m above the groundwater level to stabilize the tank wall.

(5) Prevent mud leakage; prevent ground water such as rainwater from flowing into the trough. ^[2]

Before excavation of the trough section, guide walls are constructed along the longitudinal axis of the continuous wall and cast in-situ concrete or reinforced concrete.

The depth of the guide wall is generally 1.2 to 1.5 m, and the top surface is slightly higher than the ground 10 to 15 cm to prevent surface water from flowing into the guide trench. The thickness of the guide wall is generally 100 ~ 200mm, the inner wall surface should be vertical, and the net distance of the inner wall should be the design thickness of the continuous wall plus the construction allowance (generally 40 ~ 60mm). The allowable deviation of the distance between the wall surface and the longitudinal axis is ± 10mm, the distance between the inner and outer guide walls is allowed to be offset by ± 5mm, and the top surface of the guide wall should be kept horizontal.

The guide wall should be built on a dense cohesive soil foundation. The back of the wall should be replaced by a soil wall to prevent surface water outside the tank from penetrating into the tank. If backfill soil is needed on the back side of the wall, cohesive soil should be used for layer compaction to avoid slurry leakage. The guide wall in each slot section shall be provided with an overflow hole.

Before excavating the foundation trench, a guide wall is used to protect the upper opening of the foundation trench. The wall is protected by mud. The groove is dug according to the designed wall width and depth. A reinforced skeleton is placed. . Continuous construction step by step into a continuous wall. The main construction techniques are guide walls, mud wall protection, trench construction, underwater concrete pouring, wall joint treatment, etc.

Underground diaphragm wall guide wall

Guide walls are usually reinforced concrete structures poured in place. The main functions are: to ensure the geometric size and shape of the design of the underground continuous wall; to store part of the mud to ensure the stability of the liquid level during the construction of the trench; to bear the load of the trenching machinery, to protect the soil wall of the slot from damage, and to serve as a framework for the installation of the steel skeleton Benchmark. The guide wall depth is generally 1.2 to 1.5 meters. The top of the wall is 10-15 cm higher than the ground to prevent the inflow of surface water and affect the mud quality (Figure 1). The bottom of the guide wall should not be located in the loose soil layer or the place where the groundwater level fluctuates.

Mud wall for underground continuous wall

Pressure is applied to the groove wall by the mud to protect the shape of the deep groove that is dug, and the concrete is replaced by the poured concrete. Mud materials usually consist of bentonite, water, chemical treatment agents and some inert substances. The role of the mud is to form an impervious mud skin on the tank wall, so that the hydrostatic pressure of the mud can effectively act on the tank wall, prevent groundwater seepage and the spalling of the tank wall, and maintain the stability of the wall surface. At the same time, the mud and suspended soil Slag and the function of carrying soil slag out of the ground.

Slots in the gravel layer can be used to prevent slurry leakage if necessary. There are two types of mud use methods: stationary and circulating. When the mud is used in circulation, purification devices such as vibrating screens and cyclones are used. After the indicators have deteriorated, it is necessary to consider using chemical methods to dispose of or discard old pulp and use new pulp.

Underground continuous wall trough construction

The special machines for slot formation in China are: rotary cutting multi-head drills, guide grabs, impact drills, etc. Construction should be selected according to the geological conditions and the depth of the wall. Generally, the soil is soft. When the depth is about 15 meters, ordinary guide grabs can be used. For dense sand or gravelly soil layers, multi-head drills or heavy-duty hydraulic guide grabs can be used. In the case of large gravel or rock foundations, For middle grooves, it is better to use impact drills. The unit length of the slot section is generally 6 to 8 meters, which is usually determined based on the soil conditions, the weight of the reinforcing steel frame and the structural size, and the division of the section. After the tank is formed, it needs to stand for 4 hours, and the specific gravity of the mud in the tank is less than 1.3.

Underwater continuous concrete pouring into underground wall

The pipe method is used to carry out the underwater concrete pouring method, but before the pipe is started to be poured into the concrete to prevent the mud from mixing into the concrete, a pipe plug can be suspended in the pipe, and the mud in the pipe is squeezed out by the pressure of the poured concrete. The concrete should be continuously poured and the concrete pouring volume and rising height should be measured. The overflowed mud is returned to the mud sedimentation tank.

Underground continuous wall wall joint processing

The underground continuous wall is composed of many wall sections. In order to maintain continuous construction between the wall sections, the joint adopts a lock pipe process, that is, a diameter and a groove are pre-inserted at the end of the groove section before the concrete of the groove section is poured. After the concrete is initially set, the steel pipe is slowly pulled out after the steel pipe of the same width, that is, the lock pipe, to form a semi-concave joint at the end. There are also rigid joints set according to the stress requirements of the wall structure, so that two successive wall sections are integrated. ^[4]