Grouting after pile injection refers to the injection of cement slurry through the grouting conduit preset in the pile body and the connected pile end and pile side grouting valves for a certain period of time after the pile is completed. The soil (including sediment and mud) at the end and side of the pile is reinforced, thereby increasing the bearing capacity of the single pile and reducing settlement.
There are three construction methods:
1. Set up a grouting chamber at the bottom of the hole. When using this process, the steel cage needs to be lowered to the bottom of the pile.
2. After the cast-in-place pile is formed into a hole, a grouting pipe is installed in the hole. The bottom of the grouting pipe needs to be threaded and sealed with a pipe cap. The steel cage needs to extend 15-20cm from the bottom of the grouting pipe so that the grouting valve can be inserted smoothly into the bottom of the hole. Before pouring concrete, pour gravel or rocks into the bottom of the hole so that the slurry outlet is buried in the gravel or rocks, and then pour concrete.
3. Fix the grouting pipe on the steel cage (steel pipe or black iron pipe). Use a one-way special grouting valve at the bottom of the grouting pipe and insert it into the pile bottom soil for 20 to 30cm. Due to the use of a one-way grouting valve, grout will not be poured into the valve when pouring concrete on the pile body, and grout will not flow back during grouting.
The first method has complex process and high cost, and is rarely used in China. The second method is mainly used to reinforce pile bottoms and has been tested or used many times in China. However, because the process is too simple, it is easy to block the grout outlet and cause grouting failure. The third process uses a one-way shut-off valve to create a grouting port, the grouting success rate can reach more than 97%, the pressure is relatively stable, and the grouting effect is remarkable.
Extended information
Notes
1. In order to prevent the cement slurry from being squeezed out from the grouting pipe joint of the hollow part, the grouting of the hollow part must be Pipe joints should be sealed with raw material tape, and the steel pipes in the hollow parts should be connected by entire long steel pipes.
2. The grouting should be done at low speed and slowly, thinning first and then thickening. Low-grade slow pressure can not only effectively prevent the sudden increase in pressure and prevent grouting, but also prevent slurry from running along the pile body or emerging from other places, so that the pile end or the soil around the pile is gradually filled with cement slurry. As the amount of grouting increases, the pressure will naturally increase gradually.
3. If one of the grouting pipes of the same pile cannot be grouted or the grouting amount is insufficient, the corresponding grouting amount should be supplemented when the other grouting pipe is grouting. Adjacent grouting pipes adjacent to piles should also make up the corresponding grouting volume.
4. If the grouting amount does not meet the design requirements and slurry emerges from the ground, the grouting should be suspended and the cement slurry in the grouting pipe should be replaced with retarded cement slurry. Stop Re-pressurize again in about 1 hour, and so on, until the designed grouting volume is reached.
5. When grouting occurs near the site or the grouting volume meets the requirements but the pressure is low, grouting cannot be terminated blindly assuming that the grouting volume meets the requirements. At this time, methods such as interval repressurization, early strength agent addition, and grouting channel sealing should be adopted to ensure the effective grouting amount.
Baidu Encyclopedia - Post-grouting of cast-in-place piles