Why does sediment appear in construction?

Sediment phenomenon

The amount of sediment at the bottom of the hole exceeds the specification, the hole inspection fails, and the injection cannot be performed.

Causes of sediment formation

Process selection problems, low mud quality, low liquid level, high sand content, brutal operation, scraping of steel cages.

Preventive measures

Improve mud quality, raise mud liquid level, select drilling tools, control axial pressure and single-bucket drilling depth, and reduce sand content.

Drilling rig hole cleaning, positive circulation mud punching, gas lift reverse circulation, slag cleaning pump.

No matter what kind of construction technology is used, there may be sediment at the bottom of the hole after the hole is formed, especially when the mud static pressure technology is used, the amount of sediment is more prominent.

Sediment Specifications

Too much sediment will affect the bearing capacity of the pile foundation. Therefore, the sediment must be cleaned to ensure the quality of the pile hole. In addition, if the sediment does not meet the standard, the pouring process cannot be implemented without the supervisor's signature.

Analysis of sediment formation

Process selection

No construction process was selected according to hydrology and rock and soil, and the dry hole forming process was directly used. The loose/plastic geology in the hole, under the action of groundwater erosion, partially collapsed the hole and formed sediment at the bottom of the hole.

Mud quality

Although the mud static pressure process is adopted, the filling is clear water, no solid phase drilling fluid, no wall protection layer, the hole wall cannot be well protected, the hole is partially shed or collapsed, and the bottom of the hole is formed. Sediment: The sand content of the mud is too high. After the hole is formed, wait for the hole to be inspected and the steel cage to be lowered. The sand will settle and form sediment.

Mud liquid level

After the small pile diameter is lifted, the liquid level drops rapidly, or the hole is parked for too long, the mud loss rate is high, the liquid level drops, the hole wall below the casing loses the mud pressure support, and the local hole collapses. sediment.

Drilling tools

Double-bottom drilling tools are used in loose geology, but body-opening, single-bottom or even auger drills are used, resulting in the slag container not being sealed. During the drilling process, the drilling slag falls and melts in the mud, increasing the mud content. Sand rate and fall to the bottom of the hole.

Control

The drilling depth of the single bucket is not controlled, and the drill slag that has been drilled does not enter the drill body; the axial pressure output is too large, the hole wall is partially damaged and the hole is collapsed, the bottom plate is not closed and the drill is lifted, and the drill slag falls out.

Scratches on the lower reinforcement cage

The reinforcement cage is not vertically hoisted, the main reinforcement at the bottom opening has not been treated, touches the hole wall, and the loose hole wall falls off to form sediment.

Multistage reaming of large apertures results in high sand content in the mud, and the particles in the suspended mud settle to the bottom of the hole to form sediment after the hole is formed.