How Does Self-drilling Rock Bolt Drill in Quicksand Geological Condition?

Time:2022-05-07From:sinorock View:

With the rapid development of modern construction projects, the depth of the foundation pit has gradually increased, the rock formation has become more and more complex, and support has become an indispensable link to ensure the safety of the foundation pit project. Many projects near the sea or near the water area will encounter quicksand layers. Due to the quicksand layers have the characteristics of strong fluidity, it brings a lot of difficulties to the support of various projects.

How Does Self-drilling Rock Bolt Drill in Quicksand Geological Condition

Difficulties in bolt construction in quicksand layer

Contains groundwater

The sand grain size of the quicksand layer is relatively uniform and the porosity is large. It is a sandy soil layer in a fluid state. The quicksand layer has the characteristics of loose structure, poor shear strength and high groundwater level. It generally occurs in areas with many rivers and rich groundwater. In the foundation engineering, the quicksand layer needs to pay attention to the sand blocking and water conduction.

Thixotropy

The rock layers above and below the quicksand layer are generally impermeable rock layers, and the clay quicksand layer has thixotropy. When subjected to mechanical vibration, it will flow in a liquefied manner. The speed of the flow is related to the vibration frequency. The rapid flow caused by the violent vibration will have a serious impact on the stability of the foundation project, and the destructive force will be large.

Collapsed hole

Many people choose casing drill to support when they encounter quicksand layers, but it should be noted that as the depth of the hole increases, the casing will bend and so on. Once the casing is withdrawn, there will be subsidence holes, making construction difficult, and even affecting the safety of the surrounding environment of the foundation pit.

The pull-out resistance is not up to standard

After the rock bolt construction in the quicksand layer was barely completed, the pull-out test was carried out. Most of the projects would have the problem that the pull-out bearing capacity could not meet the design requirements. The reason is that after the casing is pulled out, the anchor hole collapses, and the amount of slurry eaten by the bolt decreases, resulting in the failure of the anchor to bond effectively with the soil.

Construction method of self-drilling bolt in quicksand layer

Construction preparation

The working surface needs to be kept flat and solid to prevent the rig from retreating due to the reaction force generated by the construction of the self-drilling bolt. The width of the working surface should not be less than 6 meters, so as to avoid affecting the self-drilling bolt and the operation of personnel. Since the quicksand layer has the characteristics of containing groundwater, it is necessary to set up a drainage ditch at the foot of the slope to drain the water in time.

Positioning

The self-drilling bolt needs to be measured and positioned according to the design before construction. In the positioning of the quicksand layer, attention should be paid to the distance between the bolt and the bottom of the pit, because during the construction process, mud sand and cement slurry will flow out of the anchor hole. Drill self-drilling rock bolt need to be 200-300mm from the bottom of the pit.

Drilling and grouting

The self-drilling bolt can realize the function of grouting while drilling. Because the quicksand layer is unstable, it is necessary to always pay attention to whether the inclination angle of the bolt meets the design requirements during drilling. If not, the drilling rig needs to be adjusted. Grouting while the self-drilling bolt is being drilled can effectively reinforce the soil, increase the bond strength and improve the bearing capacity.

Secondary grouting

Since the quicksand layer has a large amount of slurry, it needs to be supplemented twice after the grouting is completed. After the anchor body reaches a certain strength, carry out secondary high-pressure grouting. This step is very important and will directly affect the bearing capacity of the self-drilling bolt.

Fixed

After the drilling and grouting is completed, if there is a leakage of slurry at the orifice, it is necessary to replenish the slurry in time. After completion, install the backing plate and nut on the self-drilling anchor rod, fix the rod body, and prohibit moving the anchor rod during maintenance to avoid displacement.

Test

After the construction is completed, the pull-out test of the self-drilling rock bolt needs to be carried out. Before tensioning, the tensioning equipment needs to be calibrated to prevent the mutual influence between adjacent self-drilling rock bolt. The interval tensioning construction method is adopted, and the total number of self-drilling rock bolt is randomly selected. 5% for the acceptance pull-out test.

The above is the answer to the question of how to construct the bolt when it encounters the quicksand layer. During the construction of the quicksand layer, in addition to the construction method, the selection of the product is also very important. The application of self-drilling rock bolt in quicksand layers is about 30% higher than that of ordinary self-drilling rock bolt. If you are interested in self-drilling rock bolt, or encounter difficult drilling geology, please contact We, we will provide you with self-drilling bolt solutions.

Return The List