How Does Self Drilling Anchor Bolt Work in the Complex & Unstable Conditions

How Does Self Drilling Anchor Bolt Work in the Complex Unstable Conditions ?

Time:2021-12-28From:sinorock View:

In projects that use self-drilling hollow anchor rods, it is inevitable that the cover layer is soft and broken, and the rock layer is hard. Under such geological conditions, the construction of self-drilling hollow bolts is definitely not the same. So, how is the construction done? Today, Sinorock will lead you to learn that together with specific project cases.

In the left bank shaft project of a hydropower station, the geological conditions are very complicated. The geological conditions of the overburden layer from top to bottom are: 24-33m alluvial deposits, mainly composed of gravel and clay, loose, broken, and easy to collapse; 42-55m glacial deposits, mainly sandwiched by basalt fragments It is composed of breccia sand, which has poor self-stability and is easy to collapse; the ancient landslide accumulation of 36~51m is mainly composed of sand shale and limestone fragments, and the rock is relatively hard.

In the early stage of the project, ordinary mortar bolt spraying protection, pipe shed grouting and self-drilling hollow bolt construction were tested, and the results found that: after the ordinary mortar bolt was used to form a hole, the borehole collapsed and the bolt could not be carried out. Construction; the pipe shed grouting construction program can solve the above problems, but the construction efficiency is low and the cost is high; self-drilling hollow anchor rod construction, drill rod drilling and anchor rod placement are completed simultaneously, and the grouting effect can meet the construction needs. Although the cost is high, the construction progress is relatively fast. Moreover, the design of a certain downward inclination angle during the construction of the anchor rod can play the role of advanced consolidation and grouting, which is conducive to the next cycle of construction and can meet the requirements of the construction quality and safety requirements, while saving time compared with pipe shed construction, it was finally decided to use self-drilling anchors for construction.

Although it is determined that self-drilling hollow bolts are used for construction, the choice of drilling rigs and drill bits is still a tricky matter.

Since the construction work surface is uneven after the slag is discharged, and the height of each cycle is different from the drilling position, it is necessary to choose a drilling rig that is convenient for construction, easy to operate, and can be used for construction in a narrow space. After discussion, the construction party decided to use a crawler bolt drill. The drilling diameter is 50~70mm, and the maximum drilling depth is 25m.

Regarding the selection of drill bits, the project adopts ordinary cast in-line drill bits in the initial stage of construction based on the test results. However, when self-drilling hollow anchor rods are drilled into glaciers and ice-water accumulations, due to their high rock strength, the inline drill bit is severely worn, and the replacement of the drill bit requires the anchor rod to be reversed out of the hole, which seriously affects the construction progress. Therefore, the follow-up construction uses a high-strength alloy cross-shaped drill to improve the construction efficiency.

t76 self drilling anchor bolt system of Sinorock

In this project, the self-drilling hollow bolt has two main advantages: one is that the drilling and grouting are carried out simultaneously, so there is no need to worry about the hole collapse; the other is that the cross alloy drill bit has high strength and wear resistance, avoiding frequent replacement Drill bits increase engineering costs. It can be seen that, as a new type of supporting material, self-drilling hollow bolts have the irreplaceable advantages of ordinary mortar bolts.

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