Five Common Causes of Collapsed Drill Holes in Slope Drilling

by Anchor S. Web Designer

The problem of collapsed holes in slope engineering is common in broken rocks and loose soil, which makes it difficult to drill holes with anchor bars, thus lengthening the construction period. First of all, we need to find out the cause of collapsed holes in slope drilling, and then design a matching support method according to the construction geology and environment.

Causes of Slope Borehole Collapse

1. Unreasonable gradient of the excavation

Different soil layers result in different geological characteristics. Before designing the slope, it is necessary to investigate the support stratum situation comprehensively and make a reasonable slope design to avoid the hole collapsing due to instability.

2. Scour of Surface water

Surface water scouring will cause an increase in the water content of slope soil. The soil becomes sticky and wet, and the internal bearing capacity of the slope decreases, which will eventually cause problems such as collapsed holes and stuck drills during construction.

3. Erosion of Groundwater

If the groundwater level is over-limited, it will also lead to a significant decrease in the bonding force of the soil, which can seriously even cause accidents such as landslides and collapse. The more the groundwater content, the more serious the collapsed holes will be.

4. Excessive top pressure

If the load-bearing weight on the top of the slope is too large, the internal shear stress of the slope will increase, which will lead to soil instability and the collapse of the hole. Excessive vibration of the surrounding soil by external forces causes soil displacement, which can also cause problems such as the collapse of the hole when drilling.

5. Loose Soil

If the slope rock is strongly or moderately weathered, the integrity of the rock mass will be relatively broken. When the rock strata with large particles or high fracture degree of borehole wall encounter water, the soil in the borehole will collapse.

Treatments Measures for Hole Collapse of Slope Drilling

1. Drainage

On slopes with surface water or groundwater, drainage measures need to be done in advance to intercept surface water and groundwater to avoid the slope surface being hollowed out by scouring and to prevent destabilization and hole collapse when drilling on the slope.

2. Drilling with Casing

Drilling with casing is a special drilling method in which the casing is pressed in while drilling. After drilling is completed, the drill rod and center bit are pulled out, then insert the anchor rod and start grouting. After grouting, pull out the casing pipe. This method can prevent the hole wall from collapsing or the flowing sand from filling the hole during drilling and is suitable for drilling loose strata and gravel layers. Pipe drilling is a traditional construction process that is relatively complicated.

3. Self-drilling Anchor Bolt Support

The self-drilling anchor bolt is a new type of support material that integrates drilling, grouting, and anchoring, and can be grouted while drilling, which can effectively prevent drill hole collapse and blockage during drilling. It is especially effective for difficult geological conditions such as soft soil and sandstone soil.

The above is the analysis of the causes of collapsed drill holes in slope drilling. For this kind of geology, the applicability of using self-drilling anchor bolts for construction will be better, and the comprehensive cost and construction efficiency will be lower and more cost-effective.

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