Self-drilling soil nail support technology is a new type of anchoring construction technology that has been widely used by many design institutes and construction companies abroad in recent years. The self-drilling soil nail realizes the integration of drilling, grouting, and anchoring functions during construction, the construction process is simple, and the construction period can be greatly shortened. Today, Sinorock will introduce some precautions in the construction of self-drilling soil nails in repairing the original retaining wall of the subgrade and reinforcing the subgrade through a specific case, hoping that everyone can avoid similar problems.

The project is located in Tianlin County, Nankun Line. The geological conditions of the project are sand clay, sandstone, and mudstone, and the weathering is serious. Moreover, due to the great influence of the fault, the rock layer is seriously crushed and crushed, and it is basically fragmented, similar to the geology of broken rock layers. In order to ensure the safety of the line, after careful research by the design institute, a reinforcement construction scheme based on self-drilling soil nailing technology is adopted.
During the construction of the project, many problems were encountered. The main points of attention are listed as follows:

1. Before the drilling construction, the cracks of the original retaining wall should be grouted and strengthened to prevent the secondary collapse of the retaining wall during the construction process;
2. When drilling, strictly control the impact force of the drilling rig, especially under the geological conditions of the soft and hard interlayer, the impact force of the drill bit is too large, which is easy to bend and break the self-drilling soil nails, causing unnecessary troubles such as construction stagnation. During the drilling process of the drill-type soil nail, it is necessary to ensure that the force of the rod body is uniform.
3. When drilling in ordinary soil layers, ordinary drilling rigs can be used to complete; when drilling in hard rock layers, special self-drilling soil nailing rigs with impact function should be used, which can greatly improve the drilling speed and reduce the drill bit is worn, but the impact force must also be controlled, otherwise, the self-drilling soil nail will be damaged.
4. When drilling in hard rock formations, wear-resistant and impact-resistant alloy drill bits should be selected, and ball-tooth alloy drill bits or cross alloy drill bits can be selected. The effect of drilling a hole with one drill bit avoids the situation where drilling a hole requires multiple replacement of the drill bit or cannot be drilled.
5. The water-cement ratio of the grouting liquid should be controlled at 0.4~0.5 to ensure the bonding effect of the grout on the rock mass, cracks and bolts; at the same time, the pressure of the grouting machine should be ensured during grouting to ensure that the grout can enter the cracks of the rock mass and strengthen the Anchor effect.
6. In order to ensure the quality of bolt consolidation after grouting, the self-drilling soil nail pullout test should be carried out under the same construction conditions, and the necessary parameters should be obtained before construction.
7. The specifications of self-drilling soil nails should be selected according to the designed drilling depth. If the length of the anchor rod cannot meet the design requirements, it must be connected with a connecting sleeve as strong as the rod body. Other connecting sleeves cannot be used, so as not to affect the anchoring effect.

Self-drilling soil nails have simple construction technology, high rod strength, good anchoring effect, and good economic benefits. They are very suitable for applications in slopes, dangerous rocks, deep foundation pits, embankments, and tunnel advance support.