(1)Project Overview:

The geological conditions of the target layer in the goaf of Hejiadi Tunnel on the Shanghai - Kunming High - speed Railway are complex, especially with diverse strata lithology, complex geological structures, and well - developed karst. There are influences from coal mine goafs, as well as surface deformations caused by the migration of the basin even when the impact of the goaf is not significant. Through surface mapping, no new surface landslides, slumps, etc. were observed on the back hill of coal mine on the left side of the line. However, on the back hill of coal mine on the right side of the line, obvious slope deformation signs were found, and phenomena such as surface cracking, slumping, and small - scale landslides were relatively common.

Considering the above characteristics, the main purposes of this horizontal directional drilling implementation include:

1）Conduct experimental exploration of pre - treatment grouting measures under special geological conditions.

2）Control surface deformation through directional boreholes.

3）Perform grouting and sealing treatment on special disaster - prone strata during this construction, combining multi - branch directional drilling technology and curtain grouting technology.

4）Implement directional drilling according to the engineering geological and hydrogeological conditions of the designed branch tunnel.

Based on the comprehensive drilling objectives, taking Drill Site B as an example, a total of three main boreholes were arranged. Among them, the main hole of B1 is 335 meters deep with 6 branches; the main hole of B2 is 200 meters deep with 6 branches; and the main hole of B3 is 200 meters deep with 7 branches. The plan layout of the drill site is shown in the figure.

Project Site Situation

Borehole Layout Diagram

(2) Material Usage

In order to achieve comprehensive treatment of special disaster - prone strata, MidwestSGS - type materials were used for grouting and leakage blocking. Through grouting reinforcement, the comprehensive application of these materials in special strata was realized.