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Gaojiaping Tunnel

Project Background

Zhengzhou-Wanzhou high-speed railway has a construction length of 818 kilometers, an estimated total investment of CNY 118 billion, and a design speed of 350 km/h. After opening to traffic, the journey time from Zhengzhou to Chongqing will be shortened to less than 4 hours.

rock bolt used as pipe umbrella system

The project is the Gaojiaping tunnel in the ZWZQ-5 bid section in Hubei section of Zhengzhou-Wanzhou high-speed railway. The Gaojiaping tunnel is located in Limiao Town, Nanzhang County, Xiangyang City. The center mileage is DK451+786, and starting and ending mileage is DK449+037~DK454+535. The total length of Gaojiaping tunnel is 5498m, and the maximum buried depth is about 320m. The tunnel adopts two-way tunneling at the entrance and exit.

Project Overview

Catalog Detail Information
Project Duration: August 2017 – December 2017
Service Scope: Anchoring materials, anchoring rigs, and on-site technical services
Application: Pre-support with pipe-roofing for railway tunnel
Application Structure: Self-drilling rock bolts used as pipe umbrella system
Quantity Consumption: About 5,000m
Geological Conditions: Grade-V surrounding rocks in some locations are mainly moderately weathered shale, with soft rock, broken rock mass, and poor self-stability. The lining type is Vcw composite lining. As a ridge-crossing tunnel, the overlying soil on the slope is thin, the bedrock is partially exposed, and the surface is mostly cultivated as dry land.

Questions and Challenge

According to geological conditions, full-face excavation was adopted, and the original design adopted steel flower pipes as pipe-roofing. However, during construction, it was found that it was extremely difficult to make a hole after drilling under a broken rock. The construction party has tried every possible means, but it’s still unable to insert into the hole, resulting in project suspension.

pipe umbrella


The construction party adopted our suggestion to use R51 self-drilling anchor bars as pipe-roofing. The drill bit is ESF R51/76, and the drilling depth is 25m (each hole adopts a 4*5+3m arrangement mode).

The self-drilling rock bolt system consists of a hollow anchor bar, coupler, and drill bit. Grouting after drilling to achieve an anchoring effect and anchor bar can be used as a drill rod and reinforcement body.

pipe umbrella system

Construction Process

Materials prepared → Survey lofting→ Drilling jumbo in place → Connect hollow anchor bar and drill bit → Percussive rotary drilling→ Couple next anchor bar → Repeated drilling and grouting → Drilling completion → Grouting →Enter into next circle → Installation completion

Construction Equipment

Drilling Rig: ZYS113 three-boom drilling jumbo

Construction Efficiency

High efficiency, net drilling time is about 1m/min