Anchorage performance of a high-pressure pre-tightening resin anchor with a compressed grouting body.

Jiansheng Tian,Li Hu,Ming Dao

doi:10.1371/journal.pone.0171653

Abstract

Supports for deep mine roadways located in soft surrounding rock face several problems: difficulty in applying pre-tightening force, low bearing capacity, and poor initial support. To solve these problems, this study proposes a high-pressure pre-tightening resin anchor with a compressed grouting body for use in soft and fractured rock surrounding a deep roadway. Using model experiments, we analyzed the anchorage performance of the proposed anchor and a conventional tensile-type anchor for three different values of the elastic modulus of the surrounding rock. The results showed that regardless of the surrounding rock type, the peak micro-strain (642–541) and displacement (6.09–6.5 mm) at the pull-out end of the proposed anchor were always smaller than the peak micro-strain (1433–1105) and displacement (8.77–9.2 mm) at the pull-out end of the conventional anchor. Furthermore, as the anchor’s pre-tightening force increased from 20 kN to 120 kN, the anchor’s strain remained concentrated over a length of 0.4 m from the bearing end. Compared with conventional tensile-type anchors, the proposed high-pressure pre-tightening resin anchor with a compressed grouting body has a higher ultimate bearing capacity, allows the grouting length to be decreased to 0.4 m, and provides initial support resistance.

Highlights

As a rule, coal mining proceeds from a shallow stratum to a deep stratum
A grouting anchor or a resin anchor cannot achieve the support required for both a high pre-tightening force and rapid initial support while simultaneously filling in the crevices in soft and fractured surrounding rock [13,15,16,17]. To overcome these deficiencies and to improve the design of supports for deep roadways in soft surrounding rock, this study proposes a new type of anchor supporting method that is suitable for soft and cracked surrounding rock: a high-pressure pre-tightening resin anchor with a compressed grouting body
The following conclusions can be drawn from the current study: 1. The proposed high-pressure pre-tightening resin anchor with a compressed grouting body is a new bolting technology that provides rapid, high-strength pre-tightening for initial

Summary

Introduction

Coal mining proceeds from a shallow stratum to a deep stratum. When deep roadways are used for mining, the crustal stress significantly increases with increasing mining disturbance intensity. Before a pre-tightening force can be applied to the anchor, the grouting body must first be cured and allowed to reach a certain strength This process generally lasts 7 days, and this length of time is a severe disadvantage for deep roadways, which require timely and sufficiently strong support during the initial excavation stage. The proposed anchor, for which invention patent ZL 2014 1 0124180.4 has been obtained, represents a new type of bolting technology This anchor combines the rapid coagulation of resin with the excellent bearing capacity of cement mortar after coagulation to provide a rapid, high-strength pre-tightening force during the initial stage and continuous stable anchorage thereafter. This study compared and analyzed the strain distributions of the anchors, determined the trends in the bearing capacity for different pre-tightening forces and different values of the elastic modulus of the surrounding rock, and verified the validity of the theoretical analysis

Design of the experimental model

Conclusions