Strength Restoration of Cracked Sandstone and Coal under a Uniaxial Compression Test and Correlated Damage Source Location Based on Acoustic Emissions

PLoS One. 2015 Dec 29;10(12):e0145757. doi: 10.1371/journal.pone.0145757. eCollection 2015.

Abstract

Underground rock masses have shown a general trend of natural balance over billions of years of ground movement. Nonetheless, man-made underground constructions disturb this balance and cause rock stability failure. Fractured rock masses are frequently encountered in underground constructions, and this study aims to restore the strength of rock masses that have experienced considerable fracturing under uniaxial compression. Coal and sandstone from a deep-buried coal mine were chosen as experimental subjects; they were crushed by uniaxial compression and then carefully restored by a chemical adhesive called MEYCO 364 with an innovative self-made device. Finally, the restored specimens were crushed once again by uniaxial compression. Axial stress, axial strain, circumferential strain, and volumetric strain data for the entire process were fully captured and are discussed here. An acoustic emission (AE) testing system was adopted to cooperate with the uniaxial compression system to provide better definitions for crack closure thresholds, crack initiation thresholds, crack damage thresholds, and three-dimensional damage source locations in intact and restored specimens. Several remarkable findings were obtained. The restoration effects of coal are considerably better than those of sandstone because the strength recovery coefficient of the former is 1.20, whereas that of the latter is 0.33, which indicates that MEYCO 364 is particularly valid for fractured rocks whose initial intact peak stress is less than that of MEYCO 364. Secondary cracked traces of restored sandstone almost follow the cracked traces of the initial intact sandstone, and the final failure is mainly caused by decoupling between the adhesive and the rock mass. However, cracked traces of restored coal only partially follow the traces of intact coal, with the final failure of the restored coal being caused by both bonding interface decoupling and self-breakage in coal. Three-dimensional damage source locations manifest such that AE events are highly correlated with a strength recovery coefficient; the AE events show a decreasing tendency when the coefficient is larger than 1, and vice versa. This study provides a feasible scheme for the reinforcement of fractured rock masses in underground constructions and reveals an internal mechanism of the crushing process for restored rock masses, which has certain instructive significance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acoustics*
  • Arsenites*
  • Coal*
  • Compressive Strength*
  • Engineering
  • Materials Testing*
  • Stress, Mechanical

Substances

  • Arsenites
  • Coal
  • arsenite

Grants and funding

This work was supported by The Fundamental Research Funds for the Central Universities (NO. 2014XT01), received by NZ, the role of this funding is to provide financial support for our research in this manuscript, it also has data collection and analysis function. This work was also supported by the National Natural Science Foundation of China (51274193), received by NZ, the role of this funding is to provide financial support for possible publishing fees concerning the research, and it had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Lastly it was supported by the Program for Changjiang Scholars and Innovative Research Team in University (IRT_14R55), received by NZ, this funder provides supporting money for all members who joining the research, like transportation fees, accommodation fees, service fees, and the like, this funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.