Experimental Investigation of Dynamic Compression Mechanical Properties of Frozen Fine Sandstone

Jiehao Wu,Qi Zong,Ying Xu,Haibo Wang

doi:10.1155/2020/8824914

Abstract

Aiming at the dynamic mechanical properties of weakly cemented fine sandstone in the rich water-bearing strata in western China under dynamic loading, a 50 mm rod diameter separation Hopkinson pressure bar (SHPB) test was used to study the Paleogene fine sandstone in a coal mine in Ningxia. The system carried out the impact compression tests of −15°C, −20°C, and −30°C and the average strain rate of 28 s−1–83 s−1 and obtained the dynamic compressive strength of the frozen fine sandstone specimens under different test conditions. The strain curve and the fracture morphology were analyzed for the relationship between dynamic peak stress, peak strain, dynamic strength growth coefficient (DIF), and fracture morphology and strain rate. The results show that the peak stress of frozen fine sandstone increases from the decrease of freezing temperature under the same average strain rate. The peak stress of the specimen increases from the increase in the average strain rate of the same freezing temperature. The failure modes of specimen are mainly divided into axial splitting tensile failure and compression crushing failure. To the splitting tensile failure and the compression crushing failure, the main factors determining the two failure modes are the strain rate, while the temperature affects the severity of the impact damage. In the load strain rate and temperature range, the DIF of the frozen fine sandstone is linearly correlated with the strain rate, and the lower the temperature, the slower the growth rate of the DIF.

Highlights

In the construction of coal mine shafts in western China, Paleogene fine sandstone is often encountered, which disintegrates in water to form quicksand, seriously endangering the safety of workers and equipment at the working face [1, 2]. e freezing method is widely used in shaft construction in water-rich strata due to its effective water shutoff [3,4,5]. e frozen bedrock section of the shaft is usually constructed by drilling and blasting
The Paleogene fine sandstone is mostly nondiagenetic or slightly semidiagenetic and has poor cementation. e study of the dynamic mechanical properties of frozen fine sandstone under a dynamic load is of great value of practical applications because it ensures the safety of the frozen sidewalls and guides drilling and blasting construction
According to the basic principle of the separation Hopkinson pressure bar (SHPB) test, the data were processed using the three-wave method to obtain the mechanical parameters, such as the dynamic stress and strain, of the frozen fine sandstone specimens. σd is the dynamic peak stress and εf is the corresponding strain of the specimen. e dynamic increase factor (DIF) is defined as the ratio of the dynamic compressive strength to the static compressive strength of the specimen, which represents the increase in the compressive strength of the specimen under the impact, that is, DIF σd, σs where σd is the dynamic compressive strength of the specimen and σs is the static compressive strength of the specimen

Summary

Introduction

In the construction of coal mine shafts in western China, Paleogene fine sandstone is often encountered, which disintegrates in water to form quicksand, seriously endangering the safety of workers and equipment at the working face [1, 2]. e freezing method is widely used in shaft construction in water-rich strata due to its effective water shutoff [3,4,5]. e frozen bedrock section of the shaft is usually constructed by drilling and blasting. Using freezing shaft construction in the Hujiahe Coal Mine in the Binchang Mining Area, Shaanxi, China, as the study area, Yang and Lv [6] experimentally studied the uniaxial and triaxial mechanical properties of the sandy mudstone in the main shaft and investigated the variation patterns of the strength and deformation properties under different temperatures and confining pressures. We used a Φ50 mm SHPB test device and a high-low temperature experimental chamber to make froze fine sandstone specimens at −15°C, −20°C, and −30°C. e impact compression tests were performed using an impact air pressure in 0.15 MPa, 0.25 MPa, and 0.3 MPa. e variations in dynamic peak stress, dynamic peak strain, failure morphology, and dynamic increase factor of frozen fine sandstone with temperature and strain rate are discussed and analyzed.

Impact Compression Tests of Frozen Fine Sandstone

Results and Analysis

C1-1 C1-3 C2-1 C2-2 C2-3 C3-1 C3-2 C4-1

Conclusions