Estimate of Uniaxial Compressive Strength of Hydrothermally Altered Soft Rocks Based on Strength Index Tests

Masanori Kohno,Hiroyuki Maeda

doi:10.4236/gm.2018.82002

Abstract

The purpose of this study was to clarify the relationships between results of index tests and uniaxial compressive strength (UCS) in hydrothermally altered soft rocks of the Upper Miocene, which are typical of the soft rock found in northeastern Hokkaido, Japan. Index tests were performed using point load testing machine and needle penetrometer with irregular lump specimens under forced-dry, forced-wet, and natural-moist states. The relationships between irregular lump point load strength (IPLS) index and UCS, and needle penetration (NP) index and UCS were “UCS = approximately 19 IPLS index” and “UCS = 0.848 (NP index)0.619”, respectively, in soft rocks with a UCS below 25 MPa. These relationships could be applied to on-site tests of rocks with natural moisture content. The UCS could be calculated from IPLS and NP tests on soft rocks only when UCS was below 25 MPa, using the equations obtained as a result of this study.

Highlights

The strength of rocks is generally evaluated based on uniaxial compressive strength (UCS)
The UCS could be calculated from irregular lump point load strength (IPLS) and needle penetration (NP) tests on soft rocks only when UCS was below 25 MPa, using the equations obtained as a result of this study
The following is a summary of our findings related to the UCS estimates of hydrothermally altered soft rocks from northeastern Hokkaido, Japan, based on our IPLS test and NP test results

Summary

Introduction

The strength of rocks is generally evaluated based on uniaxial compressive strength (UCS). Rock core pieces for UCS tests cannot always be obtained from outcrops of faulted, jointed, or heavily crushed rock masses. In these cases, the point load strength (PLS) or needle penetration (NP) test is a conve-. Provided that UCS can be estimated from a PLS or NP value, PLS and NP tests are more convenient and cheaper

Objectives

Methods

Results

Conclusion