The classification of mudrocks for engineering purposes

Abstract

Summary A classification of mudrocks for engineering purposes was considered necessary in order to improve the common qualitative use of a variety of geological terms. There has been a lack of agreement between authors on the precise definition of these terms. Mudrock is defined as a fine- to very finegrained, siliciclastic sediment or sedimentary rock. Quantitative boundaries for this group of rocks are proposed using meaningful soil and rock index parameters, at changes in mechanical or material behaviour. The basic division is between fine-grained engineering soil, non-durable rock and durable rock, at compressive strengths of 0.6 and 3.6 MN/m 2 . The mudrock soils are classified according to the British Standard Classification of Soils (BSCS) with the addition of the term silty clay. Fissile or anisotropic rocks are termed shales, including clayshales where non-durable. Isotropic ones are classed as siltstones, mudstones and claystones according to their quartz contents. Tectonically induced strength and fabric anisotropy can be important and may result in slaty shales where the rock microfabric has been well aligned. An upper compressive strength limit of 100 MN/m 2 is proposed to distinguish diagenetic mudrocks from their metamorphic equivalents.

Numerical Study of the Effect of Verification Core Hole on the Point Bearing Capacity of Drilled Shafts

“…The theoretical bearing capacity factor of 4.5 corresponds to the UCS of approximately 0.82 MPa in Figure 2-17. This UCS value is slightly above the lower limit (0.6 MPa) of UCS for non-durable rock or clay shale (Grainger, 1984;Morgenstern and Eigenbrod, 1974). This observation is intriguing because the key characteristic of rock (not soil) is the existence of fractures or fissures and their influences on the overall behavior of rock mass.…”

“…List of Tables ....................................................................................................... xiii List of Figures ..................................................................................................... xvi CHAPTER 1: INTRODUCTION ........................................................................1 Table 2-1 Typical attributes of classification system for in situ rock (Deen, 1981) ........... Table 2-2 Field estimates of unconfined compressive strength (modified from Hoek and Brown, 1997) ........................................................................................................ Table 2-3 Geological classification of mudrocks (Blatt, 1982) ........................................ Table 2-4 Suggested geological classification of argillaceous materials (Gamble, 1971) Table 3-17 Cation Exchange Capacity of typical clay minerals (Gray et al, 1980) ........ ....................................................................................................... xiv Table 4-2 Back calculated UCS, and constant m ............................................................ Table 5-1 Gamble's Slake Durability Classification (Gamble, 1971) ............................ Table 5-2 Engineering classification of intact rock on the basis of UCS (Deere, 1968) Table 5-3 Engineering classification of intact rock on the basis of modulus ratio (After Deere, 1968) ....................................................................................................... (Hawkins, 1998) ........ (Mead, 1938;Underwood, 1967). ............. (Grainger, 1984) ... (Schmitt et al, 1994) . (Botts, 1998) .....................................................................…”

“…In addition, it was found that the slake durability index is influenced by clay mineral content, calcite content, and the presence of microcracks (Russell, 1982). (Grainger, 1984) The non-durable mudrock is divided into five members as shown in Figure 2-8.…”

“…Figure 2-8 Classification of non-durable mudrock (Grainger, 1984) 2.3 WEATHERING Clay shales are notorious materials that are very sensitive to the change in moisture content owing to the abundance of clay content. In such formations,…”

Reduction of lateral pressure propagation due to dissipation into ambient mudrocks during geological carbon dioxide storage

“…It is common for storage studies to focus only on the target formation and to exclude ambient mudrocks, defined as a fine‐ to very fine‐grained siliciclastic sediments or sedimentary rocks [ Grainger , ] bounding the reservoir because low‐permeability mudrocks prevent vertical migration due to high capillary entry pressure. However, most regional aquifers are not closed and also the overlying and underlying mudrocks are not perfectly impermeable [ Neuzil , ; Dewhurst et al ., ].…”