Coal Measures mudrocks: composition, classification and weathering processes

Abstract

British Coal Measures mudrocks are dominantly non-marine, mature sediments with a high average clay minerals content of over 75%. A geological classification based on quartz content does not differentiate the dominant durable mudrocks from the non-durable types and overconsolidated clays in the formation. A uniaxial compressive strength greater than 3.6 MN/m 2 with a three cycle slake durability value of over 60% is suggested as an appropi'iate division between durable and non-durable mudrocks of this age. Physical breakdown, which acts as a control on chemical weathering triggered by pyrite oxidation, is considered to be governed by incidence of sedimentary structures, slaking and expandable mixed-layer clay content.Shear strength reduction during post-glacial weathering can be significant. A tentative fully weathered effective stress peak strength for the weakest mudrocks and clays is deduced to be q~'= 22 ~ (c'=0). Colliery tip investigations indicate that chemical weathering effects on the shear strength of the mudrocks are small. A diagenetic rank factor applies both to peak shear strength and slake durability of mudrocks excavated from UK coal mines.

Durability Assessment of Clay-Bearing Soft Rocks By Using New Decay Index

“…The slake durability test is used widely for evaluation of slaking behavior of rocks as a result of wettingdrying processes [7][8][9][10][11][12][13]. However, due to mechanical breaks occurring during the test, immersion of samples in water for only 10 min and the assumption that fragments larger than 2 mm are durable, the slake durability test has some limitations [14]. Many researchers have tried to overcome these limitations.…”

“…Many researchers have tried to overcome these limitations. For improving time limitation Taylor [14] and Gokceoglu et al [9] suggested that a 3 and 4 cycle test is more reliable test that 2 cycle test to determine durability. A valuable work was done by Erguler and Shakoor [15] to overcome the problem with standard test mesh size (2 mm).…”

Degradação hidromecânica de rochas brandas silto-argilosas

“…Taylor (1988) destaca que a desintegração física é controlada por três fatores principais: (a) a expansão de minerais argilosos em razão da absorção de água, (b) degradação (secagem e umedecimento, também conhecida como quebra ao ar) e (c) presença de descontinuidades. Simões (1987) Neste trabalho, o termo degradação hidromecânica refere-se aos processos físico-químicos que ocorrem na atenuação dos parâmetros geomecânicos da rocha intacta, em consequência do processo físico-cíclico de umedecimento e secagem.…”

“…Segundo Taylor (1988), quando um fragmento lamítico é desidratado, o ar é puxado para dentro de vazios e capilares e a alta (negativa) pressão de sucção é desenvolvida. No processo reverso, o ar aprisionado é pressurizado enquanto a água é puxada para a rocha argilosa por capilaridade.…”

“…Relativamente comum em rochas sedimentares argilosas, a pirita ocasiona a desagregação desses litotipos em razão do aumento de volume (PEJON, 2000;TAYLOR, 1988;POTTER et al, 2005). Outro sulfeto muito frequente em rochas argilosas é a pirrotita (FeS2), geralmente confundida em análises de DRX com a pirita, porém identificada quando da realização de MEV ou quando visível a olho nu em função do seu magnetismo.…”