True triaxial strength and deformability of the siltstone overlying the Chelungpu fault (Chi‐Chi earthquake), Taiwan

Abstract

[1] We conducted true triaxial compression tests to examine the effect of the intermediate principal stress (s 2 ) on brittle failure and deformability of the siltstone overlying the Chelungpu fault, Taiwan. For constant minimum stress (s 3 ) a pattern of increased strength (s 1 ) as a function of s 2 , unpredicted by common strength criteria, was observed. Strength data are well fitted by a Mogi-modified Nadai criterion relating the octahedral shear stress at failure to the mean normal stress on the induced shear fracture or fault. The induced fault strikes subparallel to s 2 and dips steeply in the direction of s 3 . Significantly, fault dip angle steadily increases as s 2 rises for unchanged s 3 . SEM inspection of tested specimens reveals only sporadic localized intergranular microcracks associated with the creation of the fault. The modulus of elasticity and the onset of dilatancy exhibit a similar behavior to that of s 1 , as they increase with s 2 when subjected to a constant s 3 .

Response of Castlegate sandstone to true triaxial states of stress

“…Chang and Haimson [2000], who examined amphibolite, noted that for constant s 3 , the s 1 required to fail a specimen increased with increasing s 2 . This behavior was also seen by Oku et al [2007] in a siltstone from the Chelungpu fault. In a review paper on the influence of s 2 , Haimson [2006] reports strength differences of 10% to 50% based on experiments conducted on a wide variety of rocks.…”

Introduction to Suggested Methods for Failure Criteria

“…Their results largely confirmed those obtained by Mogi (1971). Additional true triaxial testing also supported previous findings regarding the effect of the intermediate principal stress on the compressive strength of Long Valley, California, hornfels and metapelite, a Korean rhyolite, and several Taiwanese sandstones and siltstones Haimson 2005, 2007;Oku et al 2007;Haimson and Rudnicki 2010). The working group agreed to prepare suggested methods for the most known failure criteria applied to rock and to make recommendations about when each criterion may be applied, highlighting wherever possible the extent to which the effect of the intermediate principal stress is accounted for.…”

Recent Advances in Studies of the Strength of Rocks Under True Triaxial Compression Conditions / Postępy W Badaniach Nad Wytrzymałością Skał W Warunkach Prawdziwego Trójosiowego Ściskania

“…Loading on the third pair of sample faces (direction 3) is applied directly by hydraulic fluid inside the pressure vessel. Using rectangular prismatic samples 19 × 19 mm square and 38 mm high, Haimson and his fellow researchers studied the behavior of Westerly granite Chang, 2001), KTB amphibolite Chang, 2001;, Long Valley hornfels and (2), 9 -fixed platen (Mogi, 1971a(Mogi, ,b, 2006(Mogi, , 2012 metapelite , Taiwan Chelungpu Fault siltstone (Oku et al, 2007) and San Andreas Fault granodiorite (Lee & Haimson, 2011) under high σ 2 and high σ 3 conditions. For a detailed review of true triaxial test results obtained at the University of Wisconsin see Haimson (2006Haimson ( , 2011Haimson ( , 2012.…”