Compositional Features and Swelling Potential of Two Weak Rock Types Affecting Their Slake Durability

Abstract

Weak and weathered rocks are well known for their sensitivity to changes in moisture content. Degrading behavior is common in weak rocks with moisture-sensitive mineral components and present numerous stability problems. The slake durability is a measure of the resistance to weakening and disintegration of rock materials which quantitatively distinguishes durable from non-durable rock materials. Several rock material parameters interact on the process of disintegration when exposed to cyclic moisture changes, whereby the content of clay is believed to play a major role. This manuscript evaluates the overall material composition of flysch and serpentinite rocks cored from the wall of the shotcrete-lined headrace tunnel of a hydropower project, including minerals, structure, porosity, the presence of micro-discontinuities, and swelling potential, and links these properties to the slake durability. Further, the different methods used to assess compositional features affecting the durability of weak rocks are evaluated and discussed. The manuscript argues that the mineralogical composition and microstructures present in the intact rock and the content of moisture-sensitive constituents, as swelling clays, control the long-term durability of weak rock material. It is demonstrated that XRD assessments are not sufficient to detect the content of brucite and swelling components, and that methods as thin section and SEM analyses should be carried out in the assessment of weak and weathered rock mass.

Study on Expansion Characteristics and Expansion Potential of Gypsum Rock

“…The ultimate expansion force [13,14,39] is not only the most important index for judging the expansion potential of expansive soil but also the most important parameter for structural design. No matter the reason for the expansion, its ultimate expansion force corresponds to the same expansion potential grade; the mineral composition and expansion mechanism only affect the expansion rate and do not affect the expansion potential grade.…”

“…At present, expansive rocks are divided into two categories [13][14][15][16][17][18]: the first one is caused by chemical expansion reaction, the mechanism is complex, and the time is long (such as anhydrite and glauberite); the second one is caused by hydrophilic minerals, and the expansion of this type of rock is cyclically reciprocated under the action of water absorption and loss (such as mudstone and tuff) [19]. The main indicators for judging the expansion potential of expansive rocks include water content [20][21][22], viscous material content [9,15,[23][24][25], free expansion rate [25], ultimate expansion rate [26], dry saturated water absorption rate [27], and ultimate expansion force [9,25].…”

“…Huang et al [38] use environmental factors to guide machine self-learning to predict landslides. Therefore, in this paper, the free expansion rate test, the ultimate expansion rate test, the ultimate expansion force test, and the BET-specific surface area test were carried out on the gypsum rock from the Wuzhishan Tunnel; at the same time, based on the existing methods [13,14,18,30], the expansion potential of gypsum rocks can be quickly and accurately predict by combining the ultimate expansion rate and specific surface area indexes.…”