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Groundwater Problems for Excavations in Rock
Published in Pat M. Cashman, Martin Preene, Groundwater Lowering in Construction, 2020
Depending on the nature of the bedrock and the geological movements that gave rise to faulting, the hydraulic properties of faults can vary widely: Faults in hard or brittle rocks can result in intensely fractured zones (sometimes known as ‘fault breccia’) that can be of significantly greater permeability than the host rock (Figure 8.18a).Many faults contain ‘clay gouge’ – a very low-permeability material created from the host rock by the stress and disturbance of the faulting. This can cause a fault to act as a low-permeability feature, which can form a barrier to horizontal groundwater flow (Figure 8.8a). Vertical displacement of alternating higher- and lower-permeability beds can offset the beds, impeding groundwater flow along the beds (Figure 8.8b).
A multi-disciplinary approach to active fault rupture risk characterization: 3D geological modelling of the Willunga fault, Mt Bold Dam, South Australia
Published in Jean-Pierre Tournier, Tony Bennett, Johanne Bibeau, Sustainable and Safe Dams Around the World, 2019
S.R. Macklin, Z. Terzic, J.F. Barter, P. Buchanan, M. Quigley
The upper 9 m of the borehole encountered a thickly bedded sandstone/quartzite inferred to be the Stoneyfell Quartzite. Beneath that interbedded phyllite and quartzite in varying proportions was encountered. Between 46 and 75 m core depth four significant zones in the core were inferred to be related to strands of the Willunga Fault system. These comprised crush seams of iron stained quartzite and phyllite; highly fractured and weathered phyllite; and, a one metre apparent thickness “fault breccia” comprising phyllite and quartzite clasts in a high plasticity clay matrix. Optical and acoustic downhole tele-viewer geophysical logging indicated that the surface projection of the fault structures could be correlated with the trace of a strand of the east dipping Willunga Fault.
Investigation and Exploration of Dam and Reservoir Site
Published in Suchintya Kumar Sur, A Practical Guide to Construction of Hydropower Facilities, 2019
Before going through the details of the investigation process, it is essential to clarify and define some special and extraordinary geological features to the readers, especially those who are students, to have a clear understanding of the adverse geological constraints/problems. These features, if remained unidentified and untreated, may pose a threat to the stability of the dam. Joints: Fractures along which particularly no displacement of rocks has occurred. A crack produced in the rock under the action of internal forces during its cooling and drying.Fault: Fractures along which the rocks on one side have been displaced relative to those on the other side. A fault is a fracture surface along which rocks have been relatively displaced in both directions vertically and horizontally. An earthquake may occur due to the sudden movement of a big fault.Fault breccia: Angular or sub angular rock fragments produced by fracture and grinding during faulting and distributed within or adjacent to the fault plane that will have very low bearing capacity.Cleavage: Fissures that develop in rocks under the action of external tectonic factors.Fissures: A long, narrow opening that has occurred in the rock by cracking or dislocation.Seam is a thin layer or strata of rock, coal or mineral, etc.Bedding: Some rocks such as sedimentary and metamorphic rocks occur in the form of layers or strata bounded by parallel surface.FoliationCavitiesDykeSinkhole
Numerical Modeling of Reverse Fault Rupture and Its Impact on Mountain Tunnels
Published in Journal of Earthquake Engineering, 2023
Zhen Wang, Mi Zhao, Jingqi Huang, Zilan Zhong, Xiuli Du
The second component specifies the energy dissipated during failure. The energy dissipated by the damage process is termed as fracture energy (Gf) and equal to the area under the cohesive law, as shown in Fig. 5. The fracture energy of fault rocks varies with lithology. Bazant and Kazemi (1990) reported that Gf for different types of rocks ranges between tens to hundreds of newtons per meter. The fault rocks in region affected by the damage zone primarily consist of limestone, basalt, cataclasite, and fault breccia. Their strength and elastic modulus are lower than that of intact rock. In this numerical study, the fracture energy actually represents the energy required for the destruction of the cohesive element, used to simulate the fault core. Owing to the poor petrophysical properties of the rock masses in the fault core, Gf was assumed as 5–50 N/m for the parametric study.
Hundalee Fault, North Canterbury, New Zealand: late Quaternary activity and regional tectonics
Published in New Zealand Journal of Geology and Geophysics, 2023
David J. A. Barrell, Mark W. Stirling, Jack N. Williams, Katrina M. Sauer, Ella J. van den Berg
The Birches-1 and the Oaro coast fault exposures are respectively 2 km north-northeast and 6 km northeast of the Okarahia trench site (Williams et al. 2018). The coast bedrock exposure is no more than ∼2 m wide, consisting of intensely crushed greywacke on the northern side of the near-vertical 2016 rupture plane. The Birches-1 exposure is documented in figure 8 of Williams et al. (2018). The exposure is on the west (upthrown) side of the 2016 rupture plane and comprises a ∼5 m wide zone of gouge and brecciated greywacke, including several discrete <10 cm thick gouge zones dipping 60° to the northwest. West of the breccia, highly fractured greywacke comprises the ∼55 m wide remainder of the exposure. Warren (1995) drew the Hundalee Fault (i.e. the bedrock fault) ∼0.5 km farther east, where the Birches-3 fault scarp was formed in 2016. Thus the ∼5 m wide fault breccia at Birches-1 is probably not a full characterisation of the Hundalee Fault’s bedrock structure.
Segmentation and fault–monocline relationships in the Lapstone Structural Complex, Sydney Basin, New South Wales
Published in Australian Journal of Earth Sciences, 2023
C. L. Fergusson, P. J. Hatherly
In the Lapstone–Leonay area, the Hawkesbury Sandstone and overlying units are well exposed in abundant road cuttings as well as natural exposures. Here the structure of the Lapstone Monocline is well known. Detailed geological maps of the area were published by Branagan and Pedram (1990) and Fergusson et al. (2011). An updated map including mapping by Carter (2011), Hatherly (2020) and the authors is given in Figure S11. The structure is dominated by a simple east-facing monocline (Figure S12), although the lower limb is not flat-lying but dipping 7–8°E. Detailed mapping of the distribution of the Rickabys Creek Gravel shows that this unit has been folded along the face of the monocline (Hatherly, 2020), supporting observations of Branagan and Pedram (1997), and has not formed as several uplifted alluvial-cut terraces, as has been suggested (Pickett & Bishop, 1992). The recognition of Londonderry Clay on the Old Great Western Highway Track (Figure S12d) also indicates that this unit has been uplifted and folded (Carter, 2011; Gale, 2021). Local fault breccia and fractures have been documented by Branagan and Pedram (1997) in the Lapstone area, but no significant fault offset has been demonstrated associated with the Lapstone Monocline. South of Lapstone to Nortons Basin, the Lapstone Monocline has a wide, low-dipping, central limb and is well displayed in reflection seismic line CE88-214 (Figure 8a).