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Fate and Transport in the Subsurface
Published in Benjamin Alter, Environmental Consulting Fundamentals, 2019
The materials in the subsurface generally fall into two categories: bedrock and soils. Bedrock consists of either igneous, sedimentary, or metamorphic rock. Igneous rocks originate from cooling magma that has welled up from deep within the earth’s crust, or from cooling lava from volcanoes at the surface of the earth. Sedimentary rocks are formed by the consolidation of sediments by the removal of water from their pore structure, usually due to the pressure of overlying sediments or dessication at or near the surface, or through chemical or biological activity, as in the case of limestone. Metamorphic rocks are created by changing the molecular structure its component minerals by the application of heat and pressure to igneous or sedimentary rocks.
Foundations
Published in Alan J. Lutenegger, Soils and Geotechnology in Construction, 2019
In some projects where the depth to good bedrock is relatively shallow and the expected loads may be high, it is often more feasible to place drilled foundations in the rock. A drilled shaft installed to produce load capacity in rock is sometimes referred to as a “rock socket” and is typically embedded 1.5 to 3 shaft diameters below the top of sound rock. Depending on the type of rock, special drilling equipment may be needed, including rock-roller bit drills or coring tools, as shown in Figure 6.48. In soft rock, such as clay shales or mudstones, traditional auger-drill tools are used to create the rock socket. The capacity will be dependent on the characteristics of the rock and the geometry of the foundation. Design procedures for end bearing of drilled shafts in rock have been presented by Zhang and Einstein (1998).
Strategic Issues in Environmental Remediation
Published in Timothy J. Havranek, Modern Project Management Techniques for the Environmental Remediation Industry, 2017
Subsurface earth materials can be placed into two broad classifications: unconsolidated materials and consolidated bedrock. In general, unconsolidated material refers to the loose soil materials which result from the erosion of bedrock. These loose materials include gravel, sand, silt, and clay. Previously excavated materials and construction debris can also be included in the category of unconsolidated materials. Consolidated bedrock includes (1) sedimentary rocks such as shale, sandstone, and limestone; (2) igneous rocks such as granite; and (3) metamorphic rocks such as slate and marble.
Improved landslide susceptibility mapping using unsupervised and supervised collaborative machine learning models
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2023
Chenxu Su, Bijiao Wang, Yunhong Lv, Mingpeng Zhang, Dalei Peng, Bate Bate, Shuai Zhang
The geomorphic features of the study area are largely determined by the development of complex faults, folds, structural fissures, etc. The altitude of the mountains is generally between 1000 and 3000 m, and the relative elevation difference of the deep, precipitous valley is about 1000. Determined by the geological structure, the mountains mostly have NE-SW orientation. The area features significant river incision phenomena and generally “V”-shaped valleys. The bedrock primarily consists of magmatic rock and metamorphic rock. The study area is highly prone to rockfalls, landslides and debris flows. The lithological properties include a composition of mainly diorite, medium fine-grained granite and alluvium. The fairly steep topography of the study area is due to the hard rocks. Meanwhile, on the west of the study area starting from the Maoxian–Wenchuan fault, the lithological composition turns into phyllite, sandstone and limestone. Such a peculiar lithological contrast contributes to the disparate landslide scenarios, leading to explicit landslide boundaries. Strongly weathered rock slopes with outward inclined joint sets are widely spread on both sides of the PR303 in the study area, particularly on the upper part of gullies.
Unseen and overlooked: methods for quantifying groundwater abstraction from different sectors in a data-scarce region, British Columbia, Canada
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2019
Within the mapped region, aquifers generally fall into six aquifer types which describe unconsolidated sand and gravel aquifers, and bedrock aquifers (Wei et al. 2014; Wei et al. 2007). Average aquifer size ranges by type from 4 – 27 km2, and are generally constrained by the mountainous terrain and limited to valleys and floodplains. Unconsolidated aquifers are generally of glacial or fluvial depositional origin, mainly composed of sand and gravel material with small discontinuous silt or clay layers, in particular along streams of lower energy (Wei et al. 2014). The bedrock geology of the Cordillera is complex and regionally varying due to the regions geologic, tectonic, and volcanic history (Wei et al. 2014). Despite the complexity of the bedrock material, bedrock permeability exists primarily due to the development of fractures and faults from mechanical weathering processes and/or unloading causing relatively high fracture density (Welch and Allen 2014) and the permeability is often anisotropic as the fractures and faults have specific orientations (Wei et al. 2007). Bedrock aquifers can be composed of fractured sedimentary rock, fractured igneous intrusive, metamorphic, or volcanic rock.
Using water stable isotopes for tracing surface and groundwater flow systems in the Barlow-Ojibway Clay Belt, Quebec, Canada
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2018
Nathalie Rey, Eric Rosa, Vincent Cloutier, René Lefebvre
The regional geological framework, as conceptually represented in Figure 2, is described in detail in numerous previous studies (Veillette 1986, 1987a, 1987b; Veillette et al. 2004; Paradis 2005, 2007; Thibaudeau and Veillette 2005; Nadeau et al. 2015, 2017; Cloutier et al. 2016) and it is thus only briefly presented here. Table 1 provides a summary of the hydrological domains (atmosphere, surface, subsurface), components (precipitation [snow, rain], surface water, groundwater, springs) and aquifers (granular [unconfined and confined], fractured rock [unconfined and confined]) that are discussed in this study, in relation with the main geological units of the region. The bedrock of the study area (geological unit A in Figure 2) is composed of a wide variety of igneous, metamorphic and metasedimentary rocks of the Abitibi and Pontiac sub-provinces, both components of the Superior Geological Province. Groundwater flow within the bedrock is controlled by the architecture of structural discontinuities. Cloutier et al. (2016) estimated hydraulic conductivities ranging between 10−9 and 10−4 m/s for this unit. However, there are currently insufficient data to propose a regional-scale interpretation of bedrock hydrogeological characteristics based on structural interpretations. Nevertheless, Rouleau et al. (1999) proposed that groundwater flow within the bedrock of the study area is most likely restricted to depths shallower than 75 m where sub-horizontal fractures are sufficiently interconnected to allow significant groundwater flow. Most of the domestic wells of the region are withdrawing groundwater from this unit using wells that are cased through surficial sediments and open across the bedrock.