Subsurface Excavations

Military and civilian applications large-scale earth moving, subsurface excavation, mineral extraction from underground... 

The subsurface excavation of Metro tuimel is located in mengjiacun, which is a part of Beijing Subway Line 10. There are 4 existing residential buildings completed in 1990 over the tunnels (left and right line). The spatial relationships between them are shown in Figure 1 3. 

If you work for a utility that is covered by the Occupational Safety and Health Administration (OSHA), there are specific regulations (29 Code of Federal Regulations 1926 Subpart P) that govern most subsurface excavations. 

Some of the larger projects involving subsurface excavations are those that involve construction of tunnels to move water or wastewater. See if you can find at least one such project that either is ongoing or has just been completed, and describe it. 

Medium to high viscosity particulate suspensions is injected into the ground between a subsurface excavation and a structure in order to negate or reduce settlement of the structure due to ongoing excavation. 

Principal Option for Containment/ Recovery Excavation Vacuum extraction Temporary cap/cover Hydraulic modification No action Groundwater pumping Subsurface drains Hydraulic barriers Low permeability barriers No action Overflow/underflow containment (i.e. oil booms) Run off/run on control Diversion/collection No action Capping/ nsulation Operations modifications Gas collection/removal No action... 

Hematite in the soil is concentrated in spherules and their fragments, which are abundant on nearly all soil surfaces. Several trenches excavated using the rover wheels showed that the subsurface is dominated by basaltic sand, with a much lower abundance of spherules than at the surface. Olivine-bearing basaltic soil is present throughout the region. At several locations along the rover s traverse, sulfate-rich bedrock outcrops are covered by no more than a meter or so of soil. 

Subsurface drains function like an infinite line of extraction wells, and can be used to contain and remove a plume or to lower the groundwater table (Figure 16.12). They are more cost-effective than pumping for shallow contamination problems at depths of less than 12 m (40 ft). Depths may be increased if the site is stable, if the soil has a low permeability, and if no rock excavations are encountered. 

Soil auguring can be applied to a wide variety of sites, including wood treatment facilities, oil and gas production units, bulk storage sites, pipeline, manufactured gas plants and other sites contaminated with residual oils, petroleum products, VOCs, semi-VOCs, and other contaminants. This technology is also applicable to sites with complicated, heterogeneous subsurface geology that can render more traditional approaches ineffective, or at sites where excavation is not cost-effective or practical. 

The site is a carwash facility located in the city of Escondido, in southern California. A sequence of investigative and remedial activities has been performed since 1987 that established the presence, nature, and extent of subsurface hydrocarbons derived from former USTs. Since conducting these activities, the former USTs have been removed and the hydrocarbon-affected soil surrounding the USTs has been excavated. Additionally, all potentially recoverable LNAPL (i.e., gasoline) has been removed, leaving only residual hydrocarbon saturation (i.e., smear zone) in place at the water table. Subsequent pump-and-treat activities have reduced dissolved BTEX concentrations to asymptotic levels (Figure 13.9). 

Subsurface obstructions and dense soil or waste layers may cause tool rotation to halt. Shallow obstructions (<20 ft deep) should be excavated prior to applying the MecTool system. 

Molasses has been used as a nutrient source to encourage the anaerobic bioremediation of soil and groundwater contaminated with metals, explosives, and chlorinated solvents. The nutrient source can be added to excavated, screened soil, or injected directly into the subsurface via wells. Several vendors and developers have conducted bench-, pilot-, and full-scale demonstrations of the technology. Some of the molasses technologies are commercially available. 

This technology is able to remove soil contaminants without the need to excavate, retrieve, and perform ex situ treatment. Electrical heating can be used to heat soil and remove contaminants hundreds of feet underground. Also, heating soil improves subsurface conditions for biodegradation of residual contaminants. 

We need to make a decision related to the disposition of soil that has been excavated from the subsurface at a site with lead contamination history. Excavated soil suspected of containing lead has been stockpiled. We may use this soil as backfill (i.e. place it back into the ground), if the mean lead concentration in it is below the action level of 100 milligram per kilogram (mg/kg). To decide whether the soil is acceptable as backfill, we will sample the soil and analyze it for lead. The mean concentration of lead in soil will represent the statistical population parameter. 

We use sampling grids mainly for surface soil sampling, however, it is not unusual to place soil borings and collect subsurface samples on a grid pattern. Grids are also used for soil sampling from the bottom and sidewalls of excavation pits and trenches. 

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