OasisLMS

Abstract: The CSO 52 project located in Lynchburg, VA, consist of constructing a new CSO storage Tunnel, two diversion structures, a tunnel dewatering pump station, an electrical building and appurtenant work. The upstream (CSO 52) and downstream (CSO 134) sites containing the diversion structures, pump station and electrical building, are located adjacent to Blackwater Creek. During intense rain events, the sites are exposed to significant flood risk. Soils at the CSO 52 site are very soft cohesive soils, and at the CSO 134 sites are alluvial soils contaminated by industrial activities.

This paper will focus on the temporary support of excavation (soil and rock) and groundwater cutoff measures needed to enable the work for the pump shaft (approximately 120-ft deep) and diversion structures, as well as the permanent 4-ft diameter caissons with permanent casing and 12-ft deep rock socket required for foundation support of the Electrical Building designed to resist the 500-yr flood.

Temporary SOE for soil and water at the pump shaft consisted of a circular sheet pile system designed to provide protection for 100-yr flood during construction. Shotcrete and rock bolts were used within the rock strata. An extensive rock grouting program was conducted to reduce the seepage into the rock shaft excavation during construction. Temporary SOE for the CSO 52 diversion structure consist of sheet pile with 3 tiers of internal bracing since all soils need to be removed to top of rock due to unsuitable bearing soils.

The paper will describe the design and construction challenges, as well as the various solutions needed for the project’ s unique conditions such as access constraints, reduced headroom due to high voltage transmission lines, and several unforeseen obstructions in the soil matrix.

Mr. SIXTO FERNANDEZ; Jake Coibion

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