Location

New York, New York

Session Start Date

4-13-2004

Session End Date

4-17-2004

Abstract

The Reservoir is a component of the water supply system of a major city in the northeastern United States. The reservoir receives water conveyed by aqueducts and pressure tunnels from several watershed reservoirs. It is a balancing reservoir that regulates water flow and maintains the elevation head needed for the water tunnel distribution system to the south of the reservoir, which services the city inhabitants. The reservoir water surface is approximately 90 acres, and is contained by a man-made rim earth embankment, 40 feet in average height. The reservoir, which has an oval shape, is lined with a paneled concrete slab and is divided into an east and west basin of about equal size by a concrete dividing wall that traverses the reservoir along its longer axis. The wall, completed in 1916, stands 45 feet tall and has a 34.7 feet wide base. A by-pass aqueduct was built within the wall. After about eighty years of uninterrupted operation, the basins were cleaned of accumulated sediments. The paper describes the stability issues of the dividing wall during cleaning the basins. The original wall design did not account for dewatering one basin while the other remains in service with the uplift pressures developed in the foundation since start of first operation in 1917. The stability of the wall had to be improved in order to make possible the complete draining of one basin while the other remains fully operational. Although, initially, post-tensioned anchors into bedrock were considered to increase the wall stability against unbalanced water thrusts, additional assessments of the foundation material lead, instead, to the use of a temporary well-point dewatering system installed along the full length of the wall 20 feet into the underlying Glacial Till. The wellpoints were used to reduce uplift pressures under the wall base. The paper describes the stabilizing and monitoring procedures adopted during dewatering. It describes the analyses and monitoring of safe drawdown rates of the reservoir basins to prevent failure of the rim embankment slopes. It also describes in detail the designs, new factors of safety and test results, and construction of permanent stabilizing mass concrete buttresses that provide the necessary passive resistance for future dewatering of either basin for maintenance, cleaning and/or additional future construction.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Fifth Conference

Publisher

University of Missouri--Rolla

Publication Date

4-13-2004

Document Version

Final Version

Rights

© 2004 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Apr 13th, 12:00 AM Apr 17th, 12:00 AM

Stabilization of the Dividing Wall at a Drinking Water Reservoir

New York, New York

The Reservoir is a component of the water supply system of a major city in the northeastern United States. The reservoir receives water conveyed by aqueducts and pressure tunnels from several watershed reservoirs. It is a balancing reservoir that regulates water flow and maintains the elevation head needed for the water tunnel distribution system to the south of the reservoir, which services the city inhabitants. The reservoir water surface is approximately 90 acres, and is contained by a man-made rim earth embankment, 40 feet in average height. The reservoir, which has an oval shape, is lined with a paneled concrete slab and is divided into an east and west basin of about equal size by a concrete dividing wall that traverses the reservoir along its longer axis. The wall, completed in 1916, stands 45 feet tall and has a 34.7 feet wide base. A by-pass aqueduct was built within the wall. After about eighty years of uninterrupted operation, the basins were cleaned of accumulated sediments. The paper describes the stability issues of the dividing wall during cleaning the basins. The original wall design did not account for dewatering one basin while the other remains in service with the uplift pressures developed in the foundation since start of first operation in 1917. The stability of the wall had to be improved in order to make possible the complete draining of one basin while the other remains fully operational. Although, initially, post-tensioned anchors into bedrock were considered to increase the wall stability against unbalanced water thrusts, additional assessments of the foundation material lead, instead, to the use of a temporary well-point dewatering system installed along the full length of the wall 20 feet into the underlying Glacial Till. The wellpoints were used to reduce uplift pressures under the wall base. The paper describes the stabilizing and monitoring procedures adopted during dewatering. It describes the analyses and monitoring of safe drawdown rates of the reservoir basins to prevent failure of the rim embankment slopes. It also describes in detail the designs, new factors of safety and test results, and construction of permanent stabilizing mass concrete buttresses that provide the necessary passive resistance for future dewatering of either basin for maintenance, cleaning and/or additional future construction.