Retaining Wall

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  • Topic: Slurry wall, Geotechnical engineering, Soil
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Nicholson Construction Company 12 McClane Street Cuddy, PA 15031 Telephone: 412-221-4500 Facsimile: 412-221-3127

Diaphragm Walls
by

Thomas D. Richards, Jr. P.E. Nicholson Construction Company, Cuddy, Pennsylvania

Presented at: Central PA Geotechnical Conference Hershey, Pennsylvania March 23-25, 2006

05-01-145

Diaphragm Walls
Thomas D Richards, Jr P.E. Nicholson Construction Company Central PA Geotechnical Conference - March 23-25, 2005

INTRODUCTION The purpose of this paper is to describe the application, construction process, and design methods for diaphragm walls, since this topic has not been addressed much if at all at previous Hershey conferences. Diaphragm walls are a method of creating a cast in-situ reinforced concrete retaining wall using the slurry supported trench method. As such, they are often known as slurry walls. However, the term “diaphragm walls” Concrete diaphragm slurry walls were first introduced in the United States in the 1960s, and have found a niche in urban environments such as Boston, New York City, and Washington, DC. APPLICATIONS Diaphragm walls are most commonly used : • • • • • in areas with dense and historic urban infrastructure, where a very rigid earth retention system is required, where noise and vibration must be limited, where the geology and groundwater preclude the use of conventional earth retention systems and/or where dewatering is not practical

Compared to other wall types, diaphragm walls are considered to be very stiff with respect to ground movement control (Clough and O’Rourke, 1990). Diaphragm walls are often attractive in granular soils with a high groundwater level, especially when a low permeability layer underlies the granular soils. The diaphragm walls are typically terminated in the underlying low-permeability layer which can consist of soil or rock. Keying into this low permeability layer reduces groundwater seepage below the wall. (Pearlman, 2004) Projects that have used these walls include: • • • • • • below grade parking/ deep basements cut and cover subway tunnels highways as cut and cover tunnel walls and for underpasses shafts for deep sewers dam appurtenances landslides

For highway projects, diaphragm walls were employed extensively on the Central Artery Tunnel and also have been used in Denver, CO and Baltimore, MD.

Diaphragm Walls 21st Central PA Geotechnical Conference - March 23-25, 2005

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BENEFITS Diaphragm walls can:
• • • • • • • • • •

be formed to depths of several hundred feet, through virtually all soil types and through rock, and with great control over geometry and continuity facilitate excavations below groundwater while eliminating dewatering provide fairly watertight walls provide structural stiffness which reduces ground movements and adjacent settlements during excavation be load bearing transferring loads to the underlying layer be reinforced to allow incorporation of many structural configurations, accommodate connections to structures be easily adapted to both anchors and internal structural bracing systems be constructed in relatively low headroom (say 15 feet) and in areas of restricted access be installed before excavation commences provide economic solutions in cases where temporary and permanent support can be integrated or redesigned into one retaining structure

Diaphragm walls combine into a single foundation unit the functions of temporary shoring, permanent basement walls, hydraulic (groundwater) cutoff, and vertical support elements. Because of this combination, they have proven to be an economical alternative in many circumstances (Pearlman, 2004).

Diaphragm Walls 21st Central PA Geotechnical Conference - March 23-25, 2005

Page 3 of 17

CONSTRUCTION PROCESS Overview The trench excavation is performed using slurry for support. The slurry is typically bentonite and water or polymer and water. Diaphragm walls are constructed in the following steps: • • • • • • • •...
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