Location

New York, New York

Session Start Date

4-13-2004

Session End Date

4-17-2004

Abstract

Preloading of sites underlain by compressible soils is a well-established site development procedure to reduce post-construction settlements of structures supported on shallow foundations. Considerable reduction in the preload duration can often be achieved by installation of vertical drains. It is desirable to extend vertical drains down through the compressible soils impacted by the preload and terminate the drains within relatively incompressible soils. If this cannot be achieved, then the potential exists for unacceptable post-construction differential settlements due to greater settlement below the center of the building than along its edges. If no relatively incompressible soils exist below the compressible soils impacted by the preload, the length of the vertical drains may be increased along the perimeter to achieve similar preload settlements throughout the site due to lesser increases in soil stresses along the preload edges. The site development loads at the subject site, comprising fill required to raise site grades by about 4.0 m and building loads, would induce consolidation below the maximum depth reachable with conventional wick drain mandrels. These loads would induce the greatest post-construction building settlements near the center of the site due to a smaller increase in soil stresses along the perimeter of the site. Hence, increasing the postconstruction settlements along the site perimeter, relative to those below the center of the development, would reduce the post-construction differential building settlements. In an attempt to reduce the post-construction differential building settlements, the wick drains at the subject site were installed to three depths ranging between 25 m and 35 m with the depth reducing towards the building perimeter. This paper will briefly present the results of geotechnical site investigations and the inferred subsurface conditions, which will be followed by a discussion on the preload design and performance. Detailed monitoring was carried out of surface settlement gauges and of deep settlement gauges installed to 43 m depth, in addition to monitoring of pneumatic and standpipe piezometers. The results of the instrumentation monitoring will be presented to assess the conformance of actual preload settlements with those predicted.

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

Ground Improvement by Optimized Preload Program

New York, New York

Preloading of sites underlain by compressible soils is a well-established site development procedure to reduce post-construction settlements of structures supported on shallow foundations. Considerable reduction in the preload duration can often be achieved by installation of vertical drains. It is desirable to extend vertical drains down through the compressible soils impacted by the preload and terminate the drains within relatively incompressible soils. If this cannot be achieved, then the potential exists for unacceptable post-construction differential settlements due to greater settlement below the center of the building than along its edges. If no relatively incompressible soils exist below the compressible soils impacted by the preload, the length of the vertical drains may be increased along the perimeter to achieve similar preload settlements throughout the site due to lesser increases in soil stresses along the preload edges. The site development loads at the subject site, comprising fill required to raise site grades by about 4.0 m and building loads, would induce consolidation below the maximum depth reachable with conventional wick drain mandrels. These loads would induce the greatest post-construction building settlements near the center of the site due to a smaller increase in soil stresses along the perimeter of the site. Hence, increasing the postconstruction settlements along the site perimeter, relative to those below the center of the development, would reduce the post-construction differential building settlements. In an attempt to reduce the post-construction differential building settlements, the wick drains at the subject site were installed to three depths ranging between 25 m and 35 m with the depth reducing towards the building perimeter. This paper will briefly present the results of geotechnical site investigations and the inferred subsurface conditions, which will be followed by a discussion on the preload design and performance. Detailed monitoring was carried out of surface settlement gauges and of deep settlement gauges installed to 43 m depth, in addition to monitoring of pneumatic and standpipe piezometers. The results of the instrumentation monitoring will be presented to assess the conformance of actual preload settlements with those predicted.