Soil Improvement to Mitigate Settlements under Existing Structures

Al-Alusi, H. R.; ,

Soil Improvement to Mitigate Settlements under Existing Structures

by H. R. Al-Alusi, (M.ASCE), Pressure Grout Co, Hayward, United States,

Document Type: Proceeding Paper

Part of: Vertical and Horizontal Deformations of Foundations and Embankments

Abstract:

Settlements of sites with existing structures are more difficult to mitigate than those of sites without structures. Equipment access, work area, noise, dust, vibrations, and cost are amplified and become more critical. Following are three case histories involving mitigation of settlements under three different types of structures. The first case, an office building in the San Francisco Bay Area, involved soil densification under piles to mitigate further settlements. The compaction grout densification process was extended beyond the bottoms of the piles to treat fill materials under the footprint of the building. Additional lense grout reinforcement was required to reinforce the hillside soils to reduce downward movements. Five years after completion of remediation work, the site showed no detectable movement. The second case concerned a maintenance facility at the June Lakes Ski Resort in the Sierra Mountains, where a structure had been built on top of a fill that was underlain by a layer of gravel and cobbles. Within a year of construction, signs of structural distress were evident. Geotechnical investigations revealed that settlements were caused by at least two factors; the downward migration of the upper fill layer into the large pores of the lower layer, and the possible densification of the upper fill under its own weight. The remedial work consisted of providing a barrier between the two layers to allow for an effective compaction grout densification effort of the upper fill layer and to prevent further migrations into the gravel and cobbles layer. No structural distress or any movement has been detected since the remedial work was completed six years ago. The third case presents the treatment of the old and new footings of the Rose Bowl Stadium in Southern California. A permeation grouting system was selected, designed, and implemented to solidify zones of the sand-gravel-cobbles mixture of the foundation soils to act as pedestals for underpinning the old footings and supporting the new ones.

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