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Title: Precompression for improving foundation soils
Authors: Johnson, Stanley J.
Keywords: Soil consolidation
Soil compaction
Soil mechanics
Publisher: U.S. Army Engineer Waterways Experiment Station.
Engineer Research and Development Center (U.S.)
Description: Miscellaneous Paper
Introduction: In the 16 years that have elapsed since the first conference on soil stabilization at the Massachusetts Institute of Technology, significant changes have occurred in subsoil stabilization procedures that have made it possible to construct buildings, highway embankments, earth dams, and a wide variety of tanks and structures at reduced cost in many areas of poor subsoils: In 1952, precompression techniques for improving weak and compressible soils sufficiently to support structures had been used but were not well known, were not always successful, and had not always been carefully thought out. At the 1952 conference, interest was centered primarily about the concept of precompression and not about details involved. Since then, the concept has been more widely accepted and principal interest is proper application of the concept and in details that affect final results. The rapidly increasing interest in precompression techniques is due to the large savings that often result and to the increasing scarcity of advantageously located land that is available and that offers good foundation conditions. Large areas of poor subsoils, including many that are partially or totally submerged, are found in or near many of the major cities of the world. These marginal areas can be reclaimed at a small fraction of the cost of other alternatives, and precompression is often applicable for this purpose. Densification or improvement of soils through use of preloading techniques is discussed from the viewpoint of a practicing engineer considering preloading techniques to improve foundation subsoils which, in their natural conditions, are unsuitable for supporting a structure. The procedures discussed are based on current application of appropriate practical and theoretical knowledge, and significant improvements or modifications can be expected from research in progress. While settlements resulting from secondary compression are not generally evaluated in foundation engineering, it is necessary to do so with the precompression technique. Because preloading is generally designed to avoid settlement of permanent structures resulting from primary consolidation, postconstruction settlements from secondary compression start immediately and may be significant during the life of structures. Postconstruction settlements resulting from secondary compression can be evaluated and reduced where necessary. While the procedures for doing this are approximate and in a stage of development, they are considered suitable for design purposes where properly and conservatively applied. Whereas it may be desirable from a research viewpoint to regard primary consolidation and secondary compression as parts of a continuous physical phenomenon, it is more convenient from a practical standpoint to consider these phases separately. For design purposes, it is satisfactory to accept the physical phenomenon of secondary compression, leaving explanations of its basic cause for further research.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Miscellaneous Paper

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