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|Design and construction of mat foundations
|Johnson, Lawrence D.
|Geotechnical Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
|Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; GL-89-27.
Abstract: Mat foundations commonly support all types of structures. Flat mats from 2 to 8 ft in thickness of ten containing two-way steel reinforcement top and bottom usually support multistory or heavy structures. Mats less than 1 ft thick are often constructed with steel reinforced ribs or stiffening crossbeams and usually support light one or two story structures. Many of these mats have been designed and constructed for supporting permanent military facilities, particularly in heaving/shrinking and compressible soil. Some of these mats have experienced significant differential movement leading to cracking in the structure and have required costly remedial work. Attempts to reduce such maintenance expenses of some structures have lead to substantially increased design and construction costs format foundations. This report provides information on serviceability of structures, guidelines for evaluation of soil, and some structure input parameters for design analysis and guidelines for design and construction of ribbed mat foundations in expansive soils. Methods have been developed for evaluation of effective soil elastic moduli and stiffness of structures. New concepts are proposed for determining some soil input parameters for design in expansive soils such as the depth of the active zone for heave and edge moisture variation distance. Several case history studies of ribbed and flat mat foundations have been investigated to assist determination of suitable procedures for calculating deformation behavior of mat foundations. Analysis of the performance of a large ribbed mat foundation supporting building 333, Red River Army Depot, proves the viability of selected instrumentation and methodology. The observed earth pressure distribution shows extremely large concentrations of soil pressure near the perimeter indicating rigid behavior on an elastic soil or soil shear at the perimeter. The extended distribution of earth pressures from column loads indicates the effectiveness of stiffening beams in spreading applied loads. Evidence is presented indicating that concrete shrinkage and foundation distortions during construction may sometimes let stiffening beams of ribbed mats hang in the trenches without soil support, which may contribute to mat fractures when superstructure loads are applied. Observed strains in the concrete mat were generally consistent with observed deformation patterns. A preliminary systematic damage record system was developed to catalog most frequent damages, assist identification of causes of damage from foundation movements, and assist determination of requirements for maintenance and repair of military facilities. Recommendations are made for field surveys of detailed surface soil and foundation movement patterns and other work to investigate a new frequency spectrum approach and ground modification methods to improve understanding and performance of military facilities, improve design of foundations, and reduce maintenance and repair requirements. NOTE: This file is very large. Allow your browser several minutes to download the file.
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