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Description
The purpose of this thesis is two-fold. One is to provide an understanding of a typical geotechnical investigation. The other is to perform an actual field investigation for a local geotechnical firm. Many people outside the field of geotechnical engineering are unaware of the principle roles of an engineering geologist. The geologist performs the field reconnaissance, research, subsurface exploration, geologic analysis of site conditions, and, along with the geotechnical engineer, project analysis. Before and during site reconnaissance, the geologist makes observations and assumptions about on-site soil conditions. During subsurface exploration, the geologist evaluates the soils in different locations by either a) stepping into a trench, b) watching spoils come up from an auger, or c) by going "down hole." He/she also collects samples for future lab analysis. During project analysis, the geotechnical engineer and the geologist discuss a) potential hazards, b) site conditions, c) excavation equipment and locations, and d) excavation logs and drilling complications ( such as anticipated depth of drilling not reached due to rock or caving). With laboratory results available, the engineer and geologist then write the geotechnical report. field study was conducted by a Southern California Soil & Testing (SCS&T) geotechnical engineer, engineering geologist, and myself in the vicinity of Escondido, just north of Lake Hodges. Hallmark Communities plans to develop two adjacent tracts ofland into a 17-lot subdivision and an 11-lot subdivision, Tracts 710 and 711, respectively. Field-testing included 16 air-track borings of Tract 710 and 7 backhoe trenches of Tract 711. Previous work in 1987 by SCS&T included both backhoe trenching and seismic traverses of Tract 710. Bulk & chunk samples were acquired from the trenches of Tract 711 in 1999. Trench logs from the subsurface investigation, design specifications, and discussion between the geotechnical engineer, engineering geologist, and myself helped determine the needed laboratory tests. The tests included sieve analysis (for grain size distribution), direct shear (for lateral strength of soil), expansion index (for ground swell potential), and collapse tests (for potential settlement). The final laboratory tests helped to make the evaluations and recommendations that in Tract 710 there is adequate rippability for all sites except lot 17. In Tract 711 compressible alluvial soils underlie lots 1, 10, & 11, and relatively loose fill underlies lots 6 & 7. These soils will require removal and replacement as recompacted fill.
