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Module 1 : Site Exploration and Geotechnical Investigation

Lecture 1 : Introduction [ Section 1.1 : Planning For Subsurface Exploration ]


3.	Preliminary Exploration
	In this phase a few borings are made or a test pit is opened to establish in a general manner the stratification, types of soil to be expected, and possibly the location of the groundwater table. One or more borings should be taken to rock, or competent strata, if the initial borings indicate the upper soil is loose or highly compressible. This amount of soil exploration is usually the extent of the site investigation for small structures. A feasibility exploration program should include enough site data and sample recovery to approximately establish the foundation design and identify the construction procedures. It is common at this stage to limit the number of good quality samples recovered and rely heavily on strength and settlement correlations using index properties such as liquid limit, plasticity index, and penetration data together with unconfined compression tests on samples recovered during penetration testing.
4.	Detailed Exploration
	Where the preliminary site investigation has established the feasibility of the project, a more detailed exploration program is undertaken. The preliminary borings and data are used as a basis for locating additional borings, which should be confirmatory in nature, and determining the additional samples required. If the soil is relatively uniform in stratification, a rather orderly spacing of borings at locations close to critical superstructure elements should be made. On occasion additional borings will be required to delineate zones of poor soil, rock outcrops, fills, and other areas which can influence the design and construction of the foundation. Sufficient additional samples should be recovered to redefine the design and for any construction procedure required by the contractor to install the foundation. This should avoid an excessive bid for the foundation work, cost overruns, and damage to adjacent property owners from unanticipated soil conditions discovered when the excavation is opened.