Stages in Sub - Surface Exploration One needs to know the characteristic of the soil formation on which the foundation rests before the design of foundation. A well planned sub‐surface investigation is a prerequisite for a safe and economical foundation design, to avoid any difficulties during construction and to protect adjacent structures. Site investigation describing the character, nature, load bearing capacity and settlement capacity of the soil shall be done before constructing a new building and structure or for alteration of the foundation of an existing structure. The experienced Engineers can make an intelligent, practical and pragmatic plan if he is conversant with the various elements of soil investigation. Sub - Surface explorations are generally carried out in the following stages: • Assembly of all available information: Assembly of all available information on dimensions, column spacing, type and use of the structure, basement requirements, any special architectural considerations of the proposed building, and tentative location on the proposed site. Foundation regulations in the local building code should be consulted for any special requirements. For bridges the soil engineer should have access to type and span lengths as well as pier loadings and their tentative location. This information will indicate any settlement limitations and can be used to estimate foundation loads. • Reconnaissance: This may be in the form of a field trip to the site, which can reveal information on the type and behavior of adjacent structures such as cracks, noticeable sags, and possibly sticking doors and windows. The type of local existing structures may influence to a considerable extent the exploration program and the best type of foundation for the proposed adjacent structure. Since nearby existing structures must be maintained in their "as is" condition, excavations or construction vibrations will have to be carefully controlled, and this can have considerable influence on the "type" of foundation that can be used. Erosion in existing cuts (or ditches) may also be observed, but this information may be of limited use in the foundation analysis of buildings. It also includes the information on evidence of groundwater, exposures in quarries and borrows areas, areas of instability, difficulties during excavation, history of the site, geology of the site, survey data with plans showing the structure and the location of all investigation points, local experience in the area, Information about the seismicity of the area. For highways, however, runoff patterns, as well as soil stratification to the depth of the erosion or cut, may be observed. Rock outcrops may give an indication of the presence or the depth of bedrock. • Preliminary Exploration: The aim of a preliminary exploration is to preparation of a borehole layout plan which includes determination the depth, thickness, extent and composition of each soil stratum at the site. The depth of the bed rock and the ground water table is also determined. The preliminary explorations are generally in the form of a few borings or test pits. Preliminary exploration also includes the height of building, the depth of basement, etc. • Detailed Exploration: The purpose of the detailed exploration is to determine the engineering properties of the soils in different strata. It includes an extensive boring program, sampling and testing of the samples in a laboratory presentation of field and laboratory test results, writing of report, etc. Field tests, such as vane shear tests, plate load tests and permeability test are conducted to determine the properties of the soils in natural state.
Posted on: Wed, 04 Sep 2013 13:09:13 +0000
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