HOW TO PLAN A SITE INVESTIGATION PROGRAM?

Site information plays an important role in the safe and economical development of the site. A thorough examination of the site is an essential preparatory to any civil engineering construction work. Public building authorities may require soil data, along with the recommendations of a geotechnical consultant, before issuing a building permit. The elimination of site exploration, which typically accounts for about 0.5 to 1 percent of the total construction cost, only after construction begins to reveal that the foundation must be redesigned, is certainly false economy. This is generally recognized, and it is doubtful whether any major structures are currently designed without exploration.

Site Check Objectives

The primary objectives of soil exploration are mentioned below:

  • To access the general suitability of the site
  • To achieve safe and economical design of foundation and temporary works
  • To know the nature of each layer and the engineering properties of soil and rock, which may influence the design and mode of construction of the proposed structure and foundation.
  • To foresee and provide for difficulties that may arise during construction due to land and other local conditions
  • Locating sources of building materials and selecting sites for disposal of water or surplus materials
  • To investigate the occurrence or causes of all natural and man-made changes in circumstances and the consequences arising out of such changes
  • To ensure the safety of the surrounding existing structures
  • Designing for failed structures or remedial measures for structures considered unsafe
  • To find out the potentially corrosive effect of soil and water on ground water level and foundation material

Site exploration program planning includes the location and depth of boring, the test pits or other methods used, and the methods of sampling and testing. The purpose of the exploration program is to determine, within practical limits, the stratification and engineering properties of the soil beneath the site. The key properties of interest will be strength, deformation and hydraulic characteristics. The program should be planned so that maximum amount of information is obtained at minimum cost. In the earlier stages of an investigation, the available information is often insufficient to allow a firm and detailed plan to be made.

Hence the investigation is done in the following steps:


  1. Fact Finding and Geological Survey
  2. military test
  3. preliminary investigation
  4. detailed exploration

1. Fact Finding and Geological Survey

Gather all information on dimensions, column spacing, structure type and use, basement requirements, and any particular architectural considerations of the proposed building. Foundation regulations in local building codes should be consulted for any special requirements. For bridges the soil engineer must have access to the type and length of span as well as the pier loading. This information will indicate any settlement limits, and can be used to estimate foundation loads.

2. military test

This can be in the form of a field trip to the site that may reveal information about the type and behavior of adjacent sites and structures such as cracks, noticeable sags, and possibly chipped doors and windows. The type of local existing structure can, to a large extent, influence the exploration program and the best foundation type for the proposed adjacent structure. Since existing structures nearby must be maintained, excavation or vibration will have to be carefully controlled. Erosion can also be seen in the existing cut (or trench). For highways, runoff patterns, as well as soil stratification by erosion cut depth, can be observed. Rocky outcrops may indicate the presence or depth of a bedrock.

3. preliminary investigation

In this stage some boring is done or a test pit is dug in a general way to establish the location of the stratification, the expected soil type, and possibly the groundwater table. One or more borings should be moved to a rock, or capable level, if initial borings indicate that the top soil is loose or overly compacted. This amount of soil exploration is usually the limit of site investigations for smaller structures. A feasibility exploration program should include sufficient site data and sample retrieval to establish an approximate foundation design and identify construction processes. Limiting the number of good quality samples recovered at this stage and strength and settlement by using unconfirmed compression tests on samples recovered during penetration testing as well as index properties such as liquid limit, plasticity index, and penetration data It is common to rely heavily on correlations.


4. detailed exploration

Where initial site investigations have established the feasibility of the project, a more detailed exploration program has been initiated. The initial boring and data are used as a basis to detect additional borings, which should be confirmatory in nature, and determine the additional samples required. If the soil is relatively uniform in stratification, a systematic spacing of borings should be made at places adjacent to important superstructure elements. On occasion additional boring will be required to delineate areas of poor soil, rock outcrops, fill and other areas that may affect the design and construction of the foundation. Sufficient additional samples must be recovered for any construction process required by the contractor to redefine the design and to install the foundation. This should avoid exorbitant bidding for foundation work, cost escalation, and damage to adjacent property owners from unforeseen soil conditions discovered at excavation openings.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.