Thursday, December 13, 2012

Stages of a Ground Investigation: Procedure.

The stages of a ground investigation are given in Table 3.2.

A ground investigation consists, basically, of four main operations:

(1) Study of existing information (known as desk-top study) and preliminary site reconnaissance (site walkabout).
(2) Soil investigation and testing.
(3) Analysis and appraisal of results.
(4) Writing and distribution of soil reports.

In the same way that structural design is a continuous decision-making process and interactive with detailing, other members of the design team, building control and services authorities and the client, so too is the site investigation.

Decisions must be made:

(1) At the start of the survey to determine objectives and methods to achieve the objectives.
(2) On choice of site equipment, where and how best to use the equipment.
(3) On choice of samples to be tested, how to test and interpretation of the test results.
(4) On methods of analysis and recommendations to lead to efficient and economic design and construction.

There should be interaction between the designer and site investigator:

(1) The preliminary design should give the investigator  an indication of the proposed positioning of the struc-
ture on the site, an estimate of foundation loading, any special requirements of basements, services, vibrating or stamping plant and similar information.

(2) The investigator should report periodically to the designer on the findings so that, if necessary, the scope
of the site investigation, the position of the building,  the foundation loading, or the preliminary foundation proposals may be amended.

(3) When the designer has the final site investigation  information the final design can be refined.

(4) The site investigator, given the final design, can refine the report.

(5) Either the designer alone or in collaboration with the
site investigator can then write the final report.

(6) Both the designer and investigator should monitor  the progress of foundation construction and post- construction structural behaviour. This will determine whether the ground conditions were as predicted; whether there were any unexpected excavation problems; whether the magnitude and rate of settlement was as calculated; whether movement joints performed satis- factorily and if the structure remained fully serviceable (i.e. no cracking, undue settlement, etc.). It is difficult for a busy designer to find time to go back and examine past projects, but from long experience it has been found beneficial for progress in foundation design to make time to go back and look critically at past projects.

1. Site survey plan and Study of existing information   1 Site survey planIf a site survey has not been done, or provided by the client, then a topographical survey should be carried out. The survey should show the site location and access, give site boundaries, building lines, position of proposed structure, levels ...(more)

2. Preliminary site reconnaissance and site walkabout    With the above information, presented clearly in an easily digested report, the senior design engineer should visit the site and the immediate neighbourhood to develop a feel for the site. It is sometimes advisable for the senior engineer to visit the site...(more)

 Table 3.2  Stages of a ground investigation.

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