Friday, December 14, 2012

Recording Information – Trial Pit and Borehole Logs and Soil Profiles.

Before embarking on expensive laboratory testing of soil samples it is advisable to record (log) the information gained on site in order to plan the test programme. To facilitate the reading of logs and boreholes the soils and rocks should be indicated by standardized symbols. Widely accepted diagrammatic symbols are given in Fig. 3.4.

A typical trial pit log of the engineer’s observations is given in Fig. 3.5.

A borehole log should give details of the foreman driller’s log, the observations of the supervising engineer and the results of any site tests. A typical borehole log is shown in Fig. 3.6.

Trial pits, trenches and boreholes should be given reference numbers, located on plan, their ground level noted and the date of excavation recorded. It is advisable to record the  following additional information:

(1) Type of rig, diameter and depth of bore or width of bucket.
(2) Diameter and depth of any casing used and why it was necessary.
(3) Depth of each change of strata and a full description of the strata. (Was the soil virgin ground or fill?)
(4) Depths at which samples taken, type of sample and sample reference number.
(5) In situ test depth and reference number.
(6) The levels at which groundwater was first noted;  the rate of rise of the water; its level at start and end of
each day. (When more information on permeability, porewater pressure, and the like is required, then it is vitally important that the use of piezometers should  be considered.)
(7) Depth and description of obstructions (i.e. boulders), services (drains) or cavities encountered.
(8) Rate of boring or excavation (useful to contractors and piling sub-contractors as such information gives some guidance in ease of excavation or pile driving).
(9) Name of supervising engineer.
(10) Date and weather conditions during investigation.

Fig. 3.4 Recommended symbols for soils and rocks

Fig. 3.5 Typical trial pit log (Weltman, A.J. & Head, J.M., Site Investigation Manual, CIRIA (1983),

Fig. 3.6 Example of a typical borehole log (BS 5930, Fig. 22).

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