Description

Brown sandy TOPSOIL

medium dense to dense red brown silty sand and fine gravel

Stiff light brown laminated silty clay, with layers of sand

Medium dense becoming dense brown sand

Compact brown silty Sand with layers of silty clay

Compact brown sand and gravel

Dense grey-brown clayey sand with occasional gravel

Hard mottled red-brown, grey and green coarse grained basaltic tuff

Soft and medium hard weathered mottled red-brown, grey-green basaltic tuff

Hard mottled grey-green basaltic tuff

Remarks: Penetration test continued beyond normal drive from 3.45m. 40mm diameter perforated standpipe 18.00m long inserted, surrounded by gravel filter with bentonite seal and screw cap at surface._

Key:

D Disturbed sample

B Bulk sample

W Water sample

* Core recovery

S(30) Standard penetration test

C(27) Cone penetration test

(27) No blows for 300mm pentn.

V In situ vane shear test

Ul/70 Undisturbed sample 100mm dia

/70 Blows to drive sample 450mm

U-/70 U/d sample - no recovery

LCP Light cable percussion

DP Rotary diamond drilled

Fig. 14.5 Borehole log (courtesy of Whatlings (Foundations) Ltd, Glasgow).

Some mention is made of the general geology of the area, whether there are old mineral workings at depth and, if so, whether the report has considered their possible effects or not. A map, showing the site location and the positions of any boreholes put down, is usually included in the report.

Description of subsoil conditions encountered

This section should consist of a short, and readable, description of the general subsoil conditions over the site with reference to the borehole journals. Generally the significance of any in situ testing carried out is mentioned.

Borehole journals

A borehole journal is a list of all the materials encountered during the boring. A journal is best shown in sectional form so that the depths at which the various materials were met can be easily seen. A typical borehole journal is shown in Fig. 14.5. It should include a note of all the information that was found, ground water conditions, numbers and types of samples taken, list of in situ tests, time taken by boring, etc.

Description of laboratory soil tests

This is simply a list of the tests carried out together with a set of laboratory sheets showing particle size distribution curves, liquid limit plots, Mohr circle plots, etc.

Conclusions

It is in this section that firm recommendations as to possible foundation types and modes of construction should be given. Unless specified otherwise, it is the responsibility of the architect or consultant to decide on the actual structure and the construction. For this reason the writer of the report should endeavour to list possible alternatives: whether strip foundations are possible, if piling is a sensible proposition, etc. For each type listed an estimation of its size, working load and settlement should be included.

If the investigation has been limited by specification or finance and the conclusions have been based on scant information, it is important that the fact is mentioned so that any possible allegations of negligence may be refuted.

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