Uniform clayey sand


When classification tests are carried out on a stony soil sample any particles nominally greater than 60 mm are removed by sieving (with a standard 63 mm sieve) and their percentage determined. The tests are then carried out on the remaining soil. The material removed is classed as cobbles, 60 to 200 mm in size, with symbol Cb, or boulders, greater than 200 mm in size, with the symbol B.

Fine and coarse soils that contain cobbles, or cobbles and boulders are indicated in symbols by the use of the addition sign. For instance, a well graded SAND with gravel and cobbles would have the group symbol SWG + Cb.

Although the BSCS is intended to be a classification system associated with laboratory test results there is no doubt that an experienced operator can often identify a soil by visual inspection only, as described in the earlier section dealing with soil classification in the field. This facility can be very useful when no laboratory is available or when some form of rapid assessment is essential. A full guidance for in situ classification is given in Table 6 of BS 5930 which suggests that any group symbols decided upon, such as GW, SWM, etc., should be encased in brackets, (GW), (SWM), etc., to indicate that they are estimated.

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