Quality Assurance Handbook for Rural Roads Volume-I - pmgsy

2. SECTION 300 : EARTHWORK
253
Quality Assurance Handbook for Rural Roads
2.1 : Earthwork and Subgrade/ Improved Subgrade in Embankment/ Cutting
1. Quality of Material for Embankment/ Subgrade/ Improved Subgrade
(a) For earthwork in embankment, check its suitability by soil type and its soil group. This can
be determined by adopting a Visual Soil classification System, using only hand-feel tests, as
shown at Annex 1. Details of the three hand-feel tests required for classifying fine-grained
soils are given in Appendix-1, paras 1.1, 1.2 and 1.3.
A quick supplementary procedure for determining the presence of clay is performed by
cutting a lump of dry or slightly moist soil with a knife. A shining surface imparted to the
soil indicates highly plastic clay, while a dull surface silt or clay of slight plasticity.
Using the following the suitability of soil as a fill material can be ascertained:
Dry Unit Weight estimated from the soil group as per Table (Annex 300.2) on Average
Engineering Properties of Soil Groups.
Wherever suspect, Deleterious Material Content (Appendix 1, Para 4) should be
determined.
Wherever suspect, pH value to be determined using litmus paper strips (if pH>8.5,
the soil is sodic in nature and unsuitable for use)
Check, if the subgrade soil meets all the requirements of fill material as above, has the
maximum dry unit weight (Proctor Test) and soaked CBR not less than the specified
value.
(b) Where a clayey subgrade soil/ black cotton soil with very low CBR value is to be improved
by lime treatment, as per the provisions of the Contract, check from records if the purity of
lime used for the purpose has been tested. It should be not less than 70% by weight of
quicklime (CaO).
(c) Check the lime treated soil for its Plasticity Index (PI).
(d) Check, if prior to mixing of soil with lime, pulverization of soil clods was carried out as per
requirements i.e, 100% passing 26.5 mm sieve and 80% passing 5.6 mm sieve.
(e) Check, if the mixing of pulverised soil with lime was carried out thoroughly by using
appropriate equipment like tractor-towed disc harrows/ tractor-towed Rotavator.
2. Compaction
(a) Check, if the moisture content in the soil during compaction is close to the optimum by
taking a handful of the wet soil on the palm of hand and attempting to make a ball out of it
(Appendix 1, Para 5). The moisture content at which the ball of wet soil can retain its round
shape is approximately the optimum. At moisture contents below the optimum, the ball
tends to crumble while at moisture contents wet of optimum, the water will tend to ooze out
of surface.