38 stiffening plates these diameter and 25 mm

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Unformatted text preview: cm 3.9 Miscellaneous Apparatus - Datum bar of 5 m length with suitable dial gauge attachments, pick axes, showel, trowel, spatula, spirit level and plumb bob. 4. TEST PROCEDURE 4.1 Two alternative test procedures may be followed. More accurate tests are made with a 75-cm plate, and a load reaction arrangement, a loading jack, a proving ring to measure the load and three dial gauges placed diagonally apart about 10 mm from the rim to measure the vertical deflection. 4.2 Preparation of Test Area - K-value tests should be conducted on representative area. Most soils exhibit a marked reduction in the modulus of subgrade reaction with increase in moisture content, which cannot be generalized. Conditions of moisture content, density, and type of material all enter into the interpretation of test results to give a design value which will represent the condition of equilibrium that ultimately will exist in the subgrade. Generally, subgrade is composed of either natural ground or Preparation of an area for testing will depend on composifill-material. tion of subgrade. 4.2.1 Preparation of Tut Area for flatural Ground - Strip off an area equal to twice the area of the bearing plate to the proposed elevation of the subgrade surface. In any case, it is necessary to remove the top 25 cm of the soil before testing. The effect of surcharge can be eliminated by having supports of datum bar at least 1.25 m away from ‘the nearest edge of bearing plates. 7 IS:9214- 1979 On fine grained soils the bearing plate, with its lower surface oiled, shall be placed and rotated. When the plate is removed the irregularities in the surface, being marked with oil shall be trimmed off. This process is repeated until the plate is in contact with the soil over the whole area. When the test is made on granular subgrade, extreme care shall be taken not to disturb the natural condition of the subgrade while the test site is being prepared. Prior to placement of 75 cm diameter plate, the area should be cleared of loose material and levelled. On gravely soils flat bearing surface can best be obtained with plaster of paris, which should be levelled with the plate before the plaster has set. The K-value test should not be started until the plaster has sufficiently hardened. 4.2.2 Prebaration of Filled-Up Area - In case the test is to be conducted on subgrade composed of fill materials, a test embankment of about 75 cm height should be constructed, after necessary stripping. For design purposes the conditions of the moisture content and dry density of the test arca should be those which are likely to exist when the subgrade ha reached a state of relative equilibrium subsequent to the construction J pavement. Generally, the subgrade will be compacted at optimum moisture content and specified density. If ordinary compaction equipment is not available, approximate compaction may be obtained by hand tamping in layers. The test should be conducted keeping in view elimination of bearing pressures of reaction frame and datum bar, as mentioned in 4.2.1. The bearing plate with its lower surface oiled shall be placed on the When the plate is removed all proud porprepared surface and rotated. tions indicated by oil marks shall be as levelled as possible. If levelling is difficult due to presence of granular material, a layer of fine dry sand at no place thicker than 5 mm may be laid and the plate seated properly. 4.3 Loading Procedure - There are two methods for determination modulus of subgrade reaction as given...
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This note was uploaded on 03/14/2014 for the course CE 684 taught by Professor Prof.deepankarchoudhury during the Spring '13 term at IIT Bombay.

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