Natural Water Content (NZS 4402 Test 2.1)
Mass of water: M2- M3=7.05g
Mass of dried soil: M3- M1=23.20g
Wn=30.4% (3sf-in compliance with NZS 4402)
Wn=30% (to nearest whole number)
All guidelines within the NZS 4402 methodology were adhered to as closely as possible: The tin base and lid were both cleaned and dried prior to weighing (to the nearest 0.01g), while handling the soil, dry, clean hands we ensured in order to avoid altering the water content of the soil and it was also stored within a ‘sealed’ tin container during the weighing process to further eliminate any un-accounted water loss.
Liquid Limit Test (N.Z.S. 4402 Test 2.2)
All guidelines within the NZS 4402 methodology were adhered to as closely as possible. At all times, the soil sample was kept under a plastic sheet in order to minimise its moisture loss due to the heat of the students, each soil sample was thoroughly compacted/consolidated within the brass cup of the Casagrande apparatus in order to minimise the presence of any air voids and an attempt was made to maintain a drop frequency of 2 per seconds (although there was some tendency to slow this rate as the touching soil surface neared 13mm). Prior to the drop, soil around the edge of the brass cup was removed in order to minimise any energy transfer/dynamic process which negate against result accuracy and soil samples were taken from the drop soil as opposed to the soil on the mixing board. Distilled water, as opposed to tap water was also used to moisten the soil in order to prevent any minerals interfering with the soil plasticity.
Although the cone-penetromenter test is regarded as the more accurate of the two for determining the liquid limit of a soil, the lack of tested soils for this device lead to me using the water content from the Casangrande test as the liquid limit. Interpolating from the flow curve, 25 blows gives rise to a water content (liquid limit) of 46.0%.
Cone Penetration Limit (N.Z.S. 4402 Test 2.5)
During the conduction of this test, effort was made to ensure that both the cone and shaft were dry and clean before testing each individual soil sample. On top of this, to ensure precision and avoid any parallax errors, when reading off of the gauge and lining up the cone with the surface of the soil sample, eye level measurements were taken. Using the same water contents for samples 2 and 5 calculated above, and interpolating the graph of soil penetration depth (mm) against soil water content(%), a water content of 46%(46.2%) corresponded to a soil penetration depth of 20mm – this was therefore our liquid limit for the cone penetrometer test.
Plastic Limit Test (N.Z.S. 4402 Test 2.3)
To eliminate the complexities associated with the drying of particular organic and inorganic “colloids”, testing was performed on the natural water-content soil sample. While rolling the threads, care was taken to ensure that an even pressure was applied across the length of the thread in order to maintain and constant cross-sectional area across the thread’s length. Sufficiently dried samples were also kept in a sealed tin during the rolling process to minimise any loss of water and the glass rolling surface was cleaned between rolls such to prevent the coating of fresh threads with dried soil material.
Mass of Water: 3.47g
Mass of Dry Soil: 12.68g
Wp=27.4% (in compliance with NZS 4402)
Wp=27% (to the nearest whole number)
Calculating Plasticity Index:
Ip= Wl- Wp Ip=46.0-27.4
The plasticity index is a range of water content percentages over which the clay soil behaves in a plastic manner. Plotting this plasticity index against the liquid limit of the soil tested, we can broadly classify the soil using the plasticity chart developed by Casagrande. Our soil sample falls just above the A-line of the chart and so can be classified as CL (an inorganic clay of low to medium plasticity). The higher a soil plots above the A-line, the lower it’s shear strength, and...
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