New methods of determination of atterberg limits of Philippine soils.

The liquid limit is the water content of the soil at which the soil passes from a plastic to a liquid state. The plastic limit is the lowest moisture content at which soil passes from the plastic state to the crumbly semi-solid condition. These limits define the range of water content over which soil exhibits plastic behavior. The range itself is referred to as the plasticity index. Liquid limit is determined either by the percussion (Casagrande) method or by the drop-cone or fall-cone penetrometer method. The percussion has been found to be subject to the skill of the operator and condition of the instruments, while data from drop-cone tests gave higher correlation coefficients than those from percussion tests. The current method of plastic limit determination is the thread rolling technique while a procedure based on the principle of the drop-cone penetrometer is gaining favor worldwide. This research for new measurement method results from the fact that the standard thread rolling technique is quite arbitrary, the results are very much affected by the skill of the operator and the procedure itself requires tedious effort. The unification of the determination methods of the liquid limit and plastic limit based on the drop-cone or fall-cone principle can provide for the desired simplicity, reliability and repeatability while eliminating subjectivity of the procedure. Comparative evaluation of the percussion (Casagrande) and the drop-cone methods of determining liquid limit, and the thread rolling and the drop-cone methods of determining plastic limit using eight soil sample from Laguna in the Philippines is presented in this paper. This paper proposes for the adoption of the 30 deg-80 gm drop-cone penetrometer for the determination of both the liquid and plastic limits of soils. More research work must however be done before such a redefinition of national standards can be made.