Study of compressibility characteristics of peat soil using large strain consolidometer

Abstract

Peat has been identified as one of the major group of soil in Malaysia. The area covered by peat deposit is about 3.0 million hectare or 8% of the total area of Malaysia. Among them, 6300 Ha of peat deposit is found in West Johore i.e.: Pontian, Batu Pahat and Muar. Despite of this fact, not much research has been focused on compression characteristics and behaviour of peat. The study was conducted to gain a better understanding on the compression behaviour peat soil by using samples of peat from Kampung Bahru, Pontian, a location of peat deposit closed to UTM. Generalization of research data was not attempted in this research since it is fully understood that the properties of peat soil are uniquely site specific. The study focuses on the analysis of compressibility characteristics of peat soil based on the time-compression curves obtained from Oedometer and Rowe consolidation tests and the effects of surcharge on the behavior of peat soil. The sampling of the peat soil was designed and executed in such a way that disturbance could be minimized. Preliminary laboratory test was conducted to identify the soil and to compare the results to published data especially on Malaysia’s peat. Oedometer test was done to establish the bases for the selection of range of pressure to be applied to the hydraulic consolidation test. The evaluation on compressibility parameters was made based on the results of large strain consolidation test. Analysis of settlement was performed for a hypothetical problem. The results showed that the peat soil found in Kampung Bahru, Pontioan can be classified as fibrous peat with a very high organic content which is typical of peat soil in Peninsular Malaysia. Degree of decomposition according to von Post scale is H4. undrained shear strength is very low (2-3 kPa); the fact discourages the construction work to take place on the deposit. Initial permeability is 1.20 x 10-4 m/s which is similar to that of sand and it is decreases significantly with pressure. The results of both oedometer test and large strain consolidation test indicate that the secondary settlement is dominant in fibrous peat under study. However, the analysis of settlement showed that the large portion of settlement is still due to primary consolidation owing to the high initial void ratio and the time required for the completion pore water pressure dissipation. The results also showed that the secondary consolidation can be better by large strain consolidation test.