This research is focusing on clay soil. The shear strength that is or will be developed by each soil type is different. Shear strength of soil is able to influence the stability of buildings structure. Soil with high shear strength will be able to support buildings structure without failing. Otherwise, the structure will not be stable and side effects will occur either in short term or long term depends on the shear strength. That is why research regarding to shear strength should be carried out to ensure the capability of soils in supporting loads.
The shear strength of soil depends on the water content. Most geotechnical failures involve a shear-type failure of soil. This is due to the nature of the soil, which is composed of individual soil particle that slide when the soil is loaded. The shear strength parameters of soil are known as cohesion, c and angle of friction, Ø. The higher values of cohesion, c and the angle of friction, Ø is higher the shear strength of the soil.
Clay soils can be classified into four conditions according to the amount of water content. They are solid, semisolid, plastic and lastly liquid [1]. The continuous increment of water content will change solid clays soil to semisolid, followed by plastic and liquid. This process not only changes the condition of clay soils, it also weakens the cohesion value of the soil.
The variations in water content of clays are important for a wide variety of reasons. They affect the engineering properties of the soil and thus the building design. For the contractor, the effect can be more prosaic but very important. For example, the jobsite that is dry and easy to move construction equipment about can become a quagmire if enough rain raises the water content of the soil towards and beyond the liquid limit. This may necessitate matting in order to move equipment around, or even affect the type of equipment that is brought on site. The contractor must be prepared for this type of change if conditions are not the same as when the job was bid or began [9].
Very soft to medium clays are very troublesome when they must be supported or excavated and often are unsatisfactory materials for temporary foundations in shoring systems [9]. In brittle soils, yielding may lead to the formation of shear slip surface, over which sliding movement takes place, e.g. landslips, rotational slope and excavation failures. Measures of shear strength are required in the analyses and design of geotechnical structure, such as foundations, retaining walls, earth slopes and road bases [2].
Any change in the ambient conditions will bring about a change in moisture content. If water is taken in a swelling, pressure will be exerted and the volume will tend to increase. Shrinkage will take place if the adsorbed layer is compressed, forcing water out or if suction reduces the moisture content. The swelling potential of clays is very high. In soil masses in general, shrinkage manifests itself as a series of polygonal cracks emanating downward from the surface [2]. Base on the statements, shows that the amount of water content may influence the stage of soils strength.
The main objectives of this study are:
- To determine the strength of clay soil resulting to the change of water content
- To determine the percentage of water content needed in clay soil to perform maximum shear strength
The chosen location for this research is RECESS which is located in KUiTTHO's campus in about 20 km from the Batu Pahat town center towards Ayer Hitam. The scope of this study is to determine the shear strength of clay soil according to the water content. It includes of disturbed and undisturbed samples. Samples will be taken at depth of 1.5 meters from the surface. There are 31 samples will be needed. The total of 21 samples will be used for direct shear test, 3 samples for free swell test and the other 7 samples will be used for vane shear test.
The percentages of water content that will be involved in both tests are starting from 15% until 65% with gap of 10%. Clay soil with optimum water content will produced the highest shear strength.
Importance and Contribution of Study
In producing buildings, there are many factors that should be considered. One of them is the capability or strength of soils in supporting loads. Any failure that happens to supporting soils will affect the building structures. This aspect is also important in process of digging and removing soil in order to prepare a site for construction and services. The problems here are closely related those of support. In the case of both natural and built slopes (embankments), it is necessary to determine their intrinsic ability for self-support. Problems of shear failure, in which possible collapse mechanisms are investigated where rupture surfaces develop due to the shear strength of the soil being exceeded.
