| Abstract | This thesis is a theoretical study of the regional settlement in the Bangkok area due to ground water development. Information relating to the soil characteristics and ground water in the area was collected from several sources. The available data,
however, are not adequate for reasonably predicting the general settlement behaviour in the region, since the trend of change in the hydrostatic pressure in the subsoil cannot yet be discerned. Estimation of settlement is made on the basis of assumed compressible Bangkok clay profiles at four locations under four assumed conditions of decrease in hydrostatic pressure. It is
estimated that, when the water table drops below the compressible layer, or when the hydrostatic pressure at the base of the Bangkok clay stratum all but dissipates, the ground settlement may be as much as 1,0 m. The tolerable drawdown of the water table from the present level is estimated as being 1,0 m., and the tolerable limit of decrease in hydrostatic pressure at the base of the Bangkok Clay stratum, with the water table remaining
constant at the present level, is approximately 2.0 ton/m^.
Secondary compression in the process of settlement of the
Bangkok area may be very significant, since the load conditions can be considered to be such that the load increment ratio is very small and the load increment duration is very long. The estimation of the rate of settlement has to be based on theories of consolidation under time-dependent loading, and the rate of decrease of hydrostatic pressure in the subsoil has to be defined in order to estimate the rate of settlement.
Settlements will inevitably have detrimental effects on
engineering structures and facilities. Even foundations on piles may settle, particularly if compressions take place in deep zones. It is recommended that the amount and rate of settlement of the ground surface should be investigated by establishing a network of levelling controls. The settlement that takes place in various depth ranges in the subsoil should be observed from embedded settlement points. The change in hydrostatic pressure in the subsoil should be monitored with piezometers and the aquifer characteristics should be investigated by means of pumping tests. Deep borings are required to furnish more soil data. The depth of some of the instrumentation would have to be as great as 200 m., which is the depth of the deepest principal aquifer. |
