UNDISTURBED SAMPLING OF COHESIONLESS SOILS BY CHEMICAL IMPREGNATION (FLUID INJECTION, FLOW EQUATIONS, AGAR, FREEZING)
Abstract
Existing methods to obtain and test high-quality undisturbed samples of cohesionless soil below the water table depend at some stage on freezing. This limits the range of application to clean sands, and even for those soils the freezing operation is delicate, time-consuming and costly. Recognizing these limitations, and the desire to obtain high-quality undisturbed samples from materials other than clean sands, such as silty sands, motivated the search for an alternate sampling technique; namely, chemical impregnation. Efforts concentrated on finding a chemical which could easily flow into the soil, would then solidify in situ, thus permitting sampling and/or laboratory preparation of the stabilized soil, and finally could be reliquefied again and removed. Agar, a natural polymer, has been identified as an optimum impregnation material. Agar powder dissolves readily in hot water to form a clear solution of low viscosity. On cooling, the solution remains liquid until a gelation temperature of 35(DEGREES)C to 40(DEGREES)C is reached, when the mass sets to a strong, rigid gel even at low concentrations, such as 1%. The gel does not melt again when immersed in water or during handling, but it can be reliquefied at a temperature above the gelation temperature. The properties of the impregnation material, which are important for geotechnical engineering applications, have been isolated and are presented in this dissertation. Theoretical equations to provide approximations to practical problems have been developed, describing the flow of the impregnation fluid into water-saturated soil. The solutions provide estimates of such quantities as impregnation time, flow rate, interface velocity and hydraulic gradients. This new approach has been used successfully under laboratory conditions, and the potential of the impregnation technique to obtain undisturbed samples in the field was evaluated in a recent field investigation. The original contributions presented in this dissertation include the identification of Agar as a prime candidate for an impregnating fluid, the demonstration of its potential using laboratory experiments, and the indication of its feasibility for field use by means of field trials. It is recommended that the research be continued to develop a simple and reliable field procedure which can be used in practice.
Degree
Ph.D.
Subject Area
Civil engineering
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