Using coefficient of consolidation to assess response time and reading accuracy of piezometers in grouted boreholes in fat clays

dc.contributor.advisorEl Mohtar, Chadi Saiden
dc.contributor.advisorGilbert, Robert B. (Robert Bruce), 1965-en
dc.creatorBrewster, Alexander C.en
dc.creator.orcid0000-0002-2406-9606en 2015en
dc.description.abstractReading accuracy of a piezometer in a fully grouted borehole has typically been assessed by comparing the hydraulic conductivity of the grout (K[subscript grout]) to that of the soil (K[subscript soil]). The field conditions of interest to this study represent the case of a relatively permeable cement – bentonite grout (the fill material of choice for borehole applications) being installed in a relatively impermeable fat clay. The soil and grout are assumed to be incompressible and fully saturated with an incompressible fluid. Using a steady state approach, error is defined for a given K[subscript grout]/K[subscript soil] ratio. Each of the three studies that investigate K[subscript grout]/K[subscript soil] propose a significantly different failure criterion. An experimental program was developed, with the critical area of focus being on the highly inconsistent K[subscript grout]/K[subscript soil] criteria used to predict grouted piezometer reading error. This study investigated the merits of coefficient of consolidation (c[subscript v]) theory in predicted such errors. It was discovered that pressure pulses (like those experienced within a grouted borehole) migrate through a specimen under a different gradient than those experienced in a typical consolidation environment. This discovery extends beyond existing literature, which makes no distinction between consolidation and pressure propagation. As such, a new term has been coined: the coefficient of pore pressure propagation (C[subscript p]). C[subscript p] was found to be characterized as a single-valued function of C[subscript v], making it a particularly useful term (i.e. calculating C[subscript v] allows for C[subscript p] to be accurately predicted). The testing program consisted of CRS and triaxial approaches that measured the K, C[subscript p] (attained from pulse tests), and C[subscript v] (attained from conventional consolidation tests) as a function of consolidation pressure and volumetric water content. These parameters were successfully measured for sands, sand-bentonite mixtures (SBM), and fire clay specimens. It was discovered that a C[subscript p] framework is better suited to assess reading error than the prevailing K theory. Experimental data demonstrates that pressure equalization rates within the grout are highly dependent on stiffness and degree of saturation, neither of which is adequately captured in the K data. Furthermore, relying on K theory led to widely varying predictions of response time that were experimentally determined to be inaccurate. A numerical model was developed using the C[subscript p] theory. Even in a reasonably conservative state, the model predicts that no currently-available cement-bentonite grouts are suitable for use in a fat clay installation. If future studies fail to identify a viable grout for such installations, the fully grouted method may need to be abandoned altogether for installations in fat clays.en
dc.description.departmentCivil, Architectural, and Environmental Engineering
dc.subjectHydraulic conductivityen
dc.subjectCoefficient of consolidationen
dc.subjectCoefficient of pore pressure propagationen
dc.subjectFully grouteden
dc.subjectFat claysen
dc.subjectDegree of saturationen
dc.subjectResponse timeen
dc.subjectPiezometer reading erroren
dc.titleUsing coefficient of consolidation to assess response time and reading accuracy of piezometers in grouted boreholes in fat claysen
dc.typeThesisen, Architectural, and Environmental Engineeringen Engineeringen University of Texas at Austinen of Science in Engineeringen

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