Axial Strength of Cement Borehole Plugs in Granite and Basalt: Topical Report on Rock Mass Sealing.

摘要

This report describes experimental and theoretical studies of the axial strength of cement plugs installed in boreholes drilled coaxially in granite and in basalt cylinders. Experimental work has consisted of loading the cement plugs to failure while measuring loads and displacements. Such tests have been performed on borehole plugs with a diameter and a length ranging from 2.5 cm to 10 cm. Results from over one hundred experiments show that the strength is high, sufficient for anticipated loads at repository depths, but very variable, complicating the design of very short plugs. Significant residual strength is observed. A frictional model of the interface shear strength, in combination with the assumption of an exponential shear stress distribution or plug-rock load transfer, provides the simplest realistic model for plug strength characterization. The integrated strength thus calculated compares moderately well with experimental results. An extensive review is given of more sophisticated analysis procedures that should be of value for general plug design applications. Generic analyses and their implications for plug performance are included. Variability of experimental results complicates the assessment of their direct detailed applicability.