Experimental infrared-radiometric investigations of stress variations on a borehole face in a model of the soil mass

Abstract

Research conducted in recent years at the Scientific-Research Institute of Foundations and Underground Structures [1-3, and others] has demonstrated the principal feasibility of using measurements of the intensity of infrared (IR) radiation from the surface of soil volumes to diagnose "quasi-adiabatic," i.e., in fact, relatively rapid changes, in their stress state over time.The studies were conducted on small-dimension laboratory specimens. To expand the boundaries of application of the procedure developed as applies to in-situ conditions, it is necessary to increase considerably the geometric dimensions of the domains being tested. Described below are experiments in which, as a result of expansion of the test domain, it was found possible to model changes in the stress state on the face of a borehole as changes occurred in the stress state in the enclosing soil mass under laboratory conditions.To develop the procedure for IR diagnostics of stress variations near the free surface of the soil in the near-face zone of a "borehole," we constructed a laboratory bench (Fig. 1), which makes it possible to apply an alternating load to a volume (specimen) of soil, install a model "borehole" in the volume being inspected, and take measurements yielding information on stress variations near its face and within the "mass."The basic component of the bench is a cylindrical trough with an inside diameter of 520 and height of 400 mm, which is fashioned from a steel sheet 8 mm thick. Prior to the tests, a pure quartz sand of medium fineness was placed in the trough and compacted in layers by manual tamping. When the trough had been filled to approximately half its height, two standard strain-measuring elements designed by the Central Scientific-Research Institute of Structural Parts (load-cell strain gages) are embedded in the soil on opposite sides of the same diameter at a distance of 30-40 mm from the walls of the trough.