Development of a Calibration Chamber System for Testing at High Confining Pressures

Abstract

Cone penetration testing with pore pressure measurement (CPTu) represents a state of practice tool to assess the in situ state parameter, strength, and liquefaction susceptibility of sandy soils and mine tailings. Many techniques for the interpretation of CPTu data are based on the results of calibration chamber test programs on sand and, more recently, mine tailings. While these efforts have led to the current methods to interpret CPTu data, two factors relevant to CPTu interpretation require consideration: (i) the available calibration chamber data is dominated by tests with consolidated mean effective stresses < 200 kPa; and (ii) tailings storage facilities are being constructed to heights such that in situ effective stresses are far higher than those of the available calibration chamber test database. While much of CPTu interpretation is carried out in a dimensionless framework, there is evidence that existing relationships between stressnormalised tip resistance and state parameter are dependent on effective stress. This stress-dependence has been attributed to a variation in shear rigidity with effective stress, which is not accounted for in many interpretation techniques. However, at high stresses, other factors such as the curvature of the critical state line in an e-log(p’) plane may contribute. To assess CPTu of sands at high stresses, a novel small-scale calibration chamber employing a miniature cone capable of testing soils consolidated to a mean effective stress up to 2,000 kPa is outlined. Test results are presented for tests carried out over a range of mean effective stresses up to 1,000 kPa.

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