Pressuremeter tests on stiff clays and soft rocks: factors affecting measurements and their interpretation

Abstract

Results from pressuremeter tests performed on a number of stiff clays and soft rocks are summarized. The tests measurements and the resulting interpretations made are shown to depend upon a number of factors including the type of instrument used and the methods of insertion, the soil: its fabric and stress history, and the methods of analysis. The pressuremeter results are compared with those from other test methods and the full scale performance of instrumented foundations. These comparisons have proved most valuable in assessing the most appropriate methods to be used in the interpretation of the results. I Po <%oPo > °ho Po = %0 = 511 kPa Fig. 3. Obtaining Oho from pressuremeter tests using Marsland-Randolph iteration procedure.

Foundations in Gault Clay

“…Comparisons between in situ plate load tests on Gault and other methods of determining deformation parameters are reported by Kay & Parry (1982) and Marsland & Powell (1990). In both cases plate load tests gave a reasonable correlation with modulus values Table 6.…”

“…Depths of burial for Gault outcrops quoted in the literature range from 150 m at Cambridge (Marsland & Powell 1990) to 425 m and 520 m in Hertfordshire (Smith 1978) and about 980 m in the Weald Basin (Fookes & Denness 1969). Exhumation by erosion from the point of maximum burial has led to vertical stress relief and accompanying fissuring which in turn facilitates an increase in water content and relative softening, below the depths associated with normal weathering processes.…”

“…Published case histories utilizing other techniques include CPT, push-in and self boring pressuremeter, (Garrett & Barnes 1984), (Marsland & Powell 1990) and screw plate loading tests (Kay & Parry 1982). As shown the triaxial derived profiles typically give the lowest strength profiles.…”

“…The most comprehensive published comparison of in situ testing techniques has been carried out at Cambridge and reported by Kay & Parry (1982) and Marsland & Powell (1990). These workers have compared CPT, pressuremeter, 865 mm diameter plate loading tests and 100 mm diameter screw plate tests and found that the self-boring pressuremeter yields the highest strength profiles, particularly in the less weathered and fresh Gault Clay.…”