Essential Findings in Pressuremeter Theories

The pressuremeter, used for in situ soil testing, has undergone significant development both in its technical applications and in the interpretation methods employed for a range of parameters. Several methods have been developed to evaluate the undrained strength of a soil using a pressuremeter. Test results based on these methods show distinctive discrepancies. Different methods for evaluating the limit pressure are also presented. The values of these limit pressure evaluations vary based on the evaluation method used. In any given test, the limit pressure results also affect the values deduced for undrained shear strength. The discrepancies in the undrained shear strength values exceeded 80 % for the same test when evaluations were made with different interpretation methods. Because of the large discrepancies in the results of the undrained shear strength when using different analysis methods, the Gibson and Anderson method is recommended as being most reliable in deducing undrained shear strength values from pressuremeter tests, particularly for use in the design of foundations.     

Effect of Strain Rate on the Strength Characteristics of Soil–Lime Mixture

The effects of rate of strain on strength and deformation characteristics of soil–lime were investigated. Five strain rates (0.1, 0.8, 2.0, 4.0 and 7.0 %/min), five lime contents (0, 3, 6, 9 and 12 %) by dry soil weight and three cell pressures (100, 200 and 340 kN/m²) were carried. Triaxial tests, under unconsolidated condition, were used to study the effect of strain rate on strength and initial modulus of elasticity of soil and soil–lime mixture after two curing periods 7 and 21 days, respectively. A total of 405 triaxial specimens have been tested, where 225 specimens have been tested with first curing period (7 days). The testing program includes nine specimens for each strain rate, and each lime content was carried out, including natural soil with zero lime content. Another set of triaxial tests with a total of 180 specimens for the second curing period (21 days) was prepared at optimum moisture content, and the corresponding maximum dry density was also tested. The effects of strain rate and curing period on each of stress–strain behavior, type of failure, deviator stress at failure, cohesion and angle of internal friction and initial modulus of elasticity were studied thoroughly for the natural soil as well as soil–lime mixtures. For natural soil, the test results showed that the undrained shear strength, the initial modulus of elasticity and the cohesion increase significantly as the strain rate increase, while for soil–lime mixture at different curing periods, the undrained shear strength, initial modulus of elasticity and the cohesion increases to a maximum and then decreases as the strain rate and lime content increase. Also, the same variables and angle of internal friction increase with increasing curing period.     

Different Results in Pressuremeter Theories

The limit pressure that evaluated from pressuremeter tests has been shown to represent a key constitutive relationship for bearing capacity and shallow foundation design. The theoretical and the conventional limits pressure have been evaluated from different methods of interpretation using different theories. This paper provides a new method for interpretation the conventional limit pressure, the new method showed very good agreements with other methods used for evaluating the conventional limit pressure. The new method named as conventional limit pressure. The results of Menard pressuremeter conducted in Abu-Dhabi site been analyzed in five methods of interpretation for conventional and theoretical limit pressure. The deduced results from different methods showed some discrepancies for the same tests. The tested soil can be described as poorly graded sand with silt.     

Distinctive Effects of Horizontal At-Rest Pressure on Conventional Limit Pressure Results

Pressuremeter testing plays an important role in the design of foundations, where several parameters can be deduced from a single test result. Conventional and theoretical limit pressures can be interpreted from pressuremeter tests and are considered key to bearing capacity calculations and shallow foundation designs. Limit pressure can be evaluated using different methods, all of which show discrepancies in values obtained from the same tests. Horizontal at-rest earth pressure can similarly be deduced from different methods of analysis, which also show distinctive differences in results for the same tests. This research explored the important finding that the values of the conventional limit pressure experience considerable discrepancies when using different values of the horizontal at-rest pressure. Values calculated for conventional limit pressure showed considerable increases when increasing the value of the horizontal at-rest pressure, but there was no effect on the theoretical limit pressure.