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The Becker penetration test (BPT) is the only tool available for characterizing gravelly soils with a probe diameter that is meaningfully larger than that of the standard penetration test (SPT) and the cone penetration test (CPT).... more
The Becker penetration test (BPT) is the only tool available for characterizing gravelly soils with a probe diameter that is meaningfully larger than that of the standard penetration test (SPT) and the cone penetration test (CPT). Measurements on the BPT system during operation provide information on how penetration is controlled by the driving energy and frictional resistance along the shaft. This has led to development of the instrumented Becker penetration test (iBPT), which uses measurements of force and acceleration obtained directly behind the drill string tip to compute the residual energy and displacement induced by each hammer blow. These measurements are used to produce a continuous profile of normalized blow counts that are repeatable, unaffected by varying driving energy or accumulated shaft resistance, and can be used to directly estimate equivalent SPT N60 blow count values as per DeJong et al. and Ghafghazi et al. in their 2017 studies. The measurements obtained also ...
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Soil particles break during shear, with the intensity of the breakage depending on the stress level amongst other factors. Particle breakage has important implications for the soil׳s critical state, which is an input to the majority of... more
Soil particles break during shear, with the intensity of the breakage depending on the stress level amongst other factors. Particle breakage has important implications for the soil׳s critical state, which is an input to the majority of advanced constitutive models. This work examines a micromechanical framework where particle breakage shifts down the critical state locus in void ratio versus mean effective stress space without changing its slope. The framework assumes that detectable particle breakage in sand does not occur unless the contraction potential of the material, solely by the sliding and the rolling of the particles, is exhausted and a soil specific stress level threshold is surpassed. A series of triaxial compression tests conducted to investigate the validity of the framework is presented. It is shown that particle breakage is a factor, working alongside dilatancy, imposing additional compressibility on the soil.
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: A comprehensive field and laboratory testing program was carried out to characterize cyclic stress strain behavior of various low plasticity clay layers. Undisturbed samples were collected using the fixed piston sampling technique.... more
: A comprehensive field and laboratory testing program was carried out to characterize cyclic stress strain behavior of various low plasticity clay layers. Undisturbed samples were collected using the fixed piston sampling technique. Consolidation, monotonic and cyclic direct simple shear tests were performed on select soil samples. Cone Penetration Testing was used for site characterization as well as delineating different subsurface soil layers. The low plasticity clays tested in this site showed a " clay-like " behavior. The Cone Penetration Test proved useful in characterizing the soil profile but necessary for identifying sampling depths. The over-consolidation ratio was shown to be a helpful index for characterizing monotonic and cyclic response of the low plasticity clays in this study. The materials were observed to develop significant excess pore water pressures and large shear strains under cyclic loading. The post cyclic monotonic tests suggested dilative behavi...
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The sandy deposits along the Fraser River delta in British Columbia, Canada tested for CANLEX provide a rare combination of reliable in situ measure-ments and laboratory element testing on undisturbed and reconstituted samples, al-lowing... more
The sandy deposits along the Fraser River delta in British Columbia, Canada tested for CANLEX provide a rare combination of reliable in situ measure-ments and laboratory element testing on undisturbed and reconstituted samples, al-lowing for direct evaluation of the capability of analytical methods in obtaining ground truth. This work presents an analytical procedure to obtain the state parameter from CPT tip resistances in the CANLEX dataset. It includes calibration of a critical state constitu-tive model through triaxial compression tests, and analysis of the cone penetration us-ing the spherical cavity expansion analogy. The effects of differing gradations and soil fabrics have been captured and reflected in the resultant state parameter interpre-tation. Accuracy is evaluated by comparison to in situ density measurements and comparison to other methods.
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The idea that soils sheared to very high values of strain will eventually reach a constant void ratio, e c , and friction angle, φ cv , is well established in soil mechanics. This constant volume state, usually termed the critical state,... more
The idea that soils sheared to very high values of strain will eventually reach a constant void ratio, e c , and friction angle, φ cv , is well established in soil mechanics. This constant volume state, usually termed the critical state, is also inherent in many, if not most, advanced constitutive soil models, which are sensitive to the estimated shear strength parameters. Hence it is important that geotechnical engineers have access to good parameter estimates based on good industry quality data. However, despite the importance of the critical state to understanding soil behaviour, measurement of φ cv remains problematic. This paper uses good industry quality triaxial data from two well-known Erksak and Ticino sands to investigate the accuracy of four different methods of obtaining shear strength parameters. Based on theoretical and practical limitations of these methods, recommendations are made on how to obtain the most reliable shear strength parameters from a limited amount of ...
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The cone pressuremeter test (CPT) is widely used to determine the in situ “state” of cohesionless soils. However, although the CPT is simple, inexpensive, and accurate the subsequent interpretation contains substantial uncertainties even... more
The cone pressuremeter test (CPT) is widely used to determine the in situ “state” of cohesionless soils. However, although the CPT is simple, inexpensive, and accurate the subsequent interpretation contains substantial uncertainties even with modern approaches. Self-bored pressuremeters (SBP) have the opposite attributes. Obtaining good SBP data is difficult in sands, but the subsequent evaluation can be rather precise. This paper compares estimates of the in situ state parameter, ψ, from CPT and SBP tests carried out in a uniform hydraulic fill. This case history is unusual in that (i) the fill was well controlled and uniform, (ii) comprehensive laboratory strength data exists, (iii) the CPT was calibrated for the fill in a large chamber, and (iv) good SBP data exist. These SBP and CPT tests are independently analyzed using a calibrated critical state model implemented in a large strain finite element code. The effects of ageing and fabric are considered. The resulting most probabl...