The electric cone penetration test (CPT) has been in use for over 40 years and is growing in popularity in North America. This paper provides some recent updates on the interpretation of some key g...

Interpretation of cone penetration tests — a unified approach

Stationarity or statistical homogeneity is an important prerequisite for subsequent statistical analysis on a given section of a soil profile to be valid. The estimation of important soil statistics such as the variance is likely to be biased if the profile is not properly demarcated into stationary sections. Existing classical statistical tests are inadequate even for simple identification of stationarity in the variance because the spatial variations of soil properties are generally correlated with each other. In this paper, a modified Bartlett statistical test is proposed to provide a more rational basis for rejecting the null hypothesis of stationarity in the correlated case. The accompanying rejection criteria are determined from simulated correlated sample functions and summarized into a convenient form for practical use. A statistical-based soil boundary identification procedure is then developed using the modified Bartlett test statistic. Based on the analysis of a piezocone sounding record, two a...

Identification of statistically homogeneous soil layers using modified Bartlett statistics

Determination of ocr in clays by piezocone tests using cavity expansi0n and critical state c0ncepts

The interpretation of in-situ geotechnical test data needs a unified approach so that soil parameters are evaluated in a consistent and complementary manner with laboratory re- sults. A common thread in assessing in-situ tests is the focus on the geologic stress history, often expressed by the overconsolidation ratio (OCR). For clays, the OCR can be measured by con- solidation tests on undisturbed samples, yet for sands is rather problematic to address. For 6 clays, a hybrid cavity expansion - critical state model is used to match responses measured CPT, CPTu, and DMT. Specifically, tip stress, sleeve friction, penetration porewater pressures, and flat dilatometer readings are fitted by parametric input of OCR, void ratio, friction angle, rigid- ity index, and compressibility parameters. The undrained shear strength (su) of clays is best han- dled via critical-state concepts. Discussions are included for pressuremeter, vane, and T-bar tests. For sands, select empirical methods derived from laboratory chamber testing on reconsti- tuted clean quartz and siliceous sands are reviewed, specifically for effective friction angle φ', OCR, and K0. In a novel look, a special set of undisturbed (frozen) sand samples from 15 loca- tions in Japan, Canada, Italy, Norway, and China is used to check interrelationships for the fol- lowing in-situ penetration tests: SPT, CPT, and Vs. Stiffness of all soils begins with the small- strain shear modulus (G0 = Gmax = ρT Vs 2 ) that can be used together with strength (su or φ') to evaluate stiffness over a range of strains. Supplementary testing by PMT and/or DMT can pro- vide intermediate stiffnesses for tuning of modulus reduction schemes, as well as independent assessments of K0 and OCR.

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In-Situ Test Calibrations for Evaluating Soil Parameters

In this paper, the effects of penetration rate on cone resistance in saturated clayey soils are investigated. Shear strength rate effects in clayey soils are related to two physical processes: the increase of shear strength with increasing rate of loading and the increase of shear strength as the process transitions from undrained to drained. Special focus is placed on this second effect. Cone penetration tests were performed at various penetration rates both in the field and in a calibration chamber, and the resulting data were analyzed. The field cone penetration tests were performed at two test sites with fairly homogeneous clayey silt and silty clay layers located below the groundwater table. Additionally, tests with both cone and flat-tip penetrometers in sand-clay mixtures were performed in a calibration chamber to investigate the change in drainage conditions from undrained to partially drained and from partially drained to fully drained. A series of flexible-wall permeameter tests were conducted in the laboratory for various clayey sand mixtures prepared at various mixing ratios in order to obtain values of the coefficient of consolidation, which is required to estimate the penetration rates below which penetration is drained and above which penetration is undrained. A correlation between cone resistance and drainage conditions was established based on the results of the calibration chamber and field penetration tests.

Effect of Penetration Rate on Cone Penetration Resistance in Saturated Clayey Soils

Cone penetrometers from 8 organizations have been studied by performing laboratory tests and field tests The testing show that pore pressure and temperature zero shift affect significantly uncorrected cone resistance and sleeve friction The magnitude of the measured pore pressure depends on the location of the porous filter By correcting for temperature zero shift and pore pressure effects, one may significantly reduce the differences in the cone resistances derived from the different cones Differences in sleeve friction values are also reduced by the corrections, but not as much

T Lunne

Papers

Laboratory and field evaluation of cone penetrometers