Interpretation of Cone Penetration tests in Cohesive Soils

Abstract

Prepared in cooperation with the Indiana Department of Transportation and Federal Highway Administration. AbstractThis report focuses on the evaluation of the factors affecting cone resistance measurement during cone penetration in saturated clayey soils and the application of the result to pile shaft capacity analysis. In particular, effects of drainage conditions around the cone tip were studied. Rate effects related to both drainage and shear strength dependence on loading rate were studied. In order to investigate the effects of drainage during penetration, penetration tests were performed with various velocities in the field and in a calibration chamber, and the obtained data were analyzed. For the field tests, two sites which have homogeneous clayey soil layers below the groundwater table were selected, and CPTs were performed with various penetration rates. Penetration tests in the calibration chamber were performed to investigate the transition points between undrained and partially drained, partially drained and fully drained conditions based on cone penetration rate and the coefficient of consolidation.A series of flexible-wall permeameter tests were conducted for various mixing ratios of clays and sands to obtain values of the coefficient of consolidation, which is a key variable in determining the drainage state during cone penetration. Nine piezocone penetration tests were conducted at different rates in calibration chamber specimen P1 (mixture of 25 % clay and 75 % sand) and eight penetration tests were carried out in calibration chamber specimen P2 (mixture of 18 % clay and 82 % sand). From the results of the penetration tests in the calibration chamber, a cone resistance backbone curve, with q c plotted versus normalized penetration rate, was established.Guidelines were proposed for when to interpret CPT tests, whether in estimating soil properties or in estimating pile resistances, in soils for which penetration takes place under conditions that cannot be established as either drained or undrained a priori. Key WordsCone Penetration Test (CPT), Pile Design, Bearing Capacity, Clay, Clayey Soils. Distribution StatementNo restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161 TECHNICAL SummaryTechnology Transfer and Project Implementation Information TRB Subject Code: 62-1 Foundation Soils December 2006 Publication No.FHWA/IN/JTRP-2006/22, SPR-2632 Final Report INTERPRETATION OF CONE PENETRATION TESTS IN COHESIVE SOILS IntroductionVarious types of in situ tests are relied on for estimating soil properties or directly designing foundations. Among the various in-situ tests, the use of the Cone Penetration Test (CPT) has been increasing steadily. There are many factors affecting the cone resistance measured during penetration through saturated clayey soils. These need to be understood and quantified for effective interpretation of CPT results.An important use of cone resistance is in the design of pile foundations. In effect,...

Assessment of undrained shear strength based on Cone Penetration Test (CPT) for clayey soils

“…The following conclusions can be drawn from the study: 1. The cone factor, which is most important for reliable estimation of undrained shear strength from cone resistance, is influenced by soil type, penetration rate during CPT and test Kim et al (2006). Results show all the cases are undrained ones.…”

“…The drainage conditions considering rate effect during CPT have been examined with results from Kim et al (2006). According to the Kim et al's criterion, all the drainage conditions of soil samples fall within the undrained penetration and are shown in Table 5.…”

“…The drainage condition during CPT has been verified with the criteria (Kim et al, 2006). Nine sites in the state of Indiana were determined using the boring log database of the Indiana Department of Transportation (INDOT) and CPTs were performed at the sites.…”

Geotechnical Design Based on CPT and PMT

“…The fact that all of the specimens tested were over-consolidated (OC) clay is verified by the behavior of excess pore pressure. As mentioned before, excess pore pressures for over-consolidated clays (OC) start to develop as positive, approach zero and then, for samples with an over-consolidation ratio (OCR) greater than about 6, become negative (Salgado, 2006). The excess pore pressure distribution for RB-31 (US-31), which has the highest OCR at 11.8, shows the steep (1) nature of load support (friction and end-bearing piles),…”

“…Undrained Shear Strength Behavior of Clay Soils Figure 2, developed by Bishop and Henkel (1962) Figure 5. For over-consolidated clays (OC), excess pore pressures start to develop as positive, approach zero and then, for samples with an over-consolidation ratio (OCR) greater than about 6, become negative (Salgado, 2006). Bishop and Henkel (1962) showed the effects of over-consolidation ratio (OCR) on the pore pressure changes during shear with f A parameter in Figure 6 for samples of both Weald Clay and London Clay.…”