Cone penetration-induced pore pressure distribution and dissipation Jin-Chun Chai a,⇑ , Md. Julfikar Hossain a , John Carter b , Shui-Long Shen c a Graduate School of Science and Engineering, Saga University, 1 Honjo, Saga 840-8502, Japan b Faculty of Engineering and Built Environment, the University of Newcastle, NSW 2308, Australia c Department of Civil Engineering, Shanghai Jiao Tong University and State Key Laboratory of Ocean Engineering, 800 Dong Chuan Road, Minhang District, Shanghai 200240, China article info Article history: Received 31 October 2013 Received in revised form 16 January 2014 Accepted 18 January 2014 Keywords: Piezocone test Model test Coefficient of consolidation Excess pore pressure Cavity expansion abstract The excess pore water pressure distribution (u) induced by the penetration of a piezocone into clay and its dissipation behaviour have been investigated by laboratory model tests, theoretical analysis and numerical simulation. Based on the results of the tests and the analysis, a semi-theoretical method has been proposed to predict the piezocone penetration-induced pore pressure distribution in the radial direction from the shoulder of the cone. The method can consider the effect of the undrained shear strength (s u ), over-consolidation ratio (OCR) and rigidity index (I r ) of the soil. With a reliably predicted initial distribution of u and the measured curve of dissipation of pore water pressure at the shoulder of the cone (u 2 ), the coefficient of consolidation of the soil in the horizontal direction (c h ) can be back-fit- ted by analysis of the pore pressure dissipation. Comparing the back-fitted values of c h with the values directly estimated by a previously proposed method indicates that the previously proposed method can be used reliably to estimate c h values from non-standard dissipation curves (where u 2 increases ini- tially and then dissipates with time). Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The piezocone is now widely used as an in situ site investigation tool. From the results of a piezocone penetration test, the soil pro- file and the undrained shear strength (s u ) of a clayey deposit can be estimated, normally quite reliably (e.g., [2]). Numerous research results have also been published on estimating the in situ hydrau- lic conductivity (e.g., [3]) and the coefficient of consolidation of soil in the horizontal direction (c h ) (e.g., [4,16]) from the results of piezocone penetration and dissipation tests. For a standard piezocone with the filter for pore water pressure measurement located at the shoulder of the cone (u 2 type), two types of piezocone dissipation curves have been reported in the lit- erature. One displays monotonic reduction of the measured pore water pressure (u 2 ) with time (e.g., [16]), i.e., the so called ‘‘stan- dard’’ dissipation curve; and the other is a ‘‘non-standard’’ curve, for which the measured value of u 2 increases initially and then re- duces with time [1,4,15]. The reason for a non-standard dissipation curve is that at the beginning of the dissipation the pore pressure at the filter element location is lower than the pore pressures in the soil nearby. The causes for this kind of initial pore water pressure distribution are thought to be: (1) the shear-induced dilatancy effect for overconsolidated clay or dense sandy soil, which results in lower initial pore water pressure being generated in zones of soil with significant shear strain, i.e., in the zone close to the surface of the cone (e.g., [1,4]); and (2) the partial unloading ef- fect when a soil element moves from the face to the shoulder of the cone during cone penetration (e.g., [4]). Kim et al. [10] reported laboratory model test results of the piezocone penetration-induced pore water pressure distribution (u) in the radial direction at the level of the shoulder of the cone. The measured data show that for the normally consolidated case, values of u reduced with radial distance, but for overconsolidated cases (OCR > 5) values of u at the shoulder of the cone (the filter location) are lower. Peak values of u were reached at a radial dis- tance of about 1.4–2.2 times the radius of the cone and then u re- duced with increasing radial distance. Unfortunately, the dissipation curves for these tests were not reported. The numerical results of Chai et al. [4] indicate that even for a slightly overconsol- idated clayey soil, the initial value of u at the shoulder of the cone is lower than values in the nearby soil region. It is clear that knowledge of the initial distribution of u induced by piezocone penetration is very important for establishing a suitable method to evaluate c h from the piezocone dissipation test results. However, due to physical restrictions, such as the size of a piezometer, the limited number of piezometers that can be installed in the ground or in a laboratory test specimen, it is diffi- cult to measure a precise distribution of u around a cone, even in a http://dx.doi.org/10.1016/j.compgeo.2014.01.008 0266-352X/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +81 952288580. E-mail addresses: chai@cc.saga-u.ac.jp (J.-C. Chai), John.Carter@newcastle.- edu.au (J. Carter), slshen@sjtu.edu.cn (S.-L. Shen). Computers and Geotechnics 57 (2014) 105–113 Contents lists available at ScienceDirect Computers and Geotechnics journal homepage: www.elsevier.com/locate/compgeo