Fugro- CPT Handbook

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complete handbook on CPT
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  Copyright - Fugro Ltd DSC - Feb 96  CONE PENETRATION TESTING (CPT) Simplified Description of the Use and Design Methods for CPTs in Ground Engineering   The attached notes are a preliminary, simplified description of the interpretation, use and designmethods for Cone Penetration Testing (CPTs) in Ground Engineering.Detailed analysis of CPTs can be a complex subject and a number of papers have been written onthis subject. A number of these papers have been summarised to some extent in A.C. Meigh's book  Cone Penetration Testing - Methods and Interpretation (Ref. 1) and reference should be made tothis for a more detailed study of the subject.It is hoped that the following notes give a simplified introduction to CPTs and takes away some of the myth of the Black Art ; thereby allowing the average design engineer to appreciate the benefitsof CPTs and their use in everyday Ground Engineering working situations. For further information contactPaul JacobsFugro Limited18 Frogmore RoadHemel HempsteadHerts HP3 9RTTel. +44 (0)1442 240781www.fugro.co.uk   Copyright - Fugro Ltd DSC - Feb 96  TABLE OF CONTENTS 1. INTRODUCTION ........................................................................................1 1.1. GENERAL ...................................................................................................... 1 2. SOIL IDENTIFICATION ..............................................................................3 2.1. GENERAL ...................................................................................................... 32.2. SOIL CLASSIFICATION ................................................................................. 32.3. EXAMPLES .................................................................................................... 4 3. ENGINEERING PARAMETERS ..................................................................5 3.1. COHESIVE SOILS (CLAY) ............................................................................. 53.2. COHESIONLESS SOILS (SAND/GRANULAR) .............................................. 83.3. ADVANCEMENTS IN CPT'S .......................................................................... 10 4. FOUNDATION DESIGN ..............................................................................11 4.1. GENERAL ...................................................................................................... 114.2. SHALLOW FOUNDATIONS - STRIPS/PADS ................................................. 124.3. DEEP FOUNDATIONS - PILES ...................................................................... 20 5. REFERENCES .............................................................................................37  Copyright - Fugro Ltd Page 1 DSC - Feb 96  1. INTRODUCTION1.1.GENERAL During a CPT, an electrical cone on the end of a series of rods is pushed into the ground ata constant rate of 2cm/s. Continuous measurements are made of resistance to penetrationof the cone tip( qc ) and the frictional resistance(  f  s ), or adhesion, on a surface sleeve setimmediately behind the cone end assembly. Measurements can also be made of other soil parameters using more specialised cones such as pore water pressure (piezocone),electrical conductivity, shear wave velocity (seismic cone), pressuremeter cone, etc.The CPT has three main applications:1.to determine the soil profile and identify the soils present.2.to interpolate ground conditions between control boreholes.3.to evaluate the engineering parameters of the soils and to assess the bearingcapacity and settlement of foundations.In this third role, in relation to certain problems, the evaluation is essentially preliminary innature, preferably supplemented by borings and by other tests, either  in situ or in thelaboratory. In this respect, the CPT provides guidance on the nature of such additionaltesting, and helps to determine the positions and levels at which in situ tests or samplingshould be undertaken. Where the geology is fairly uniform and predictions based on CPTresults have been extensively correlated with building performance, the CPT can be usedalone in investigation for building foundations.Even in these circumstances it is preferable that CPTs be accompanied by, or followed by, borings for one or more of the following reasons:1.to assist where there is difficulty in interpretation of the CPT results.2.to further investigate layers with relatively low cone resistance.3.to explore below the maximum depth attainable by CPT.4.if the project involves excavation, where samples may be required for laboratorytesting and knowledge of ground water levels and permeability is needed.  Copyright - Fugro Ltd Page 2 DSC - Feb 96  The CPT has four main advantages over the usual combination of boring, sampling andstandard penetration testing:1.It provides a continuous, or virtually continuous record of ground conditions.2.It avoids the disturbance of the ground associated with boring and sampling, particularly that which occurs with the Standard Penetration Test (SPT).3.It is significantly cheaper.4.It is faster by a factor of about 10.Furthermore, the disturbance resulting from the advancement of the cone is consistent between one test and another.The following sections describe some of the characteristics of CPTs and methods of interpretation of soil parameters, namely: ã soil stratification and estimation of soil type ã soil strength characterisation ã soil deformability characterisationwith associated examples of interpretation where appropriate.Data from the standard Fugro soil description brochure has been augmented to facilitateinterpretation of the differing soil types, and this should be referenced accordingly.
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