Defence Works Functional Standards 09 Geotechnical Investigations for Design and Construction of Airfield Pavements Defence Works Services Ministry of Defence London: HMSO © Crown copyright 1994 Applications for reproduction should be made to HMSO First published 1994 ISBN 011 772813 6 NOTE: This standard reflects the current practices in Ground Investigation and supercedes Airfield Liaison Memorandum No. 64 (1987) published by Directorate of Civil Engineering Services, Property Services Agency (DOE). The Standard is intended for use throughout MOD and shall be used as a guide only. DEFENCE WORKS FUNCTIONAL STANDARD GEOTECHNICAL INVESTIGATIONS FOR DESIGN AND CONSTRUCTION OF AIRFIELD PAVEMENTS CONTENTS PAGE No SECTION ONE - GENERAL 1 Introduction 1 2 Definitions 1 3 Scope 2 4 Responsibilities of the Designer 2 5 Design Principles 3 6 Design Practice 4 SECTION TWO - GENERAL CONSIDERATIONS OF GEOTECHNICAL INVESTIGATIONS 5 7 Primary Objectives of Site Investigations for New and Existing Airfield Pavements 5 8 Design Standards 6 9 Extent and Sequence of Geotechnical Investigations 7 9.1 General 7 9.2 Desk Study 7 9.3 Ground Investigations and field testing for Maintenance and Reconstruction of Existing Pavements 8 10 Ground Investigation and Field Testing Techniques 11 10.1 General 11 10.2 Drilling, In situ Testing and Sampling 11 10.3 Recommendations for Exploratory Hole Depths and Spacing 15 10.4 Design Considerations 16 10.5 Remote Methods of Investigation (including Geophysical) 18 11 Design of Instrumentation and Monitoring 19 12 Geotechnical Investigation Reporting Requirements 20 12.1 General 20 12.2 Factual Reporting 20 12.3 Interpretative Reporting 20 13 Soils Classification and Evaluation 21 13.1 General 21 13.2 Soils Classification and Evaluation of Subgrade Strength 22 13.3 General Classification Tests in the Laboratory 23 13.4 Notes on Special Requirements for Testing Contaminated Soils 26 DEFENCE WORKS FUNCTIONAL STANDARD GEOTECHNICAL INVESTIGATIONS FOR DESIGN AND CONSTRUCTION OF AIRFIELD PAVEMENTS CONTENTS (Continued) PAGE No SECTION THREE - DESIGN CONSIDERATIONS 27 14 Design Parameters 27 14.1 The Modulus of Subgrade Reaction (k) 27 14.2 The California Bearing Ratio (CBR) 27 14.3 Compaction of Subgrade 28 15 Design Guidance 31 15.1 Subsoil and Subgrade Drainage 31 15.2 Very Weak Subgrade (Except Peat) 32 15.3 Subgrade Improvement 33 15.4 Expansive Soils 33 15.5 Frost Susceptibility 34 15.6 Peat 34 15.7 Spring thaw and permafrost 35 15.8 Construction Practice 35 16 Aggregates for the Construction of Pavements 35 17 References Tables 1 General Methods of Drilling and Sampling Techniques 12 2 Recommended Sampling Techniques 13 3 Class of Sample Quality 13 4 Recommended Chemical Sample Preservation and Storage Details 15 5 Spacing of Exploratory Holes 16 6 Sampling Frequencies 17 7 Minimum Sample Mass Required for Testing 17 8 Geophysical Methods of Investigation 18 9 Commonly Used Instrumentation 19 10 Recommended Testing 24 11 List of General Soils Testing 25 12 Relative Compaction Requirements for Subgrade 30 13 List of Recommended Aggregate Testing 36 DEFENCE WORKS FUNCTIONAL STANDARD GEOTECHNICAL INVESTIGATIONS FOR DESIGN AND CONSTRUCTION OF AIRFIELD PAVEMENTS FIGURES 1 Effect of Granular Sub-Base on the Modulus of Subgrade Reaction (k) for Rigid Pavements APPENDICES A Extended Casagrande Soil Classification and CBR/k Relationship Table A1 - The Extended Casagrande Soil Classification Table A2 - Extended Soil Classification with Material Characteristics Figure 2 - California Bearing Ratio versus Modulus of Subgrade Reaction B Standard Cone Penetrometer Interpretation Charts C Interpretation of Pavement Visual Survey Data D CBR versus Soil Suction Curve and Soil Desiccation Potential DEFENCE WORKS FUNCTIONAL STANDARD SECTION ONE - GENERAL 1. INTRODUCTION 1.1 The Defence Works functional standard deals with the investigation of sites for assessing the suitability for the construction of Airfield Pavements and their associated structures (such as culverts, bridges, concrete trunking boxes, maintenance areas, hangers and embankments) and of acquiring the geotechnical and ground contamination characteristics of the site. The objectives of such investigations are to provide information to ensure an economical design and construction of the works by reducing to an acceptable level the uncertainties and risk that the ground poses and ensuring the security of neighbouring land and property. 1.2 The detailed design of ground investigation is very important for the accurate identification and evaluation of the site conditions and pavement formations and cannot be overemphasized. 1.3 This standard does not attempt to cover the wider economic considerations affecting the selection of the site, neither does it cover the structural design of the airfield pavement. 2. DEFINITIONS 2.1 Any investigation in advance of construction works, including earthworks shall involve considering what is a soil and/or rock and their mechanics. Definitions in terms of soils and their testing are given in BS 5930, BS 1377 and BS 6031. Engineering geological descriptions of rocks including the recommended testing are also given in BS 5930. Unless otherwise stated reference shall always be made to the latest editions. 2.2 The following terms are specific to this document: 2.2.1 Site Investigation: Determination of physical characteristics of sites as they affect design and construction of building and civil engineering works and stability of neighbouring structures. 2.2.2 Ground Investigation: Exploration and recording of the location and characteristics of soil and rock, and groundwater conditions. 2.2.3 Designer - The Designer of the site investigation, may be an engineer with a consultant or a contractor. The Designer shall fulfil the requirements of the definition of a Geotechnical Specialist in terms of qualifications and experience (ICE Site Investigation in Construction). 2.2.4 Geotechnical Specialist - A Chartered Engineer or a Chartered Geologist with a postgraduate qualification in geotechnical engineering or engineering geology, equivalent to at least a MSc and with three years post chartered experience in geotechnics or a Chartered Engineer or Chartered Geologist with at least 5 years post-chartered experience in geotechnics. Additional specialist advice on ground contamination should be provided by an environmental scientist, chemist or environmental engineer with a minimum of five years relevant professional experience. 3.0 SCOPE 3.1 This standard sets out detailed guidance, formal procedures, technical standards and gives standard practices (where not covered by other existing standards) for the assessment, design and construction of Airfield Pavements. 3.2 For the purpose of this standard, ground investigation shall include the following: a) desk study b) site reconnaissance c) geomorphological mapping d) procurement of ground investigation contract e) exploratory fieldwork f) in situ testing and sampling g) laboratory test scheduling h) instrumentation and monitoring i) factual reporting j) interpretative reporting 3.3 The use of soil and rock as construction materials is treated only briefly; and reference should be made to BS 6031: Code of Practice for Earthworks. 4. RESPONSIBILITIES OF THE DESIGNER 4.1 Designers shall be responsible for implementing the requirements of this standard in conjunction with current British Codes, Standards and Practices. The Designer should ensure that:- a) an adequate desk study with geotechnical / ground contamination site inspection is carried out; b) following the desk study the ground investigation is then planned, designed and directed; c) appropriate standards of work are then specified; d) the work shall be properly supervised to ensure that the technical standards are met; e) the work is reported in accordance with technical standards. 2 4.2 The Designer shall always consult with the Airfield Property Manager before starting any works on an existing airfield and before writing any Safety requirements specific to a particular site. The Designer shall also consider safety aspects in accordance with the Construction (Design and Management) Regulations 1994, throughout the design process and develop these in the design of the site investigation. These shall include but not be limited to: (a) Effect of work on neighbouring land and structures. (b) Protection of site staff and the public around the site. (c) Access for materials. (d) Access and manoeuvring space for plant. (e) Protection of aircraft and permanent accesses during all stages of the works. (f) Locations of existing services, including drainage, tunnels, electrical, communication and signalling equipment. (g) Temporary works including shoring of trial pits, scaffolding platforms for boring rigs. (h) Backfilling of exploratory holes and pits. (i) Protection of monitoring installations 4.3 The Designer shall consult with all Statutory Authorities with regard to the determination of the presence or absence of services and any special requirements of Statutory Authorities (ie: The National Rivers Authority (NRA)). 4.4 Where Made Ground (possibly contaminated) ground is likely to be encountered, the Designer shall carry out a Risk Assessment and COSHH Assessment in accordance with the Management of health and safety at work regulations (1992). Both statements shall be forwarded to the contractor at the tender stage who shall prepare a separate and detailed COSHH statement for the site work. The Designer shall provide the contractor with all available information concerning the contamination of the site and development history of the site. 4.5 The British Drilling Association (BDA) Guidance Notes for the Safe Drilling of Landfills and Contaminated Land65, DD 175 Code of Practice for the identification of potentially contaminated land and its investigation 57, CIRIA report "A Guide to Safe Working Practices for Contaminated Sites", and the ICE Site Investigation in Construction Volume 455 can be used to assist in the preparation of the above information. 5.0 DESIGN PRINCIPLES 5.1 All pavements are relatively thin constructions, in terms of civil engineering construction, in intimate contact with the ground. The importance of the proper application of soil mechanics principles depends upon the pavement type and their life expectancy. For thin flexible pavements with a thin granular base the influence of the soils is very large, whereas for a substantial reinforced concrete pavement with a thick sub-base it will be much less so. 3