Geoguide 2 Guide to Site Investigation Geotechnical Engineering Office Civil Engineering and Development Department The Government of the Hong Kong Special Administrative Region Geoguide 2 Guide to Site Investigation Geotechnical Engineering Office Civil Engineering and Development Department The Government of the Hong Kong Special Administrative Region 2 © The Government of the Hong Kong Special Administrative Region First published, September 1987 Reprinted, December 1990 Reprinted, December 1993 Reprinted, September 1996 Reprinted, October 2000 Continuously updated e-version, 18 December 2017 Prepared by: Geotechnical Engineering Office, Civil Engineering and Development Department, Civil Engineering Building, 101 Princess Margaret Road, Homantin, Kowloon, Hong Kong. This Geoguide is a continuously updated version incorporating amendments issued since the Geoguide was last published. The continuously updated version is released in e-format only on the CEDD website. This Geoguide is to be cited as “GEO (2017). Guide to Site Investigation (Geoguide 2) (Continuously Updated E-Version released on 18 December 2017). Geotechnical Engineering Office, Civil Engineering and Development Department, HKSAR Government, 349 p.” 3 Foreword This Geoguide presents a recommended standard of good practice for site investigation in Hong Kong, the need for which was formally recognized as early as July 1983 by the Subcommittee of the Building Authority Working Party on Geotechnical Regulations. In its format and content, the Geoguide follows closely the British Standard BS 5930 : 1981, Code of Practice for Site Investigations, but the recommendations in the British Standard have been adapted to suit local conditions and practices. It should be used in conjunction with the companion document, Guide to Rock and Soil Descriptions (Geoguide 3). These Geoguides expand upon, and largely replace, Chapter 2 of the Geotechnical Manual for Slopes. This Geoguide covers Sections l to 7 of BS 5930, while Section 8 is dealt with in Geoguide 3. It has been prepared in such a way that the organization and format of the British Standard have generally been preserved. Where portions of BS 5930 have been adopted in the text without significant amendment, this is clearly denoted by the use of an italic typeface. It should be noted that this Geoguide gives guidance on good site investigation practice and, as such, its recommendations are not mandatory. It is recognized that the practitioner will often need to use alternative methods. There will also be improvements in site investigation practice during the life of the document which will supersede some of its recommendations. The Geoguide was prepared in the Geotechnical Control Office (GCO) under the general direction of Mr J.B. Massey. The main contributors to the document were Dr A. Cipullo, Mr K.S. Smith and Mr D.R. Greenway, with significant contributions during the final stages of preparation from Dr P.L.R. Pang and Dr R.P. Martin. Many other members of the GCO made valuable suggestions and contributions. To ensure that the Geoguide would be considered a consensus document of the civil engineering profession in Hong Kong, a draft version was circulated widely for comment in early 1987 to contractors, consulting engineers and Government Departments. Many organizations and individuals made useful and constructive comments, which have been taken into account in finalizing the Geoguide, and their contributions are gratefully acknowledged. Practitioners are encouraged to comment at any time to the Geotechnical Control Office on the contents of this Geoguide, so that improvements can be made to future editions. E.W. Brand Principal Government Geotechnical Engineer September 1987 4 Contents Page No. Title Page 1 Foreword 3 Contents 4 Part I : Introduction 17 1. Scope 18 2. Terminology 20 Part II : General Considerations 21 3. Primary Objectives of Site Investigation 22 4. General Procedures 23 4.1 Extent and Sequence of Investigation 23 4.1.1 General 23 4.1.2 Adjacent Property 23 4.2 Desk Study 24 4.3 Site Reconnaissance 25 4.4 Detailed Examination and Special Studies 25 4.5 Construction and Performance Appraisal 25 4.6 Site Investigation for Tunnel Works 26 5. Earlier Uses of the Site 28 5.1 General 28 5.2 Tunnels 28 5.3 Mines and Quarries 28 5.4 Waste Tips 28 5.5 Other Earlier Uses 28 5.6 Ancient Monuments 29 6. Aerial Photographs 30 6.1 General 30 6.2 Topographic Maps and Aerial Photographic Imagery 30 5 Page No. 6.2.1 Map and Plan Scales 30 6.2.2 Aerial Photographic Imagery 30 6.2.3 Orthophoto Maps and Plans 31 6.3 Aerial Photograph Interpretation 31 6.3.1 Identification and Interpretation of Ground 31 Features 6.3.2 Examples of API in Hong Kong 32 Part III : Planning the Ground Investigation 33 7. Introduction to Ground Investigation 34 7.1 Objectives 34 7.2 Planning and Control 35 8. Types of Ground Investigation 37 8.1 Sites for New Works 37 8.2 Defects or Failures of Existing Features or Works 37 8.3 Safety of Existing Features and Works 38 8.3.1 Effect of New Works upon Existing Features and Works 38 8.3.2 Types of Effects 38 8.3.3 Procedure 39 8.4 Materials for Construction Purposes 39 9. Geological Mapping for Ground Investigation 41 10. Extent of the Ground Investigation 42 10.1 General 42 10.2 Character and Variability of the Ground 42 10.3 Nature of the Project 43 10.3.1 General 43 10.3.2 Slope and Retaining Wall Construction 43 10.3.3 Foundations for Structures 43 10.4 Preliminary Investigation 43 10.5 Location 44 6 Page No. 10.6 Spacing 44 10.7 Depth of Exploration 45 10.7.1 General 45 10.7.2 Foundations for Structures 45 10.7.3 Embankments 47 10.7.4 Cut Slopes 47 10.7.5 Pavements 47 10.7.6 Pipelines 47 10.7.7 Marine Works 48 10.8 Specific Guidance for Silt- and Clay-rich Layers of Rock Cut 48 Slopes 10.9 Specific Guidance for Tunnel Works 50 10.9.1 Preliminary Design Stage 50 10.9.2 Detailed Design Stage 51 11. Selection of Ground Investigation Methods 53 11.1 General 53 11.2 Site Considerations 53 12. Effect of Ground Conditions on Investigation Methods 55 12.1 General 55 12.2 Granular Soils Containing Boulders, Cobbles or Gravel 55 12.3 Granular Soils 56 12.4 Intermediate Soils 57 12.5 Very Soft to Soft Cohesive Soils 57 12.6 Firm to Stiff Cohesive Soils 57 12.7 Cohesive Soils Containing Boulders, Cobbles or Gravel 58 12.8 Fill 58 12.9 Rock 59 12.10 Soils Derived from Insitu Rock Weathering 59 12.11 Discontinuities 60 12.12 Cavities 61 7 Page No. 13. Aggressive Ground and Groundwater 62 13.1 General 62 13.2 Investigation of Potential Deterioration of Concrete 62 13.3 Investigation of Potential Corrosion of Steel 62 13.4 Investigation of Fill Containing Industrial Wastes 63 14. Ground Investigations over Water 64 14.1 General 64 14.2 Stages and Platforms 65 14.3 Floating Craft 65 14.4 Working between Tide Levels 66 14.5 Locating Borehole Positions 66 14.6 Determination of Reduced Levels 66 14.7 Drilling, Sampling and Testing 67 15. Personnel for Ground Investigation 68 15.1 General 68 15.2 Planning and Direction 68 15.3 Supervision in the Field 68 15.4 Logging and Description of Ground Conditions 69 15.5 Laboratory Testing 70 15.6 Specialist Advice 70 15.7 Interpretation 70 15.8 Operatives 70 16. Review during Construction 72 16.1 General 72 16.2 Purpose 72 16.3 Information Required 73 16.3.1 Soil and Rock 73 16.3.2 Water 73 16.4 Instrumentation 73 16.5 Tunnel Works 73 8 Page No. Part IV : Ground Investigation Methods 75 17. Introduction to Ground Investigation Methods 76 18. Excavations and Boreholes 77 18.1 Shallow Trial Pits and Slope Surface Stripping 77 18.2 Deep Trial Pits and Caissons 78 18.3 Headings or Adits 78 18.4 Hand Auger Boring 78 18.5 Light Cable Percussion Boring 79 18.6 Mechanical Augers 79 18.7 Rotary Open Hole Drilling and Rotary Core Drilling 79 18.7.1 General 79 18.7.2 Flushing Medium 80 18.7.3 Inclined Drilling 81 18.8 Wash Boring and Other Methods 82 18.8.1 Wash Boring 82 18.8.2 Other Methods of Boring 82 18.9 Backfilling Excavations and Boreholes 83 19. Sampling the Ground 84 19.1 General 84 19.2 Sample Quality 85 19.3 Disturbed Samples from Boring Tools or Excavating 85 Equipment 19.4 Open-tube Samplers 86 19.4.1 Principles of Design 86 19.4.2 Sampling Procedure 87 19.4.3 Thin-walled Samplers 88 19.4.4 General Purpose 100 mm Diameter Open-tube Sampler 88 19.4.5 Split Barrel Standard Penetration Test Sampler 89 19.5 Thin-walled Stationary Piston Sampler 89 19.6 Continuous Soil Sampling 89 9 Page No. 19.6.1 General 89 19.6.2 The Delft Continuous Sampler 90 19.7 Sand Samplers 90 19.8 Rotary Core Samples 90 19.9 Block Samples 92 19.10 Handling and Labelling of Samples 92 19.10.1 General 92 19.10.2 Labelling 93 19.10.3 Disturbed Samples of Soil and Hand Specimens of Rock 93 19.10.4 Samples Taken with a Tube Sampler 94 19.10.5 Rotary Core Extrusion and Preservation 95 19.10.6 Block Samples 96 20. Groundwater 97 20.1 General 97 20.2 Methods of Determining Groundwater Pressures 98 20.2.1 Response Time 98 20.2.2 Observations in Boreholes and Excavations 98 20.2.3 Standpipe Piezometers 99 20.2.4 Hydraulic Piezometers 99 20.2.5 Electrical Piezometers 100 20.2.6 Pneumatic Piezometers 100 20.2.7 Installation of Piezometers 101 20.2.8 Varying Groundwater Pressures 102 20.2.9 Soil Suction 103 20.3 Groundwater Samples 103 21.