Contents. Glossary 9. Foreword 10

Transcription

1 Glossary 9 Foreword 10 1 Design considerations Introduction Client's general requirements The ground The concept of effective stress Ground profile Groundwater conditions Global movements Methods and types of construction Retaining walls Foundations Ground gases Site Investigation Structural analysis Protective measures Durability and waterproofing Safety Legal and contractual issues Communications 19 2 Ground movement Introduction Causes of movement when excavating General Clays Granular soils Mixed alluvial soils (sands/silts/clays) Soft rocks Fill materials Quantifying movements due to basement construction General Vertical movement within the basement area External movements Effect of excavation geometry Effect of ground movement on surrounding structures and services General Tolerance of buildings Concluding remarks on predicting ground movement Monitoring ground movements 32 3

2 3 Groundwater control Introduction Methods of groundwater control Pumping from sumps Wellpointing Disposal of pumped water Pumping from deep wells Pumping using cut-offs Relief wells Recharging Grouting Ground freezing Permanent groundwater control Changes in groundwater regime 41 4 Methods and type of construction Introduction Methods of construction Construction in open excavation Construction within soil slopes of increased inclination Bottom-up excavation Top-down construction Semi-top-down construction Bottom-up and top-down methods Flying shores Observational Method Types of wall Sheet piles King post walls Contiguous bored pile walls Secant pile walls Diaphragm walls Selection of wall type Types of support system Temporary restraint Permanent restraint Effect of installation of sheet piles and soil retention walls Groundwater 56 5 Design and analysis of retaining walls Introduction Stability considerations Limiting earth pressures Water pressures and the effects of seepage Gravity walls Cantilever walls Singly-propped walls Multi-propped walls Circular basements Factors of safety Temporary works design Base heave failure 63 4

3 5.3 Earth pressures Backfilled walls Initial in-situ earth pressures and the coefficient of earth pressure at rest K o Effects of wall and prop stiffness Design earth pressures Design of wall members Applied wall forces Bending moments and shear forces Wall movements and cracking Computer programs for designing retaining walls Limit equilibrium programs Beam-on-spring model Boundary element programs Full numerical analysis 67 6 Foundations Introduction Loads Water pressures Buoyancy and flooding Water pressure on foundations The influence of excavation on strength and bearing capacity Ground movements Spread foundations Bearing capacity of piles Piled rafts and piles in tension The use of piles to strengthen soils in front of a retaining wall Vertical bearing capacity of piled walls 74 7 Gas in deep basements Introduction Precautions 78 8 Site Investigation Introduction Desk Study Physical investigation of the site Groundwater investigation Parameters for design Classification tests Stiffness parameters In-situ stresses Chemical testing 82 9 Excavation Introduction Methods of excavation Considerations affecting the use of plant in deep excavations Unrestricted sites 85 5

4 9.5 Restricted sites General Diaphragm walls Obstructions 9.7 General removal of spoil from site Piling within basements Protective measures Introduction Internal structural measure: strutting and sequence External structural measure: underpinning General advice Shallow underpinning Deep underpinning External structural measure Strengthening De-sensitisation Load transfer Ground treatment Compensation grouting Ground improvement Structural strengthening Groundwater control Materials, workmanship, durability and water-resisting construction Introduction Reinforced concrete design for foundation engineering structures Durability 'Waterproofing' Structural details Crack control Thermal effects Flexural cracking Design guidelines Maintenance Basement grades, types and details Steel construction Materials and sections Durability Water-resisting construction in steel sheet-piled structures Safety considerations General Legal Health and Safety at Work, etc. Act Management of Health and Safety at Work Regulations Construction (Design and Management) Regulations Construction (Health, Safety and Welfare) Regulations Confined Spaces Regulations

5 12.3 Hazards Underground and overhead services Excavation stability Exceptional circumstances Backfill materials Diaphragm walls Strutting and shoring Ramps and site transport Settlement Piling Erection and support of steel reinforcement Methane, oxygen deficiency and other atmospheric hazards Fencing, lighting, etc Electricity Noise and vibration Contaminated ground Failures leading to injury or death Supervision of work on site Practical difficulties in construction on site Risk assessment Production of a typical risk assessment Legal and contractual issues Forms of contract and procedures Problems specific to basement contracts Specialist contractors Responsibility for Site Investigation Delineation of temporary and permanent works Responsibility for temporary works Use of permanent works to support temporary works Adjacent structures Statutory requirements Communications Importance of communications Information supplied by the engineer Information submitted by the contractor Post-contract and construction stages Quality requirements 127 Appendix A Archaeological implications 128 Appendix B Special services: requirements for deep basements 130 B.1 Introduction 130 B.2 Requirements for fire-fighting ventilation and smoke outlets 130 B.3 Plant rooms 130 Appendix C Statutory requirements (see also Chapter 12) 131 7

6 Appendix D Monitoring 133 D.1 Introduction 133 D.2 Precise level 133 D.3 Total station 134 D.4 Inclinometers 134 D.5 Electrolevels 134 D.6 General 135 Appendix E The Observational Method (OM) 136 E.1 Introduction 136 E.2 The traditional predefined design method and the Observational Method 136 E.3 Recent developments in using the Observational Method 138 E.4 Implementation 138 E.5 Progressive modification approach 138 E.6 Risk, contractual aspects and value engineering 139 Index 141 8