ASCE GSP 74-1997 Guidelines of Engineering Practice For Braced and Tied-Back Excavations.pdf

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1、 GEOTECHNICAL SPECIAL PUBLICATION NO. 74Guidelines ofEngineering:PracticeFor Braced andTied-BackExcavationsBy the Committee on Earth Retaining Structuresof The Geo-lnstituteof The American Society of Civil EngineersPublished byAmerican Societyof Civil Engineers1801 Alexander Bell DriveReston, VA 201

2、91-4400GEOINSTITUTEAbstract:When an excavation is made in soil or rock, materials adjacent to the cut face lose their natural lateralsupport. It then becomes necessary to support the excavation by using braces and tiebacks. These willprovide the lateral restraint needed for safety. These guidelines

3、have been prepared to aid civil engineersin making the essential decisions regarding construction safety and excavation activities. They are alsointended to provide information and conceptual orientation for owners, funding agencies, contractors,and engineering and architectural staff.Library of Con

4、gress Cataloging-in-Publication DataAmerican Society of Civil Engineers. Committee on Earth Retaining Structures.Guidelines of engineering practice for braced and tied-back excavations / by the Committee on EarthRetaining Structures of the Geo-Institute of the American Society of Civil Engineers.p.

5、cm.Includes bibliographical references and index.ISBN 0-7844-0293-01. Excavation. 2. Retaining walls. 3. Shoring and underpinning. I. Title.TA730.A44 1997 97-36244624.152-dc21 CIPThe material presented in this publication has been prepared in accordance with generallyrecognized engineering principle

6、s and practices, and is for general information only. This informationshould not be used without first securing competent advice with respect to its suitability for any generalor specific application.The contents of this publication are not intended to be and should not be construed to be astandard

7、of the American Society of Civil Engineers (ASCE) and are not intended for use as a referencein purchase specifications, contracts, regulations, statutes, or any other legal document.No reference made in this publication to any specific method, product, process or serviceconstitutes or implies an en

8、dorsement, recommendation, or warranty thereof by ASCE.ASCE makes no representation or warranty of any kind, whether express or implied, concerningthe accuracy, completeness, suitability, or utility of any information, apparatus, product, or processdiscussed in this publication, and assumes no liabi

9、lity therefore.Anyone utilizing this information assumes all liability arising from such use, including but notlimited to infringement of any patent or patents.Photocopies. Authorization to photocopy material for internal or personal use under circumstances notfalling within the fair use provisions

10、of the Copyright Act is granted by ASCE to libraries and other usersregistered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided thatthe base fee of $4.00 per article plus $.25 per page is paid directly to CCC, 222 Rosewood Drive,Danvers, MA 01923. The identificatio

11、n for ASCE Books is 0-7844-0293-0/97/$4.00 + $.25 per page.Requests for special permission or bulk copying should be addressed to Permissions GEOTECHNICAL ANDCONSTRUCTION CONSIDERATIONS64) OBSERVATION AND MODELING IN NUMERICAL ANALYSIS AND MODEL TESTS INDYNAMIC SOIL-STRUCTURE INTERACTION PROBLEMS65)

12、 DREDGING AND MANAGEMENT OF DREDGED MATERIAL66) GROUTING: COMPACTION, REMEDIATION AND TESTING67) SPATIAL ANALYSIS IN SOIL DYNAMICS AND EARTHQUAKE ENGINEERING68) UNSATURATED SOIL ENGINEERING PRACTICE69) GROUND IMPROVEMENT, GROUND REINFORCEMENT, GROUNDTREATMENT: Developments 1987-199770) SEISMIC ANALY

13、SIS AND DESIGN FOR SOIL-PILE-STRUCTURE INTERACTIONS71 ) IN-SITU REMEDIATION OF THE GEOENVIRONMENT72) DEGRADATION OF NATURAL BUILDING STONE73) INNOVATIVE DESIGN AND CONSTRUCTION FOR FOUNDATIONS ANDSUBSTRUCTURES SUBJECT TO FREEZING AND FROST74) GUIDELINES OF ENGINEERING PRACTICE FOR BRACED AND TIED-BA

14、CKEXCAVATIONSThis page intentionally left blank CONTENTSPREFACE viiCHAPTER 1: INTRODUCTION 11.1 Function of a Braced or Tied-Back Excavationand Role of these Guidelines 11.2 Characteristics of the Supported Excavation . . 11.3 Difficulties with Supported Excavations 21.4 Assignment of Responsibility

15、 41.5 Definitions of Parties of the Work 51.6 Objectives and Organization of the Guidelines . 61.6.1 Readership 61.6.2 Organization of Contents 7CHAPTER 2: INVESTIGATIONS FOR DESIGN AND FORCONSTRUCTION CONTROL 82.1 Introduction 82.2 Subsurface Investigation 92.2.1 Special Requirements Relating toBra

16、ced Excavations2.2.2 Boring and Sampling Procedures 102.2.3 Rock Core Drilling and Logging 02.2.4 Special Investigation Techniques 112.3 Soil Laboratory Testing 122.3.1 Tests for Shear Strength 122.3.2 Consolidation Testing 42.3.3 Stress-Strain Properties 152.3.4 Sensitivity to Vibration 52.3.5 Perm

17、eability Testing 152.4 Preconstruction Survey of AdjacentProperties and Utilities 52.5 Field Observations During Construction 172.5.1 Surface Measuring Points 172.5.2 Inclinometer Devices 172.5.3 Measurements on Excavation SupportSystem 182.6 Availability of Records of FieldInvestigations 92.7 Refer

18、ences 9CHAPTER 3: CONTROL OF SURFACE WATER ANDGROUNDWATER 223.1 Need for Water Control 23.2 Division of Tasks 23.3 Field Investigations 233.4 Specification Requirements for WaterControl 24vii3.4.1 Performance Specifications 253.4.2 Method Specifications 253.5 Maintaining a Dewatered Excavation 263.6

19、 Controlling Surface Water 63.7 Controlling Groundwater 273.7.1 Available System Capacity 273.7.2 Differential Head 73.7.3 Excavation Geometry 283.7.4 Excavation Support System 283.7.5 Subsoil Conditions 83.7.6 Methods of Achieving Drawdown 343.8 Reducing Water Pressures on the SupportSystem 343.9 M

20、inimizing Disturbance of the ExcavationBottom 63.10 Preventing Bottom Blowout 363.11 Effects of Dewatering on Adjacent Areasand Control Measures 73.12 Monitoring Groundwater Changes 383.12.1 Quantity of Flow 393.12.2 Quality of the Effluent 393.12.3 Groundwater Levels 93.13 References 39CHAPTER 4: S

21、YSTEM STABILITY AND WALL LOADING 404.1 Fundamental Considerations 404.1.1 System Stability 404.1.2 Concepts of Earth Loading 404.1.3 Relationship Between Movement andEarth Loads 24.1.4 Preloaded Versus Unpreloaded Systems . .424.2 Stability Analysis 424.2.1 General Trial Solutions 424.2.2 Stability

22、Charts 444.2.3 Vertical Unsupported Slopes inCohesive Soils 44.2.4 Heave into the Bottom of a SupportedExcavation - Required Wall Penetration . 474.2.5 Stability of Internal Berm 474.3 Design Checklist for SupportedExcavation Stability 504.4 Earth Pressure Loadings for Activeor Near-Active Condition

23、s 514.4.1 Apparent Loading Diagrams 514.4.2 Alternatives to Apparent LoadingDiagram for Effects of Surcharge,Seepage, Nonhomogeneity 544.4.3 Loading on Embedded Section of theWall 544.4.4 Charts for Sloping Soil Surfacesand Sloping Walls 56viii4.4.5 Increased Earth Loadings Due toEarthquake 564.5 Ea

24、rth Pressure Loadings for Other thanActive Conditions 64.5.1 Criteria for Greater than ActiveLoadings 564.5.2 Design Loadings 594.6 Effects of Groundwater Loadings 594.7 Ancillary Loadings 614.7.1 Frost Action 14.7.2 Temperature Fluctuations on Braces . 614.7.3 Earthquake Liquefaction of SaturatedSa

25、nds 624.8 Design Checklist for Loading of SupportedExcavations 24.9 Selection of Shear Strength Parameters 634.9.1 Soil Strength Increases with Depth . 634.9.2 Layered Soil Profile, Soft toMedium Clays 654.10 Safety Factors Incorporated into DesignProcedure 654.11 References 6CHAPTER 5: WALLS OF BRA

26、CED AND TIED-BACKEXCAVATIONS 685.1 Introduction 85.2 Driven Sheetpile Walls . 695.2.1 Section Properties 95.2.2 Installation Problems 745.2.3 Extraction of Sheeting 45.3 Soldier Pile and Lagging Walls 45.3.1 Soldier Piles 755.3.2 Lagging Materials 55.3.3 Selection of Wood Lagging 765.3.4 Installatio

27、n Problems 765.4 Cylinder Walls 775.4.1 Small Diameter Piles 75.4.2 Large Diameter Cylinders 775.4.3 Special Conditions 785.5 Concrete Diaphragm Walls 85.6 Special Wall Types 795.7 Selection of Wall Type 805.8 Design Loads and Structural Requirements 815.8.1 General Design Considerations 815.8.2 Wor

28、king Stresses and Safety Factor . 825.9 Wall Specification Requirements 825.10 References 83IXCHAPTER 6: INTERNAL SUPPORT SYSTEM 846.1 Introduction 846.2 Components of Internal Support Systems 856.2.1 Horizontal Tiers of Bracing 856.2.2 Inclined Braces 906.2.3 Special Methods of Support 916.3 Loads

29、in the Support System 926.4 Structural Design Criteria 46.5 Pre-loading of Bracing Systems 76.6 Specifications and Construction Requirements . . 986.7 References 100CHAPTER 7: TIEBACK SUPPORT SYSTEM 1017.1 Introduction 1017.2 Anchor Types and Selection 1047.3 Design, Analysis, and Review 47.3.1 Mass

30、 Stability Analysis 1047.3.2 Tieback Layout and Arrangements 1047.3.3 Capacity of Individual Tiebacks 1077.3.4 Estimating Pullout Resistance 1087.3.5 Vertical Component of Tieback Force . . 1097.3.6 Permanent versus Temporary TiebackInstallations 1097.4 Tieback Anchor Installation 1107.4.1 Proof Tes

31、ting 1107.4.2 Jacking and Measurement Procedures . . 1107.4.3 Other Testing 37.5 Summary 1147.5.1 Tieback Anchor Advantages 1147.5.2 Difficulties with Tiebacks 47.6 References 115CHAPTER 8: SYSTEM CONSTRUCTION AND PERFORMANCE . . 1178.1 Introduction 1178.1.1 Responsibility for Support SystemDesign 7

32、8.1.2 Liability and Insurance 1178.2 Performance Difficulties to be Considered . . 1188.2.1 Deficiencies in the Support System . . 1188.2.2 Excessive Movement 1198.2.3 Unsatisfactory Water Control 1198.2.4 Construction Coordination . 1208.2.5 Avoiding Subgrade Disturbance 1208.3 Integration with Per

33、manent InteriorStructures 1208.4 Pile Driving Problems 1228.5 Problems of Rock in the Excavation 1248.6 Protection of Adjacent Structures 4X8.7 Specifying the Excavation Support System . . . 1278.8 Inspection and Observations 1298.8.1 Resident Engineer and Field Inspector . 1308.8.2 Record Keeping 1

34、308.8.3 Provisions for Job Review and TakingRequired Action 1318.9 Response to Construction Difficulties 1318.9.1 Difficulties with Installation 1318.9.2 Loads in the Support System 1328.9.3 Conditions of the Excavation Interior . 1328.9.4 Response to Field Observations 1338.10 References 133Index 1

35、35XIThis page intentionally left blank PREFACEWork on these guidelines was initiated at the suggestion of the late George W.Sowers, then chairperson of the Earth Retaining Structures Committee of theGeotechnical Engineering Division, at the ASCE 1970 Specialty Conference onLateral Stresses in the Gr

36、ound and Design of Earth Retaining Structures. Thework was continued by successive committee chairpersons including: James P.Gould, Harry W. Schnabel, Thomas D. ORourke, Donald R. McMahon,Lawrence A. Hansen, and Richard J. Finno. It was originally intended to take theform of an ASCE manual, but the

37、Committee found that consensus could not bereached among members representing different industry interests on manyfundamental issues. Therefore, it was finally agreed that guidelines could bestexpress the difference in viewpoints while allowing the user to choose anappropriate approach for a project

38、 without the constraints of a manual or astandard. These guidelines are intended for the use of the professional civilengineer involved in the work of a braced or tied-back excavation. This documentis not a standard.Many members of the Earth Retaining Structures Committee contributed commentsand con

39、cepts to the making of the Guidelines. Those who were particularly helpfulin providing text sections and in reviewing text sections include the followingmembers: H. A. Aldrich, R. A. Alperstein, W. J. Armento, R. A. Bell, G. W.Clough, R. D. Darragh, J. P. Gould, L. A. Hansen, A. J. Nicholson, T. D.O

40、Rourke, H. W. Schnabel, W. L. Schroder, R. vanLeuwen, and D. Weatherby.Text preparation, figure preparation, and final editing of the report were performedby Mary J. S. Roth and Thomas F. Boni.xiiiThis page intentionally left blank CHAPTER 1: INTRODUCTION1.1 Function of a Braced or Tied-Back Excavat

41、ion and Role of TheseGuidelinesWhen an excavation is made in soil or rock the materials adjacent to the cut facelose their natural lateral support. The deeper the excavation and steeper the cut,the greater is the stress unbalance caused by removal of lateral support. If theresulting shear stress exc

42、eeds the materials strength the mass can fail by sliding.Facilities or structures outside the excavation can be damaged, work within theexcavation disrupted and personnel endangered. When it is impractical to provideslopes flat enough for safety, it becomes necessary to support the excavation.Braces

43、 and tiebacks replace the lateral restraint that was provided by materialwhich was removed.Excavation work, especially in urban areas, involves decisions about complexissues, such as construction methods, support loads, base stability, grounddeformation, ground water control, and influence on adjace

44、nt property. Theseguidelines have been prepared to aid the civil engineer in making such decisions.They also are intended to provide information and conceptual orientation forowners, funding agencies, contractors, and engineering and architectural staff.The guidelines deal exclusively with braced an

45、d tied-back excavations utilized inconstruction of buildings or other civil engineering structures. Not included arethe special cases of temporary support of tunnels or underground chambers, mines,cofferdams placed in open water, excavation schemes for quarries, permanentsloped open cuts such as for

46、 highways or site grading and problems of rock slopestability.The guidelines do not cover trench support placed according to code requirementsor empirical rules without engineering design. This omission is not intended tominimize the importance of trench construction and the potential for failure un

47、derthese circumstances. However trench sheeting and bracing often are selected bya contractor based on experience without the participation of a professional civilengineer. For such a situation there are various standard rules in building codesor in Federal safety and health regulations. Such empiri

48、cal rules are not includedor utilized herein.1.2 Characteristics of the Supported ExcavationThe essential elements of an excavation support system comprise a wall, supports,and a reaction to or anchorage for the loads transmitted through the bracing. This1apparently simple arrangement has a number o

49、f features which distinguish it fromordinary civil engineering structures:1. Installation of the support system is coordinated with the excavation and isgenerally built from the top downward. Excavation and support installationusually are performed in stages and the critical condition for variouselements of the support system may occur at some intermediate stage duringthis construction.2. The support system usually is temporary in nature with a life ranging fromseveral months to several years. In special cases