LIST OF SYMBOLS (continued)moist (total) unit weightYt, Ytot△Acalibrationfactorforapplied suction of membrane in air△Bcalibrationfactorforapplied expansionofmembrane in airAechange in void ratioAHchange in height of soil upon wetting△RmincreaseinradiusofpressuremeterprobeAuchange in pore pressureAWchange in work per unit volume8deformation (of circular membrane).smaximum rateof displacementordisplacement required to achievepeak strength of soilOnnormal displacementosshear displacement8axial strain&fstrain at end of increment8istrain at beginning of increment&paxial strain to reach peak strengthEvvertical strainμvane shear correction factorvPoisson's ratioPoisson's ratio of rockVRppump constantforboreholedilatometerdry mass densityPa, Pdrymoist (total) mass densityPt, Ptotaeffectivestresso1'major principal effective stress03'minor principal effective stress0euniaxial compressivestrengthofrock orconsolidationpressureofstress at end of strain incrementOho'in-situ horizontal effective stress0istressatbeginningofstrain incrementOnnormal stressOn'effective normal stressoppreconsolidation stressovvertical effective stressOvototal vertical stressOvo'in-situ vertical effective stressTshear stressXXV
LIST OF SYMBOLS (continued) xxv γt, γtot moist (total) unit weight ∆A calibration factor for applied suction of membrane in air ∆B calibration factor for applied expansion of membrane in air ∆e change in void ratio ∆Hc change in height of soil upon wetting ∆Rm increase in radius of pressuremeter probe ∆u change in pore pressure ∆W change in work per unit volume δ deformation (of circular membrane) • δ maximum rate of displacement δf displacement required to achieve peak strength of soil δn normal displacement δs shear displacement ε axial strain εf strain at end of increment εi strain at beginning of increment εp axial strain to reach peak strength εV vertical strain µ vane shear correction factor ν Poisson’s ratio νR Poisson’s ratio of rock ρ pump constant for borehole dilatometer ρd, ρdry dry mass density ρt, ρtot moist (total) mass density σ' effective stress σ1' major principal effective stress σ3' minor principal effective stress σc uniaxial compressive strength of rock or consolidation pressure σf stress at end of strain increment σho' in-situ horizontal effective stress σi stress at beginning of strain increment σn normal stress σn' effective normal stress σp' preconsolidation stress σv' vertical effective stress σvo total vertical stress σvo' in-situ vertical effective stress τ shear stress
LIST OF SYMBOLS (continued)peak shear strengthTmaxtrresidual strengthΦfriction angleoeffective stressfriction angle$:instantaneous friction angled:residual friction angledssecant friction angleΦttotal stress friction anglexxvi
LIST OF SYMBOLS (continued) xxvi τmax peak shear strength τr residual strength φ friction angle φ ' effective stress friction angle φ i' instantaneous friction angle φ r' residual friction angle φ s' secant friction angle φ T total stress friction angle
CHAPTER 1INTRODUCTIONTOGEOTECHNICALENGINEERINGCIRCULARONSOILANDROCKPROPERTIES1.1INTRODUCTIONThe purpose of this document is to provide the practicing highway design professional with specificrecommendations regarding the appropriate methods to obtain engineering properties of soil androck materials that may be encountered duringconstruction of a widerange of transportationfacilities.The target audience for Geotechnical Engineering Circular (GEC) No. 5 includesprimarily geotechnical engineers and civil engineers who are responsiblefor establishing subsurfaceexploration programs and directing/overseeing the field and/or laboratory testing programs.Thedocument is equally intended for structural engineers, engineering geologists, or geologists who maybe responsible for these programs.The document is written to provide both general and specificinformationregarding the assessmentof soil and rock propertiesto a potentiallydiverse audience.GEC No.5 was developed ina very specific manner due in large part to the diverse background ofpotential readers.It is recognized that every civil engineer, and many geologists, have had classesrelated to this subject and there are several excellent textbooks and Federal Highway Administration(FHWA)-sponsored courses, demonstration projects, and guidance manuals dealing with the subjectmatter.Additionally, because site investigations and laboratory testing are critical steps in virtuallyall highway projects, every state Department of Transportation (DOT)has had to deal with thesubject and resolve issues related to soil and rock properties on a day-to-day basis. Therefore, it isanticipated thatalmost everyreaderhas an opinion, or at leastan experience, regardingthe subjectofsoil and rock properties.The purpose of this document is to provide each reader,regardless of theirlevel of experience, with guidance related to appropriate techniques for evaluating soil and rockproperties.1.2 BACKGROUNDTextbooks and FHWA courses and documents are invaluable in terms of providing generalrecommendations concerning site investigation and laboratorytesting.Basic information regardinghow many holes to advance, how many samples to obtain, and how to conduct specific laboratorytestscanbefoundinthesesources.Theoneelementmissingfrommostofthesedocuments/coursesis a rationale for the “judgment" that must be applied to decide which specific tests are going toprovide the specific information needed for a specific project and how to appropriately interpretthese test results.Without judgment, the site exploration and field/laboratory testing phases canbecome prescriptive (e.g.,advance ten boreholes to refusal, spaced at 60-m centers obtainingStandardPenetrationTest(SPT)samplesat1.5-mverticalintervals).Thisapproachmaymissthefact that previous explorations in the area identified a weak 0.6-m thick clay layer at a depth of 5 mbelowgroundsurfacethatwill controlthestabilityoftheproposed embankmentconstructedoverthedeposit.Therefore,there is a need to assist thedesign professional in making rationale decisions1
1 CHAPTER 1 INTRODUCTION TO GEOTECHNICAL ENGINEERING CIRCULAR ON SOIL AND ROCK PROPERTIES 1.1 INTRODUCTION The purpose of this document is to provide the practicing highway design professional with specific recommendations regarding the appropriate methods to obtain engineering properties of soil and rock materials that may be encountered during construction of a wide range of transportation facilities. The target audience for Geotechnical Engineering Circular (GEC) No. 5 includes primarily geotechnical engineers and civil engineers who are responsible for establishing subsurface exploration programs and directing/overseeing the field and/or laboratory testing programs. The document is equally intended for structural engineers, engineering geologists, or geologists who may be responsible for these programs. The document is written to provide both general and specific information regarding the assessment of soil and rock properties to a potentially diverse audience. GEC No. 5 was developed in a very specific manner due in large part to the diverse background of potential readers. It is recognized that every civil engineer, and many geologists, have had classes related to this subject and there are several excellent textbooks and Federal Highway Administration (FHWA)-sponsored courses, demonstration projects, and guidance manuals dealing with the subject matter. Additionally, because site investigations and laboratory testing are critical steps in virtually all highway projects, every state Department of Transportation (DOT) has had to deal with the subject and resolve issues related to soil and rock properties on a day-to-day basis. Therefore, it is anticipated that almost every reader has an opinion, or at least an experience, regarding the subject of soil and rock properties. The purpose of this document is to provide each reader, regardless of their level of experience, with guidance related to appropriate techniques for evaluating soil and rock properties. 1.2 BACKGROUND Textbooks and FHWA courses and documents are invaluable in terms of providing general recommendations concerning site investigation and laboratory testing. Basic information regarding how many holes to advance, how many samples to obtain, and how to conduct specific laboratory tests can be found in these sources. The one element missing from most of these documents/courses is a rationale for the “judgment” that must be applied to decide which specific tests are going to provide the specific information needed for a specific project and how to appropriately interpret these test results. Without judgment, the site exploration and field/laboratory testing phases can become prescriptive (e.g., advance ten boreholes to refusal, spaced at 60-m centers obtaining Standard Penetration Test (SPT) samples at 1.5-m vertical intervals). This approach may miss the fact that previous explorations in the area identified a weak 0.6-m thick clay layer at a depth of 5 m below ground surface that will control the stability of the proposed embankment constructed over the deposit. Therefore, there is a need to assist the design professional in making rationale decisions
when encountering real (as opposed to textbook) soil deposits. The designer must make decisionsregarding: (1) the layout and organization of the subsurface exploration program; (2) the type of insitu or laboratory test to run on the encountered material; and (3) the proper techniques to employ ininterpreting multiple test results and developing design parameters.In reviewing the text and course materials that are currently available, it is recognized that twoimportantareas arenot addressed.First,over thepast15to 20years,several in situtestingtechniques have moved from the arena of university research to routine engineering practice.Today,in situ testing plays a critical role in assessing soil properties and, to a lesser extent, rock properties,particularly by complementing laboratory-derived data.The designer needs to understand what insitu tests are applicable for specific soil deposits and specific soil properties.The second area that isnot addressed in current literature is that the data resultingfromtherange of laboratory and in situtests are often not completely consistent with other data obtained for the project and/or soil depositThedesigner needs to develop a rationale for accepting or rejecting data and for resolvingpotentialinconsistencies between data provided by different laboratory and field tests.This document was prepared to provide the design professional with tools to assist in the rationaldevelopment of subsurface investigation as well as in the execution and interpretation of laboratoryand field testing programs.This document attempts to provide this rationale for the entire range ofmaterialspotentially encountered bya stateDOT.This includes soft clay to intactrock and allvariationsofmaterialbetweentheseextremes.1.3DOCUMENT ORGANIZATIONTo assist the reader, the rationale for evaluating soil and rock properties has been organized intoeight specific chapters.After this initial Chapter 1 that provides a general introduction to the entiredocument, the remainder of the GEC No. 5 is organized as follows:Chapter 2 provides an overview of the remainder of thedocument by describing an FHWA-recommended“process"for obtaining soil and rock properties.Chapter 3 describes the rationale and procedures for developing a subsurface investigationprogram in soil and rock deposits.Chapter 4 provides a general introduction and description of field and laboratory tests.focusing on specific tests, the resulting data from the tests, and the limitations of the tests.Chapter 5 describes the procedures for selecting specific tests for soil and for interpretingthe resulting data from these tests.Chapter 6describes rock mass classification and theprocedures for selecting specific testsfor rock and rock masses and for interpreting the resulting data from these tests.Chapter 7 provides a discussion on special materials (e.g., expansive soils, loess, organicmaterials, colluvium, talus, and degradable materials) that could be encountered by a designprofessional.2
2 when encountering real (as opposed to textbook) soil deposits. The designer must make decisions regarding: (1) the layout and organization of the subsurface exploration program; (2) the type of in situ or laboratory test to run on the encountered material; and (3) the proper techniques to employ in interpreting multiple test results and developing design parameters. In reviewing the text and course materials that are currently available, it is recognized that two important areas are not addressed. First, over the past 15 to 20 years, several in situ testing techniques have moved from the arena of university research to routine engineering practice. Today, in situ testing plays a critical role in assessing soil properties and, to a lesser extent, rock properties, particularly by complementing laboratory-derived data. The designer needs to understand what in situ tests are applicable for specific soil deposits and specific soil properties. The second area that is not addressed in current literature is that the data resulting from the range of laboratory and in situ tests are often not completely consistent with other data obtained for the project and/or soil deposit. The designer needs to develop a rationale for accepting or rejecting data and for resolving potential inconsistencies between data provided by different laboratory and field tests. This document was prepared to provide the design professional with tools to assist in the rational development of subsurface investigation as well as in the execution and interpretation of laboratory and field testing programs. This document attempts to provide this rationale for the entire range of materials potentially encountered by a state DOT. This includes soft clay to intact rock and all variations of material between these extremes. 1.3 DOCUMENT ORGANIZATION To assist the reader, the rationale for evaluating soil and rock properties has been organized into eight specific chapters. After this initial Chapter 1 that provides a general introduction to the entire document, the remainder of the GEC No. 5 is organized as follows: • Chapter 2 provides an overview of the remainder of the document by describing an FHWArecommended “process” for obtaining soil and rock properties. • Chapter 3 describes the rationale and procedures for developing a subsurface investigation program in soil and rock deposits. • Chapter 4 provides a general introduction and description of field and laboratory tests, focusing on specific tests, the resulting data from the tests, and the limitations of the tests. • Chapter 5 describes the procedures for selecting specific tests for soil and for interpreting the resulting data from these tests. • Chapter 6 describes rock mass classification and the procedures for selecting specific tests for rock and rock masses and for interpreting the resulting data from these tests. • Chapter 7 provides a discussion on special materials (e.g., expansive soils, loess, organic materials, colluvium, talus, and degradable materials) that could be encountered by a design professional
Chapter 8provides a brief summary of techniquesavailabletothe engineerto resolveinconsistencies in test results from different tests and to appropriately select design values.The final portion of the document presents three Property Selection Examples in which the conceptsidentified in Chapters 2 through 8 are put into practice. For each of the examples, a “real" soilprofile is used and the example provides a step-by-step approach in conducting the subsurfaceinvestigation program, performing laboratory and field tests, and interpreting the test results toobtain recommended soil and rock properties that may be required for typical highway relateddesigns.A few final notes are warranted with regards to the document.It is expressly noted that thedocument presents a summary of the state of-the-practice as of the document date for a wide rangeof subsurface conditions.As such,many of the relatively“new"investigation and testing techniquesthat are currently available to DOTs, particularly in situ testing methods, have been included in thedocument.Thedocument provides specific recommendations regarding thebest tests to run foragiven soil and the proper method to interpret these tests.By providing a rationale for obtainingrealistic and appropriate soil and rock properties, it is anticipated that an “improved"or a“better"understanding and estimation of these properties will result relative to historical practices.Thedesigner must assess how these properties affect the selected design, as many of the current designmethods are semi-empirical and based largely on the historical (i.e., not the improved) techniques forevaluating soil and rock properties. Finally, it is intended that this document be read cover-to-cover,more as anovel"than as a“cookbook."In the latter case, the reader may desire specificinformation regarding a specific test and therefore can read a few pages from the text to secure ananswer.With this document,recommendationsaremadeasexplicitparagraphsand sometimestherationaleisexplained aspartoftheoverallphilosophy.Therefore,itisintendedthatthereaderinitiallyreadthedocumentcover-to-cover.Later,referencetospecificsectionsandtorecommendations can be made, but this later reference is provided once the spirit of the entiredocument has been understood. Although the authors have attempted to address the widest range ofpotential conditions encountered by the designer, there will certainly be cases that are not addressedin this document.By applying thephilosophy and extrapolating the recommendations to these newand potentially more complex scenarios, the authors believe the reader will be able to use thisdocumentforeven themost complexhighwaydesign applications.3
3 • Chapter 8 provides a brief summary of techniques available to the engineer to resolve inconsistencies in test results from different tests and to appropriately select design values. The final portion of the document presents three Property Selection Examples in which the concepts identified in Chapters 2 through 8 are put into practice. For each of the examples, a “real” soil profile is used and the example provides a step-by-step approach in conducting the subsurface investigation program, performing laboratory and field tests, and interpreting the test results to obtain recommended soil and rock properties that may be required for typical highway related designs. A few final notes are warranted with regards to the document. It is expressly noted that the document presents a summary of the state of-the-practice as of the document date for a wide range of subsurface conditions. As such, many of the relatively “new” investigation and testing techniques that are currently available to DOTs, particularly in situ testing methods, have been included in the document. The document provides specific recommendations regarding the best tests to run for a given soil and the proper method to interpret these tests. By providing a rationale for obtaining realistic and appropriate soil and rock properties, it is anticipated that an “improved” or a “better” understanding and estimation of these properties will result relative to historical practices. The designer must assess how these properties affect the selected design, as many of the current design methods are semi-empirical and based largely on the historical (i.e., not the improved) techniques for evaluating soil and rock properties. Finally, it is intended that this document be read cover-to-cover, more as a “novel” than as a “cookbook.” In the latter case, the reader may desire specific information regarding a specific test and therefore can read a few pages from the text to secure an answer. With this document, recommendations are made as explicit paragraphs and sometimes the rationale is explained as part of the overall philosophy. Therefore, it is intended that the reader initially read the document cover-to-cover. Later, reference to specific sections and to recommendations can be made, but this later reference is provided once the spirit of the entire document has been understood. Although the authors have attempted to address the widest range of potential conditions encountered by the designer, there will certainly be cases that are not addressed in this document. By applying the philosophy and extrapolating the recommendations to these new and potentially more complex scenarios, the authors believe the reader will be able to use this document for even the most complex highway design applications