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タイトル Japanese Geotechnical Society Standard (JGS3551-2020) Method for in-situ direct tension test on rocks
著者 The Japanese Geotechnical Society
出版 Japanese Geotechnical Society Standard (JGS3551-2020) Method for in-situ direct tension test on rocks
ページ 発行 2021/03/01 文書ID os202103010002
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  • Japanese Geotechnical Society Standard (JGS3551-2020) Method for in-situ direct tension test on rocks
  • 著者
  • The Japanese Geotechnical Society
  • 出版
  • Japanese Geotechnical Society Standard (JGS3551-2020) Method for in-situ direct tension test on rocks
  • ページ
  • 発行
  • 2021/03/01
  • 文書ID
  • os202103010002
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  • JGS 3551-2020Japanese Geotechnical Society Standard (JGS 3551-2020)Method for in-situ direct tension test on rocks1Scope of applicationThis standard specifies the methods of testing for obtaining the strength and deformation characteristics ofspecimens prepared in in-situ rock masses when subjected to axial tension in the unconfined state. Thestandard is mainly applicable to rock masses ranging from soft rocks to hard rocks.Note 1: The standard is not only applicable to homogeneous and/or continuous rock masses, but also to heterogeneousand/or discontinuous rock masses. Moreover, it is applicable to fracture zones and the like.Note 2: The standard is also applicable for obtaining the bond strength between rock masses and concrete.2Reference standards and specificationsThe following standards shall form a part of the requirements of this standard by virtue of being referenced inthis standard. The latest versions (including addendums) of these reference standards shall be applicable.JIS A 0207 Technical terms for geotechnical engineeringJIS B 7507 Vernier, dial and digital calipersJIS B 7510 Precision levelsJIS B 7512 Steel tape measuresJIS B 7516 Metal rulersJGS 2134 Test method for water content of rocksJGS 2511 Method for preparation of rock specimens3Terminology and definitionsThe main terminology and definitions used in this standard shall be in accordance with JIS A 0207 and/or thefollowing.3.1SpecimenSpecimen shall refer to a rock body that cuts the outcrop and the bottom of the tunnel into a columnar shape3.2Axial stress, σaAxial stress shall refer to the stress acting in the longitudinal direction of the specimen.3.3Axial strain, εa,tAxial strain shall refer to the normal strain, taken as positive in extension, in the longitudinal direction of thespecimen.3.4Lateral strain, εr,tLateral strain shall refer to the normal strain, taken as positive in extension, in either the circumferential or theradial direction of the specimen.© JGS 2021 – All rights reserved1 JGS 3551-20203.5Direct tensile strength, stDirect tensile strength shall refer to the maximum tensile stress acting in the axial direction on a specimen.3.6Deformation modulus, EtDeformation modulus shall refer to the secant slope and the tangent slope of the axial stress-axis strain curve.The deformation moduli determined by the secant slope and the tangent slope at 50% of the direct tensilestrength are expressed as Ets,50 and Ett,50, respectively.4Test equipment4.1Equipment to prepare specimenThe equipment for preparing the specimen is a device for cutting out the specimen, and shall be configuredfrom a coring device, a grinder, etc.Note: When the specimen is a prism, a cutting machine may be used.4.2Direct tension test apparatusThe direct tension test apparatus shall be configured from a tension device, a loading plate, a reaction guide, aload cell, and displacement transducers, and shall satisfy the following conditions.Note: Fig. 1 shows the configuration of the direct tension test apparatus. In this configuration, since the specimen is a hollowcylinder, preparation of the specimen is easier than the case in which the specimen is a prism. Furthermore, it isadvantageous that the specimen be less likely to be bent by taking the reaction force to the central axis and pulling the loadplate straight up. The direct tension test apparatus shall be selected according to the site conditions, etc. Other configurationsare shown in Appendix A.a)The reaction guide and the tension device shall have sufficiently high load-bearing strength and loadcapacity with respect to the maximum tensile force applied to the specimen.b)It shall be possible to continuously apply axial displacement or axial stress at a constant rate.c)It shall be possible to measure the axial tensile force up to the maximum axial tensile force of the specimenwithin an allowable tolerance of ± 1%.d)It shall be possible to measure the axial displacement within an allowable tolerance of ± 0.1% of the heightof the specimen. For the purpose of determining the deformation characteristics, strain gauges or localdisplacement transducers shall be installed on the side of the specimen to obtain the axial strain or localaxial displacement. In the example given in Fig. 1, the axial displacement is also measured by an externaldisplacement transducer.Note: When the axial displacement is only measured by an external displacement transducer on the loading plate, etc., anda local displacement transducer is not installed on the side of the specimen, it should be kept in mind that the measuredresults include the effects of the bedding errors at the top of the specimen and the deformations of the ground below thelower end of the specimen. The local displacement transducer shall be installed in the range not affected by the upper and/orlower ends of the specimen. The measurement length of the local displacement transducer is preferably about 50% to 70%of the specimen height.e)4.3a)If the displacement or strain in the circumferential or lateral direction is measured, it shall be possible tomeasure it with the same accuracy as that of the axial displacement or the axial strain.Other equipmentSpecimen dimension measuring equipment© JGS 2021 – All rights reserved2 JGS 3551-2020Measurement of the diameter of the specimen shall be by a vernier caliper. The caliper shall be inaccordance with JIS B 7507. Measurement of the height of the specimen shall be by a steel tape measureor a metal straight ruler. The steel tape measure shall be in accordance with JIS B 7512. The metal straightruler shall be in accordance with JIS B 7516. Measurement of the inclination of the upper end face of thespecimen shall be by a precision level. The precision level shall be in accordance with JIS B 7510.Note: If it is difficult to measure the diameter with a vernier caliper, the length of the circumference may be measured witha steel tape measure to calculate the diameter. The steel tape measure shall be in accordance with JIS B 7512.b)Specimen retrieval deviceWhen the specimen is to be retrieved after the test, the specimen can be cut at its lower end and lifted up.Fig. 1 Example of test equipment5Preparation of specimens5.1Selection of test locationsA suitable test area that is representative of the target rock mass shall be selected based on the geologicalobservation of the roughly excavated ground surface and the outcrop and of the drilled cores obtained aroundthe site.Note 1: It is desirable to conduct tests on three or more specimens. Geological observation and other methods shall beused to confirm that the characteristics of the rock masses at the chosen test locations are the same.Note 2: The number of tests shall be determined according to the characteristics of the rock masses because the test resultsare more variable than those of compression tests.5.2a)Shape and dimensions of specimensThe shape of the specimen shall be a straight hollow cylinder.© JGS 2021 – All rights reserved3 JGS 3551-2020Note: This standard can also be applied to specimens of straight cylinders and straight prisms.b)The diameter of the specimen shall be 300 mm to 600 mm.Note 1: This standard can also be applied to specimens of straight hollow cylinders with diameters of 100 mm to 1000 mm.Note 2: When testing rocks having coarse-grained crystals or conglomerates, the diameter of the specimen should be atleast 5.0 times the largest dimension of the constituent particles.c)The height of the specimen shall be 0.3 to 1.0 times the diameter. It is permissible if it is 0.1 to 2.0 times.Note 1: When the loading plate has a concave shape (a structure in which the end of the specimen is fitted) or when theadhesive protrudes from the loading plate, the height of the specimen shall be the specimen height excluding the height ofthe concavity and the protruding part of the adhesive.Note 2: When anchors are used to fix the loading plate on top of the specimen, the height of the specimen shall be theheight of the exposed part of the specimen to be broken excluding the anchor part.d)5.3The axial direction shall be vertical so that bending does not act on the specimen.Preparation of specimensa)The upper end face of the specimen shall be shaped flat with a grinder. It may be made to be flat bycovering it with mortar, etc.b)The coring device shall be installed at a prescribed position so that the drilling axis is vertical. The specimenshall be drilled to a prescribed diameter.5.4Measurement of specimensa)The inclination of the upper end face of the specimen shall be measured with a precision level. Assumingthat the central axis of the specimen is vertical, this inclination shall be confirmed to meet the requirementsspecified by JGS 2511.b)The diameter of the specimen shall be measured with a vernier caliper in two orthogonal directions nearthe top of the specimen, and the average value of these measurements shall be recorded as the initialdiameter D0 of the specimen.Note: A steel tape measure or a metal straight ruler may be used.c)The height of the specimen shall be measured at three or more positions with a steel tape or metal straightruler, and the average value of these measurements shall be recorded as the initial height H0 of thespecimen.d)If necessary, a representative sample shall be taken of the rock fragments produced when forming thespecimen, and the initial water content w0 of the specimen shall be calculated using JGS 2134 and recorded.e)The initial condition of the specimen shall be geologically observed and recorded with sketches,photographs, etc.6Assembling of test equipment6.1Bonding of specimen and loading plateThe specimen shall be attached with an adhesive and/or anchored so that the central axis of the specimencoincides with the central axis of the loading plate.Note 1: When an adhesive is used, the adhesive shall have sufficient strength so as not to cause breakage inside of theadhesive itself or along the boundaries between the adhesive and the specimen and the loading plate.© JGS 2021 – All rights reserved4 JGS 3551-2020Note 2: In principle, the adhesive should not protrude to the side of the specimen. If sufficient adhesive strength cannot beobtained, however, it is acceptable if the amount of protrusion is about 50 mm or less from the end face. Even in the casewhere the loading plate has a concave shape (a structure in which the end of the specimen is fitted), it is acceptable if theamount of protrusion is about 50 mm or less from the edge of the end face.Note 3: When anchors are used, the structures, components, number, arrangement, and installation method of the anchorsshall be such that the anchors will neither break nor come out, and/or that the specimen will not break near the top surface.6.2Installation of local displacement transducersThe local displacement transducers in an axial direction shall be installed on the side of the specimen.Note: If necessary, local displacement transducers may be installed in a circumferential or lateral direction.6.3Installation of tension deviceThe reaction guide, the load cell, and the tension device shall be installed so that their central axes coincidewith the central axis of the specimen. After that, the external displacement transducers shall be installed.7Test methoda)Zero values for the load cell and the displacement transducers shall be confirmed.Note: Zero values for the circumferential or lateral displacement transducers shall be confirmed, if necessary.b)Axial tension shall be applied continuously at a constant strain rate. The axial strain rate shall be 0.01 to0.1%/minute. However, if it is difficult to maintain a constant axial strain rate, the specimen may be loadedat an axial stress rate equivalent to this axial strain rate.Note: If it is not possible to control the loading at either a constant axial strain rate or a constant axial stress rate, the loadingrate at which the test is completed in about 1 to 15 minutes is taken as the reference value.c)During axial tension loading, axial force P (kN), axial displacement ∆H (mm), and axial strain εa (%) shall bemeasured and recorded.Note 1: The measurement interval shall be set such that it is possible to draw a smooth principal stress difference - axialstrain curve.Note 2: The axial strain shall be measured and recorded by the local displacement transducers installed on the side of thespecimen.Note 3: If necessary, circumferential displacement ∆l (mm) or lateral strain ∆εr shall be measured and recorded.d)The axial tension loading shall be terminated after confirming that the load has dropped below the estimatedweight of the specimen after the axial tensile force shows the maximum value.e)The tension device, the load cell, the loading plate, the external displacement transducers, and the localdisplacement transducers, etc. shall be dismantled. After that, the specimen can be lifted and collected, ifnecessary.f)The failure condition and the deformation of the specimen shall be observed and recorded.Note: The deformation and destruction of the specimen after the test shall be observed and recorded from the direction inwhich those conditions are the most noticeable. Also, if a failure plane is observed, it shall be observed from the direction inwhich the angle of failure plane is the steepest, and it shall be recorded so that the approximate angle can be read. Moreover,the inhomogeneous nature of the specimen, the nature of the discontinuities, and the inclusions of foreign matters, etc. shallbe observed and recorded.g)If necessary, a representative sample of the rock fragments of the specimen shall be taken after the test,and the water content w of the specimen shall be calculated using JGS 2134 and recorded.© JGS 2021 – All rights reserved5 JGS 3551-20208 Processing of test resultsa)The axial strain εa,t (%) of the specimen shall be calculated by the following equation. If axial strain εa,t isdirectly measured, its value shall be converted into a percentage.εa,t = (∆H / H0) x 102where,∆H (mm): axial displacement of the specimenNote: If the displacement in the circumferential or lateral direction is measured, the lateral strain εr,t (%) of the specimen andPoisson’s ratio νt shall be calculated by the following equations. Also, if lateral strain εr,t (%) is directly measured, Poisson’sratio νt shall be calculated using the same equation.εr,t = (∆l / πD0) x 102 = (∆d / D0) x 102νt = - (∆εr,t / ∆εa,t)where,∆l (mm): circumferential displacement of the specimen∆d (mm): lateral displacement of the specimenb)When the axial strain is εa,t (%), axial stress σa,t (MN/m2) shall be calculated by the following equation.σa,t = (P / A0) x 103where,P (kN): axial tensile force applied to the specimenA0 (mm2): initial cross-sectional area of the specimenc)The axial stress - axial strain curve shall be drawn with axial stress σa,t (MN/m2) as the vertical axis andaxial strain εa,t (%) as the horizontal axis.d)The maximum value for the axial stress shall be obtained from the axial stress - axial strain curve and takenas direct tensile strength st (MN/m2), and rounded off to three significant figures. Also, the strain at that timeshall be failure strain εf,t (%) and rounded off to three significant figures.e)Deformation modulus Et (MN/m2) shall be calculated by the following equation. The secant slope Ets,50(MN/m2) of the axial stress - axial strain curve at 50% of the direct tensile strength shall be obtained androunded off to three significant digits.Et = (∆σa,t / ∆εa,t) X 102where,∆εa,t (%): axial strain increment∆σa,t (MN/m2): axial stress increment corresponding to the axial strain incrementNote: If necessary, tangent slope Ett,50 (MN/m2) shall be obtained.9Reporting9.1Map of test siteA drawing that shows the test site and the surrounding area shall be shown.© JGS 2021 – All rights reserved6 JGS 3551-20209.2a)Rock mass condition at test siteName of the test site and depth to the top surface of the specimen from the ground surfaceNote: If necessary, the groundwater level at the test site and the condition of the spring water shall be shown.b)Rock type, lithological characteristics, and conditions of discontinuities such as joints and cracksNote: For example, sandstone, granite, tuff, etc. shall be indicated.c)Rock mass classification of the test site and rock mass classification system that is applied, if a rock massclassification system is appliedd)Sketches and photographs of the rock conditions at the test site before testing9.3Items related to specimena)Shape and preparation method of the specimenb)Initial height and initial diameter of the specimenNote: If the water content is measured, the water content of the specimen in its initial state or after the test shall be reported.c)Results of observation of the specimenNote: The angles of bedding, lamination, and cracks, with respect to the axis of the specimen, and the geological features,such as lithological characteristics, shall be reported.9.4Items related to test methodsa)Loading method (loading device, loading pattern, etc.)b)Measurement method (measuring apparatus, arrangement of the displacement transducers, etc.)c)With or without a spherical joint and its structure (if with)d)Method of bonding the specimen and the adhesive9.5Items related to test resultsa)Axial strain rate or axial stress rate during the axial tension processb)Axial stress – axial strain curveNote 1: If the lateral strain is measured or calculated, the axial stress – lateral strain curve and the axial stress – Poisson’sratio curve shall be reported, as needed.Note 2: The range over which the deformation modulus is calculated shall be indicated, as needed.c)Direct tensile strength st (MN/m2) and failure strain εf,t (%)Note: If the bond strength is measured, it shall also be reported.d)Deformation modulusThe deformation modulus obtained from the slope of the secant, Ets,50, and the deformation modulus obtainedfrom the slope of the tangent, Ett,50, as needed, shall be reported. If the lateral strain is measured or calculated,Poisson's ratio νt shall be reported, as needed.e)Failure state of the specimenPhotographs and sketches of the side and the failure planes of the specimen after loading shall be reported.Note: If the failure occurs in the vicinity of the adhesive surface or anchors, it shall be reported.© JGS 2021 – All rights reserved7 JGS 3551-20209.6Other special itemsIf a method that is partially different from this standard is used, the content shall be reported.Appendix AExamples of configurations for the direct tension test apparatus, other than those shown in Fig. 1, are givenbelow.The example shown in Fig. A1 illustrates an apparatus in which a specimen of a straight cylinder is used. It hasa structure similar to that shown in Fig. 1, but the presence or absence of a sliding portion and the position ofthe tension device are different. In the case of this example, attention must be paid to the influence of the frictionat the sliding portion.The example shown in Fig. A2 illustrates a specimen for which a square prism is employed. A spherical joint isused to reduce the influence of the bending acting on the specimen. Care must be taken to align the centralaxis of the loading plate to that of the specimen.Fig. A1 Example of test equipment (Option 1)© JGS 2021 – All rights reserved8 JGS 3551-2020Fig. A2 Example of test equipment (Option 2)© JGS 2021 – All rights reserved9 Japanese Geotechnical Society Standard (JGS3551-2020)Method for in-situ direct tension test on rocksPublished byThe Japanese Geotechnical Society4-38-2 Sengoku, Bunkyo-ku, Tokyo 112-0011, JapanE-mail: jgs@jiban.or.jpURL: https://www.jiban.or.jp/e/C 2021 The Japanese Geotechnical Society○All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means electronic ormechanical, including photocopying, recording or any information storage and retrieval system now known or tobe invented, without written permission from the publisher.ISBN978-4-88644-123-2
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