# ASTM D7276-16

Designation: D7276 − 16Standard Guide forAnalysis and Interpretation of Test Data for ArticulatingConcrete Block (ACB) Revetment Systems in Open ChannelFlow1This standard is issued under the fixed designation D7276; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.1. Scope1.1 The purpose of this guide is to provide recommendedguidelines for the analysis and interpretation of hydraulic testdata for articulating concrete block (ACB) revetment systemsunder steep slope, high velocity flow conditions in a rectangu-lar open channel. Data from tests performed under controlledlaboratory conditions are used to quantify stability perfor-mance of ACB systems under hydraulic loading. This guide isintended to be used in conjunction with Test Method D7277.1.2 This guide offers an organized collection of informationor a series of options and does not recommend a specific courseof action. This document cannot replace education or experi-ence and should be used in conjunction with professionaljudgment. Not all aspects of this guide may be applicable in allcircumstances. This ASTM standard is not intended to repre-sent or replace the standard of care by which adequacy of agiven professional service must be judged, nor can thisdocument be applied without considerations of a project’smany unique aspects. The word “Standard” in the title of thisdocument means only that the document has been approvedthrough the ASTM consensus process.1.3 The values stated in inch-pound units are to be regardedas standard. The user of the standard is responsible for any andall conversions to other systems of units. Reporting of testresults in units other than inch-pound shall not be regarded asnonconformance with this test method.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and ContainedFluidsD6026 Practice for Using Significant Digits in GeotechnicalDataD6684 Specification for Materials and Manufacture of Ar-ticulating Concrete Block (ACB) Revetment SystemsD6884 Practice for Installation of Articulating ConcreteBlock (ACB) Revetment SystemsD7277 Test Method for Performance Testing of ArticulatingConcrete Block (ACB) Revetment Systems for HydraulicStability in Open Channel Flow3. Terminology3.1 For definitions of common terms used in this standard,see Terminology D653.4. Summary of Guide4.1 The analysis and interpretation of data from hydraulictests of articulating concrete block (ACB) revetment systems isessential to the selection and design of a suitable system for aspecific application. This guide provides guidelines for assist-ing designers and specifiers in developing a correspondencebetween the test data and the stability parameters used fordesign.4.2 This standard addresses the analysis of hydraulic testdata that is generated from a test or series of tests conducted inaccordance with Test Method D7277.5. Significance and Use5.1 This standard is intended for use by researchers anddesigners to assess the stability of articulating concrete block(ACB) revetment systems in order to achieve stable hydraulicperformance under the erosive force of flowing water.1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.25 on Erosion and SedimentControl Technology.Current edition approved April 1, 2016. Published April 2016. Originallyapproved in 2008. Last previous edition approved in 2008 as D7276 - 08. DOI:10.1520/D7276-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.2 An articulating concrete block system is comprised of amatrix of individual concrete blocks placed together to form anerosion-resistant revetment with specific hydraulic perfor-mance characteristics. The system includes a filter layercompatible with the subsoil which allows infiltration andexfiltration to occur while providing particle retention. Thefilter layer may be comprised of a geotextile, properly gradedgranular media, or both. The blocks within the matrix shall bedense and durable, and the matrix shall be flexible and porous.5.3 Articulating concrete block systems are used to provideerosion protection to underlying soil materials from the forcesof flowing water. The term “articulating,” as used in thisstandard, implies the ability of individual blocks of the systemto conform to changes in the subgrade while remaininginterconnected by virtue of block interlock or additional systemcomponents such as cables, ropes, geotextiles, geogrids, orother connecting devices, or combinations thereof.5.4 The definition of articulating concrete block systemsdoes not distinguish between interlocking and non-interlockingblock geometries, between cable-tied and non-cable-tiedsystems, between vegetated and non-vegetated systems orbetween methods of manufacturing or placement. This stan-dard does not specify size restrictions for individual blockunits. Block systems are available in either open-cell orclosed-cell varieties.6. Procedure6.1 Data Analysis:6.1.1 This section describes the analysis and interpretationof the data collected during a test, including the determinationof hydraulic conditions, qualitative observations and descrip-tions of any damage to the revetment system, and quantifica-tion of threshold hydraulic stability values resulting from thisanalysis that are characteristic of the tested system.6.1.2 Typical test environments incorporate a flow regimethat is supercritical, characterized by high velocities withrelatively shallow depths of flow. In supercritical flow, smallvariations in measured depth can result in relatively largevariations in calculated energy and shear stress. The analyticalmethods suggested in this section have been selected based ontheir suitability to analyze these hydraulic conditions.6.2 Hydraulic Conditions:6.2.1 Accurately quantifying the hydraulic conditions thatexisted during the test is fundamental to the establishment ofstability performance thresholds. The important hydraulic vari-ables that characterize open channel flow include total dis-charge Q, section-averaged velocity V, flow depth y, slope ofthe energy grade line Sf, resistance coefficient (for example,Manning n-value), and boundary shear stress τ.6.2.2 Total Discharge, Q, is determined by use of a primaryflow measurement device such as an in-line flow meter, weir,Parshall flume, or other device appropriate to the facility’smeans for delivering water to the test section.Alternatively, thedischarge may be computed at each of the measurementcross-sections by the continuity equation:Q 5 A~V0.6! (1)where:V0.6= centerline point velocity at six-tenths of the depth offlow at each station, ft/s, (L/T), andA = the cross-sectional area of flow at the same station,measured perpendicular to the direction of flow,ft2(L2).6.2.2.1 The accuracy of the discharge measurement shall bereported as described in Section 7 of this standard.6.2.3 Flow Depth, y, is computed as the difference in themeasured centerline water surface elevation and the elevationof the revetment surface, corrected for the slope angle θ asappropriate, at each measurement station:yi5 ~hi2 zi!cosθ (2)where:yi= depth of flow at station i (perpendicular to the bed), ft(L),hi= water surface elevation at station i, ft (L),zi= bed elevation (top of blocks) at station i, ft (L), andθ = slope angle measured from the horizontal.6.2.4 Energy Grade Slope, Sf, at each measurement stationis calculated from other measured or computed variables as:Sfi5Fn~Vi!KuG21yi4/3(3)where:Sfi= slope of the energy grade line at station i, ft/ft (L/L),n = Manning’s resistance coefficient,Vi= velocity at station i, ft/s (L/T), andKu= units conversion coefficient, equal to 1.486 for U.S.Customary Units and 1.0 for SI Units.6.2.4.1 Eq 3 assumes that the flume walls are significantlysmoother than the revetment surface, such that the totalresistance is due solely to the roughness of the bed.6.2.5 Step-Forewater Analysis—Knowing the total dis-charge Q, flume width b, and the elevations of the watersurface and revetment surface at each of the measurementstations, a forewater calculation can be performed to obtain theoptimal value of the Manning’s n coefficient.6.2.5.1 For supercritical flow, it is recommended that thewater surface profile be computed by solving the momentumequation using the standard step method and proceeding in thedownstream direction:h25 h1112g~v11v2!~v12 v2! 2L2~Sf11Sf2! (4)where:h1,h2= upstream and downstream water surface eleva-tions at stations 1 and 2, ft (L),v1,v2= upstream and downstream velocity at stations 1and 2, ft/s (L/T),Ls = slope length between stations 1 and 2, ft (L), andSf1,Sf2= upstream and downstream energy grade slopes atstations 1 and 2 as defined by Eq 3, ft/ft (L/L).NOTE 1—Other numerical methods are available for computing thewater surface profile, for example the direct step method. The standardstep method is being recommended here because it allows computation ofhydraulic conditions at the actual locations of the flume measurementstations.D7276 − 1626.2.5.2 The objective function to be minimized is definedas:ξ 5(i5i1inabs~hpred2 hobs! (5)where:i1= beginning station for analysis,in= ending station for analysis,hpred= predicted water surface elevation at station ii, ft (L),andhobs= observed water surface elevation at station ii, ft (L).6.2.5.3 By examining a range of Manning’s n values, theoptimal Manning’s n is identified as that which yields theminimum value of the objective function defined by Eq 5. Theoptimal Mannings n value is then used to calculate the watersurface elevation that best fits the observed data. An exampleof such a forewater calculation is provided in Appendix X1.6.2.6 Section-Average Velocity, Vave, is computed as dis-charge Q (determined above) divided by the cross-sectionalarea A, normal to the embankment surface, at each measure-ment station along the test section.6.2.7 Energy Grade Line Elevation, EGL, is determined ateach measurement station by the following equation:EGLi5 zi1yi~ cos θ!1~Vi!22g(6)where:EGLi= elevation of the energy grade line at station i, ft (L),andg = gravitational constant, 32.2 ft/s2(L ⁄T2).6.2.7.1 The procedure for determining energy slope shouldbe performed for the data representing the flow field on thedownstream slope of the test section. If a measurement stationhappens to coincide with the point of the break in slope, datafrom that station should not be used because of the severe flowcurvature at that location.6.2.8 Shear Stress, τ0—If gradually varied flow character-izes the flow field, the maximum boundary shear stress at thebed, τ0, is determined from measured or calculated variablesas:τ05 γ~y!~Sf! (7)where:τ0= bed shear stress, lb/ft2(F ⁄L2),γ = unit weight of water, 62.4 lb/ft3(M ⁄L3),y = depth of flow measured perpendicular to the bed, ft (L),andSf= slope of energy grade line as defined by Eq 3.6.2.8.1 The above equation requires the use of representa-tive data from two or more stations on the downstream slope todetermine the slope of the energy grade line Sf, and therepresentative depth associated with that determination.Typically, a linear regression is performed to determine theslope of the energy grade line. The measured depths from thestations used in this regression analysis are averaged todetermine the representative depth y in order to calculate thebed shear stress.6.2.8.2 Alternatively, the momentum equation across a rep-resentative control volume of finite length L may be used tocalculate τ0:τ05γ2~y11y2!sinθ11LFγ2~y122 y22!cosθ 2 ρq2S1y221y1DG(8)where:γ = unit weight of water, 62.4 lb/ft3(M ⁄L3),y1,y2= flow depths at the upstream and downstream ends ofthe control volume, respectively, ft (L),v1,v2= flow velocity at the upstream and downstream endsof the control volume, respectively, ft/s (L/T),L = length of the control volume along the slope, ft (L),ρ = unit mass of water, 1.94 slugs/ft3(M ⁄L3), andq = unit discharge, ft3/s per foot width (L3/T per Lwidth).6.2.8.3 Both methods given above for quantifying shearstress depend on the judgment of the practitioner to define thedata that best represents the stable performance of the blocksystem. In practice, many data sets will include one or morepoints where the energy grade is not consistent with theexpected trend. In most cases, outliers can be most readilyidentified by plotting the elevation of the energy line versusdistance along the embankment. Note that when Eq 8 is used,the x-axis plotting position for the calculated shear stress τ0islocated halfway between stations 1 and 2.6.2.8.4 Appendix X1 provides an example of such a plot,and illustrates the use of the step-forewater analysis procedureto quantify the hydraulic conditions in areas where datavariability exists. Fig. 1 provides a definition sketch for thevariables presented in this section.6.3 Qualitative Observations of Stability:6.3.1 The hydraulic conditions at the threshold of failuredetermine the hydraulic stability parameters that characterizethe revetment system’s performance. Both shear stress andvelocity at the threshold of failure are typically used forpurposes of developing selection and design criteria for aparticular block system.6.3.2 The researcher’s determination of “failure” of a revet-ment system during a test is somewhat subjective, and dependson his interpretation of the point on the embankment at which“loss of intimate contact” between the revetment system andthe subgrade soil occurred. In practice, all of the followingconditions have been used as guidance for this interpretation(listed in decreasing order of frequency of occurrence):6.3.2.1 Vertical displacement or loss of a block (or group ofblocks).6.3.2.2 Loss of soil beneath the geotextile, resulting invoids.6.3.2.3 Liquefaction and mass slumping/sliding of the sub-soil.3456.4 Stability Threshold Conditions:3Chen, Y. H., and Anderson, B. A., “Development of a Methodology forEstimating Embankment Damage due to Flood Overtopping,” Final Report, Simons,Li channel stability; erosion;erosion control; open channel flow; overtopping; revetment4Clopper, P. E., “Hydraulic Stability of Articulating Concrete Block RevetmentSystems During Overtopping Flow,” Final