RWIIP Ch 4 Risk Assessment and Asset Management (F...identified risks, the NYSDOT’s value improvement platform includes a risk assessment program. The goal of risk assessment is

NYSDOT Retaining Wall Page 4-1 October 31, 2018Inventory and Inspection Program

RETAINING WALLINVENTORY AND INSPECTION PROGRAM

CHAPTER 4

RISK ASSESSMENT AND ASSET MANAGEMENT


(Intentionally left blank)

Table of Contents


4.1 RETAINING WALL RISK ASSESSMENT PROGRAM .............................................. 4-4

4.2 QUALITATIVE GEOTECHNICAL RISK ANALYSIS................................................. 4-54.2.1 Risk ...................................................................................................................... 4-64.2.2 Phase 1 - Qualitative Risk Analysis..................................................................... 4-74.2.3 Risk Ratings ....................................................................................................... 4-10

4.3 QUANTITATIVE GEOTECHNICAL RISK ANALYSIS............................................ 4-124.3.1 Service Life ........................................................................................................ 4-154.3.2 Phase 2 - Quantitative Risk Analysis................................................................. 4-15

4.4 REFERENCES .............................................................................................................. 4-17

APPENDIX 4-A Quantitative Geotechnical Risk AnalysisMSES Wall Investigations - Sample Retrieval, Storage,Measurements, and Testing Protocol ....................................Appendix 4A-1

4-B Quantitative Geotechnical Risk AnalysisMSES Wall Investigations - Sample Measurement Plan......Appendix 4B-1

CHAPTER 4Risk Assessment and Asset Management


4.1 RETAINING WALL RISK ASSESSMENT PROGRAM

As explained in RWIIP Chapter 1 Introduction and Purpose, risk management is defined by theMAP-21 legislation as the processes and framework for managing potential risks, includingidentifying, analyzing, evaluating, and addressing the risks to assets and system performance.

In order to provide an assessment of identified risks (in terms of the likelihood of theiroccurrence and their impact, and consequence, if they do occur) and to evaluate and prioritizeidentified risks, the NYSDOT’s value improvement platform includes a risk assessment program.The goal of risk assessment is to identify and describe the risk(s) associated with a retaining wallfailure and to examine and evaluate the potential impacts of that risk. Risk assessmentprocedures can include both qualitative and quantitative methods.

In qualitative assessments, descriptive or categorical treatments of information are used in lieu ofquantitative numerical estimates. Quantitative risk assessment relies heavily on sample sets witha statistical approach to determine likely outcomes and the probabilities of their occurrence.

For the retaining wall asset management plan, a qualitative risk analysis is proposed for the firstphase of the overall Retaining Wall Risk Assessment Program. The first phase will develop riskratings (based on wall condition, age, failure consequence, AADT, and height) that will provide aperformance indicator to be judged against targeted performance measures and objectives. Thesecond phase of the overall Retaining Wall Risk Assessment Program will be instituted for wallswhich constitute an elevated risk as determined via phase 1 analysis and are selected as anappropriate candidate for further in-depth analysis (i.e. highest risk walls). This second phaseconsists of a quantitative risk analysis to predict remaining service life through statisticallyrepresentative measurements, non-destructive testing, and/or sampling that is obtained/measuredusing rational and stringent, repeatable procedures that are applied consistently.



4.2 QUALITATIVE GEOTECHNICAL RISK ANALYSIS

The Qualitative Retaining Wall Risk Assessment Program process steps include the following:

The process steps include the following:a. Inventory – Determination of what wall assets exist and the associated element

parameters.The AgileAssets retaining wall inventory will be developed in stages. The first

stage will focus on the mechanically stabilized earth system walls in Region 8. This stagewill be used as a test of data assessment and result appraisal. The second stage willincorporate the remaining mechanically stabilized earth system walls throughout theState. The remaining stages will delve into other types of retaining walls as inventory andinspection data become available.

b. Condition – Determination of wall asset conditions based on known data obtainedthrough inventory, inspection, and department records.



c. Performance Measures/Targets – Determination of existing wall performance relative toperformance measures and targets such as mobility and condition.

d. Performance Indicators – Assessment of performance relative to targets that areestablished in accordance with NYSDOT performance goals or recommended wheregoals are not defined.

A Maintenance step is included to identify the implementation of recommendedlow-cost, routine, preventative measures to sustain the performance of the wall.

e. Mitigation Alternatives – Development of asset management options to improve orprevent further degradation of performance.

f. Prioritization Planning and/or Cost-Benefit Analysis – Feasibility evaluation for proposedalternatives.

g. Decision Support – Preparation of reports and plan documents to address the processoutcomes.

4.2.1 Risk

In this plan, risk is defined as the product of likelihood and consequence for an adverse event,such as a wall failure or deterioration in wall condition or condition states. A variety of directfield observations are used to develop condition state ratings used to establish likelihood. Thedevelopment of a condition state rating may use the following references:

FHWA Publication No. FHWA-CFL/TD-10-003, Retaining Wall Inventory andCondition Assessment Program (WIP), National Park Service Procedures Manual (2010),

NCHRP Report Guide to Asset Management of Earth Retaining Structures (2009), NCHRP Synthesis 437 Assessing the Long-Term Performance of Mechanically Stabilized

Earth Walls (2012), FHWA/NC/2014-10 Retaining Wall Inventory and Assessment System, North Carolina

Department of Transportation (2015), Retaining and Noise Wall Inspection and Asset Management Manual, Colorado

Department of Transportation (2016)

Risk is a means to evaluate the potential threats to NYSDOT performance areas such as mobilityor maintenance expenditures. When considering mobility performance measures, retaining wallsand wingwalls typically will have a higher risk relative to noise walls due to the potential forgreater impacts to mobility (i.e. there will likely be a greater disturbance to travel lanes from aretaining wall collapse as opposed to a noise wall collapse). The financial consequences typicallywould be greater as well. Furthermore, fill walls that directly retain traffic or bridge approachescould have higher risk relative to a retaining wall supporting an uphill slope adjacent to the right-of-way, due to the threat to traffic. By using risk analysis in the asset management process, theNYSDOT wall asset management approach will direct limited funds to the assets that present thegreatest performance risk. This results in a plan that manages the performance of the wall ratherthan the wall.



4.2.2 Phase 1 – Qualitative Risk Analysis

As we focus on mechanically stabilized earth system walls for the initial stage of the plan, deskstudies have been completed and we have plans, shop drawings, material specifications, and, insome locations, backfill testing data for each structure. In addition, we have routine inspectiondata containing visual observations providing a subjective assessment of the structures condition,broken down into various problem indicators:

Aesthetics- Vegetation- Construction Hardware- Panel Staining- Panel Spalling- Panel Cracking

Structural- Bulging- Rotation- Horizontal Joint Alignment- Vertical Joint Alignment- Sloughing of Slope Above Wall- Pavement Cracking

Based on the existing available information, a qualitative risk analysis may be developed toprovide relative risk ratings as follows:

Scoring criteria is outlined in the following tables:



Condition State:

Condition Condition State 1 Condition State 2 Condition State 3 Condition State 4GOOD FAIR POOR SEVERE

Entire Wall New to GoodCondition:Wall is plumb andtrue. None tomoderate extent oflow severitydistress. Defectsmay include thosetypically causedfrom fabrication orconstruction, orminormisalignment orsettlement.Distress presentdoes notsignificantlycompromise theelement function,nor is theresignificant severedistress to majorstructuralcomponents of anelement. No actionis required.

Satisfactory to FairCondition:Elements of thewall have isolatedor minordeterioration. Highextent of low-severity distressand/or low tomedium extent ofmedium-severitydistress. Theremay be moderatecracking,settlement or othersigns of wallmovement. Littleto no settlement ordepressions of theground above orbelow the wall.

Flawed to PoorCondition:Elements of thewall havemoderatedeterioration.Medium to highextent of medium-severity distress.Significant tomajor cracking,settlement and/orbulging of thewall. There may besubsidence ofground above orbelow the wall.

Critical to SevereCondition:Elements of thewall haveadvanceddeterioration.Medium to highextent of high-severity distresswhich couldthreaten overallstability of thewall. Evidence ofmovement,misalignment,settlement and/orbulging of thewall.

Source: adopted and modified from FHWA-CFLHD Retaining Wall Inventory and Condition AssessmentProgram (WIP): National Parks Service Procedure Manual.

Age:

Age Rating Age Rating Definition

1 Constructed less than 25 years ago

1.25 Constructed between 25 – 50 years ago

1.5 Constructed more than 50 years ago



Consequence of Failure:

Failure Consequence ofFailure 1

Consequence ofFailure 2



NEGLIGIBLE MINOR MAJOR CRITICALEntire Wall The transportation

infrastructureconditionexperiences littleto no impact onsystemperformance andthere is no loss ofmajor assets. Noimpacts tostructures,roadways, or off-NYSDOT ROWproperty.

The transportationinfrastructure istemporarily atlimited capacity orunable to operateat the source of thefailure, but canreturn to servicewithout aninterruption ofmore than one day.A minor numberof assets may bedamaged but themajority of thefacility is notaffected. No toslight impact tosystemperformance(temporary: lessthan 1 day).

The transportationinfrastructure maybe temporarily atlimited capacityfor a period of upto two weeks and aportion of thefacility at thesource of thefailure may beclosed for anextended period oftime (less than onemonth). Impactbeyond NYSDOTROW and/ordebris on roadway.The connectivityof the facilityremains intact butnoticeable impactto systemperformance.

The transportationinfrastructure isdamaged beyonduse at the source ofthe failure. Mostassets within thearea are damagedand extensiverepairs are needed.Collapse of at leastone travel lane(essentialstructure) andsignificant impactto systemperformance.



Annual Average Daily Traffic (AADT)

AADT Rating AADT Rating Definition

1 AADT less than 2,500

1.25 AADT between 2,500 – 5,000

1.5 AADT between 5,000 – 10,000

2 AADT between 10,000 – 50,000

2.25 AADT greater than 50,000

Wall Height:

Wall HeightRating

Wall Height Rating Definition

1 Wall heights less than 15 feet.

1.1 Wall heights of 15 feet or more.

4.2.3 Risk Ratings

Risk ratings are determined based on the product of the inventory parameter (condition state),and age of the structure, that addresses the likelihood of an adverse event (or failure) and theconsequence of the event as it may impact system performance (i.e. traffic).

The calculation for the risk score is presented below.

Risk Score = [Wall Condition x Age Factor] x[Failure Consequence x AADT Factor x Height Factor]

Risk scores will be grouped into three categories representing relative risk: Elevated Risk,Moderate Risk, and Low Risk. The thresholds that bound these categories are as follows:

Low Risk: risk score of less than 15 Moderate Risk: risk score between 15 and 20 Elevated Risk: risk score of 20 or higher



The risk score results may be used as Performance Measures/Targets for use in NYSDOT Risk-Based Asset Management Plan Performance Measures and Objectives. Furthermore, the riskscore results may be used as Performance Indicators for use in NYSDOT Policy GuidingStatewide Plan Development.



4.3 QUANTITATIVE GEOTECHNICAL RISK ANALYSIS

The Quantitative Geotechnical Risk Analysis is a subdivision of the qualitative geotechnical riskanalysis whereby the condition state of the wall is determined through thorough and exhaustivesampling, non-destructive testing, and possibly invasive testing to obtain factual measurementsand indicators to conclude a presumptive remaining service life of the wall.

The steps include the following:

a. Wall Candidate Selection – If it is determined that the risk score is unacceptable and thealternatives for mitigation (whether to, or how to, proceed) are clouded, a more intensivequantitative risk analysis may be appropriate where sufficient, site-specific data of highquality is attainable.

Unacceptable risk score may indicate wall criticality due to factors including roadwaytype, traffic volume, detour length, wall type, wall length and height (size), wall function,wall purpose, or wall location. The selection process should focus on walls with anelevated risk which may also be considered representative of similar at-risk walls in theinventory (or a subset of the inventory).

b. Condition – Determination of wall asset conditions based on a multitude of examinationtechniques:

Sampling is the process of obtaining evidential data on retaining wall elements byremoving a nominal specimen for in-depth, systematic examination. Some samplingtechniques include: Soil Sampling, Concrete Core Retrieval, Mortar Sampling, and SteelCoupon Retrieval.

Non-destructive testing (NDT) is the process of evaluating retaining wall elements fordiscontinuities or differences in characteristics without destroying the serviceability of theelement or wall system. A variety of NDT techniques have been developed and arecommonly employed in the inspection of structures and may include: Tape Measure,Level, String Line, Caliper Gauge, Ground Penetrating Radar (GPR) surveys, AcousticMethods, Surface Hardness Determination (Rebound or Schmidt Hammer), CorrosionPotential Mapping of Reinforced Concrete, Borescope Inspection (visual means), LaserScanning (LiDAR), Slope Indicators, Tilt Meters, Crack Gauges, and Piezometers.

Invasive testing is the process of evaluating retaining wall elements through extensiveexposure of the retaining structure or retained soil mass for multipoint examination ofdiscontinuities or differences in characteristics between wall elements. Some invasivetesting techniques include: Test Pits, Soil Reinforcement Retrieval, and Flatjack Tests



c. Data Analysis – Correlate variables to develop trends or relationships and quantify theassociated uncertainties:

Correlations identify relationships between quantitative variables (i.e. how things arerelated). Correlations may be used to make predictions about future behavior of walls.However, it should be noted that correlation does not strictly imply causation. Althoughthe fluctuation of one variable may reliably predict a similar fluctuation in anothervariable, there may be an unknown factor that influences both variables similarly.

Quantifiable Uncertainties is a parameter characterizing the range of values withinwhich the value of the measured can be said to lie within a specified level of confidence(i.e. how tightly constrained the unknowns are). The measurement provides an indicationas to the quality of the result.

Statistical Analysis is used to make sense of, and draw some inferences from, the data.In order to do so with some degree of reliability, the set of data needs to be large enoughto accurately represent the phenomenon being studied (i.e. statistically significant).Statistical significance is the likelihood that a relationship between two or more variablesis caused by something other than random chance. A data set is deemed to be statisticallysignificant if the probability of the phenomenon being random is less than 1 out of every20 (p-value of 5%).

Monte Carlo Simulation is a mathematical technique that generates random variablesfor modelling risk or uncertainty of a certain system. The simulations are used to modelthe probability of different outcomes in a process that cannot easily be predicted due tothe intervention of random variables.

d. Stability Analyses – Determine whether the existing retaining wall geometry meets therequired safety and performance criteria. Once the existing geometry has been modeledand subsurface conditions have been determined, the stability of the system may beassessed using a limit-equilibrium analysis. Various models will need to include theepisodic degradation of the wall elements.

Degradation Curve is a graph of a retaining walls condition or remaining servicepotential plotted over time. It describes the increase of degradation levels over time due todamage accumulation and changes in the corresponding design parameters.

e. Service Life Prediction – The service life of a wall element or system could be more thanthe target design life of the wall system. The end of service life for a wall element,component, or subsystem does not necessarily signify the end of wall system service lifeas long as the wall element, component, or subsystem could be replaced or repaired toresume its function.



Design Life. The period of time on which the statistical derivation of transient loads isbased – 75 years according to the LRFD Specifications.

Service Life. The period of time during which the retaining wall element or systemprovides the desired level of performance, or functionality, with any required level ofrepair and maintenance (i.e. an expected period of operation). It is unrelated to design life.



4.3.1 Service Life

As stated previously, the actual service life of a retaining wall may differ from its designed lifeand it depends largely on the performance demands (which in turn are related to the quality ofconstruction, operational environment, and applied loads). Factors that can cause a retaining wallnot to reach its designed life have been outlined in Chapter 1 Introduction and Purpose, and arecategorized as Design Related Failures, Construction Related Failures and Destructive ForceRelated Failures.

The difficulty in service life prediction is that the factors causing premature breakdown of a wallelement or wall system are hidden behind the wall face and only become evident through theappearance of various external signs of distress (e.g. bulging, deflection, cracking, or staining). Areliable estimate of remaining service life can be obtained only by identifying these conditionsand by observing their rate of change. Therefore, thorough (routine) inspection anddocumentation are critical components in the service life analysis.

Some rudimentary approaches for developing an initial estimate for the remaining service life ofa wall may include:

Repetition of inspection through many cycles and charting escalating maintenance andrepair costs to project a remaining service life for a given wall class (e.g., all MSES wallstructures). Criteria, such as when the repair and maintenance costs exceed more than50% of the replacement cost of that wall class, would need to be established.

Measure the performance of similar wall structures built over a long period of time.

A more progressive approach for developing an estimate for the remaining service life is outlinedin the Quantitative Risk Analysis section.

4.3.2 Phase 2 – Quantitative Risk Analysis

As we focus on mechanically stabilized earth system walls for the initial stage of the plan, it isthe inextensible reinforcing elements that strengthen the soil (reinforced mass) and allow theconstruction of a vertical wall. For metallic reinforcement, the life of the structure will depend onthe corrosion resistance of the reinforcement. The process of predicting service life usesstatistical methods to appropriately account for uncertainties related to the corrosion rate. Thegeneral steps in predicting service life are as follows:

General Data Acquisitiona. Identify reinforcement degradation rates in MSES walls through NDT and/or direct

sampling of soil and reinforcement from a set of walls that are considered representativeof the walls in the inventory. Obtain resistivity measurements on the soil samples at thelocation where the corresponding corrosion rate measurements are acquired on the



reinforcement. Generate multiple combinations of reinforcement corrosion rates and soilelectrochemical properties (resistivity’s).

Note - corrosion rates vary with time, both during a single year and during the life ofthe MSES structure, based on the age of the structure and changes in theelectrochemical environment. A single set of corrosion readings requires theassumption that a uniform constant rate of corrosion has been occurring since thestructure was completed (generally, an invalid assumption).

b. Correlate reinforcement corrosion rates to soil resistivity and quantify the uncertaintiesassociated with this relationship. This requires data that is obtained/measured using arational and stringent procedure that is applied consistently and correctly. Minimizeuncertainties in the data set related to human factors so that a meaningful relationship,with manageable and acceptable scatter, can be obtained between corrosion rate andresistivity.

Wall Service Life Predictionc. Retrieve soil samples from the MSES wall currently being evaluated. Perform soil

resistivity testing on the soil samples and select a representative resistivity for the wall (orzones within the wall).

d. Using this correlation and its associated uncertainties developed in Step b., generate,using Monte Carlo simulation, a large number of corrosion rates corresponding to therepresentative resistivity selected for the MSES wall being evaluated (e.g. 1000 corrosionrates).

e. Each corrosion rate generated in Step d. represents one possible outcome of the MSESwall being analyzed. For a given age of wall, apply each of the 1000 generated corrosionrates to determine 1000 remaining cross-sectional areas of the reinforcement.

f From Step e. and for a given age of wall, obtain 1000 remaining cross-sectional areas ofreinforcement. Perform 1000 slope stability analyses to determine the factor of safety ofthe wall corresponding to each one of the remaining reinforcement cross-sectional areas.

g. Using the 1000 values of computed factors of safety for a given age of wall, count thenumber of outcomes where the factor of safety is less than 1.0. The probability of failure,at that given wall age, is calculated as the ratio of the number of cases with factor ofsafety less than 1.0 to 1000.

h. Repeat Steps e. through g. for several wall ages to develop a relationship betweenprobability of failure and wall age. Using this relationship, the service life correspondingto a predetermined limiting probability of failure for wall service (say 0.05 or 5%) can bedetermined.



4.4 REFERENCES

Brutus, O. and Tauber, G., Guide to Asset Management of Earth Retaining Structures, GandhiEngineering Inc., National Cooperative Highway Research Program, October, 2009,http://onlinepubs.trb.org/onlinepubs/nchrp/docs/nchrp20-07%28259%29_FR.pdf

Investopedia, Financial Education Website,https://www.investopedia.com/terms/m/montecarlosimulation.asp

Mertz, D.R., and Wasserman, E.P. Defining the Service Life of Bridges, ASPIRE The ConcreteBridge Magazine, Winter, 2017, http://www.aspiremagazinebyengineers.com/i/768999-winter-2017/11

Moving Ahead for Progress in the 21st Century Act (MAP-21) legislation, 23 CFR Parts 515 and667 Asset Management Plans and Periodic Evaluations of Facilities Repeatedly RequiringRepair and Reconstruction Due to Emergency Events, Federal Register / Vol. 81, No. 205 /Monday, October 24, 2016, https://www.gpo.gov/fdsys/pkg/FR-2016-10-24/pdf/2016-25117.pdf

Poukhonto, L.M., Durability of Concrete Structures and Construction: Silos, Bunkers,Reservoirs, Water Towers, Retaining Walls, A.A. Balkema, 2003

Structure Inspection Manual, Wisconsin Department of Transportation,http://wisconsindot.gov/Pages/doing-bus/eng-consultants/cnslt-rsrces/strct/inspection-manual.aspx

US Army Corps of Engineers Institute for Water Resources, Risk Assessment – QualitativeMethods, Corps Risk Analysis Gateway,http://www.corpsriskanalysisgateway.us/lms/course.cfml?crs=3&crspg=30

Walters, B.X., et al., Colorado Retaining and Noise Walls Inspection and Asset ManagementManual, Version 1.0, Colorado Department of Transportation, April, 2016https://www.codot.gov/library/bridge/retaining-and-noise-wall-inspection-and-asset-management-manual

Whole Building Design Guide (WBDG), National Institute of Building Sciences,https://www.wbdg.org/resources/threat-vulnerability-assessments-and-risk-analysis


NYSDOT Retaining Wall Appendix 4A-1 October 31, 2018Inventory and Inspection Program

Appendix 4-A

Quantitative Geotechnical Risk AnalysisMSES Wall Investigations –Sample Retrieval, Storage, Measurements & Testing Protocol

BackgroundThe purpose of this procedure is to provide relevant information to assist in carrying out effectiveinvestigations at suspect or underperforming Mechanically Stabilized Earth System (MSES)Walls. This procedure provides information relative to sample retrieval, storage, measurementsand testing.

ObjectiveAssess design and construction conditions, as compared to project documents, and evaluate thein-situ condition of various wall elements.

Prior to InvestigationPrior to conducting an investigation all pertinent design, construction, and post-construction testdata for each wall section should be assembled and summarized.

A project specific sampling template must be developed to determine the reinforcement and fillmeasurement locations. This sampling template will eliminate sampling bias by the Engineer inthe field. The template will indicate where to take soil samples and in-situ reinforcementdimension measurements as well as where larger samples are to be exhumed and transported tothe laboratory for additional measurements and/or testing.

Wall SelectionWall selection and specific sections selected for investigation, sampling and testing should bebased on the following variables:

Walls which are representative of others with respect to vulnerability to corrosion (e.g.,little or no exposure to high likelihood of corrosion) within the respective projectconstruction phase or project conditions,

Maintenance of traffic, Presence of utilities, Application (free standing wall or supporting a bridge or other structure) External factors (deicing chemicals, surface and subsurface drainage, topography,

longitudinal and traverse alignment, upslope and downslope conditions), visual conditionof wall facing).

Sample StorageSamples should be stored away from external elements (sun, wind, precipitation) and extremeconditions (temperature) while in the field and during the laboratory measurement and testingphases.



Investigation & Sample MeasurementThe following items are of importance during the wall investigation:

Obtain global external photos of the wall and record pertinent external factors (e.g.surface drainage pattern, presence of subsurface drainage system, roadway superelevation, and application of deicing chemicals).



Record (photograph) visual condition of the facing (bulging, global vertical andhorizontal deformations, individual facing element distress and misalignment, loss ofbackfill material through joints).



Evaluate the facing- Record (photograph) visual condition of the facing (as indicated above).- Obtain representative samples of the facing element if possible (typ. 3 heights, 3

samples at each height). Note that this may not be practical for precast concretepanel facings.

- Conduct a visual and qualitative assessment of the backfill (both reinforced andretained) quality and density (rodding).

- Obtain a representative sampling of the wall components (if possible) and basedon facing type perform some or all of the following tests: Freeze thaw and wet dry soundness, to assess the potential for backfill

material deterioration during the wall’s design life Gradation to evaluate compatibility in relation to retention of salts in the

reinforced and retained backfill and drainage potential.- Clearly document the location of samples retrieved and tag with visible

identification label. Record (photograph) the presence of the (geotextile) separator between reinforced fill and

facing and its condition of placement. If the wall is directly supporting a roadway indicate whether a geomembrane detail was

designed and placed beneath the pavement (at the top of the reinforced soil volume) Using the sampling template, obtain samples of reinforced fill and retained soil and

perform tests to:- Document the location and condition of the reinforced backfill and retained soil.- Establish mechanical properties (moisture content, density, shear strength, top size

and complete gradation and plasticity index) and- Establish electrochemical properties of the reinforced fill and retained soil (See

Section on Laboratory Testing)



Using the sampling template, record the condition (photograph) and obtain samples of thereinforcement:

- Record any areas of “completely” and “significantly” corroded reinforcement- Soil and loose rust should be removed from the reinforcement measuring location

by scraping along the reinforcement with a steel file and/or steel brush.- The minimum reinforcement dimensions (on the predetermined sampling interval)

should be measured using calipers graduated in 1/64 inch increments. Record thesmallest dimension along the measurement location by cleaning and by takingmultiple measurements with a digital micrometer to an accuracy of 0.001 in.Record only the smallest dimension within the sample (this is considered to be aconservative approach to account for pitted corrosion).

- Supplement the field measurements with additional laboratory measurements todetermine minimum dimensions on each segment of retained reinforcementsamples and to confirm field measurement results.



Perform visual observation of the surface and subsurface drainage system (back and frontof wall drain). For surface drainage note any drop inlet locations, extent of curbs, surfacedrainage upslope, signs of seepage beneath the wall bottom.

Record condition of the excavated slope material (back of wall) (if present) and notepresence of any seepage and runoff.

Example of Sampling Template with Measurements1:

1 Example is for a welded wire faced wall with welded wire reinforcing elements.

Laboratory TestingIt is recommended to establish electrochemical properties of the reinforced fill and retained soilby conducting laboratory testing. The table below provides the preferred test method for eachproperty to be tested.

Property Preferred Test Method

Resistivity AASHTO T-2881

Chlorides ASTM D4327Sulfates ASTM D4327Sulfides ASTM D24922

pH AASHTO T-289Organic Content AASHTO T-267



1AASHTO T-288 is used for soil fills, and requires testing on the fraction of the material thatpasses a No. 10 sieve. This test method could be problematic when using coarse reinforced fillsthat have very little to no material finer than the No. 10 sieve. Attempt to obtain a sufficientamount of fines from the sample for testing. If enough fines cannot be collected, fines may begenerated from the construction of a test pad using representative construction equipment andtechniques. Do not crush material to obtain sufficient volume of fines. Alternatively, ASTMD1125 provides a procedure where the aggregate is submerged in water for 24 hours. Thespecialized resistivity testing is performed on the remaining water after draining.


NYSDOT Retaining Wall Appendix 4B-1 October 31, 2018Inventory and Inspection Program

Appendix 4-B

Quantitative Geotechnical Risk AnalysisMSES Wall Investigations –Sample Measurement Plan

BackgroundThe purpose of this plan is to provide a suitable sampling procedure to enable probabilisticservice life analysis for Mechanically Stabilized Earth System (MSES) walls. The samplingprocedure includes recommendations on sampling locations, number of samples, and the types ofmeasurements to be performed.

Objectives Assess inventory of samples Calculate required number of measurements (data points) Determine measurement procedures

Sample InventoryCollect and inventory all samples collected from the site. Samples should be stored away fromexternal elements (sun, wind, precipitation) and extreme conditions (temperature) while in thefield and during the laboratory measurement and testing phases.

Number of MeasurementsThe number of measurements must satisfy two requirements:

1. Statistical2. Geotechnical Engineering Soundness

A minimum number of measurements should be taken for each strap size to satisfy the statisticalrequirement. Compute this number using a basic statistical concept pertaining to sample sizes(presented in most introductory statistics textbooks) which will represent the number of samplesrequired to be 95% confident that the mean strength of the measured samples will be within 5%of the true population mean strength. It should be noted that this number of samples is for thesimple case where all walls being considered to have similar corrosion characteristics and thatthe corrosion characteristics for a given wall is homogeneous throughout its entire profile andarea.

To satisfy the geotechnical engineering soundness, a representative number of measurementsmust be taken along each strap to develop a profile of corrosion along the strap length (e.g. onemeasurement taken for each 6 ft. interval – results in 4 measurements for a 26 ft. long strap).

For MSES walls utilizing different types of strap width/thicknesses, additional considerationsmay need to be included (e.g. if three types of straps were used in the construction of an MSESwall (60 mm x 3 mm, 80 mm x 3 mm and 90 mm x 3 mm) and most, if not all, of the failedstraps were 60 mm x 3 mm, the minimum amount of measurements to satisfy the statistical



requirement must be taken on the 60 mm x 3 mm straps, followed by the maximum numberpossible for any other straps.)

Sample Measurement Procedure1. Depending on the exhuming process and amassing procedure, separate and straighten

each strap.

2. For labeling process malfunctions, separate labeled straps from unlabeled/lost-labeledstraps. Assign designations to unlabeled straps with duct tape and marker.

3. Mark the face end (“beginning”) of the strap. Note that these straps had unused bolt holesin their tail ends when installed. If orientation cannot be determined, mark one end andrecord it as the assumed face end.

4. Remove soil and loose rust by scraping each strap with a “light pass” of a steel wire brushto the extent that the recorder will be able to visually identify areas of “most severe”corrosion.

5. Measure and record total length of strap to nearest 0.1 foot with flexible tape.

6. Examine each side of the strap and determine which side has more severe corrosion(Photograph this side and use it to select measurement locations). Starting at the face endof each strap, mark 4 foot intervals along the length of the strap.



7. Record visual observations including a numerical ranking in Column B of the InventoryData Sheet.

The following ranking descriptions 1-4 should be used:

Ranking Description

1 No corrosion along strap interval, galvanization present2 Light to Moderate corrosion along strap interval3 Moderate corrosion along majority (50% or more) of strap interval

4Moderate corrosion along majority (50% or more) of strap interval withareas of severe corrosion and/or areas with 0% area remaining.

8. Photograph significant areas (on more severe side identified in Step 6) with the tape andinclude a visual identification marker. Record photo ID in Column C.

9. Photograph significant areas (on more severe side identified in Step 6) with the tape andinclude a visual identification marker. Record photo number in Column C.

10. Within each 4-foot interval along the length of the strap, by observation, select thelocation of strap with the most severe corrosion (least amount of remaining cross-sectional area). If present, a location with no strap remaining (complete corrosion) shouldbe considered as fully corroded. Broken pieces that go to knife edge should be recordedas 100% area loss.

11. Record the distance from the face end of the strap to where the measurements will betaken in Column D.

12. Use the wire brush and/or wire files to remove any remaining dirt and rust at themeasurement locations.

13. Measure the width of the strap at the most severely corroded location within each 4-footinterval using digital calipers to the nearest 0.001 inch and record in Column E.



14. Measure the thickness of the strap at the most severely corroded location within each 4-foot interval at points A, B, and C using digital calipers to the nearest 0.001 inch andrecord in Column F.

1 The presence of zones of complete corrosion along the length of the strap whose distance fromthe face end cannot be determined would result in a sample set that does not capture part of or allcases of most extreme corrosion (where there is no strap remaining). In order to minimize thisdeficiency, every effort should be made to determine the locations of these zones so that thesemost severe cases are included in the sample set.

Every effort should be taken to identify the locations of complete corrosion so that the deficiencymentioned above is either minimized or eliminated.

The following table provides the Inventory Data Sheet

0’ (face) 4’3.1’ 8’

xxx

Point A

Point B

Point C



Project #: Date: Staff ID:

Wall ID: Design Strap Width:

Panel ID: Design Strap Thickness:

Strap ID: Design Strap Length:

Notes:

A B C D E F G HLocation alongstrap1

Ranking2/Description Photo ID Samplelocation1

Samplelength (in)

Minimum samplethickness3 (in)

Minimum samplewidth3 (in)

Weight ofsample4 (g)

0 – 6 ft.

6 – 12 ft.

12 – 18 ft.

18 – 24 ft.

24 – 30 ft.

Total length of strap

1 Length measured from the face end of strap to the edge of the sample closest to the face end2 Ranking 1-4

1. No corrosion along strap interval2. Light to Moderate corrosion along strap interval3. Moderate corrosion along majority (50% or more) of strap interval4. Moderate corrosion along majority (50% or more) of strap interval with areas of severe corrosion and/or areas with 0% area remaining

3 Length measured with 4 inch digital calipers to the nearest 0.01 inch4 Weight measured on calibrated scale to the nearest 0.01 gram

Documents

RWIIP Ch 4 Risk Assessment and Asset Management (F...identified risks, the NYSDOT’s value improvement platform includes a risk assessment program. The goal of risk assessment is