Guidelines for Condition Assessment and Rehabilitation of Large Sewers

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Guidelines for Condition Assessment and Rehabilitation of Large

Sewers

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Guidelines For Condition

Assessment And

Rehabilitation Of Large Sewers

Jack Q. Zhao, Ph.D., P.Eng., Project Manager Shelley E. McDonald, P.Eng.

Yehuda Kleiner, Ph.D., P.Eng.

Published by

Institute for Research in Construction National Research Council Canada Ottawa, Canada

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DISCLAIMER

Although the infonnation and recommendations set forth in this book are represented in good faith and believed to be correct as of the date of publication, the publisher, the authors, and the organiza-tions to which the authors belong make no representations or warranties, either express or implied, as  to completeness or accuracy thereof.  Infonnation is  presented upon the  condition that the persons  receiving same will make their own detennination as to its suitability for their purposes prior to use.  In  no event will the publisher, the authors, or the organizations to which the authors belong, be respon-sible for damages of any nature whatsoever resulting from the use or reliance on the infonnation  contained  in  this book. 

©200 1 National Research Council of Canada   All rights reserved.  

Reproduction of any kind., in any fonn, is strictly prohibited without the written consent of the   National Research Council of Canada.  

NRCC 45130  

NR35-251200 IE   ISBN 0­660­18614­4  

ACKNOWLEDGEMENTS

This Guideline was prepared with valuable contributions from the following members ofthe project  Steering Committee.  The project was jointly funded by the National Research Council of Canada and  the municipalities and private firms represented by the Steering Committee members. 

Members of Steering Committee Reg Andres, P.Eng.  Mark Andrews, P.Eng.  Russ Black, P. Eng.  Terry Fedick, P.Eng.  Wayne Green, P.Eng.  John Hodgson, Ph.D., P.Eng.  Betty Matthews­Malone, P.Eng.   Seamus McDonnell, P.Eng.   Ross Newman   Gary Nieminen, P.Eng.   Balvant Rajani, Ph.D., P.Eng.   Cal Sexsmith, P.Eng.   Gerry Taylor, P.Eng.   Participating Organizations R.Y. Anderson Associates Limited  M.E. Andrews & Associates Limited  Greater Vancouver Regional District  City ofCalgary  City of Toronto  City ofEdmonton  City ofHamilton  Capital Regional District (Victoria, Be)  City of Waterloo  City ofRegina  IRClNRC City of Saskatoon  City of Ottawa  The following people have also contributed to the development of this Guideline:  Ken Collicott, P.Eng.  Gerald Bauer, P.Eng.  Art Lingren, P.Eng.  Rob Neroutsos, P.Eng.  Gord Baguley, P.Eng.  Ken Chua, P.Eng.  R.V. Anderson Associates Limited  R.V. Anderson Associates Limited  Greater Vancouver Regional District  Greater Vancouver Regional District  City ofHamilton  City ofEdmonton  The feedback and comments received during the IRC's cross­Canada seminar tour in 2000 provided  valuable input for this Guideline. 

Table of Contents

1.  General... .  1   1.1  Introduction  1   12  Scope  2   1.3  Terminology  2   2.  Health and Safety  5   3.  Failure Impact Assessment  7   3.1  Failure Impact Assessment of Sewer Pipes  7   3.1.1  Failure impact determination  7   3.1.2  Sewer location  8   3.1.3  Embedmentsoil  10   3.1.4  Sewer size  10   3.1.5  Burial depth  10   3.1.6  Sewer function  11   3.1.7  Seismic zone  11   32  Failure Impact Assessment ofAccess Holes  11   3.3  Using Failure Impact Ratings to Set Priorities  11   4.  Inspection  13   4.1  Inspect Timing and Frequency  13   4.1.1  Initial inspection  13   4.12  Subsequent  inspection  14   42  Full­Line Inspection Techniques  14   4.2.1  Closed circuit television (CCTV)  15   4.2.2  Sonar/CCTV  16   4.2.3  Person­entry  inspection  16   4.2.4  Stationary camera  17   4.2.5  New inspection technology  17   4.3  Special­Purpose  Inspection Techniques  17   4.3.1  Rotary sonic device  17   4.3.2  Diver inspection  17   4.3.3  Systeme mechanique d'auscultation des  conduites (MAC)  17   4.3.4  Inspection beyond the pipe wall (void detection)  18   4.4  In­Line Testing Methods  19   4.4.1  Person­entry test methods  19   4.4.2  Other inspection methods  19   5.  Condition Assessment  for Pipe  21   5.1  LSCCR ­ Large Sewer Condition Coding and Rating  21   5.2  Structural Defect Coding for Pipe  ,  22   5.2.1  Fracture  22   5.2.2  Crack  25   5.2.3  Deformation  ,  25   5.2.4  Collapse  26   5.2.5  Broken pipe  TJ 52.6  Joint displacement  TJ 5.2.7  Joint opening  28   5.2.8  Surface damage  ,  29   5.2.9  Sag  29   5.3  Weights  for Structural Defects  29  

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5.4  Defect Coding for Brick Sewers  31   5.4.1  Displaced brick  31   5.4.2  Missing brick  31   5.4.3  Mortar missing  31   5.4.4  Dropped invert  31   5.5  Serviceability Defect Coding  33   5.5.1  Roots  33   5.5.2  Debris  34   5.5.3  Encrustation  34   5.5.4  Protruding services  34   5.5.5  Infiltration  35   5.6  Weights for Serviceability Defects  35   5.7  Pipe Condition Ratings  36   5.8  Condition from  Previous Inspections  36   5.9  Condition Assessment for Rehabilitated Sewers  37   6.  Rehabilitation of Pipe  39   6.1  Decision Making on ActionINo Action  39   6.2  Selection of Rehabilitation Techniques  39   6.3  Rehabilitation Options  41   6.3.1  Internal and external grouting  41   6.3.2  Localized repairs  41   6.3.3  Lining  41   6.3.4  Pipe replacement  44   6.3.5  Excavation and pipe replacement  44   6.4  Cost Estimates of Rehabilitation Techniques  44   7.  Condition Assessment and Rehabilitation for Access Holes  47   7.1  AHCCR ­ Access Hole Condition Coding and Rating  47  

7.1.1  Defects  in  access holes  47  

7.1.2  Physical condition coding  48   7.1.3  Structural and service ability condition ratings  50   7.2  Rehabilitation ofAccess Holes Based on Structural Condition Rating  50   7.3  Rehabilitation Methods for Access Holes  51   7.4  Other Considerations  51   7.4.1  Size of access holes  51   7.4.2  Distance between access  holes  52   8.  Data Management  53   8.1  Introduction  53   8.2  Database  Structure  53  

8.3  Data Access,  Updating and  Maintenance  58  

9.  Summary and Conlusions  61   References  63 Appendix A:  Defect Code Conversion Tables  67   Appendix B.  QuantitativelRisk­based Methods for Forecasting Sewer Condition  71   B.1  General  71   B.2  MEDIC  71   B3  The ISO/CD Factor Method  73   B.4  The Markov Chain Method  ,  75   B.5  Corrosion Prediction for Concrete Sewer  75   B.6  Semi­Markov Approach for Scheduling Rehabilitation or Inspection in Large Sewers  76   B.7  Summary  78  

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List of Tables

Table 3.1  Table 3.2  Table 3.3  Table 3.4  Table 3.5  Table 3.6  Table 3.7  Table 3.8  Table 3.9  Table4.1  Table 4.2  Table 4.3  Table 5.1  Table 5.2  Table 5.3  Table 5.4  Table 5.5  Table 5.6  Table 6.1  Table 6.2  Table 6.3  Table 6.4  Table 7.1  Table 7.2  Table 7.3  Table 7.4  Table 7.5  Table 7.6  Table 8.1  Table 8.2  Table 8.3  Table 8.4  Table 8.5  Table 8.6  Table Al  TableA2  TableBI  TableB2  Major failure impact factors  7   Failure impact factors and weights  8   Failure impact rating  8   Sewer location factor  9   Embedment soil factor  10   Sewer size factor  10   Burial depth factor  10   Sewer function factor  11   Seismic zone factor  11   Inspection timing based on condition rating and failure impact rating  14   Full­line inspection techniques  15  

Special­purpose  inspection  techniques  17  

Major structural  defects for types of pipes  23  

Structural defects,  codes and  weights for pipes  30  

Structural defects,  codes and weights  for brick sewers  32   Serviceability defects,  codes and  weights for  pipes  35  

Structural condition rating for sewer pipes  36   Serviceability condition rating for sewer pipes  36   Rehabilitation priority  39   Sample table for recording rehabilitation information  40   Example rehabilitation costs based on  case studies  43   Rehabilitation costs (relative to pipe jacking)  45  

Structural defects,  codes and weights  for  access holes  49   Serviceability condition, codes and weights  for  access holes  50  

Structural condition rating for access holes  50   Serviceability condition rating for access holes  50   Structural condition ratings, implications and recommended actions for access holes  . 51   Defects and rehabilitation methods for access holes  52   Fields for a pipe inventory table  56   Fields for an access hole inventory table  56   Example data table for pipe structural and serviceability defects and scores  57   Example data table for access hole structural and serviceability defects and scores  57   Example of query results for pipes with condition assessment ratings of 4 and 5  58   Example of query results for access holes with   condition assessment ratings of 4  and 5  58   Structural condition code conversion to LSCCR from City ofEdmonton and   WRc  systems  68  

Serviceability condition code conversion to LSCCR from City ofEdmonton and  

WRc  systems  (f)

Suggested design life for appraisal  73  

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List of Figures

Figure 1.1  Steps  for  managing sewer assets  1  

Figure 3.1  Sewer location factor example  9   Figure 3.2  Access hole failure impact rating  12   Figure 3.3  Sample sewer impact map  12   Figure 5.1  LSCCR primary and secondary assessment units  21   Figure 5.2  Clock reference for sewer inspection and condition assessment  22   Figure 5.3  Longitudinal fractures  23   Figure 5.4  Diagonal fractures due to insufficient soil support  24  

Figure 5.5  Deformation of flexible pipe  26  

Figure 5.6  Relationship of diameter change to area change  26   Figure 5.7  Collapse modes for rigid and flexible pipes  27   Figure 5.8  Joint displacement  27   Figure 5.9  Longitudinal joint opening  28   Figure 5.10  Angular displacement joint opening  28   Figure 5.11  Root intrusion into a sewer  33   Figure 5.12  Encrustation in a sewer  34   Figure6.l  CIPP rehabilitation costs vs sewer diameter  45  

Figure 7.1  Elevation view of typical access holes  48  

Figure 7.2  Clock reference for  access holes  48  

Figure 8.1  Pipe  and access hole  database structure  53  

Figure 8.2  Relationships between data tables  54  

Figure 8.3  Example data entry form with drop­down lists  55  

Figure B.l  Probability curves for deterioration  72  

FigureB.2  Example distributions ofthe cumulative waiting times  77

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1. General

1.1

Introduction

Sewer collection systems are essential elements  of municipal services. To  ensure a high level of  reliability at the  lowest possible cost, asset  management systems  and  procedures that  include effective methods for condition  assessment and rehabilitation must be imple-mented.

This Guideline applies to large sewers (900 mm and larger) and provides owners and operators of sewer systems with suggested methods for managing the assessment and repair of large sewers. The subject areas covered in this Guideline include:

Health and safety issues for inspection and repair

Availability, applicability and limitations of existing technologies for inspection, condition assessment and rehabilitation Failure impact assessment

Collection and management ofreliable data Decision making based on sewer

conditions and failure impact

Projections of future sewer conditions Cost estimates for sewer and access hole inspection and repair.

The steps for the effective management of large sewers and their location in this Guideline are shown in Figure 1.1. In addition, the health and safety issues associated with work in the confined space of a sewer are provided in Section 2. Appendix A provides tables for converting defect codes from other rating systems to the Large Sewer Condition Code

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_{Set priority for ...}

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inspection

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(Section 5 -Sewer pipes [ Se_ction!. -ａ｣ｾ･ｳｳ  iJoles). ｄ･｣ｩｳｩｯｮｾＭＮｉ   making

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Figure 1.1. Steps for managing sewer assets

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and Rating (LSCCR) system described in this  Guideline. Appendix B contains additional  information on estimating future conditions of  sewers. 

1.2 Scope

This Guideline applies to large gravity sewers,  that is, sewers with a minimum pipe size of900  mm (the minimum accepted size for person  entry)22,51.  However, many aspects of the  Guideline are applicable to sewers of smaller  sizes. 

The Guideline provides a systematic method for  the structural defect rating of sewers, brick  sewers and access holes and provides  informa-tion about current rehabilitainforma-tion methods for large sewers.

The planning and scheduling of sewer rehabili-tation will not depend entirely on the failure impact rating and the condition ratings de-scribed in this document. Other factors such as population growth, plans for installation of other buried services and road surface rehabili-tation will also affect the timing of sewer rehabilitation.

The Guideline also provides a method for rating serviceability defects. The serviceability rating can be used to prioritize maintenance work. However, the decision-making about mainte-nance needs and appropriate techniques are beyond the scope of this Guideline.

1.3 Terminology

The principal terms used in this Guideline and their meanings are as follows:

Access hole: A structure that provides access to the sewer pipe for maintenance, inspection and rehabilitation. Access hole is used inter-changeably with maintenance hole (or manhole - MH for short) and access structure.

Condition: The condition of a sewer pipe or access hole is expressed by six condition ratings as follows: 0 - excellent, I - good, 2 - fair, 3 - poor, 4 - bad, 5 - failure or imminent failure. Condition ratings are also referred to as condition states in theoretical models for predicting future sewer conditions (Appendix B).

When the pipe or access hole is in excellent condition (or as good as new), no defects will be observed during an inspection and its condition is represented by "0".

Defect: A defect is a physical or service deficiency. Defects may originate from the manufacturing or installation process, or may be a result ofnormal wear and tear or third party damage. Defects can be classified as either affecting structural integrity or affecting serviceability.

Durability: Durability32, 12 is the ability of a pipe or access hole to satisfactorily withstand the effects of service conditions to which it is subjected. Or stated more simply, it is the ability of a pipe or access hole to resist wear and deterioration.

Embedment: Embedment is the backfill materials surrounding the pipe extending from the top of the pipe to the base ofthe trench and including bedding.

Failure: Failure of a pipe or access hole occurs when it is no longer able to function as

intended. Failure ofa sewer pipe means that the pipe is no longer able to convey sewage at its design capacity. Modes of failure vary with pipe materials. Condition 5 indicates failure or imminent failure.

Full-line inspection methods: These are inspection methods that are used for continu-ous inspection of a sewer pipe from one access hole to another.

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In-line test methods: These are test methods  used  for  localized areas, joints or lengths,  usually with specialized tools. In­line testing  usually  involves  person­entry. 

Large sewers: Sewers of900 mm and larger are  defined as  large sewers.  This size is  considered  the minimum size for which person­entry is  practical and safe. 

Person-entry activities: These are any activi-ties  requiring a person to enter the sewer.  Pipe bedding: Pipe bedding is  structural  backfill material placed between the bottom of  the pipe and the bottom of the trench. 

Service life: Service life is the expected  duration that a pipe or access hole will perform  satisfactorily based on normal maintenance  activities. (For other definitions of service life,  refer to References 25,43, and 46.) Remaining  service life is the life span of a structural  element from the current time to the time of its  failure. Design service life is the intended life  span from the time of construction to the time  offailure, based on the design criteria. Design  service life is not a true  indicator of the  deterioration rate ofthe element materials or  when the element will actually fail.  Serviceability: Serviceability is the capability  of a pipe or access hole to perform the function  for which it was designed while exposed to in-situ  conditions. 

Special-purpose inspection methods: These  are inspection methods used for localized areas  or lengths (not necessarily for the entire MH to  MH length), or to access a particular defect. 

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2. Health and Safety

Sewers are  dangerous work areas because they  contain harmful gases, bacteria and other  micro­organisms, and have insufficient oxygen  supply,  high humidity, odour and slippery  working conditions. Furthermore, flows in many  large  sewers cannot be diverted so  that 

inspection or rehabilitation can take place in the  absence of flows.  Health  and safety is paramount and must not  be compromised. A safety plan is required for  aU person­entry activities inside a sewer pipe.  Safety procedures must be  developed and  followed by aU  involved personnel. Before any  inspection or rehabilitation work commences,  safety procedures must be in place and trained  personnel responsible for  site  safety must be  identified. Fatalities can occur ifappropriate  safety procedures are not foUowed. 

Although  a national health and safety regula-tion does not exist in  Canada, many provinces  and municipalities have established their own  regulations  and procedures  for  confmed space  entry. Any municipality operating a sewer  system  is  urged to establish suitable proce- dures in consultation with provincial authori-ties and other municipalities. For additional  information, refer to the fol1owing documents: 

Ontario Regulation 213/91:  The  Occupational Health and Safety Act City of Toronto:  Corifined Space Entry and Exit, 1989

Capital Regional District (Victoria, BC):  Section 3 ­ Work Procedure (WP) 13:  Corifined Space Entry Procedure, CRD  ENG Policy/ProceduresManual, 1998  Region of Hamilton­Wentworth: Confined Space Entry Procedure (developed for a  specific project), 1998 

Greater Vancouver Regional District:  Corifined Space Guidelines, 1999; Confined Space Entry Guidelines for Sewer Entry, 1994; Personal Protective Equipment Policy Statement, 1993 (aU are  included in tender documents for sewer  work) 

City of Regina:  Corifined Space Entry Program, City ofRegina, 1997.  Minimum requirements for confined space   entry are:   Proper training of above­ground and  below­ground personnel participating in  the inspection and rehabilitation of sewers  Detailed contingency plans for work and  rescue  Assessment of potential hazards prior to  access hole and sewer entry  Availability of appropriate protective  clothing and equipment (harness, life­lines,  breathing  apparatus,  and  hoisting and  conveying equipment) 

Availability of appropriate tools and  equipment that are in good working order  Availability of emergency equipment  (first-aid kit and fire extinguisher)  Notification of appropriate rescue agencies  (such as the fue department) prior to  commencement ofwork  Air quality testing and monitoring prior to  and during  person­entry  Maintenance of adequate ventilation and  lighting during person­entry 

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Opening and continuous monitoring of the  access holes immediately upstream and  downstream from the work area  Effective communication between the  above­ground  and  below­ground  personnel 

Constant maintenance oflifelines  Safe control of surface traffic. 

Sewers are hazardous work environments.  Any  person entering a sewer must be trained in work  and  safety requirements for  confmed­space  entry. 

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3. Failure Impact Assessment

The impact of a failure of a large sewer depends  on  several factors and each sewer is  unique.  Decisions about sewer rehabilitation are based  on two main considerations ­ the impact of  failure and the condition of the sewer (Sections  5 and 7). 

Failure impact assessment is a way of assess-ing the consequences of failure of the different segments of a sewer system and the likelihood of failure based on the site conditions where the sewer is located. Failure impact assessment is usually done independently of on-site inspection and condition assessment.

The impact offailure is based on the likelihood of failure and the severity of consequences resulting from failure. For example, the likeli-hood offailure would be high if a fractured sewer were located in unstable soil conditions. The consequences resulting from a failure would be high if a sewer served a large area and no bypass capability existed.

The failure impact assessment rating is used in conjunction with the condition rating to provide a logical and systematic means for determining the priorities for subsequent inspections and the eventual rehabilitation of sewers.

Table 3.1. Major failure impact factors

3.1

Failure Impact Assessment

of Sewer Pipes

Table 3.1 shows the major factors that either affect the likelihood offailure or the severity of consequences resulting from failure. Local impact factors will vary from location to location whereas global impact factors will remain the same for individual MH to MH sewer segments or even for an entire urban area.

3.1.1 Failure impact determination

Numerical values are used to represent the degree of impact should failure occur. Consist-ent assignmConsist-ent of values will provide useful information about the relative degree offailure impact of one sewer or sewer segment to another. When the impact ofa factor is negligi-ble or low, a value of I is assigned, and when the impact is medium or high, values of 1.5 and 3.0 respectively are assigned (Table 3.2, page 8). Each failure impact factor has an established weighting factor that is used in combination with the degree offailure impact in Eq. 3.1 to determine the weighted failure impact factor for a sewer.

Factor Affecting Affecting Local or

the likelihood the severity of global effect

of failure consequences resulting from failure

Sewer location Local

Embedment soil Local

Sewer size Global

Burial depth Global

Sewer function Global

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I

Failure impact ratings serve two purposes:  1. They establish priorities for sewer  inspection (Section 4) and condition  assessment (sewer pipes ­ Section 5,  access holes ­ Section 7)  2.   They serve, in combination with condition  rating, as the basis for decision­making for  the timing for rehabilitation (sewer pipes -Section 6,  access holes ­ Section 7)  The degree offailure impact of each of the  maj or factors is defined in 3.1.2 to 3.1.7. The  weighted failure impact factor I is then  calculated by:  W  I" = (0.2)}; + (0.16)I -+-(0.16)1; +(0.16)1, +(0.16)1!  + (0.16));,  [3.1]  Once the weighted failure impact has been  calculated, the impact rating R _Imp is then  determined using Table 3.3.  .  Table 3.2. Failure impact factors and weights

3.1.2  Sewer location The impact of a sewer failure on the public and  the environment is affected by its  location.  Table 3.4 shows the sewer location factor

1; 

and  the failure impact as a function of land use,  traffic, access for repair, location relative to  essential facilities and environmental zoning.  Figure 3.1  shows an example of assigning sewer  location factors.  A high sewer location factor  has been assigned for the portion of the sewer  within the airport perimeter and a low location  factor assigned  for the portion outside the  airport. 

Failure  impact  factor  Weigbting  Symbol  Degree  of failure  impact  factor 

Low  Medium  Higb  Local 

Sewer  location  (Table  3.4)  0.2  1.0  1.5  3.0  Embedment  soil  (Table  3.5)  0.16  1.0  1.5  3.0  Global 

Sewer  size  (Table  3.6)  0.16  _1, 1.0  1.5  3.0  Burial  depth  (Table  3.7)  0.16 

_J.

1.0  1.5  3.0 Sewer  function  (Table  3.8)  0.16  

_!r

1.0  1.5  3.0 Seismic  zone  (Table  3.9)  0.16  

_1. 

1.0  1.5  3.0

Table 3.3. Failure impact rating

Weigbted  impact  Impact  rating,  factor,I_w R... 1.00  1 1.01  ­ 1.60  2  1.61  ­ 2.20  3  2.21  ­ 2.80  4 > 2.80  5 

, 

i

Table 3.4. Sewer location factor*

Aspects  Degree of failure impact 

Low (1;= 1.0)  Medium (I; = 1.5)  High (I; = 3.0)  Land  use 

Traffic  intensity  Access  for  repair 

Location  (under  or  adjacent  to) 

Environmental 

Industrial  )  or  2  lanes  Unrestricted  Areas  not  covered  in  the  next  two  columns  Non­sensitive  areas  Residential  3  to  5  lanes  Limited  •  high  volume  tourist  areas  •  high  risk  installations 

or  utilities 

Environmental  conservation  zones 

Commercial  6  lanes  or  more  Restricted 

•  high  risk  installations  or  utilities 

•  railroads,  rivers,  canals  or  other  bodies  of water  • buildings 

•  primary  access  to  emergency  facilities  •  airports 

Environmental  protected  zones  •  Modified  from  References  10  and  II 

［ＺｴｾＢＬ  Ｂｾ  ｾＺＬＪ ..ＬＬＬ＼ｾＮＮＮＮＬ＾  ...   ｾ   v ft le  ｾ    <;:; ｾ   ｾＬｾ   ｾＬＧ  '::-»" v l '   .;  ｾ   , Sewage flow direction

-,

...•.. MH105 Airport MH108 Open field

-.. 

" - - Fence Sewer MH107

Location factor high =3 Location factor low

1,=1 

,  '" 

;'\ 

'"'"

,

Figure 3.1. Sewer location factor example

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3.1.3 Embedment soil

The characteristics of the embedment soils and  the native soils in proximity to a large sewer are  an  indication of the susceptibility of the sewer  to failure. For example, the combination offme  embedment soils, high water table and fractures  or joint openings in the sewer pipe can result in  erosion of the soils supporting the pipe.  Silts and fme  sands are highly susceptible to  erosion) (a phenomenon commonly referred as  "piping") even when exposed to small hydro-static heads (less than 1.5 m head) and this loss of support can lead to sewer failure. Table 3.5 shows the embedment soil factor

f,

for various soil types.

Table 3.5. Embedment soil factor·

3.1.4 Sewer size

Sewer size affects the selection of rehabilitation methods, the execution of the repairs, and the degree of contamination to the surrounding environment (soil or receiving waters) in the event of a failure. Generally, repair costs increase with increasing sewer size. Table 3.6 shows the sewer size factor

f.

for various sizes of sewer.

3.1.5 Burial depth

The degree of difficulty for emergency repairs increases with increasing sewer depth. The difficulty of carrying out an inspection also increases with depth, as do health and safety concerns. Table 3.7 shows the sewer burial depth factor

1;;

for various depths.

Embedment soil Degree of failure impact

_f.

Medium to high plasticity clays

All clays if sewer was constructed by tunnelling Low 1.0 Low plasticity clays

Fine to medium gravel Well graded sandy gravel Silts, silty fine sands or fine sands

Medium 1.5 Medium to coarse sands High 3.0

*Based on Reference 52

Table 3.6. Sewer size factor·

Sewer diameter/vertical size (h), mm Degree of failure impact

< 900 Low 1.0

900 - 1800 Medium 1.5

> 1800 High 3.0

* Based on Reference 15

Table 3.7. Burial depth factor·

Burial depth (h), m Degree of failure impact

ｨｾＳ   Low 1.0

Ｓ＼ｨｾＱｏ   Medium 1.5

h> 10 High 3.0

I

.  

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3.1.6  Sewer function

The type of sewage conveyed in  a large sewer  impacts the  degree of both the soil  and/or  receiving water contamination and the repair  difficulty. In general, the failure of sanitary  sewers poses a higher degree of impact than  the failure of storm sewers44  .  Table 3.8 shows  the sewer function factor

1;

for different types of  sewers.  3.1.7  Seismic zone Earthquakes can cause more damage to  defective pipe  sections than to  non­defective  pipe sections.  The ground vibrations diminish  the soil support for the sewer, particularly for  flexible pipe because it has a higher degree of  reliance on  soil support than rigid pipe.  Consideration of the seismic factor is not meant  to eliminate damage to sewer systems during  earthquakes, but rather to minimize the degree  of damage in such events. Table 3.9 shows the  seismic zone factor

f

for different seismic  zones. Z is defmed _a

ｾｳ  

acceleration­related zone  and Zv is defmed as velocity­related zone42

• 

Table 3.8. Sewer function factor*

3.2. Failure ImpactAssessment

of Access Holes

Access  holes connect two  or more  sewer pipes  together.  These pipes can be of different sizes  and  depths and therefore the impact of their  failures may be different. The impact rating of  an  access  hole is  defined as  being equal  to  that  of the adjoining sewer pipe with the most  severe failure impact rating (Figure 3.2, page 12). 

3.3 Using Failure Impact

Ratings to Set Priorities

Impact rating maps (Figure 3.3, page 12) can be  generated for sewer collection systems using  the failure impact rating methodology explained  in this Section. Failure impact maps will help  not only for identifying priorities for inspection,  condition assessment and  rehabilitation,  but  also for planning new sewer extensions. For  instance, an impact rating might be used to  locate a new sewer away from high failure  impact rating areas. 

A comprehensive inspection plan is crucial for 

Function  Degree  of  failure  impact 

Col1ector  sewer,  stonn  sewer  Low  1.0  Major  trunk,  sanitary  or  combined  sewer  Medium  1.5  Major/regional  interceptor,  influent  and  effluent  High  3.0  to/from  wastewater  treatment  plant 

*Modified  from  references  10  and \l

Table 3.9. Seismic zone factor"2

Acceleration­related  or 

velocity­related  seismic  zone,  Z.,  Z,  Degree  of  failure  impaet 

0­2  Low  1.0 

3  ­ 4  Medium  1.5 

Access hole impact rating is equal to the highest impact rating of the pipes it connects

(In this case, the outgoing pipe) ___

ＬＭＭ｟ｾ｟ｾｷ｟ｷ｟｡｟ｧ｟･ＭＭｻ

ｾ

 

:," Impact rating, R , =2 ( \ r direction

I \ - ·

m

\

Access hole

­­

(­

­

ｾ

 

­y­

\ '"---\ _\ 

Pipe impact rating, R,mp =1

Pipe impact rating, R,mp = 2 

Plan view (NTS.)

Figure 3.2. Access hole failure impact rating

Sewage flow direction

1 

4  3  5  Failure impact rating City street

,  

, 

..

i

4. Inspection

the effective management oflarge sewers.  to specifications.  This  inspection should also  Inspection  is the fIrst step of the condition  document any changes to the original design  assessment.  The  condition of a  sewer system,  that occurred during construction (for exam-in combination with the failure impact assess- ples, alignment changes,  location of service  ment presented in Section 3,  is the basis for  connections,  or additional access holes).  making repair decisions that minimize service 

disruptions and minimize costs.  It is recommended that the initial inspection be  the basis for a full  condition assessment  Inspections provide information on the  (Sections 5 and 7).  In addition, because studies  physical  condition of the sewer and on rates of  show many defects result from poor workman-material deterioration. Inspection data help  ship and because it may take some time for  forecast future  conditions of the  sewer and  these defects to become obvious,  it is recom-help determine the need and timing for rehabili- mended that an interim inspection of a new 

tation.  sewer be made prior to the end of the warranty 

period.  The inspection should cover the entire  Optimal scheduling of inspections will result in  length ofthe new or rehabilitated pipeline.  savings and minimize the likelihood of sewer  This initial inspection will provide valuable  failure. This section provides recommendations  baseline data that can be used for comparison  for inspection frequencies as well as descrip- in  future  condition assessments. 

tions and rough cost estimates for various 

inspection techniques.  Inspection  methods  If an existing large sewer has never been  described include "full­line" and "special- inspected, an  initial inspection should be  purpose" methods.  Some commonly used "in- performed as early as possible (regardless of  line" testing methods are also included.  the age of the sewer) to benchmark the sewer 

condition. This information can be used to 

4.1 Inspection Timing and

determine maintenance and rehabilitation 

needs.

Frequency

4.1.1 Initial inspection For sewer systems that have not been part of a  comprehensive inspection plan, the following  Many sewers have defects of some kind. In  points can assist in setting priorities for fIrst  some cases, the defects result from normal in-inspection: service deterioration.  However, one studyJI  determined that the majority of sewer defects  _1.  Use the failure impact assessment method  are a result of poor workmanship. Another  _{described in Section 3 to produce a failure}  study based on the assessment of 180 km of  _{impact rating map for all large sewers in the}  sewers44 _{determined that many defects arise} 

system. during or shortly after construction. These  

fIndings confIrm the need for inspections of   _{2.  Assign high priority to sewers of known} 

new sewers.  _{(or suspected) problems such as:  high} 

inflow/infIltration (I/I), proximity to a water  It is common practice for a municipality (or its  _{main rupture, ground disturbance from}  delegate) to perform an inspection to confIrm  _{construction activity, or exposure to}  that a new sewer has been built in conformance  _{above­normal chemical concentrations.} 

, 

i

3.   Consider the schedule for road  refurbishment or nearby water main  replacement so that if replacement of the  sewer pipe by the open­cut method is  likely, it can be carried out before a new  road surface is installed.  4.   In high seismic risk zones, assign high  priority to sewers installed in soils with  high liquefaction characteristics.  4.1.2 Subsequent inspection Optimal scheduling of inspection cycles is an  important aspect of good management of large  sewers.  Many factors  must be considered: the  cost of inspection, the  anticipated condition of  the pipe based on  the  last inspection, the level  ofrisk (or likelihood offailure), and the degree  of difficulty required to complete an inspection.  Full­length inspection of large sewers should  be carried out following the modified WRc  (Water Research Centre, United Kingdom)  approach shown in Tab Ie 4.1. The recom-mended  inspection  frequency  depends  not  only on the physical condition state (Sections 5  and 7) but also on the failure impact rating of  the sewer (Section 3).  The recommended inspection timings in Table  4.1  as  well as those used by WRc and the City  of Edmonton and others are prescriptive in  nature. However, unlike other methods, the  determination ofthe timing for the next inspec-tion in Table 4.1  takes the failure impact rating  into account.  There are several reported  attempts to develop  inspection  decision  methods that are more  quantitative and thus  more specific to individual sewers. Some of  these methods are described in Appendix B. It is  recommended that inspection frequency  guidelines in Table 4.1  be followed until a better  quantitative method  is  developed and  validated  with field data. 

4.2 Full-Line Inspection

Techniques

Full­line inspection means the continuous  inspection of a given length of sewer from MH  to MH.  The inspection techniques covered in  this section are summarized in Table 4.2 and a  brief description of each of the techniques is  provided. Where project information is avail-able,  a cost range for the  inspection is  given.  Actual costs of inspection will depend on  sewer size and depth,  distance between access  holes, site and sewer conditions, and availabil-ity of inspectors locally.  In general, the quality of the inspection will be  enhanced if the sewer has been cleaned prior to  inspection. 

. Table  4.1. Inspection timing based on condition rating and failure impact rating

Condition  rating  Failure  impact  rating (R_i•.,,) Time  to  next  inspection  (years) 

5  I to 5  O' 

4  5  0+

I to 4  2 to 6 

3  5  3 

I to 4  5 to  10 

2  5  5 

I to  4  10 to  15 

I  or  0  5  10 

I to  4  15 to  25 

, 

i

Table 4.2. Full-line inspection techniques

Inspection  method  Application  limitations  Rangc  of costt  CCTV 

Sonar/CCTV  Person­entry  Stationary  camera 

Sewers  up  to  1500  mm  diameter,  above  flowline  only,  quality  decreases  as  cable  length  increases 

Some  flow  required,  above  and  below  flowline,  quality  decreases  as  cable  length  increases 

Sewers  900  mm  diameter  and  larger,  visual,  above  flowline  only,  health  and  safety  concerns 

Applicable  only  to  pipe  sections  adjacent  to  access  holes,  above  flowline  only,  used  mainly  for  preliminary  assessment 

$2  ­ $14/m  $7  ­ $IO/m  $2  ­ $20/m 

$IOO/MH 

t Costs  depend  on  actual  joh  situations  and  tend  to  increase  with  the  increase  in  pipe  burial  depth  and  sewer  size.  These  costs  are  estimates  only. 

4.2.1 Closed circuit television (CCTV)

Closed circuit television (CCTV) is an effective  tool for  the inspection oflarge sewers and it  does  not require person­entry.  The  inspection  procedure involves moving a video camera  through the sewer to record the condition of  the  interior surfaces of the sewer. Modem  video technology,  including 'pan­and­tilt' and  'fish eye', provides high­quality images of the  sewer interior.  Certified CCTV operators use the video footage  to  record the type and location of defects.  Corresponding condition assessment is  carried  out subsequently by viewing  the  inspection  tape and the  inspection report.  CCTV can only capture images ofthe portion of  the  pipe above the flowline and cannot provide  quantitative deformation measurements.  However, a skilled operator can detect features  such as a hydraulic jump that may indicate a  deformed pipe or deformed joint. If it is essen-tial to inspect the pipe below the flowline using CCTV, dewatering ofthe sewer by means of bypass or bypass pumping will be required. Most CCTV tools are suited for pipes up to 1500 rom in diameter52

• The CCTV cameras are

supported by tractors or floats and movement is controlled remotely by an operator on the

surface. For the tractor application, the CCTV camera is placed on a moveable platfonn that allows the camera to be moved closer to a defect. Some cameras have the ability to pan-and-tilt, rotate or zoom to improve inspection quality. Extra lights are often attached to the tractor to improve visibility. The inspection apparatus can be assembled in the sewer or collapsed to fit through a standard access hole and expanded to full size inside the sewer. The tractors can negotiate bends, tum on their own axis and move through areas with debris. Inspections can be perfonned from access hole to access hole. If only one access point is available, inspection is carried out as the CCTV camera travels to the furthest location, and the inspection tractor is reversed to return to the entry point.

Before the tractor- or rig-camera system is used, the expected flowline is estimated. Spacers are placed on the rig to elevate the camera to the appropriate position prior to entry. Ifthe flowline is too high, the camera will be sub-merged, rendering the survey ineffective. In areas where the flow level is high, the camera can be mounted on a float. In such cases, the extent ofthe circumference visible to the camera is diminished and ifthe flow velocity is high, movement of the float and camera may adversely affect the image quality.

, 

i

There are some drawbacks to CCTV inspection.  than for  CCTV inspection alone. As with CCTV  Depending on the  situation, set­up  can be a  inspection, the set­up time for combined sonar-large portion of the overall inspection time. CCTV inspection is usually long in relation to Although power supply cable is available up to the actual inspection time. Inspection costs 1OOOm long, image quality may deteriorate when range from $6/m to $1 O/m for sonar only, and cable longer than 500m is used35

• For long cable $7/m to $1 O/m for combination sonar and

lengths, a booster may be needed to improve CCTV55 •

image transmission. The drag weight of long

cable also becomes a limiting factor. 4.2.3 Person-entry inspection

Visual sewer inspection by trained personnel Although CCTV is an effective means of

can provide qualitative and quantitative inspecting large sewers, it is subject to operator

information about defects. For example, interpretation and an operator may fail to

inspectors can note defects and deterioration, identify defects for various reasons including

detect concrete de-lamination, measure pipe inattention, fatigue or poor image quality. CCTV

deflection, and take close-up photos. Person-operators must have formal training and

entry inspection may be the sole type of certification from a credible organization to

inspection used or may be used to acquire ensure reliability and uniformity of defect

additional information following a CCTV coding. The North America Association of

inspection. In preparation for person-entry Pipeline Inspectors (NAAPI) offers training and

inspection, it is useful to review past reports certification for CCTV operators based on WRc

and to identify locations of particular concern. (Water Research Centre, United Kingdom)

standards.

Person-entry inspectors should receive formal training for visual condition assessment and In general, CCTV inspection cost increases

certification to ensure consistency and with sewer depth because of increased set-up

comparability. In addition, person-entry time and because of the additional cable length

inspectors must have special training for work extending from the surface to the sewer. The

in confmed spaces. As described in Section 2, cost ofCCTV inspection varies from $2/m to

sewers are hazardous work areas and any $14/m55 _{(not including sewer cleaning costs).}

person-entry activity requires strict adherence to safety procedures. The set-up time for

4.2.2 Sonar/CCTV

person-entry inspection is lengthy due to Sonar/CCTV combines the use of sonar to health and safety requirements and the rate of inspect the portion of the sewer below the inspection is affected by safety factors such as flowline and CCTV to inspect above the the duration of bottled air supply.

flowline to give a complete picture of the sewer.

The sonar images can reveal the true shape of As for CCTV inspection, person-entry inspec-the pipe, sedimentation build-up at inspec-the invert tion can only observe defects above the and defects in the pipe wall greater than 4 mm21

• flowline, and there is always the possibility of a

subjective interpretation of defect type and Like CCTV, this inspection technique requires severity. Person-entry inspection may not specially trained personnel both to perform the accurately establish the location of each defect. inspections and to interpret the results. The City of Edmonton costs for person-entry set-up arrangement and length limitations are inspection range from $2/m to $20/m. similar to those for CCTV. However, the

i

I

4.2.4 Stationary camera

Stationary cameras are used to obtain quick  and  fIrst­hand  indications of pipe defects  in the  vicinity of access holes. This technique is  often  used  as a screening tool  based on the premise  that the sewer line  condition is  often poorest  near the access holes41 

• Photos are taken from 

the  access  holes  and therefore the  distance  from the access hole that can be checked  depends  on the quality of lighting and the  zooming capability ofthe camera. The cost is  approximately $1 00 per access hole. 

4.2.5 New inspection technology Several promising techniques are under  development. One of these is  Sewer Scanner  and Evaluation Technology (SSET), developed  in Japan and evaluated by the Civil Engineering  Research Foundation (CERF). SSET uses a  scanning technique  in  conjunction with an  expert database system to automatically  identify defect types on the interior surfaces of  sewers2, 23. 

4.3 Special-Purpose Inspection

Techniques

Special­purpose  inspection techniques are  those used for  extraordinary situations (such as  surcharged pipe) or are techniques specifIc to  certain pipe materials. Table 4.3 summarises the  techniques that are described  in  this  section. 

Table 4.3. Special-purpose inspection techniques

Inspection  method  Characteristics 

4.3.1 Rotary sonic device

Similar to the combined sonar­CCTV technique  described in 4.2.2, the rotary sonic device can  be used to measure deflections in a flexible  sewer pipe or a lined pipe or to determine the  loss ofmaterial from the interior surface ofa  pipe.  Sonar operates by measuring the different  travel velocities of sound in different materi-als45 

. Sonic devices  can be  used to  inspect 

portions of the pipe both above and below the  flowline, but not simultaneously. The rotary  sonic device travels  inside the pipe on carriers  similar to those used for CCTV cameras and  measures the deformation at  any given point  around the pipe.  The cost of using a rotary  sonic device ranges from $10 to $13/m 45  (excluding sewer cleaning and mobilization).  4.3.2 Diver inspection CertifIed divers can be used to perform  inspections in high flow  conditions and in  surcharged  sections  such  as  inverted  siphon  sections oflarge sewers. Visibility and extra  diffIculty in recording defect severity and  location are limiting factors. Diver inspection is  a high­risk person­entry inspection method  with specialized safety requirements.  4.3.3 Systeme mechanique

d'auscultation des conduites (MAC) The MAC system is a test technique used for  spot evaluation of the structural strength of  pipe and the integrity of the pipe­soil struc-ture47 

• The sewer must be dewatered before 

Rotary  sonic  device  Divers 

MAC  system 

Infrared  thermography  Ground  penetrating  radar 

Proven  technique,  useful  for  deflection  measurement  of flexible  pipe,  used  for  sewers  up  to  1500  mrn  in  diameter 

High  risk  technique  for  surcharged  sewers,  limited effectiveness  in  high  turbidity  Proven  technique,  dewatering  or  low  flows  required 

Developing  technique,  limited effectiveness  in  areas  congested  with  buried  utilities  Developing  technique,  soil­condition  dependent 

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testing.  Because it  is not always possible to  There are four ways of performing infrared  dewater large sewers, this technique is more  thermographic  inspections. 

easily used to  do  spot checks of new sewers 

prior to  use. A computer and  loading apparatus  The operator wears the equipment and  are then placed inside the sewer. The load is  walks along the inspection area.  applied and a sonar head measures the pipe 

deformation. The computer uses the fmite  The equipment is installed on a platform  element method to determine the longitudinal  and records the thermal images from an  rigidity, elongation and safety factor.  The  elevated  position. 

method is expensive ($50/m) and requires 

specialized equipment and personnel.  The equipment is mounted on a vehicle. 

4.3.4 Inspection beyond the pipe wall The equipment is mounted on a helicopter 

(void detection) to  inspect a large area. 

The integrity of the  supporting soil  structure is  Infrared thermography appears to be economi-very important50 _{to sewer performance, and loss} 

cal (the average cost is $5/m) and safe. Data  of soil support may lead to  collapse of the  _{can be combined with other inspection results}  sewer. Factors that affect the rate of soil loss  _{to provide greater accuracy and the results can}  include size ofa fracture or open joint in the  _{help differentiate the sections in need ofrepair} sewer pipe, groundwater table level, character- _{from those in good conditionl7.} 

istics of embedment soils, occurrence of 

adjacent water main bursts, and adjacent  _{Testing can be done  during the day or night}  construction activities  that  disturb  pipe  _{and there is  little inconvenience to the public.}  embedment. The movement of soils through  _{However, analysis can be difficult in areas}  fractures and joint openings will result in voids  _{congested  by other services.  The ground}  and  loss  of support for the pipe.  Methods of  _{surface must be dry,  with no water or snow}  void detection are relatively new and still under  _{present.  Inspection can usually be performed}  development. Therefore it is essential to  _{after at least one day without rain.} 

validate the fmdings  of void detection tests. 

Surface inspection is the careful investigation  Infrared thermography uses latent heat from  _{of the area above the sewer to  check for dips or}  fluid  or gases to detect leakage and  voids. It is  _{settlement that might indicate the presence of}  a non­contact,  non­destructive method used to  voids around the sewer pipe, or pipe deforma-inspect large areas from above ground. It can  tion. The presence of surface irregularities will  detect voids but cannot ascertain whether the  indicate a high priority need for a detailed  void is due to soil loss or is a void in a struc- _{inspection ofthe pipe interior.}  ture (such as a water valve box). In addition, it does not indicate the size of the void.  The   Ground penetrating radar (GPR) can be used  components of the  inspection include an  _{both from  inside the pipe and from the surface}  infrared scanner head and detector, real time 

to identify and locate voids in the soil sur-microprocessor, data acquisition or analysis 

rounding a pipe. GPR emits electromagnetic  equipment, and image recording and retrieving  _{energy pulses into the  ground,  and the} 

devices.  _{reflection and refraction by subsurface layers} 

or buried objects are measured. The depth of  investigation can be up to  100 m, depending on  soil types. GPR has little effectiveness for clay  soils or soils with high electrical conductivityl7. 

ｾ  

­ 

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GPR has been used successfully in combina- Coring through the pipe wall can be used to  tion with sonar and CCTV30 _{to detect cavities  determine the condition ofthe pipe's exterior} 

around sewer pipes. In one case, a remotely  surface  and  to  detect  suspected  voids  behind  controlled vehicle equipped with sonar, high- the pipe wall. Additional laboratory tests can be  resolution video and GPR was placed in the  performed on the core samples. 

sewer. The GPR transducer was placed against 

the inside wall of the sewer and the return  In­situ  strength testing uses  portable  test tools  signal was recorded as well as the position of  (for example, Schmidt Hammer) to test the  the defect. The results of the GPR survey were  strength of the pipe material. 

correlated with video and sonar data. Known 

voids were detected (grave vaults in this case)  Other methods include:  and other detected voids were confirmed by 

boring. 

Joint testing to determine joint water-tightness 

4.4 In-Line Testing Methods

Sampling interior pipe wall deposits for  In­line test methods are methods used for  _{laboratory determination of chemical}  specific testing of known  or suspected trouble  _composition  

areas.  

4.4.2 Other inspection methods 4.4.1 Person-entry test methods

Flow measurements can be used to fmd   The following tests require person­entry and   _{obstructions and flow irregularities. Automatic}  therefore they need to be done when sewer  _{flow meters (for examples, mUlti­range ultra-} 

flows are low.   _{sonic  sensor and  pressure transducer with} 

velocity doppler sensors)  can measure  and  .Impact echo is  a non­destructive test for  _{record flow depth and velocity, and can be}  

determining the thickness of the wall of sewer   _{used  to  record  surcharge events.}   pipe.  It can also detect voids in the supporting  

soil to some extent. One method uses a hammer   _{Locations of inflow and infiltration and root}   to excite the pipe wall and a load cell to measure   _{intrusions can be identified using a customized}  the force.  Geophones or accelerometers ­ two  _{infrared system}16 

• The probe  is  encapsulated to 

types of receiver transducers ­ are used to  _{protect it from the sewer conditions and is}   measure response to the impact. The  dynamic   _{placed on a skid similar to the type used for}   stiffness of the pipe material is  determined to   _{video (CCTV) inspection. This method can}   indicate whether voids or defects are present in   _{differentiate between sewer effluent and}   the pipe walp4.   _{incoming water (infiltration) based on their}   temperatures. The rate  of inspection is up to   A second method uses a hand­held radar   _400rnlday.   antenna that is  passed over the sewer wall.   This method is  able to differentiate segments   with intact sewer­soil structures from ones with   cracks, voids or other defects34.  

, 

_..

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5.

Condition Assessment for Pipe

5.1 LSCCR - Large Sewer

Condition Coding and

Rating

Careful assessment of the physical  condition of sewers is  fundamental to  sound management of a sewer  system.  The condition rating,  in  combination with the failure impact  rating described in Section 3, is the  basis for making rational decisions  for the timing of inspection, mainte-nance and repair work.

The Large Sewer Condition Coding and Rating (LSCCR) method de-scribed in this Section is based on information adopted and modified from sewer condition assessment procedures used by the City of Edmonton15

, the City ofPhoenixlo

and the Water Research Centre52 ,

(United Kingdom). It is thorough yet easy to use. Appendix A provides tables for converting condition codes from these other systems to the LSCCR system.

The Large Sewer Condition Coding and Rating (LSCCR) system uses a one-metre pipe segment as the primary unit of assessment and the MH to MH length as the secondary unit (Figure 5.1). This means the inspection data can be used to identify worst-case localized prob-lems or to identify lengths of sewer that are in poor condition overall. Where a MH to MH length is more than 120 m, it should be divided into equal sub-lengths smaller than 120 m. Certain defects represent structural deficiencies in the sewer system-others represent serviceability (or

operational) deficiencies. It is logical to separate these two general types of defects since structural deficiencies usually entail repair (rehabilitation) actions while serviceabil-ity deficiencies usually entail maintenance activities. Two physical condition ratings are used:

._----1m assessment length

\b••{••·•·•••••••·•··••

·.i••••••

ｾﾷＮ  

\\

_.

Primary assessment unit

'. MH\ MH Ground ｳｵｲｦ｡｣ｾ   I II ....· I . . . . ＭＱＭｾＭＭＢ   "

Ａｾ  

\

-E-

ｾ  

-

ＢＧＮＺＮｾ  

j' - /,' -

jf-

Sewer

:3

7 ｉｾＭＭＭＭＭｉｦＭＭＭｾ   L MH - MH assessment length Secondary assessment unit

Assessment

Unit Structural I Serviceability Scores

Primary: Peak score in a 1m length

1m length Total score in a 1m length

Mean score = Total score (score/m)

Secondary: Peak score in a MH - MH length

MH-MH Total score in a MH - MH length

Length Mean score

=

Total score/L (score/m)

­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­

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9  Structural condition rating for structural  deficiencies  Serviceability condition rating for  serviceability deficiencies. 

The clock reference system  is  used to provide  standardized defect positioning. Looking  downstream, the  12 o'clock position is the top  of the sewer pipe and 6 o'clock is the pipe  invert (Figure 5.2). For pipe shapes not covered  by Figure 5.2, the user will need to defme the  clock positions that best suit a given shape.  Chainage is used to defme the  location and  extent of defects in the longitudinal direction.  12  ｾ   12  6  a  12 2   12  

3 

­­I ｾｲ   2  1  h

31

1  h \ I 6 6 a  ｾ   

Figure 5.2 Clock reference for sewer inspection and condition assessment

5.2 Structural Defect Coding for

Pipe

Table 5.1  shows the types  of defects that can  be encountered for various pipe materials  (Section 5.4 deals specifically with brick  sewers).  Each defect is recorded using a two­ or three-letter defect coding system as follows:  First letter: defect type (for example,  fracture or crack)  Second letter (ifneeded):  identifies the  direction ofthe defect as circumferential  (direction along the circumference ofthe  pipe's cross section), longitudinal  (direction parallel to the pipe axis, or  diagonal (defects between 30° and 60° with  respect to the longitudinal direction).  Third letter: Identifies the severity of the  defect. Severity is coded as light (L),  moderate (M) or severe (S).  defect type (F,   C, D, etc.)

+

_o 

_o

₇

_{severity (L, M,  S)} 

DOD 

t direction (C, L, D) For example, the structural defect coding FLL  represents a fracture defect in the longitudinal  direction and its severity is light.  5.2.1 Fracture (F)

A fracture  is  a "through" crack and/or open  crack that is more than 5 rom wide (Figure 5.3).  Fractures are sometimes accompanied by  deformation and evidence of infiltration (traces  of soil). It is a challenge to differentiate cracks  from fractures when fractures are closed on the