tmc 401 geotechnical risk assessment and hazard … · and hazard management guidelines this...

TN 060: 2014

of 1

For queries regarding this document [email protected]

www.asa.transport.nsw.gov.au

Technical Note TN 060: 2014

Issued date: 07 August 2014 Effective date: 07 August 2014

Subject: Withdrawal of TMC 401 Geotechnical Risk Assessment and Hazard Management Guidelines

This technical note is issued by the Asset Standards Authority as a notification to remove from

use RailCorp document TMC 401 Geotechnical Risk Assessment and Hazard Management

Guidelines.

TMC 401 is a legacy document and should be used for reference purposes only. ASA standard

T HR CI 12100 ST Geotechnical Risk Assessment and Hazard Management, Version 1.0

supersedes this document.

Authorisation

Technical content prepared by

Checked and approved by

Interdisciplinary coordination checked by

Authorised for release

Signature

Name Sarath Fernando Richard Hitch David Spiteri Graham Bradshaw

Position Principal Engineer Geotech

Lead Civil Engineer Chief Engineer Rail Principal Manager Network Standards & Services

Asset Standards Authority A3520780 © State of NSW through Transport for NSW

mailto:[email protected]

http://www.asa.transport.nsw.gov.au/

Sup

erse

ded

by T

HR

CI 1

2100

ST

GEOTECHNICAL RISK ASSESSMENT AND HAZARD MANAGEMENT GUIDELINES

TMC 401

Engi

neer

ing

Man

ual

Engineering Manual Geotechnical

Version 1.1

Issued December 2009

Owner: Principal Engineer Geotechnical

Approved by: John Stapleton Authorised by: Jee Choudhury Group Leader Standards Principal Engineer

Civil

Disclaimer This document was prepared for use on the RailCorp Network only. RailCorp makes no warranties, express or implied, that compliance with the contents of this document shall be sufficient to ensure safe systems or work or operation. It is the document user’s sole responsibility to ensure that the copy of the document it is viewing is the current version of the document as in use by RailCorp. RailCorp accepts no liability whatsoever in relation to the use of this document by any party, and RailCorp excludes

ny liability which arises in any manner by the use of this document. Copyright

he information in this document is protected by Copyright and no part of this document may be reproduced, altered, tored or transmitted by any person without the prior consent of RailCorp

UNCONTROLLED WHEN PRINTED Page 1 of 23

ST

1210

0 C

I H

R

T

by

Sup

erse

ded

RailCorp Engineering Manual — Geotechnical Geotechnical Risk Assessment and Hazard Management Guidelines TMC 401

Document control Revision Date of Approval Summary of change

1.1 December 2009 Changes detailed in chapter revisions

1.0 December, 2008 First issue in this format. Replaces RailCorp document “Geotechnical Problems Affecting Rail Operations - Risk Assessment and Hazard Management Guidelines (2005)”

Summary

of changes from previous version Chapter Current Revision Summary of change

Control pages

1.1 Change of format for front page, change history and table of contents

1 1.1 Format change only







App 1 1.1 Format change only



© Rail Corporation Page 2 of 23 Issued December 2009 UNCONTROLLED WHEN PRINTED Version 1.1

Sup

erse

ded

by T

HR

CI 1

2100

ST


Contents Chapter 1 General....................................................................................................................................... 4

C1-1 Purpose....................................................................................................................................... 4 C1-2 References.................................................................................................................................. 4 C1-3 Definitions, abbreviations and acronyms ....................................................................................4 C1-4 Geotechnical Risk Management Plan.........................................................................................4

Chapter 2 Management Requirements ..................................................................................................... 6 C2-1 Civil Maintenance Engineer ........................................................................................................ 6 C2-2 Principal Engineer Geotechnical................................................................................................. 6

Chapter 3 Competencies............................................................................................................................ 7 Chapter 4 Geotechnical Risk Assessment............................................................................................... 8

C4-1 Introduction ................................................................................................................................. 8 C4-2 Risk Matrix .................................................................................................................................. 8

Chapter 5 Risk Assessment Procedure ................................................................................................. 10 C5-1 General ..................................................................................................................................... 10 C5-2 Identification of geotechnical problem ......................................................................................10 C5-3 Type of geotechnical problem...................................................................................................10 C5-4 Mechanism of failure................................................................................................................. 10 C5-5 Event ......................................................................................................................................... 10 C5-6 History of problem..................................................................................................................... 11 C5-7 Likelihood of failure ................................................................................................................... 11 C5-8 Condition of infrastructure......................................................................................................... 11 C5-9 Likelihood of failure and affecting the Track .............................................................................11 C5-10 Consequence............................................................................................................................ 12 C5-11 Track obstruction ...................................................................................................................... 12 C5-12 Type of obstruction ................................................................................................................... 12 C5-13 Size and degree of obstruction .................................................................................................12 C5-14 Track defect from geotechnical problem...................................................................................12 C5-15 Type of defect ........................................................................................................................... 12 C5-16 Degree of defect ....................................................................................................................... 13 C5-17 Likelihood of derailment ............................................................................................................ 13 C5-18 Type of derailment .................................................................................................................... 13 C5-19 Extent of the consequences from the derailment .....................................................................13 C5-20 Rock Fall during train passage .................................................................................................13 C5-21 Likelihood of rock striking a train............................................................................................... 14 C5-22 Extent of the consequences from rock fall ................................................................................14 C5-23 Extent of the consequences from the event .............................................................................14 C5-24 Risk of death, serious injury from Geotechnical Event .............................................................14

Chapter 6 Hazard Management ............................................................................................................... 15 Chapter 7 Repairs To Geotechnical Sites .............................................................................................. 16 Appendix 1 Risk Assessment Matrix and Ranking.................................................................................. 17 Appendix 2 Hazard Management Guidelines............................................................................................ 21 Appendix 3 Site Supervision and Repair Guidelines............................................................................... 23


Sup

erse

ded

by T

HR

CI 1

2100

ST

Chapter 1 General C1-1 Purpose

These guidelines present an assessment methodology to rank the risk from geotechnical problems to the safety of rail operations and infrastructure. This includes people who are travelling in trains and/or are located adjacent to the line, to railway infrastructure and operations, and to dwellings and property adjacent to the rail corridor.

A risk management model is presented for managing this geotechnical risk.

The Manual is based on the RailCorp document “Geotechnical Problems Affecting Rail Operations - Risk Assessment and Hazard Management Guidelines (2005)”.

The guidelines have been revised to incorporate the requirements of RailCorp’s SafetyManagement System.

The new Safety Risk Matrix replaces previous matrices.

The Risk Rankings replace previous Risk Categories.

The Manual includes the assessment of geotechnical risk and the hazard management required to reduce the risk.

C1-2 References SMS-06-SR-0030 V1.1 System Requirement - Safety Risk Management

TMC 203 Track Inspection

TMC 404 Recognising Geotechnical Problems

C1-3 Definitions, abbreviations and acronyms Protected Risk: Residual risk of a geotechnical problem location after imposition of risk

mitigation actions to reduce the consequences of an event affecting the track

Unprotected Risk: Geotechnical risk of a site before application of risk controls

Geotechnical Engineer:

RailCorp’s Principal Geotechnical Engineer or a competent person with delegated engineering authority for geotechnical design activities relating to risk sites

Site Supervisor: A qualified civil engineer or a competent person with delegated engineering authority for geotechnical repair works supervision

C1-4 Geotechnical Risk Management Plan A flow chart for managing geotechnical risk is included here to demonstrate where the riskassessment and hazard management processes fit in the Geotechnical Risk Management Plan for rail. Refer to Figure 1.



Sup

erse

ded

by T

HR

CI 1

2100

ST

Carry out Emergency

Remedial Works

Risk Assessment

lml r-------------~

Implement Remedial Works

Register

Hazard Management

Figure 1 : GEOTECHNICAL RISK MANAGEMENT PLAN



Sup

erse

ded

by T

HR

CI 1

2100

ST


Chapter 2 Management Requirements Regional management is responsible for ensuring that geotechnical problem locations are managed by competent persons in accordance with this Manual and the relevant Technical Maintenance Plans and Service Schedules.

The respective responsibilities of personnel assigned to the inspection, assessment and repair of geotechnical sites are detailed below:

C2-1 Civil Maintenance Engineer The Civil Maintenance Engineer must ensure that a system is place to:

− Manage inspection and assessment of geotechnical risk sites

− Manage repairs to geotechnical risk sites

− Manage track safety whilst geotechnical risk sites exist.

C2-2 Principal Engineer Geotechnical The Principal Engineer Geotechnical is responsible for the following:

− Assignment of Geotechnical Engineers to conduct inspections and risk assessments;

− Allocation of Geotechnical Engineers to respond to special requests from field staff for risk assessments and design of repairs.


Sup

erse

ded

by T

HR

CI 1

2100

ST


Chapter 3 Competencies Track inspections shall be carried out by competent persons in accordance with TMC 203 “Track Inspection”.

Geotechnical inspection of risk sites shall be carried out by a Geotechnical Engineer or Engineering Geologist.

Risk assessment of geotechnical problem locations shall be carried out by a geotechnical Engineer or Engineering Geologist.

Design of geotechnical repairs is to be approved by a Geotechnical Engineer or Engineering Geologist.

Repair work shall only be carried out under the supervision of a Site Supervisor.

Certification of the track during or after geotechnical repairs may only be undertaken by persons with the following competency:

− TDT B38 01A - Maintain track geometry.


Sup

erse

ded

by T

HR

CI 1

2100

ST


Chapter 4 Geotechnical Risk Assessment C4-1 Introduction

To assess the risk presented by a geotechnical problem site requires an assessment of both the likelihood of the event occurring and affecting the track and the expected consequences of that event.

To estimate the likelihood of a geotechnical problem affecting the track requires geotechnical expert evaluation of the ground conditions and the causes of failure associated with the particular site and an estimation of the extent and degree of failure. It is recommended to consider the problem in three stages.

− The likelihood of the event occurring

− The likelihood that the event when it occurs will affect the track

− The size of that event.

Consideration is given to the possible benefit of buffer zones beside the track when evaluating rock falls from above the track and the expected rock fall size and trajectory, based on knowledge of past events. For situations of earth fill instability an expert evaluation of the likelihood of the occurrence and potential extent and rate of track subsidence is required.

A flow chart setting this process out is presented in Figure 2.

C4-2 Risk Matrix The interaction of these two subjective assessments (likelihood and consequence) has been presented as a matrix in Appendix 1.

The matrix is the same as the RailCorp Level 2 Risk Matrix in SMS-06-SR-0030 System Requirement - Safety Risk Management with the addition of a likelihood descriptor for a geotechnical event affecting the track.

Geotechnical risk is expressed in terms of a risk ranking between A and D.

A priority sub-ranking within rankings B- and C+ has been established because of the large number and variety of problems normally assessed in these rankings. The priorities set different Target Actions and Hazard Management Guidelines within rankings B- and C+. Refer to the tables in Appendices 1 and 2.

For example, where it has been assessed that there is a possible likelihood (F4) of an event occurring and affecting the track with major consequences (C3), sites are categorised as Risk Ranking B- P1.

Table 1 in Appendix 1 presents target actions for geotechnical problem sites.

Without treatment many problems will continue to deteriorate and conversely in times of prolonged dry weather or favourable conditions the risk to safety can be less.

Where the risk to safety is resulting from deteriorating track conditions, the ability of maintenance resources to restore safe conditions is taken into account in estimating the consequences. Where the rate of deterioration is reported to exceed the capacity of maintenance staff to restore safe conditions, the deterioration will continue and may produce a derailment potential. The likelihood of derailment and the consequences are therefore considered in determining a risk ranking. This assessment will require advice on maintenance resources and track/train dynamics from the relevant staff of infrastructure maintenance.


Sup

erse

ded

by T

HR

CI 1

2100

ST

Figure 2 ·ASSESSMENT OF GEOlECHNICAL RISK TO RAIL

EVENT

H istory

LJ<elhood ofF ailure

7 Condition of

8 Lkelihood of failure and

affedrtg the track· The Event

Track Obstruction

Type of O bstruction

12

CONSEQUENCE

Trad<: Oefed

Type of Defed

Size and Degcee of Oefed

Rock fall duOOg bain

16 20 Lkelihood of Lkelihood of rode fa ll Derailment traWl

Type of Derailment

Extent of consequence ftom the Derahent

22 The Consequence



Sup

erse

ded

by T

HR

CI 1

2100

ST


Chapter 5 Risk Assessment Procedure C5-1 General

The flow chart in Figure 2 sets out the thought process in assessing the risk due to a geotechnical problem. The following sections provide an explanation for guidance in making an assessment. They are neither exhaustive nor definitive and the practitioner is required to use his /her own experience and knowledge of the particular problem in reaching an evaluation of each likelihood assessment and the risk.

Similar procedures can be used for risk assessment to adjacent property.

Where the problem is observed to be extensive and presents a high risk to safety, it may be necessary to be more objective and a quantitative risk assessment may be required. The same methodology for assessing the risk is followed with the use of more reliable information.

The assessment of geotechnical risk is to be initially considered without any hazard management in place. Hazard management and its impact on the risk will be considered independently.

C5-2 Identification of geotechnical problem The geotechnical problem has been identified by the risk management plan presented in Figure 1, is listed on the database and is either being assessed for the first time or is under review.

C5-3 Type of geotechnical problem The type of the problem is categorised as:

− Unstable cutting or hillside producing a rockfall, rockslide, landslide or mudslide problem.

− Unstable embankment or an embankment producing, or has potential to produce, track subsidence, loss of track support, ballast washaway, or total collapse.

− Failing track formation producing poor track geometry.

C5-4 Mechanism of failure It is important to have a good understanding of the mechanism of failure of the geotechnical problem before attempting to arrive at any likelihood assessments. The mechanism of failure will be deduced from the results of the site investigation if one exists, from site inspections or from the experience and knowledge of the practitioner.

Where there are numerous individual problems within the one site it is necessary to evaluate them separately to determine the highest risk for the area or report them separately.

The following are some examples:

Embankments Cuttings

- Subsidence, creep

- Sliding

- Collapse

- Washaway

- Rock slides

- Wedge, Plane and Topple failures

- Rolling rocks

- Landslides

- Mudflows

C5-5 Event It is recommended in this procedure to consider the likelihood of the Event occurring separately from the likelihood of the consequences before calculating risk.

Sections C5-6 to C5-9 refer only to the likelihood of the event occurring and affecting the track.


Sup

erse

ded

by T

HR

CI 1

2100

ST


C5-6 History of problem To understand the potential for a failure and its outcome it is necessary to research some of the history of the problem.

− What evidence is there that warning signs of failure have been observed?

− What incidences have been reported and recorded by maintenance staff and over what period?

− What information is available from geotechnical monitoring, if in place?

− What degree of problem has been experienced at the site?

An understanding of likelihood of failure can be gained from the following type of information:

− Number of rock falls per year

− Amount of ground movement over particular periods, is it creep or shear?

− The amount of maintenance effort required to provide a serviceable track.

− Correlation of events with factors such as rainfall.

C5-7 Likelihood of failure After considering the information suggested in Sections C5-3 to C5-6 make an assessment of the likelihood of failure considering the failure mechanism and the condition of the infrastructure.

C5-8 Condition of infrastructure The condition of the infrastructure will influence the occurrence of an event and therefore including this information can make a better assessment of likelihood. Infrastructure in good condition will have a lower likelihood of failure for the same mechanism than for a similar situation where the infrastructure is in poor condition. The following examples give a range of conditions that can influence the likelihood.

Good Poor

- Cuttings are clean with no vegetation

- Cess and toe drains are clean and graded uniformly

- Top drains are clear and intact and direct water to culverts

- Cut off drains are in place for up hill seepage

- Well engineered fill

- Culvert capacity adequate without ponding for design storm

- Thick vegetation over rock cuttings, active tree root activity

- Cess drains blocked and ponding water

- Water ponding at embankment toe area

- Top drains blocked or breached

- No cut off drains and seepage from uphill is active

- End tipped Fill

- Ash embankment widened on the downstream side with clay fill

- Culvert not positioned correctly - not in the lowest part of the embankment

- Culvert inadequate and ponding on upstream occurs regularly

- High potential for blockage of culvert

C5-9 Likelihood of failure and affecting the Track Having selected a likelihood of failure occurring modified by the influence of the condition of the infrastructure, review this with regard to the likelihood of it adversely affecting the track. Do this by considering the chance of the problem adversely affecting the track. To do this it is necessary to consider the site conditions and the mechanism of failure.


Sup

erse

ded

by T

HR

CI 1

2100

ST


Example

There may be a small buffer zone beside the track and with other contributing factors an assessment could be made that there was reduced chance that the rock fall would adversely affect the track. i.e., an almost certain likelihood of an event occurring with a possible likelihood of an event affecting the track may be a likely likelihood of the event occurring and affecting the track.

It is also necessary to assess the likelihood for various degrees of impact to the track.

− Will the impact on the track be major or minor?

− Where will the debris be likely to come to rest? Will it land on the track or beside the track?

− Will the embankment failure under mine the track or only affect the batter slope.

If there is a reasonable expectation that the affects could include a major impact then it would be necessary to assess all outcomes separately.

To calculate “likelihood” quantitatively it would be advisable to use an Event Tree Analysis to include all possible outcomes with numerical values for likelihood of the event occurring over a nominated time frame.

C5-10 Consequence Having arrived at an assessment of the likelihood of the event occurring and affecting the track the following Sections C5-11 to C5-21 assess the likelihood of death and serious injury from that event. It is necessary to look at the various types of outcome possible from the mechanism of failure.

C5-11 Track obstruction This note refers mostly to outcomes from cutting failures where the effect on the track is debris on the track, which will obstruct traffic.

C5-12 Type of obstruction When considering the impact of an obstruction on the track to track safety it is necessary to be aware of the particular type of obstruction that each problem will produce. In order to make a realistic interpretation on the outcome of a train colliding with the obstruction it is necessary to be reasonably confident of the manner of the collision. The following features of the obstruction need to be considered:

− single rock or scree

− shape and size of the rock

− what the debris consists of; rocks, colluvium, mud etc.,

− crushability of rock material,

C5-13 Size and degree of obstruction The outcome of a collision of a train with an obstruction is also dependent on the magnitude of the obstruction and how much of the track is affected:

− size of debris mass and its spread over the track

− depth of material over the track

C5-14 Track defect from geotechnical problem A track defect may be the result of embankment subsidence or failure of track formation.

C5-15 Type of defect This may vary from a defect only affecting the embankment shoulder and hence the lateral support to the track to one that causes a depression in one or both rails. A misalignment can also be a symptom of embankment subsidence.


Sup

erse

ded

by T

HR

CI 1

2100

ST


Loss of track support due to a collapse of the embankment or a washaway of ballast or fill is considered under this issue.

C5-16 Degree of defect The degree of track defect will depend on the particular site and the failure mechanism. The history of the problem will provide information about the rate of failure and whether the track defect will occur suddenly or slowly due to creep.

The impact on track safety will also depend on whether the failure will cause non uniform subsidence (or twist) or a uniform depression in the track over a short or long distance and whether the track becomes misaligned as a result. The background information should provide guidance on this.

C5-17 Likelihood of derailment Having considered all the information reviewed as per Sections C5-10 to C5-16 relating to the impact of the EVENT on the track an assessment of the likelihood of a derailment occurring is made.

C5-18 Type of derailment Having established that there is a likelihood of derailment occurring, before assessing the risk of death or serious injury, it is necessary to review the type of derailment that may occur.

C5-18.1 Track obstruction The nature of the obstruction will contribute to the manner of the derailment and the likelihood that the derailment will almost certainly to highly likely involve the leading loco or carriage.

C5-18.2 Track defects A derailment resulting from a track defect, caused by a geotechnical event, is highly likely to involve a trailing wagon or carriage.

C5-18.3 Manner of derailment Having understood the type of derailment it is also necessary to consider the manner or behaviour of the train after the derailment. This will involve considering the terrain around the site and the directions train travel if double track. Some possible outcomes are:

− Train or carriage stays upright and comes to rest

− Train collides with a more substantial obstruction (bridge, tunnel portal etc.) and jack knifes

− Train careers off the track and down an embankment, onto private property, over steep incline (etc. )

− The train crosses onto another track

− The train collides with a oncoming train

− The train overturns and slides to rest

− etc.

It is necessary to consider which of the above are most appropriate to the particular site and the likelihood of each occurring.

C5-19 Extent of the consequences from the derailment Having considered the possible derailment outcomes and the likelihood of each it is necessary to assess the likelihood of death or serious injury from each.

C5-20 Rock Fall during train passage From the history and mechanisms at the site it is possible that the most dangerous mechanism will involve rock fall during train passage. This will involve rocks of all sizes and the consequence will


Sup

erse

ded

by T

HR

CI 1

2100

ST


depend on their trajectory across the track. For example, if small rocks are projected across the cutting at cabin height there is a chance of striking a person.

C5-21 Likelihood of rock striking a train It is necessary to have some history of rock fall or observation of debris around the site and information on the frequency of train passages.

C5-22 Extent of the consequences from rock fall It will be necessary to have information on the type of trains on the line as the likelihood of death or serious injury will be higher for passenger trains.

C5-23 Extent of the consequences from the event It is necessary to decide the extent of the consequences ranging from extreme to minor as defined in the risk table.

C5-24 Risk of death, serious injury from Geotechnical Event Finally, a risk ranking is determined using the matrix in Appendix 1.


Sup

erse

ded

by T

HR

CI 1

2100

ST


Chapter 6 Hazard Management Hazard Management can effectively reduce the geotechnical risk facing the rail system by reducing the consequence rather than eliminating the problem where the cost or practicabilities of eliminating the hazard are prohibitive. This can be achieved by imposing operational limitations or by increasing maintenance.

The assessment of the reduced risk to rail operations due to hazard management is shown as Protected Risk by acknowledging the benefit of:

− speed limits on trains

− early warning systems

− regular maintenance activity

− increased surveillance inspections.

Where relevant, the use of “protection” measures such as train speed limits or early warning systems may reduce the assessed Unprotected Risk to a safer Protected Risk by reducing the consequences of an event affecting the track. Such protection will not change the likelihood of the event occurring. For example, in the Risk Assessment Matrix Appendix 1, an unprotected risk rank of A (F6:C3 in matrix) may be reduced to a protected risk rank of B+ (F6:C2 in matrix) because an imposed train speed limit has reduced the consequences from C3, Major to C2, Minor (the likelihood remaining at F6, Almost Certain). Where applicable, risk ranking in this document refers to the protected risk.

Surveillance is an important hazard management tool as it can give warning of deterioration of a geotechnical problem site or identify new problems. However, depending on the individual site and the level of surveillance, it may not always be relied on as a protection measure.

Definitions of the procedures and guidelines for surveillance inspections of geotechnical problem sites are described in Appendix 2. The critical features to be checked during inspections are presented and Table 2 provides a flexible system to vary surveillance to suit the current situation.

The guidelines recommend minimum levels of surveillance relating to the Risk Ranking. For the bulk of geotechnical problems (Rank C+, D) a level of surveillance provided by the Track Examination System (T) is sufficient. However for sites ranked as Rank B- or higher, more frequent inspections with greater detail are needed. Sites assessed as Rank “B-, P1” require as a minimum, monthly detailed inspections during the track patrol; and for higher Rankings, more frequent detailed inspections or full time monitoring.

Speed limits are imposed by Maintenance staff and or recommended by Geotechnical staff when it is recognised that conditions would be unsafe for normal speeds or to reduce the consequences if trains were to strike fallen rocks. Speed limits are only a temporary measure as they have a direct influence on operating reliability.

Early Warning systems are installed to provide warning of ground movement that would impact on safe operating conditions. A variety of systems exist some of which are connected to the signalling system to stop trains, while others provide a warning to train control. The intention is to give sufficient warning to prevent the running of trains over unsafe track or to provide warning to adjacent property owners.

Regular maintenance of some geotechnical problem sites such as drainage improvements may reduce the likelihood of failure while other activities such as fettling are related to the reduction of the severity of the consequences.

All sites require reviewing by expert geotechnical personnel every 12 months and every 6 months or less for Rank “B-, P2” sites or higher.

Hazard management recommendations are also mentioned in Table 1 Appendix 1.


Sup

erse

ded

by T

HR

CI 1

2100

ST

Chapter 7 Repairs To Geotechnical Sites


Timing of remedial works to geotechnical problems are mentioned in Table 1 of Appendix 1.

During the construction of the remedial works to geotechnical problems the exposed subsoil conditions should be recorded and assessed by geotechnical experts to confirm the proposed design and to make modifications if necessary.

The design of repairs to geotechnical problems is based on as thorough an investigation as the site conditions and cost would permit. The analysis and design is therefore based on the best “model” possible and not upon actual conditions.

It is therefore important to record all the information gained from the exposure of subsurface conditions by the excavations or borings associated with construction. It is possible then to modify construction if necessary where a more complete picture of the geotechnical problem is gained, that would suggest changes.

Post construction monitoring is also necessary to evaluate the effectiveness of the design and construction in correcting the geotechnical problem.

Appendix 3 sets out guidelines for the site supervision and recording repairs to geotechnical problems.


Sup

erse

ded

by T

HR

CI 1

2100

ST


Appendix 1 Risk Assessment Matrix and Ranking

Geotechnical Description of Risk Ranking (Examples are not definitive and depend on individual risk assessment.)

A. UNACCEPTABLE − Track is impassable as a result of a geotechnical event.

− Traffic is stopped (unless hazard manage measures are suitable) due to a geotechnical event which would be anticipated to result in loss of life being imminent and the situation is too dangerous to allow trains to pass.

Example 1.

High embankment constructed on side fill. Mechanism is identified as a slide, which could occur rapidly taking the track and leaving it unsupported. Track maintenance has little impact in reducing risk.

Example 2.

High narrow cutting consisting of rock which has been identified as having potential failure mechanisms which could produce large boulders that could crush a train or cause serious impact.

B. UNDESIRABLE − Safety action or hazard management, is necessary for problems identified as undesirable, to

reduce the likelihood of the event occurring or the consequences of that event. Such action which includes maintenance, speed limits & surveillance may effectively reduce the risk provided the action is continued.

Example 1.

Cutting consisting of weathered rock which has been identified as a potential failure onto the track into which the train might plough and become derailed.

Example 2.

Moderately high embankment constructed on gently sloping ground, mechanism identified has been perceived as slow or comprising small increments and track can be maintained. Lack of maintenance would lead to derailment condition.

C. TOLERABLE − Low risk problem identified and (if remedial work incomplete) is being monitored for any

deterioration to a higher risk.

Example 1.

A rock cutting which has been identified as potentially failing, or has failed, and debris from the failure falls clear of the line.

Example 2.

An embankment constructed on gently sloping ground which is experiencing instability of the slope face and which only affects an access road or embankment shoulder with no affects to the track geometry.

D. BROADLY ACCEPTABLE − Problem has been rectified and is being monitored for effectiveness of remedial work.

− Very low risk problem identified and is being monitored for any deterioration to a higher risk.


Sup

erse

ded

by T

HR

CI 1

2100

ST

RISK ASSESSMENT MATRIX - GEOTECHNICAL PROBLEMS

Incredible Rare, Improbable Unlikely Possible Likely Almost Certain GEOTECH Not expected to Not expected to May only occur lt is possible event Will probably occur Expected to occur LIKELIHOOD occur at any time occur or only under under very adverse will occur within 12 within 12 months in within 12 months in

of geotechnical event exceptional weather conditions months in adverse most circumstances most circumstances

affecting track conditions at some time weather conditions

SMS F1 F2 F3 F4 F5 F6 CONSEQUENCE > 10 fatalities

Disastrous CS 8- P1 I 8+

2- 10 fatalities

Catastrophic CS C+, P1 8- P1 I 8+

1 fatality (2- 1 0 serious injuries)

8-1 P1 8+ Critical C4 C- C+, P1

1 Major injury

Major C3 C- C+, P1 8-1 P1 8+

1 or more minor injuries

Minor C2 C- C+, P2 8-1 P2 8+

Illness. 1st aid treatment or injury not requiring

8-atment Negligible C1 C- C+, P2 P2 '

P1 & P2 = PRIORITY for 8- and C+ Safety Action reduces the risk by reducing the consequence of the event affecting the track. The likelihood of event affecting the track is assessed from a visual inspection of the site and taking into account past performance.

RailC

orp Engineering M

anual — G

eotechnical G

eotechnical Risk A

ssessment and H

azard Managem

ent Guidelines

TMC

401

© R

ail Corporation

Page 18 of 23

Issued Decem

ber 2009 U

NC

ON

TRO

LLED

WH

EN

PR

INTE

D

Version

1.1

Sup

erse

ded

by T

HR

CI 1

2100

ST


TABLE 1 - TARGET ACTIONS FOR GEOTECHNICAL PROBLEM SITES Table 1 below is to be read in conjunction with Table 2 - Guidelines for Hazard Management of Geotechnical Problem Sites. Text in italics and inverted commas is an extract from RailCorp Safety Risk Management SMS–06–SR–0030.

RISK RANKING (& Priority)

TARGET ACTIONS FOR GEOTECHNICAL PROBLEM SITES

A Unacceptable

(Extreme)

“All necessary steps should be taken to further control the hazard…..".

TRACK CLOSED. Remedial works should be immediately undertaken to eliminate possibility of an imminent geotechnical event, which is too dangerous to allow train passage or to restore track to service (where track is impassable due to geotechnical event).

B+ Undesirable

(High)

"Additional control measures should be sought and evaluated to assess their reasonable practicality." & “B+ hazards are considered to be on the verge of being unacceptable and must be given immediate priority.”

Hazard management or safety action is immediately necessary to reduce the consequences of geotechnical event. Such action, which includes speed limits, maintenance & surveillance, may effectively reduce the risk provided the action is continued.

Remedial works should be undertaken as soon as possible. Emergency possessions may be needed for remedial works depending on severity of problem (as assessed by geotechnical staff) or if hazard management/safety action is unsuitable.

Target action is to remove/reduce this risk within 1 month of identification or sooner.

B-, P1 Undesirable

(High)

Additional control measures should be sought and evaluated to assess their reasonable practicality."

During rain, hazard management or safety action, may be necessary to reduce the consequences of geotechnical event. Such action, which includes speed limits, maintenance & surveillance, may effectively reduce the risk when applied.

Remedial works should be undertaken at next planned possession if hazard management/safety action is unsuitable or the following possession.

Notional target action is to remove/reduce this risk within 6 months of identification.

B-, P2 Undesirable

(High)

“Additional control measures should be sought and evaluated to assess their reasonable practicality."

Monitoring (surveillance) should be carried out as per Table 2 to ascertain if geotechnical problem has deteriorated.

Remedial works should be planned to be undertaken at a reasonably practicable time.



Sup

erse

ded

by T

HR

CI 1

2100

ST


RISK RANKING (& Priority)

TARGET ACTIONS FOR GEOTECHNICAL PROBLEM SITES

C+, P1 Tolerable

(Medium)

"Tolerable only if risk reduction is impractical or if its cost is grossly disproportionate to improvement gained." & "Additional control measures should be sought if a significant net benefit in doing so can be demonstrated and/or there is an additional measure which is recognised as good practice in other relevant railways."


Remedial works could be carried out at the same time as works to higher ranked instability features in the same area.


C+, P2 Tolerable

(Medium)



Remedial works could be carried out at the same time as works to higher ranked instability features if in the same area and if practicable.

Notional target action is to remove/reduce this risk within 2 years of identification.

C-Tolerable

(Medium)



Remedial works could be carried out at the same time as works to higher ranked instability features if in the same area and if practicable.

D Broadly Acceptable

(Low)

"Control measures should be subject to continuous monitoring."

Monitoring (surveillance) should be carried out as per Table 2 to ascertain if geotechnical problem has deteriorated. Possible remedial works not imperative at this stage.


Sup

erse

ded

by T

HR

CI 1

2100

ST


Appendix 2 Hazard Management Guidelines

Guidelines for Surveillance Inspection of Geotechnical Problems The following features form a checklist for inspecting a site. Those, which are relevant to a particular problem, are to be noted, particularly for changes in condition between inspection visits.

A written report should be prepared for each inspection. Comments are to be made for each site and the inspection record signed and dated.

These reports are to be presented to the Team Manager immediately.

Embankments and Sidefills (slip problems) Check for:

− change in track alignment/superelevation

− tension cracks in the ground surface on the downhill shoulder or access road

− changes in width of such cracks

− dips in shoulder/access road

− leaning structures (overhead wiring structures, signals, power poles)

− note any seepage from slope (toe)

− vegetation - areas of unusual lush green vegetation

− check cess drainage (clear or otherwise, water ponding)

− check culvert condition (clear or otherwise)

− subsurface drainage (where applicable), is water running?

Cuttings (rock falls) Check for:

− note any recent rock falls or spoil onto track/cess drain, note size and origin

− recent rock falls onto bench areas or behind catch fences

− isolated or partially supported blocks of rock, due to cracks or joints

− apparent movement of prominent rock wedges/blocks

− condition of any nominated area of known instability

− excessive seepage/water flows

− slumping and/or leaning trees above cutting

− tree roots visible in rock joints

Notes: 1. The inspections are an integral part of the safety management system of the railway and are distinctly separate from the route track patrol (T). Each site should be inspected for the features relevant for that site.

Where relevant, site-specific guidelines for inspections by track patrol staff can be issued by Geotechnical staff. These guidelines may include descriptions of specific features and may include photographs of those features.

2. The same personnel with training in the geotechnical processes must carry out the inspections on a regular basis with regular supervision.

3. An inspection register should be maintained and each visit discussed with the nominated supervisor.


Sup

erse

ded

by T

HR

CI 1

2100

ST


4. Any Early Warning System register at the site is to be read and recorded.


Sup

erse

ded

by T

HR

CI 1

2100

ST


Appendix 3 Site Supervision and Repair Guidelines

Repairs to Geotechnical Problems Site Supervision and Recording 1. Works should be adequately defined prior to commencement. 2. Supervision is necessary because of variations in subsurface materials. 3. Decisions made on site to alter the design without informed advice may jeopardise success of

remedial works. 4. The Supervisor must have an appreciation of the purpose of the work. 5. Accurate recording of what work is done is necessary to:

∼ review accuracy of geotechnical model ∼ plan for future remedial work by ensuring that a treated individual instability feature is

removed from a list of numerous features ∼ understand what additional work is necessary if further problems occur ∼ review whether work was carried out according to the design/or whether it achieved the

objective. ∼ If adequate supervision is not possible with staff available, qualified staff should visit the

site periodically when work involves activities critical to the safety of the site and stability of the final solution. Guide-lines for information necessary to ensure this are set out on the following page.

Earthworks Site Supervision Geotechnical Problems (Embankments) Key points to note during work 1. Maximum depth of any excavation. - Depth below rail to be measured and recorded. 2. Date of measurement. 3. Location of excavation. ie. distance from rail and distance along rail from a known point. 4. Material visible in sides of excavation and in embankment:

∼ note peculiar features (photographs if possible ) ∼ water, source and flow ∼ ash

∼ spalls ∼ vegetation

∼ colour of material ∼ presence of top soil

5. Material placed in excavation:

∼ type:

∼ rock ∼ spall

∼ fabric

∼ etc.

∼ treatment, compaction. method of placement ∼ level of each type below rail and extent along and away from track.

6. Levels and grade of subsoil drains. 7. The above information to be recorded and filed with the infrastructure maintenance staff and

Geotechnical Services.


tmc 401 geotechnical risk assessment and hazard … · and hazard management guidelines this...

Documents