plugin-bsp-02-standard-1643 - excavation (mod 05, rev. 2.1)

8/7/2019 plugin-BSP-02-Standard-1643 - Excavation (Mod 05, Rev. 2.1)

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H S E S T A N D A R D

M O D U L E 0 5E X C A V A T I O N

BSP-02-Standard-1643

THIS DOCUMENT CONTAINSONE

MODULE IN A SETCOMPRIS ING

HSE STANDARDSFOR THE

BRUNEI SHELL COMPANIES

Revision2.1

Approved:

Document Author:

SCO/4

SCO/4x


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BSP Excavation Module 05

Excavation - Rev 2.1 Page 2 of 25

Document Control

DOCUMENT TYPE DOCUMENT OWNER SECURITY CLASSIFICATION

Standards SCO/4

DOCUMENT REFERENCE AUTHOR APPROVED BY

BSP-02-Standard-1643 SCO/4x SCO/4

KEY WORDS

Revision Record

REV REVISION DESCRIPTION DATE

2.1 Incorporating TSM/12 recommendations April 2003

Distribution Control

Distribution of this document is controlled by the Document Owner. The distribution is as follows:

-

Notice and Warning

Copyright , Brunei Shell Petroleum Company Sendirian Berhad

This document is the property of Brunei Shell Petroleum Sendirian Berhad (BSP), Seria 7082, NegaraBrunei Darussalam. Circulation is restricted to BSP and its designated associates, contractors andconsultants. It must not be copied or used for any other purpose other than which it is supplied,without the expressed written authority of BSP.

Except where provided for purposes of contractual requirements, BSP disclaims any responsibility orliability for any use or misuse of the document by any person and makes no warranty as to theaccuracy or suitability of the information to any third party. Any misuse of the document isredressable by BSP.


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Contents Page

CHAPTER 1 RESPONSIBILITIES...........................................................................5

1.1 Excavation Supervisor .......................................................................................................... ..................... 5

1.2 Worksite Supervisor ................................................................................................... ............................... 5

CHAPTER 2 REQUIREMENTS ...............................................................................6

2.1 General Requirements ................................................................................................ ............................... 62.1.1 Definitions ....................................................................................... ...................................................... 6

2.1.2 Shallow Excavations ....................................................................... ...................................................... 6

2.1.3 Unsupported Excavations .......................................................................... ........................................... 62.1.4 Deep Excavations .............................................................................. .................................................... 7

2.1.5 Deep Foundations .......................................................................... ....................................................... 7

2.1.6 Mechanical Digging ....................................................................... ....................................................... 7

2.1.7 Headings and Tunnels ................................................................................... ........................................ 7

2.2 Preparation and Permit Requirements................................................................... ................................. 9

2.3 Support System Design Requirements................................. .................................................................... 9

2.4 Written Excavation Plan ................................................................................... ........................................ 92.4.1 General Considerations ............................................................................... .......................................... 9

2.4.2 Preparation .............................................................................. ............................................................ 10

2.4.3 Work Planning ................................................................................ .................................................... 10

2.5 Identification of Underground Services............................................................................................ .....102.5.1 Prior to Start of Work ................................................................................ ......................................... 10

2.5.2 Cable Avoidance Tool .................................................................................. ...................................... 11

2.6 Pilot Trenching ......................................................................................... ................................................ 112.6.1 Requirements for Pilot Trenches .............................................................................. .......................... 11

2.6.3 Pilot Trenching Method B (see Figure 4)......... .............................................................................. 12

2.7 Disposal of Spoil and Backfilling ............................................................... ............................................. 132.7.1 Disposal of Soil ............................................................................... .................................................... 13

2.7.2 Backfilling....................................................................................................................... .................... 13

2.8 Gas Testing .................................................................................................. .............................................. 13

2.9 Ventilation .................................................................................................... ............................................. 14

2.10 Lighting ..................................................................................................... ............................................. 14

2.11 Water Removal ............................................................................................ ......................................... 14

2.11.1 Rainwater and Surface Water............................................... ........................................................... 14

2.11.2 Ground Water ....................................................................................... ........................................... 14

2.12 Access and Barriers ........................................................................................ ...................................... 152.12.1 Access .......................................................................................... .................................................... 15

2.12.2 Gangways and Bridges .......................................................................................... .......................... 15

2.12.3 Barriers .......................................................................................... .................................................. 16

2.13 Checklists ........................................................................................... .................................................... 16

CHAPTER 3 PRECAUTIONS ................................................................................17

3.1 General Precautions............................................................................................. .................................... 17


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3.2 Failure Modes .......................................................................................................... ................................. 17

3.2.1 Soft Clay...................... .................................................................................................... .................... 17

3.2.2 Stiff Clay ......................................................................................... .................................................... 173.2.3 Rock................................... ............................................................................................ ...................... 17

3.3 Support Systems ...................................................................................................... ................................. 18

3.3.1 Supports Designed and Specified On-site ............................................................. ............................. 183.3.2 Supports Designed by Specialist Designers .................................................................... ................... 18

3.4 Access ........................................................................................................... .............................................. 18

3.5 Barriers ............................................................................................... ....................................................... 18

3.6 Means of Escape ............................................................................................ ........................................... 18

3.7 Discovery of a Suspicious Object.................................................................... ........................................ 18

REFERENCES ...........................................................................................................20

Appendix 1 - Ground Conditions and Slopes ........................................................................... ........................... 21

Appendix 2 - Checklist for Excavation Plan................................................................................................... ..... 23

Appendix 3 - Checklist Prior to Start of Work ......................................................................... .......................... 24

Appendix 4 - Checklist Whilst Work is in Progress ........................................................................................... 25

This module is one of a series produced by the Brunei Shell Companies (BSC), which representminimum acceptable HSE standards for a wide variety of operations. Individual operating proceduresand/or task specifications should reflect these minimum standards and should be consulted, whereappropriate, prior to start of work.

Comment and feedback from users of this module is encouraged, in order that the series may beupdated as appropriate to reflect current requirements.

For details of the current revision status of all modules, a summary of intermediate updates published

since the last issue, and information on how to comment on this module, please refer to the lastedition of Module 00, HSE Standards Master Index, which is republished at regular intervals.

This document is unregistered and copies are available from the Company Representative.


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C H A P T E R 1 R E S P O N S I B I L I T I E S

The Process Owner of this module is SCO/4 (PPA/3, POP/2, SFE/21, EOP/1, TSM/22)

1.1 Excavation Supervisor

The Supervisor with responsibility for the excavation shall ensure that:

- no excavation is carried out in an area without the prior knowledge and approval of theAsset Holder.

- a written plan is prepared and submitted for BSC approval for all excavations which exceed1.5 metres in depth.

- all worksite supervisors are properly trained in the relevant permit to work and safetyrequirements for each proposed excavation.All possible steps have been taken to identify allunderground services in the vicinity of the intended excavation and precautions taken toprevent damage to them.

- TSM, as the Technical Authority on positioning and mapping issues, are continuouslyupdating the Asset Holders map database from B2B surveys and as-builts and wish allexcavation crews to be aware of hidden hazards.

- TSM/221 will provide on request a colour 1:500 scale Permit To Work Map showing allknown services in the intended excavation site. PTW applications will not be authorised ifan out-of-date PTW Map is submitted. PTW Maps display a three-month expiry date andTSM require all PTW signatories to refuse (in the interest of safety) all Maps that haveexpired.

- PTW Map requests must be made in person to enable TSM/22 personnel to create a map ofthe exact location of the intended excavation. TSM/22 personnel will not entertain requestmade via e-mail or telephone.

- Any services not identified on the PTW Map that are found during the excavation must benotified to the Geomatics Department for inclusion in updates to the Map Database. If thereason for excavation is to lay a new line, it is the Asset Holder's responsibility to requestpositioning services from TSM/1 or provide accurate as-laid plans that can be incorporatedin the TSM Map Database. The excavation site cannot be closed until this data is obtained.Failure of the Asset Holder to provide this data will be reviewed on its next PTW Mapapplication and PTW authorisation.

- a system of review and control is established to ensure that the safety requirements of

excavation activities are reviewed on a regular basis.

1.2 Worksite Supervisor

Prior to commencing excavation works on any BSC asset, it is the responsibility of the worksitesupervisor to ensure that:

- a permit to work, supported by an excavation certificate, has been obtained before workcommences and that permit conditions are observed.

- all personnel wear the correct personal protective equipment at all times whilst undertakingthe work.

- all persons are properly supervised at all times whilst the work is taking place.

- the excavation is adequately protected against possible collapse.- the excavation is properly protected, having proper regard to location, depth and public

accessibility.

- the safety aspects of the excavation work are properly addressed, and that any writtenexcavation plan is properly followed.


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C H A P T E R 2 R E Q U I R E M E N T S

2.1 General Requirements

2.1.1 Definitions

An excavation is any operation which lowers or disturbs the existing ground level to a depth greaterthan 0.3 metres. Examples of activities which are considered to be excavation works include excavationof trenches or ditches, insertion of spikes, piling, use of crane outriggers on soft soil, or other similaractivities. Normal gardening is not considered to be excavation.

A shallow excavation is any excavation which lowers the existing ground level to a depth of less than1.5 metres.

An unsupported excavation is an excavation where the sides of the work are battered (i.e. sloped orraked) away from the bottom of the excavation to ground level, without support.

A deep excavation is any excavation which lowers the existing ground level to a depth of 1.5 metres ormore.

A supported excavation is an excavation where the sides of the work are supported by timber, steel,concrete or other materials.

Hand digging means excavation using spades and other hand tools, but does not include use of spikes,pickaxes and the like, unless specifically permitted in writing.

Mechanical digging means use of excavators, breakers, or any similar power assisted tools.

The "total working area" is the area which is used to get the work done, i.e. the location of the trenching,the planned area where spoil is stockpiled and the area where heavy equipment travels.

"Dewatering" is the removal of water from the water table by means of a mechanical pumping unit inorder to minimise water in the excavation / soil."

2.1.2 Shallow Excavations

Unless unusual conditions are encountered, e.g. loose sand or the like, a shallow trench may usually beexcavated without being battered or supported (see Figure 1).

2.1.3 Unsupported Excavations

Unsupported excavations shall only be allowed:

- where the excavation depth does not exceed 1.5 metres,

- where the characteristics of the ground are known and

- when the behaviour of the soil can be accurately predicted.


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Figure 1 - Shallow Excavations: Trench Depth of 1.5m Maximum

The maximum angle of batter permitted, in optimum conditions for any unsupported excavation,shall be 45 degrees from the horizontal.

Appendix 1 gives a set of guidelines for the estimation of ground conditions and relevant slope angles.

Dewatering is necessary if the water table is less than 0.5m from the bottom of the intended maximumdept of the excavation (i.e


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In addition to requiring an excavation plan, the following shall be detailed for all headings and tunnelling:

- the potential hazards which may be encountered.

- the specification and quality of materials.

- the excavation techniques which will be used.

- the level of workmanship which will be required.

- the level of supervision which will be required.

A detailed design shall be included for the full length of the heading or tunnel.A competent civil engineer shall design the excavation plan for:

- any heading or tunnel which exceeds 2 metres in height or width, and

- any heading which is to be cut into rock.

Figure 2 - Trench Depth between 1.5 m and 3.0 m without Shoring


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2.2 Preparation and Permit Requirements

All excavation work on behalf of the Company involving disturbance of the ground, in buildings orworkshops and on demolition sites shall be carried out under a work permit issued in accordance with HSEStandard Module 03- Permit To Work Procedure or the BLNG Permit To Work Manual, as appropriate.

No excavation may be carried out without the knowledge and approval of the Asset Holder or hisauthorised representative.

2.3 Support System Design RequirementsThe use of supports which are designed and specified on-site shall only be allowed for:

1. Double sided, narrow trench support, not exceeding 6 metres in depth in non-water bearing ground.

2. Shallow pits or shafts, not exceeding 6 metres in depth, in non-water bearing ground.

3. Where water problems have been eliminated by other means, and the limitations in 1) and 2) abovehave not been exceeded.

All support requirements which do not fall within the specifications laid out above shall be speciallydesigned. This includes excavation adjacent to sectional foundations where standard excavation is notpossible.

Specialist advice shall be sought if there are any doubts as to the safety and sufficiency of any supportsystem which has been designed and specified on-site.

All support systems shall be designed to the Company approved standards (see Section 4 - References).

2.4 Written Excavation Plan

A written excavation plan must be prepared for all excavations intended to be greater than 1.5 metresdeep. This must be approved by the relevant Site Supervisor prior to application for any Permit to Work.For excavations intended to be greater than 3 metres deep, the Site Supervisor should consult with andgain written approval for the excavation plan from the Company Design Engineer or Senior ConstructionEngineer.

2.4.1 General Considerations

The excavation plan and attached sketches should show that consideration has been given to thefollowing:

- purpose and proposed depth of the excavation.

- the location and nature of underground services.

- predicted nature of the ground to be excavated.

- expected presence or absence of water in the ground.

- potential for water to run into the excavation from the surface.

- support system design.

- stages at which timbering or sheet piling shall be placed in the excavation as work proceeds.

- presence of loose pockets in what is otherwise firm, stable ground.

- nearness of any buildings or roads and the weight of traffic.

- whether any other important work is to be carried out adjacent to the proposed excavation.

- whether any materials are likely to be stacked nearby.

- stages of the excavation which are to be dug by machine or by hand tool.

- amount of room which will be needed for raising and lowering material in the course of work.

- whether the sides of the proposed excavation can be splayed to allow more freedom and makewedging easier, the period that the excavation will be open, the maximun allowable trench lengthand the weather that may be expected.

- whether the timbering or sheet piling can be removed safely as the backfilling proceeds.

- access to and egress from the excavation.

- emergency evacuation of the excavation.

- requirements for a gas testing programme.


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- arrangements for temporary site shelters at long-duration excavations in open areas.

The intended installation or removal of sheet piling can cause significant vibrations and thus affectsensitive computer equipment. Information on the intended use of sheetpiling shall be submitted toSCO/4 or LEN/6 Civil Section, as appropriate, for approval prior to commerncement of the work.

2.4.2 Preparation

The excavation plan shall show that checks have been made to locate:

- electric cables (including overhead cables if a mechanical excavator is to be used).

- gas, water and oil pipes.

- telephone, TV and radio cables.

- storm water, sewage and other underground transportation systems.

- the proximity of any foundations which may be affected by the excavation.

- roots of trees.

The excavation plan shall detail the relevant requirements to deal with the above obstructions in a safemanner.

2.4.3 Work Planning

The excavation plan shall specify:

- permit and excavation certificate requirements.

- detailed description of the work to be done.

- duration of the excavation work and the period for which the excavation will be open.

- details of mechanical excavation areas.

- types of machinery to be used.

- details of hand digging areas.

- amount of materials (timber, sheet piling etc.).

- air and gas monitoring equipment.

- ventilation requirements and breathing equipment.

- methods of removal of water from the excavation.

- ladders.

- safety barriers, warning signs and fluorescent tape.

- fire extinguishers and first aid requirments.

- access points, gangways and bridges.

- lighting equipment.

- pumps and compressors.

- disposal of excavated soil/waste and transportation of sand for top-up trenches, including numbersand types of vehicle required, and the route they will use to and from the excavation site.

- emergency arrangements.

The excavation plan shall show that cheeks have been made to ensure that the persons who will beresponsible for supervising the work at site are competent to do so.

2.5 Identification of Underground Services

2.5.1 Prior to Start of Work

The presence of any underground services is to be established prior to commencement of anyexcavation works by taking the following steps:

- Examine Intergraph plots of underground services.

- The total working area shall be checked on underground service plans (held by TSM ,) and shall bescanned using a Company -approved cable avoidance tool to ascertain the presence of electricalcables and underground services.

- Obtain the necessary work permits, supported by the excavation certificate.


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2.5.2 Cable Avoidance Tool

Where mechanical digging is to be used, the use of a cable avoidance tool or similar, to identify possibleburied services, is mandatory.

- The use of mechanical diggers or graders or any other mechanical means for the removal of topsoilor grass and vegetation, prior to digging pilot trenches, is strictly forbidden.

- Use of the cable locator shall be restricted to trained persons only.

- Underground services identified shall be marked with posts specifying the types and size ofservices.

- Scanning shall not be limited to the trench width, but shall include any additional areas used fordrain points, battering, benching etc..

- Where the excavation is to be greater than 1 metre width, scan at both sides of the proposedexcavation, and at every 5 metres across the trench.

2.6 Pilot Trenching

2.6.1 Requirements for Pilot Trenches

Prior to use of mechanical digging, pilot trenches shall be dug in order to locate any undergroundservices.

Note that pilot trenching may not be required if there is clear indication that the presence of undergroundservices could be extremely unlikely e.g. in virgin jungle locations.

- Pilot trenches shall always be dug by hand in maximum depth steps of 1.5 metres, relative to theadjacent ground level.

- The cable avoidance tool shall be used in conjunction with pilot trenching in order to locateunderground services. If any are detected, their whole length within the proposed excavation shallbe exposed by hand digging.

- Pilot trenching shall be carried out in accordance with either Method A or Method B described on thefollowing pages.

The proposed routeing for pilot trenching shall be the resposibility of the BSC Site Supervisor.


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Figure 3 - Pilot Trenching prior to Mechanical Excavation

2.6.3 Pilot Trenching Method B (see Figure 4)

- Request up to date drawings of underground services in the vicinity of the proposed trench.

- Use a pipe or cable location tool to scan the proposed trench.

- Excavate longitudinal pilot trench by hand along the middle of the proposed trench to either the requireddepth plus 0.3 metres, or to a maximum depth of 1.5 metres.

- Excavate transverse pilot trenches by hand every 5 metres, to the full width of the proposed excavation

and to the same depth as the main pilot trench.- Repeat the scanning of the trench with the pipe or cable location tool.

- Mechanical excavation of the areas between the hand dug pilot trenches but not exceeding the proposedmaximum width of the trench may now proceed to a maximum depth of 1.2 meters below original groundlevel.

- Where the proposed depth of the mechanical excavation exceeds 1.2 metres, further pilot trenching byhand in maximum depth steps of 1.5 metres to a maximum depth of 3.0 metres must be repeated,following the general methods above, prior to further mechanical excavation.

Note: It is suggested that Method B becomes uneconomic where the transverse pilot trench width exceeds 7metres.


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Figure 4 - Pilot Trenching prior to Mechanical Excavation

2.7 Disposal of Spoil and Backfilling

2.7.1 Disposal of Soil

Unshored excavations:

Spoil may be disposed of along the sides of the excavation, provided that the distance to the edge of thenearest portion of the spoil heap is not less than the final excavation depth (see Figure 1).

Shored excavations:

Spoil may be disposed of along the sides of the excavation, provided that the distance to the edge of the

nearest portion of the spoil heap is greater than 1 metre (see Figure 5).

2.7.2 Backfilling

Where backfilling using wheeled or tracked vehicles is to take place, or the excavation is in an areawhere it is forseeable that vehicles may attempt to approach close to the excavation, stop boards shouldbe fitted at a distance of 1.2 metres from the excavation (see Figure 1).

2.8 Gas Testing

A gas testing programme shall be devised and maintained in circumstances where:

- work must be suspended if oxygen content is greater than 21%.

- there is a potential for oxygen deficient atmospheres to occur. Work must be suspended inatmospheres where the oxygen content is 20% or less.

- the excavation takes place in ground which is known or suspected to be contaminated with oil or otherpotentially flammable materials to such a degree that a flammable atmosphere may occur. Work mustbe suspended if a Lower Flammable Limit (LFL) of 1% is exceeded.

- depending on the nature of the excavation and the location of supporting equipment, there is apotential for a build up of toxic gases such as Carbon Monoxide (emitted from internal combustionengines) or Hydrogen Sulphide (produced as a by-product of bacterial decay). Work must besuspended if half of the Occupational Exposure Standard (O.E.S) or the Short Term Exposure Limit(S.T.E.L.) for the toxic gas is reached (as specified in current edition of U.K. HSE Guidance NoteEH40).

The gas testing programme shall form part of the excavation plan.


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In circumstances where a hazardous atmosphere is found to exist, the work shall be suspended and theexcavation shall be treated as a Confined Space (see HSE Standard Module 07 - Confined Spaces).

2.9 Ventilation

In conjunction with the gas testing programme, excavations which have a potential for:

- oxygen deficient atmospheres,

- the build up of flammable gas mixtures or

- the build up of toxic gases to occur shall be artificially ventilated by means of air scoops or electricblowers.

In general, internal combustion engines should not be used inside excavations, except on a short termbasis such as compaction machines for backfilling. Where internal combustion engines are used near theedge of an excavation, care shall be taken to ensure that the exhaust fumes are directed away from theexcavation.

All electrically operated blower must be classified for the hazardous area in which they are to be used.

2.10 Lighting

Consideration should be given to illuminating excavations during the hours of darkness, especially whereexcavations are outside the Company operating areas and to which the public may have access.

When work is in progress during the hours of darkness, or in deep excavations, shafts and tunnels,

sufficient lighting shall be provided to allow work to progress safely. Such lighting shall be suitable for theenvironment in which it will be used.

2.11 Water Removal

2.11.1 Rainwater and Surface Water

Wherever surface ditches, streams etc. are incapable of draining off excess water, trenches shall beconstructed to carry the water away from the excavation.

The trenches shall be designed to cope with the maximum rainfall which may be expected whilst theexcavation is in progress. If unexpectedly high rainfall occurs during excavation operations, waterremoval by manual or mechanical means shall be carried out.

2.11.2 Ground Water

Where the presence of ground water may create difficult working conditions or may endanger thestability of the sides and/or floor of the excavation, the excavation shall be:

- surrounded by interlocking steel sheeting, an in-situ concrete diaphragm or a grout curtain toprevent the water from entering the excavation, or,

- a ground de-watering programme shall be used to keep excavations clear of water whilst workproceeds or to reduce the loads which bear on the earthworks support materials.

The ground de-watering programme shall be either by drainage, or by installing well-points around thesite and pumping out the water to lower the ground water table to below that of the excavation (seeFigures 1 and 2)

Before a ground de-watering programme is instigated, expert advice may need to be taken to establish:

- the feasibility of such a programme in the ground conditions pertaining to the excavation, and,

- that, as a result of de-watering no fine materials will be drawn from under adjacent structures withconsequent risk of settlement.


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Figure 5 - Trench Depth less than 3.0m with Shoring

2.12 Access and Barriers

2.12.1 Access

Access to all excavations shall be controlled and restricted to the minimum number of personnel requiredfor the performance of the work.

A safe means of access to and egress from the excavation shall be provided for personnel andmachinery.

Reflective or illuminated barriers shall be considered where the ambient lighting is inadequate. This ismandatory in public areas and places with a high volume of pedestrian traffic.

2.12.2 Gangways and Bridges

Personnel Access

Safe means of access shall be provided where personnel are required to cross excavations. Anygangway provided should be suitable for the intended task, and where the span or materials usedwarrant it, should be approved by competent engineers as suitable for the intended task.

Where personnel may fall 2 metres or more, gangways shall:

- be fitted with guardrails and toeboards, and,

- be at least 0.46m wide for personnel access and 0.6m wide for personnel and materials access.Material and Vehicular Access

Bridges shall be installed where plant and vehicles are required to cross excavations. All bridges shall bespecifically designed and constructed by competent engineers to ensure:

- the safety of drivers, vehicles and loads, and,

- that the edges of the excavation are not damaged or excessively loaded.

All bridges shall be clearly signposted to indicate the maximum permissible loads. Flashing lights shallbe installed on bridges that are to remain "swithed-on" at night.


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The construction of temporary bridges across excavations by the use of simple steel plates, scaffoldboards etc. is prohibited.

2.12.3 Barriers

All excavations, irrespective of the depth, shall be suitably barriered to restrict access by personnel notassociated with the excavation activities.

Barriers and stop blocks shall be erected at a suitable distance from the excavation to prevent:

- personnel or vehicular traffic from damaging the excavation and,

- accidental access to the excavation of personnel and equipment.

Additionally, the edges of all excavations, where personnel may fall more than 2 metres shall beprotected by rigid barriers or, alternatively, excavations shall be securely covered.

Non-rigid barriers may be used in areas where access for persons and transport is not required. Thematerials used shall give an obvious warning by being immediately apparent and brightly coloured.

Wherever barriers are set back from the edge of the excavation, all access to the excavation shall beconfined to proper paths and roads and materials should not be stacked in the space between thebarriers and the edge of the excavation.

2.13 Checklists

The following checklists are contained in the appendices of this document:

Appendix 2 is a checklist to be followed at the design stage of an excavation plan.

Appendix 3 is a checklist to be followed prior to the commencement of excavation work.

Appendix 4 is a checklist to be followed on a regular basis whilst work is in progress.


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C H A P T E R 3 P R E C A U T I O N S

3.1 General Precautions

Ensure that:

- the written excavation plan is followed at all times.

- the correct personal protective equipment is being worn.

- barriers are in place and are of an adequate construction.

- stops for lorries and dumpers are in place to prevent them falling into the trench.

- signs and warning lights are adequate for the purpose.

- tipping areas are clear.

- foot bridges and vehicle bridges are in a safe condition, supported and with rails in place.

- debris boards are in place.

- safe access and egress is maintained.

- the ground and water table is as assumed for the excavation plan.

- pumping operations do not remove fine particles from the soil and weaken the structure.

- wedges are secure on timbering and sheet piling and supports are safe during any compactionoperations.

- exhausts are positioned clear of the trench or excavation.

- trench sides are clear of hazards.

- the ground is not deteriorating during the work.

- proper slinging arrangements have been made for the removal of debris.

- visibility and lighting is adequate.

- the edges of the excavation are clear of soil and debris for a distance equivalent to the excavationdepth, or 1.0 metres in the case of shored excavations.

- work is suspended if an underground service is damaged. Broken cables and burst pipes must bereported to the Asset Holder as soon as possible to obtain isolations and repairs. All incidents mustbe reported in accordance with HSE Standard Module 30 - Incident Reporting and Investigation

Procedure.

Ensure that in deep trenches, pits or shafts, tests for oxygen deficiency, flammable gases and toxic gasesare carried out at least once per day, before work commences, and when work has stopped for 1 hour orlonger.

3.2 Failure Modes

In shallow and unsupported excavations ensure that the type of ground being excavated is not liable to thefailures which may occur in relatively shallow excavations.

3.2.1 Soft Clay

Ensure that unsupported or battered excavations in soft clays do not fail due to rotation.

3.2.2 Stiff Clay

Ensure that unsupported or battered excavations in stiff clays do not fail due to:

- the relief of lateral restraint which allows the top of the excavation to swell inwards, and/or,

- by rain or other surface water penetrating fissures at the surface and softening the clay (earth fallsare more frequent in wet weather).

3.2.3 Rock

Ensure that the rock being excavated in unsupported or battered rock excavations are not separated intobedding planes, cleavage planes or fissures which form planes of weakness along which the rock mayslide.

Ensure that all loose rocks hanging to the excavation face are removed as the digging proceeds.


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Large volumes of heavy rock can move short distances very rapidly. Ensure that rock excavations aresupported, even for shallow excavations, if there is any doubt over the integrity of the rock face.

3.3 Support Systems

3.3.1 Supports Designed and Specified On-site

Where excavation supports are designed and specified on-site, ensure that:

- proper account has been taken of the ground conditions when deciding the method of support,- the method of support complies with recognised good practice in all details.

Where proprietary systems are used, ensure that the installation is strictly in accordance with themanufacturers instructions.

Ensure that the system of work to be adopted is explained in detail to all of the persons engaged inplacing or removing supports, and others who will be working in the excavation.

If practicable, the system of work should be illustrated with drawings or sketches, or with suitableproprietary literature, together with checklists. Ensure that the method of work and instructions andsketches provided are strictly adhered to.

3.3.2 Supports Designed by Specialist Designers

The instructions laid down by the specialist designers should be followed at all times whilst theexcavation is in progress.

3.4 Access

Ensure that safe means of access to and egress from excavations is provided and maintained throughoutthe duration of the excavation.

Ensure that there is an easy means of escape in the event of an emergency.

Ensure that access to and from ladders is on firm ground and that the ladders are:

- placed in the supported part of the excavation.

- effectively secured, near to the top, to prevent slipping sideways, by lashing either to adjacent supportmaterial or to stakes driven firmly into the ground for the purpose.

3.5 Barriers

Ensure that barriers are erected as soon as practicable after excavation commences. (Barriers may beomitted, or moveable barriers may be placed, at specific points to allow access of personnel or themovement of plant, equipment and materials.)

Ensure that:

- barriers or stop-blocks are fitted at all locations where cranes, dumpers, lorries, tippers etc.manoeuvre close to the edge of the excavation.

- the edges of the excavation are protected from damage during vehicle manoeuvres.

3.6 Means of Escape

Ensure that the means of escape and rescue are provided and maintained throughout the duration of theexcavation activities.

Ensure that all personnel are instructed in the escape and rescue procedures which should be followed inthe event of an emergency.

3.7 Discovery of a Suspicious Object

On discovery of a suspicious object believed to be an explosive device, e.g. unexploded bomb, thefollowing action shall be taken immediately:

1. Stay clear - do not touch or try to move the object.

2. Notify FSE on telephone extensions 3269/4329 and VSL on 2999.


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3. Evacuate all personnel from the area following the normal evacuation procedure. Set up road barriersif required. For an object up to 1.0 metre in length, an area with a radius of 100 metres from theobject should be evacuated. An area with a radius of 250 metres should be cleared for larger objects.

4. Using poles and flutter tape, set up a cordon round the evacuated area then notify management of theaction taken.

5. Prevent access to the cordonned-off area until FSE or the police arrive.

6. If the object is discovered in or near a company installation, all the services in the area shall beisolated to minimise the effect of possible ruptures to pipelines and vessels. The decision to close in

hydrocarbon facilities shall be made at AUs division head level.


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R E F E R E N C E S

BS-CP 2004 Code of Practice for Foundations

BS 4074 Specification for Metal Props and Struts

BS 5930 Code of Practice for Site Investigations

BS 6031 Code of Practice for Earthworks

U.K. Construction Industry Research and Information Association (CIRIA):

Technical Note 95 Proprietary Trench Support Systems

Report 97 Trenching Practice

U.K. Timber Research and Development Association:

Sizing of Timber Supports

U.K. HSE:

Guidance Booklet HS(G)47 Avoiding Danger from Underground Services

Guidance Notes EH 40 Toxic and Hazardous Substances


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Appendix 1 - Ground Conditions and Slopes

GROUND TYPE FIELD TESTS AND DESCRIPTIONS

SAFE TEMPORARYSLOPES

(See Notes)

(DEGREES FROMHORIZONTAL)

GRANULAR 1. Particles visible

2. Sand feels gritty

3. Visually assess proportionsof Boulders/Cobbles/Sand

BOULDERS

COBBLES

GRAVEL SAND

(> 200mm)

(60-200mm)

(02-60mm)(0.06-2mm)

35/45 (6)

35/45 (6)

30/4030/35

30/40 (6)

30/35 (6)

10/3010/30

1. Particles not visible

2. When damp silt and finesand are shaken in the hand,water appears on the surface

3. Soft clay is easily mouldedby fingers

4. Firm clay is moulded bystrong finger pressure

5. Stiff clay is indented bystrong finger pressure

6. Fissure clay should beexamined for its structure

SILT

CLAY (5)

(0.002-0.06mm)

Trench Depth

Soft Clay

Firm Clay

Stiff Clay

20/40

1.2-3m 3.6m

30/45 20/30

35/45 30/40

40/45 35/45

See (6) & (7)

5/20

10/20

20/25

25/35

COHESIVE

1. Rotten or rotting vegetablematter

2. Smell of decay

3. Fibrous or non-fibrous

4. Soft, Firm or Stiff

PEAT (black,grey or brownclayey or sandy)

Soft non-fibrous

Firm non-fibrous

Firm fibrous

Stiff fibrous

10/20

15/25

35/40 (6)

35/45 (6) (7)

5/10

10/15

20/25 (6)

25/35 (6) (7)

FILL 1. All types of man-placedmaterial

2. Note constituents includingunnatural inclusions

As main soiltype (eg clay,sand, graveletc.)

According tocategory above

According tocategory above

ROCK 1. Mass stronger than theabove soil types

2. Important to notecementation, structure andorientation (fissures, joints,bedding, layers etc.)

3. Closely joined rock may actas granular and weakweathered rock as clay

As appropriateto thepredominantconstituents andcharacteristics

Checkorientation ofplanes

Check orientation ofplanes

GROUNDWATER 1. Levels of water encountered

2. Rate of entry

3. Standing level

4. Flood conditions

Full descriptionnecessary

See Note 1 (d) See Note 1 (d)

THE SUGGESTED SLOPE ANGLES ARE FOR GUIDANCE PURPOSES ONLY SEE NOTES.


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NOTES ON GROUND CONDITIONS:1. These are GUIDE figures to slopes based on and subject to:

a) Temporary conditions (i.e. generally 1 to 14 days).

b) Field safety and experience.

c) A safety limit of 45 degrees (but see Note 6 below).

d) Water seepage can cause washout and undermining.

2. Dry site: minor or no seepage from excavated faces. Minor or no surface run off.

3. Wet site: submerged or widespread seepage from excavated faces.

4. The behaviour of soils is influenced by the grading, particle size, shape and density. In mixed soilsthe maximum grain size of the smallest 15 percent by weight of the grading tends to characterisethe soil.

5. Normally consolidated clays are usually stronger within a few metres of ground level due todesiccation. However, the clay crust is fissured for the same reason (note the fissures may not bevisible) and is seldom more than 4 metres deep.

Due to the fissuring, the face becomes unstable and lumps fall into the excavation. In deeperexcavations there is a risk of toe failure due to underlying softer clay. The suggested slopes areintended to avoid danger to workers from these risks and are offered as a guide only.

6. Flatter or steeper slopes may be applicable or required subject to the evidence on:

a) Incipient (structural) failure planes

b) Safety precautions against small or large falling fragments


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Appendix 2 - Checklist for Excavation Plan

The following information will be required in order to determine the method of excavation and the needfor support. In addition, in the case of trench work in particular, what has to go into the trench orexcavation will be important. The handling of such items may well affect the form of support that canbe used. The answers to the following questions need to be considered before any decisions can betaken.1. What are the soil types and groundwater conditions?

2. Is there any knowledge of work carried out previously in the area?

3. Is the excavation adjacent to existing structures or roads?

4. Are there any obstructions to the line of the excavation? (e.g. public utility mains or cables, sewers,industrial mains, overhead cables, or limited clearance on the line of the excavation which mayrestrict choice of excavating equipment?

5. Has the condition of adjacent buildings been recorded? (e.g. cracks etc.)

6 Is there any risk of surface flooding whilst the work is being carried out? Is flooding from servicespossible?

7. Is the excavation within the Company operating area, or are special precautions necessary toprotect the public?

8. If the excavation is a pipe trench, what are the maximum depths to be supported? What size andlength of pipe have to be handled? Can pipes be tested in short lengths or does the specificationrequire testing of greater lengths?

9. In the case of wide excavations, what will be the implications of the support system to thepermanent work and vice-versa?

10. What surcharge loads are likely to arise?

11. Will the support method involve vibration? Will it affect the stability of the excavation and/oradjacent buildings?

12. Is it possible to formulate a safe excavation plan with the information available, or will otherinformation be required?

13. Are there sufficient supports?

14. Is there a dewatering and alarm system?


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Appendix 3 - Checklist Prior to Start of Work

1. Is the person directly supervising the work, fully experienced and competent in the support ofexcavations?

2. Have all services been located and proved as to position?

3. Are the necessary drawings or sketches (where on-site developed support designs are to be used)available? Have the operatives been properly briefed and instructed as to what is required of them?

4. Are all materials necessary available on site and in accordance with the drawings/sketches?

5. Has all machinery to be used in the excavation been certified as fit for use and is it suitable for thework it will be undertaking?

6. What arrangements are required with regard to site security (especially for those sites wheremembers of the public may enter the area)?

7. Is there adequate working space for the proposed plant and equipment to be used?

8. Is there adequate room for spoil heaps and are they positioned more than 1.5 metres from the edgeof the excavation?

9. Will bridges or gangways be needed? If so, are the materials and equipment ready?

10. Are there sufficient ladders available for access to and from the excavation?

11. Will lighting be required?

12. Is all the appropriate personal protective equipment available for personnel?

13. Are all personnel competent to carry out this type of excavation without additional training and/orsupervision?

14. Has the Excavation Permit bear approval ?


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Appendix 4 - Checklist Whilst Work is in Progress

The following list covers only the main points which need to be checked when inspections andexaminations are being carried out whilst work is in progress.1. Is access to and from the work face sufficient and secure from danger?2. Are all working faces secure, wedges tight and support material free from damage?

3. Is there any sign of movement or deflection in the support system?

4. Is the soil condition as predicted? If not, what action should be taken?

5. Are the spoil heaps being properly maintained and positioned more than 1.5 metres from the edgeof the excavation?

6. Are pipes, bricks and other materials kept well clear from the edge of the excavation so that there isno risk of them falling into the excavation due to accidental dislodgment?

7. Is all plant and machinery kept well clear from the edge of the excavation so that there is no risk ofvibration damaging the support?

8. Are the drawings/sketches being properly followed in installing the support? (Particularly thespacing of walings and struts.)

9. Are the walings and struts, or proprietary equipment, supported against falling downward byhangers, puncheons, lip blocks etc.?

10. Is there any risk of flammable or toxic gases entering the excavation?

11. Is there any risk of an oxygen deficient atmosphere occurring inside the excavation?

12. Has the risk of flooding been properly assessed?

13. Is resuscitation equipment, and a person trained in its use, available?

14. Have all personnel been instructed in the evacuation procedure for the excavation, and the correctrescue procedure to follow, if someone is overcome by toxic or asphyxiating gases.

15. Have all support materials been checked before installation in the excavation? In particular are thecorrect pins provided in the trench struts?

16. Is the work adequately barriered off? Have all the relevant safety signs been posted at entry/exitpoints? Is the work adequately barriered or covered and lit at night? Are watchmen needed?

17. Are personnel wearing the proper personal protective equipment? Are any other items of PPErequired?

18. In pits, shafts and tunnels, in particular, is adequate lighting provided? Is the temporary lightingsystem safe and free from damage?

19. Are gangways and bridges properly designed and constructed and in a good state of repair? Arethey the correct width? Do they have the correct guardrails and toeboards?

20. Where backfilling is required are stop blocks fitted?

21. Is the support withdrawal part of the excavation plan still feasible? Are the persons carrying out

the support withdrawal competent to carry out the work and have they been properly instructed?

22. Where pumping is taking place, is a proper check being kept to ensure that fine material is notbeing withdrawn from behind the support system?

23. Are the operatives all working in a safe and competent manner?

24. Is the excavation plan being followed? Is it working or does it require some amendment so that thetask can be performed more safely? Do you require expert assistance in any of the tasks which arebeing performed?

25.DOES THE SITE HAVE THE PROPER ONGOING SUPERVISION WHICH IS ESSENTIAL TOMAINTAIN A SAFE PLACE OF WORK?

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