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Guidelines on the Installation of Proprietary Shoring Systems

LSB Notification No. 1217001, December 17, 2003

Up Date : 2007.06.12

  1. Purpose

    These Guidelines, in conjunction with related industrial safety and health legislation, aim to avoid trench cave-ins and rock falls, thus preventing industrial accidents in work such as water supply and sewerage that is accompanied by small-scale trench excavation and work inside trenches through the installation of suitable shoring, etc., using proprietary shoring systems.

  2. Application

    These Guidelines apply to work such as water supply and sewerage that is accompanied by small-scale trench excavation in order to lay pipes, etc.

  3. Definition of Terminology

    The definitions of the main terminology used in these Guidelines, other than those specified in related industrial safety and health legislation, shall be as follows.

    1. Work Such as Water Supply and Sewerage

      Refers to construction work for waterworks, sewerage, telecommunications facilities, gas supply facilities, etc.

    2. Small-Scale Trench Excavation

      Refers to the excavation of largely vertical trenches of at least 1.5m and a maximum of 4m in depth which is no more than 3m wide, and includes both mechanical and manual excavation.

    3. Work in Trenches

      Refers to work carried out inside trenches such as laying of pipes, measurements, inspections, compaction, etc. (excludes excavation)

    4. Shoring, Etc.

      In addition to shoring, refers to independent retaining structures without waling and strut supports based on a sheet pile system.

    5. Proprietary Shoring Systems

      Refers to systems for installing shoring, etc., in advance before workers enter a trench when conducting trench excavation or work in trenches. It also allows, in principle, workers to install and remove the shoring, etc., without entering the trench.

    6. Installation and Removal of Shoring, Etc.

      In addition to the installation and removal of waling and struts for shoring, refers to the fitting and removal of all structural components related to shoring, etc., including the driving and extraction of sheet piles.

    7. Trench Collapse Accident

      Refers to an industrial accident caused by a trench cave-in or rock fall.

  4. Responsibility of the Employer and Worker

    When performing construction work such as installation of water supply and sewerage, the employer shall comply with industrial health and safety legislation and endeavor to avoid industrial accidents in work such as water supply and sewerage through the installation of suitable shoring, etc., using the proprietary shoring systems based on these Guidelines.

    Workers engaged in work such as water supply and sewerage shall comply with the matters to be observed by workers stipulated in industrial safety and health legislation, and endeavor to avoid industrial accidents in work such as water supply and sewerage by cooperating with the measures that the employer takes based on these Guidelines.

  5. Measures to Be Taken

    1. Formulation of Execution Plan Relating

      When carrying out work such as water supply and sewerage that is accompanied by small-scale trench excavation, the employer shall conduct a preliminary survey of the work location where the trench is to be excavated as follows. The employer also shall formulate an execution plan relating to the proprietary shoring system by preparing a shoring plan, a work plan, a temporary facilities plan, a safety and health management plan, and a schedule of work, and then disseminate the overall project plan to the relevant workers.

      1. Preliminary survey
        1. Ground survey

          The employer shall conduct a survey into the following matters regarding the work location where the trench is to be excavated and the surrounding ground, using methods which include field investigation, collation of past work records, confirmation with the ownersf of underground structures, and boring.

          1. Configuration, geological features and geological formations;
          2. Configuration, geological features and geological formations;
          3. Presence and condition of underground structures;
          4. Presence and condition of high temperature gases and vapor.
        2. Survey of surroundings

          The employer shall conduct a survey into and assess the condition of the roads, buildings and overhead power lines, etc., surrounding the work location that could be affected by the trench excavation and the installation or removal of shoring, etc., as well as the volume of traffic and the traffic regulations, etc., surrounding the work area that could affect the execution of work using such methods as field investigation.

        3. Application to plans

          The employer shall apply the results of the preliminary surveys in a. and b. to the preparation of the plans in (2) below.

      2. Shoring plan
        1. Selection of shoring method

          The employer shall select a method of shoring, etc., that applies to the results of the preliminary survey in (1) with reference to the Appendix of these Guidelines and formulate a shoring plan adapted for the relevant method.

        2. Structure

          The employer shall prepare a plan for shoring, etc., with a solid structure suited to the ground conditions, including the configuration of the ground and its geological features and formation, cracks, surface water run-off from precipitation, water content, springs, frozen ground, frost heaves, and underground structures, etc.

        3. Design

          The employer shall prepare a suitable design for the shoring, etc., based on calculation of the earth pressure and water pressure acting on the shoring, etc., as well as the load weighting of machinery and excavated earth, etc., the self-weight of the structural components of the shoring, and the earthquake loading, etc.

        4. Securing of structural components

          The employer shall confirm the types and quantities of the structural components suitable for use in the structure of shoring, etc., as well as confirming the machinery needed to install and remove the shoring, etc., and formulating a plan that enables them to be secured by the necessary date.

        5. Use of machinery

          When using mobile cranes and vehicle-type construction machinery, etc., in the installation and removal of shoring, etc., the employer shall formulate a plan to make clear the methods of work and service routes for such machinery.

        6. Protection of underground structures

          The employer shall indicate a method and schedule for protecting or moving underground structures, when necessary, in the shoring plan.

        7. Construction drawing

          The employer shall prepare a construction drawing that clearly shows the arrangement, measurements, quality of materials, and the schedule and order for the installation of each of the structural components in the shoring, etc.

        8. Inspection

          The employer shall indicate the methods and schedule, etc., of inspections and repairs for the shoring, etc. The matters for inspection shall include the following.

          1. The presence and condition of damage, deformation, displacement or slippage of components and materials;
          2. Condition of strut set;
          3. Condition of joints, mountings, and intersections of components and materials.
      3. Work plan
        1. Trench excavation

          The employer shall determine a method of trench excavation suited to the results of the preliminary survey in (1) and the method of shoring, etc., selected in (2) and prepare a work plan relating to trench excavation that clearly states the following matters.

          1. The type, capacity and necessary quantity of machinery for trench excavation;
          2. Details of the routes for transporting the machinery in (i) in and out, places of installation, and operation routes;
          3. When mechanical and manual excavations are conducted simultaneously, the extent and methods of the respective work;
          4. Methods when taking measures to prohibit entry during operation of the machinery in (i);
          5. The relationship between the trench excavation, the installation and removal of shoring, etc., and the work in the trench.
        2. Installation and removal of shoring, etc. The employer shall prepare a work plan that clearly states the relationship between the installation and removal of shoring, etc., based on the shoring plan in (2) and work in trenches.
        3. Work in trenche

          The employer shall prepare a work plan that clearly states the following matters relating to work in trenches.

          1. The type and content of the work in the trench;
          2. The schedule for entry by workers into the trench and the position of the work for each type of work in the trench;
          3. The types, capacities, and the necessary quantity of machinery used for each type of work in the trench;
          4. The details of the routes for transporting the machinery in (iii) in and out, places of installation and operation routes;
          5. Methods when taking measures to prohibit entry during operation of the machinery in (iii);
          6. The relationship between the work in the trench, the trench excavation and the installation and removal of shoring, etc.
      4. Temporary facilities plan

        When installing temporary facilities related to the matters below for trench excavation, the installation and removal of shoring, etc., and work in a trench, the employer shall prepare a temporary facilities plan that clearly states its relationship to each area of the work.

        1. Facilities for ascending and descending safely;
        2. Facilities to prevent falls into the trench;
        3. Pathways running to the work site;
        4. Facilities to cover path surfaces;
        5. Facilities to secure power, including power distribution boards and power lines;
        6. Other necessary temporary facilities
      5. Safety and health management plan

        The employer shall prepare a safety and health management plan that clearly states the measures to prevent industrial accidents suitable for each process of trench excavation, installation and removal of shoring, etc., and the work in the trench as well as the following matter

        1. Safety and health management system;
        2. Safety and health training;
        3. Safety and health inspections and safety and health activities.
      6. Schedule of work

        The employer shall prepare a schedule of work that clearly states the following matters for trench excavation, the installation and removal of shoring, etc., and the work in the trench.

        1. The procedure, the scheduled start and finish times for each area of work;
        2. The relationships between each area of the work;
        3. Schedule relating to safety and health management.
    2. Implementation of and Revisions to Execution Plan Relating to the Proprietary Shoring System

      The employer shall execute the series of work using a proprietary shoring system based on the execution plan relating to the proprietary shoring system formulated under V-1.

      Moreover, when the need arises to revise the execution plan, the employer shall make the revisions after fully consulting the relevant parties in advance and be certain to disseminate the revised execution plan to the relevant workers.

  6. Considerations Relating to the Execution of Proprietary Shoring

    1. Considerations in the Installation and Removal of Shoring, Etc.

      The employer shall, when carrying out the installation or removal of shoring, etc., in the proprietary shoring system, carry out the work based on the shoring plan prepared under V-1-(2) at the same time as taking the following matters into consideration.

      1. Shoring structure components

        Components for shoring, etc., that are not obsolete shall be used, and those with obvious damage, deformation or corrosion shall not be used.

      2. Installation
        1. Installation based on construction drawing

          The employer shall install the shoring, etc., in accordance with the construction drawing in V-1-(2)-g.

        2. Installation of structural components

          The employer shall install structural components such as struts and waling securely to sheet piles, etc., to prevent slippage.

        3. Installation of sheet piles

          The employer shall determine the material quality, configuration and dimensions, etc., of the sheet piles, including light weight steel sheet piles or vertical sheet pile plates, taking into account such factors as the depth of the excavation, the earth pressure, the run-off of surface water from precipitation, springs and geological features, in order to produce sheeting wall surfaces with no gaps while also taking measures to prevent collapse and displacement into the trench.

        4. Installation of waling

          The employer shall determine the quality and measurements of waling, taking into account such factors as the earth pressure and workability used for sheet piles, and shall attach it firmly and horizontally to the sheet piles.

        5. Installation of struts

          The employer shall determine the quality, measurements and method, including water hydraulic jack, oil hydraulic jack, or strut support for struts, taking into account such factors as the earth pressure and workability used for the sheet piles and waling, and install them horizontally at right angles to the waling.

      3. Dismantling
        1. Removal of struts and waling

          The employer shall remove struts and waling after the trench has been backfilled up to the position from which they are to be removed.

        2. Extraction of sheet piles

          Sheet piles shall only be extracted up to the height to which the trench has been backfilled.

      4. Work overall
        1. Appointment of operations chief of shoring, etc.

          When carrying out the installation or removal of shoring, etc., the employer shall appoint an operations chief in shoring, etc., and have that person to oversee the work directly.

        2. Prohibition of entry into trench

          When carrying out the installation or removal of shoring, etc., the employer shall prohibit workers from entering the trench except when using special work platforms, etc., to prevent trench collapse accidents.

        3. Measures to prohibit entry of persons other than authorized workers

          The employer shall take measures to prohibit the entry of persons other than authorized workers into a site where the installation or removal of shoring, etc., is being carried out.

        4. Inspections

          The employer shall conduct regular inspections based on the methods of inspection, etc., specified in V-1-(2)-h, after the installation of shoring, etc., and make immediate repairs when abnormalities are discovered.

          In addition, the employer shall give special consideration to the condition of components, materials and tools that are often used in the proprietary shoring system.

    2. Considerations in Trench Excavation and Work in Trenches

      he employer shall, when carrying out trench excavation or work in a trench, conduct the work based on the work plan prepared under 5-1-(3) at the same time as giving consideration to the following matters.

      1. Trench excavation
        1. Appointment of operations chief of excavating natural ground

          The employer shall appoint an operations chief of excavating natural ground when carrying out trench excavation, and have that person directly oversee the work.

        2. Manual excavation
          1. Commencement of manual excavation

            Manual excavation inside the trench, including leveling and excavation of corner sections, shall not be conducted until after the installation of shoring, etc.

          2. Use of hanging nets

            The employer shall direct the workers to use hanging nets and hanging bags when lifting or lowering materials and tools, etc.

          3. Elevator equipment

            The employer shall direct the workers to use elevator equipment installed based on the temporary facilities plan under V-1-(4) when ascending or descending.

        3. Ground inspection

          When carrying out trench excavation, the employer shall, before the commencement of work and after the completion of work, inspect the work location and the surrounding ground for the presence and condition of pumice stone and cracks as well as changes in the condition of surface water run-off from precipitation, water content, springs, frozen ground and frost heave while also carrying out an inspection into the presence and condition of the signs that there may be a trench cave-in shown below, and continue to monitor the situation as necessary.

          1. Distortion or movement at the top of the trench;
          2. Occurrence or development of cracks in the ground surface near the trench wall;
          3. Occurrence of new fissures in rocky ground or noises;
          4. Swelling or bulging in the side of the excavation;
          5. Swelling at the base of the excavation or subsidence of the ground surface near the trench wall;
          6. Seepage of water and sand into the base of the excavation;
          7. An increase in spring volume or changes in water turbidity;
          8. Development of an overhang.
        4. Underground structures, etc.

          The employer shall not carry out trench excavation in a location close to an underground structure, etc., or a structure such as concrete block piles until after taking preventative measures based on the shoring plan prepared under V-1-(2).

        5. Protective helmets

          The employer shall direct workers engaged in trench excavation to wear protective helmets.

        6. Lighting

          The employer shall maintain necessary lighting in an area where trench excavation is being carried out through such means as installing lighting equipment.

        7. Drainage

          When water seeps into the area where trench excavation is being conducted, the employer shall discharge the water through such means as setting up a sump for water collection and pumping it out.

      2. Work in trenches
        1. Commencement of work in trenches

          Work in trenches must not commence until after the installation of shoring, etc.

        2. Use of hanging nets, etc.

          The employer shall direct the workers to use hanging nets and hanging bags, etc., when lifting or lowering materials and tools, etc.

        3. Protective helmets

          The employer shall direct workers engaged in work in a trench to wear protective helmets.

        4. Elevator equipment

          The employer shall direct workers to use elevator equipment installed based on the temporary facilities plan under V-1-(4) when ascending or descending.

      3. Considerations in the Use of Machinery

        The employer shall, when using machinery that includes mobile cranes and vehicle-type construction machinery in trench excavation, the installation and removal of shoring, etc., and work in trenches, make appropriate use of such machinery based on the service routes and work methods specified in the shoring plan under V-1-(2) and the work plan under V-1-(3) while also considering the following points.

        1. Signals

          The employer shall, when using mobile cranes and vehicle-type construction machinery, etc., determine specific signals, designate a person to make the signals, and direct that person to make the signals.

        2. Measures to prohibit entry

          The employer shall take measures to prohibit entry to areas where there is a danger of coming into contact with the operating range of a mobile crane or vehicle-type construction machinery, etc.

        3. The employer shall, when extracting sheet piles, etc., using

          The employer shall, when extracting sheet piles, etc., using a mobile crane, determine the capacity and installation position of the mobile crane, taking into account the resistance of the sheet piles, etc. The employer shall, at the same time, give consideration to LSB Notification No. 595, October 15, 1985 gSafety Measures in Pile Extraction Using Mobile Cranes.h

        4. Driving in of sheet piles, etc.

          The employer shall, when driving in sheet piles, etc., using an excavator, press in with the bucket, and shall not strike with the bucket.

        5. Restriction on use other than main application

          When using vehicle-type construction machinery other than for its main application, such as the use of an excavator for lifting loads, in the installation and removal of shoring, etc., and work in trenches, the employer shall give consideration to Article 164 of the Ordinance on Industrial Safety and Health (Ministry of Labour Ordinance No. 32, 1972) and LSB Notification No. 542 of October 1, 1992 on Ensuring Safety in Work Lifting Loads Using Vehicle-type Construction Machinery.

Appendix
Types and Features of Shoring, etc., of
Proprietary Shoring Systems

  1. Types and Features of Shoring, Etc.

    Shoring that uses a proprietary shoring system refers to shoring, etc., that is installed before work-ers enter a trench. There are various systems, and active efforts are currently underway to design new techniques and improve on existing ones. The typical systems considered applicable to small-scale trench excavation in relatively common use at present are listed below.

    1. Toeing-in a lightweight-steel sheetpile system

      This technique assumes that the excavated ground will be self-supporting. After excavation of the trench with excavation machinery to a certain depth and the boring of the lightweight-steel sheet piles, it is pressed into the prescribed depth, and the top frame of the waling and strips and struts are installed from the ground above using a special jig. The installation of the second and subsequent frames of waling and struts is carried out using a special work platform.

    2. Driven lightweight-steel sheet pile system

      This system is commonly used in the excavation of weak ground that is sandy or swampy. After lightweight-steel sheet piles that match the width of the trench are driven in using a pile driver, the trench is excavated to the depth of installation for the top frame of struts, and the waling and struts are installed from the ground above using a special jig. The installation of the second and subsequent frames of waling and struts is carried out using a special work platform when necessary.

    3. Slide rail shoring system

      After the boring in of gslide rails,h sheeting panels called gshoring panelsh are inserted, and the pan-els and slide rails are repeatedly pushed down as the trench is excavated to a certain depth. A slide rail consists of vertical soldier posts and struts as-sembled in advance. The number of struts is deter-mined depending on the geological features of the location where shoring is to be installed and the depth of the excavation.

    4. Sheeting box shoring system

      As in (3), after the boring in of a gsheeting box,h the plate is repeatedly pushed in as the trench is excavated to a certain depth. A sheeting box con-sists of two sheet plates and struts assembled in advance. The number of struts is determined de-pending on the geological features of the location where shoring is to be installed and the depth of the excavation

    5. Other systems

      Apart from the four techniques described above, shoring, etc., using proprietary shoring systems in-cludes the open shield system, formerly called the blade shield system, etc., for larger scale excava-tions. Moreover, sheet pile systems, including steel sheet pile systems, that allow the installation of a self-supporting retaining structure without sup-ports such as waling and struts and with adequate foundation depth are also considered proprietary shoring systems, as long as the shoring is installed before workers enter an excavated trench.

  2. Selection of Shoring System

    The employer shall take the following conditions into account when selecting shoring, etc., using a proprietary shoring system.

    The criteria for selection shall generally be as in the table below.

    1. Type of work
    2. Soil characteristics, and status of soil characteristics such as presence of backfilled soil.
    3. Status of ground water
    4. Scale and shape of excavation
    5. Presence, type, depth, and condition, etc., of underground structures
    6. Condition of surroundings, including roads, buildings and overhead power lines
    7. Area of work site
    8. Traffic volume and regulations, etc.
    9. Need for countermeasures for noise and vibrations
    10. Contract terms, including work period
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