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Trenching and Shoring

Trenching and Shoring. Hershey Entertainment and Resorts Company Revised 2006 Ref 29 CFR 1926. Introduction. Instructor Introduction Class Introduction. Definitions. Aluminum hydraulic shoring – engineered shoring system comprised of aluminum hydraulic cylinders

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Trenching and Shoring

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  1. Trenching and Shoring Hershey Entertainment and Resorts Company Revised 2006 Ref 29 CFR 1926

  2. Introduction • Instructor Introduction • Class Introduction

  3. Definitions • Aluminum hydraulic shoring – engineered shoring system comprised of aluminum hydraulic cylinders • Benching – method of protecting employees from cave-ins by excavating the sides of an excavation to form one or a series of horizontal levels or steps

  4. Definitions • Cave-in – separation of a mass of soil or rock material from the side of an excavation and its sudden movement into the excavation • Excavation – any man-made cut, cavity, trench or depression in the earth’s surface which is formed by the removal of dirt

  5. Definitions • Shield – a structure that is able to withstand the forces imposed on it by a cave-in • Shoring – structure such as a metal hydraulic, mechanical or time shoring system that supports the sides of an excavation and which is designed to prevent cave-ins

  6. Definitions • Sloping – excavating to form sides that are inclined away from the excavation to prevent cave-ins • Trench – a narrow excavation made below the surface of the ground

  7. Inspections • A competent person shall conduct inspections: • Daily and before the start of each shift • As dictated by the work being done • After every rain storm • After other major weather events (i.e. earthquake) • When fissures, tension cracks, sloughing, undercutting, water seepages, bulging at the bottom or other similar conditions occur • When there is a change in the size, location and placement of the spoil pile • When there is ay indication or change or movement in adjacent structures

  8. Inspections • Soil Types • Type A – most stable; clay, silty clay, hardpan; soil is not Type A if it has ever been disturbed before • Type B – medium stability; silt, sandy loam, medium clay, unstable rock • Type C – least stable; gravel, loamy sand, soft clay, submerged soil or dense, heavy unstable rock and soil

  9. Testing Methods • Visual Test • The entire excavation site should be observed, including soil adjacent to the site and the soil being excavated • Signs of vibration should also be checked • Crack-line openings along the failure zone that would indicate tension cracks

  10. Testing Methods • Visual Test cont. • Signs of bulging, boiling or sloughing should be looked for as well as signs of water seepage • Areas adjacent should be checked for signs of foundation or other cracks

  11. Testing Methods • Manual Tests • Thumb Penetration Test • Press thumb firmly into the soil • If the thumb penetrates no further than the length of the nail, it is probably Type B • If the thumb penetrates the full length of the thumb, it is probably Type C • This is the least accurate testing method

  12. Testing Methods • Manual Tests • Dry Strength Test • Take a sample of dry soil • If it crumbles freely, it is granular (Type C) • If it falls into clumps, it is clay with gravel, sand or silt (Type B)

  13. Testing Methods • Manual Tests • Plasticity or Wet Thread Test • Take a sample of wet soil • Mold it into a ball and attempt to roll it into a thin thread approximately 1/8 inch in diameter • If you can hold it by one end and it does not break, it is probably Type B, if it does, it is probably Type C

  14. Spoil • Temporary spoil shall be placed no closer than two feet from the surface edge of the excavation, measured from the nearest base of the spoil to the cut • This distance ensures that loose rock or soil from the temporary spoil will not fall on employees in the trench • Spoil should be placed so that water run-off is away from the excavation

  15. Surface Crossing of Trenches • Should not be make unless absolutely necessary • Vehicle crossings: must be designed by and installed under the supervision of a registered professional engineer • Walkways and bridges must: • Have a minimum width of 20 in. • Be fitted with standard rails • Extend a minimum of 24 in. past the surface edge of the trench

  16. Ingress and Egress • Trenches 4 feet or more in depth shall be provided with a fixed means of egress • Ladders should be spaced such that a worker will not have to travel more than 25 feet laterally to the nearest means of egress • Ladders should be extended a minimum of 36 inches above the landing

  17. Exposure to Vehicles • Employees exposed to vehicular traffic shall be provided with and required to wear reflective vests • Trained flag persons, signs, signals and barricades shall be used when necessary

  18. Exposure to Falling Loads • All employees must wear hard hats at the excavation site • Employees may not work under loads being lifted or moved by heavy equipment • Employees must stand away from equipment that is being loaded or unlocked to avoid being struck by falling materials or spillage

  19. Warning Systems • Steps to prevent vehicles from accidentally falling into the trench: • Barricades must be installed where necessary • Hand or mechanical signals must be used as required • Trenches left open overnight shall be fenced and barricaded

  20. Hazardous Atmospheres • Employees shall not be permitted to work in hazardous atmospheres • Less than 19.5% oxygen • Combustible gas concentration of greater than 20% LFL

  21. Hazardous Atmospheres • Testing for Atmospheric Conditions • Atmospheric testing must be conducted if a trench or excavation could contain hazardous atmospheres • Testing should be done before employees enter a trench and regularly afterwards to ensure safety • If equipment is working in the trench, testing should be done more frequently

  22. Standing Water andWater Accumulation • Every precaution should be taken to keep water out of the trench • If work must be done with water in the trench, the following apply: • Use of special support or shield systems • Water removal equipment • Employees removed from trench during rainstorms • Trenches carefully inspected after each rain and before employees re-enter

  23. Benching • Two types of benching • Single • Multiple • Vertical height must not exceed 4 feet • Benching is not allowed in Type C soil

  24. Sloping • Maximum allowable slopes for excavations less than 20 feet based on soil types and angle to the horizontal field: • Type B Soil • 1:1 • 45 degrees • Type C Soil • 1 ½:1 • 34 degrees

  25. Shoring • Used when sloping is impractical • Two forms • Timber • Aluminum hydraulic • Hydraulic shoring provides advantages because the workers do not have to enter the trench to install them, unlike timber

  26. Shielding • Designed to protect workers from cave-ins and similar incidents • Generally used in open areas, can be used in combination with sloping and benching

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