Presentation on theme: "UNIVERSITY of NORTHERN COLORADO Trenching and Shoring."— Presentation transcript:
1UNIVERSITY ofNORTHERN COLORADOTrenching and Shoring
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3Injury and DeathExcavating is one of the most hazardous construction operationsMost accidents occur in trenches 5-15 feet deepThere is usually no warning before a cave-inTrenching Related Deaths2000 to 2006………..271 trenching fatalities
4RulesUnderground Utilities must be located and marked before excavations beginEmployees are not allowed in the excavation while heavy equipment is diggingAll employees on an excavation site must wear hard hatsEmployees shall be removed from the trench during a rainstormDo NOT work under raised loadsStand away from equipment that is being loaded or unloaded to avoid being struck by falling materials or spillageTrench that is 4 feet or greater in depth requires a trench inspection form filled out by the competent person.All excavations or trenches 4 feet or greater in depth shall be appropriately benched, shored, or sloped.Excavations or trenches 20 feet deep or greater must have a protective system designed by a registered engineer.
5Inspection Form To be completed by Competent Person Review Form Turn completed forms into EHS.
6Soil classification Type A Type B Fine grained Doesn’t crumble Clay LoamClayType AFine grainedDoesn’t crumbleHard to break up when dryType BGranular: coarse grainsLittle or no clay contentCrumbles easily when drySilty loamLoamAngular gravel
7Soil Classification Type C Granular soil: very coarse Minimal cohesion SandGravelLoamy sandType CGranular soil: very coarseMinimal cohesionExamples:SandGravelLoamy sandSubmerged soil or soil with freely seeping waterSubmerged rock that is not stable.
8Definitions “Competent person” is someone who: Can identify existing or predictable hazards in an excavationHas authority to take corrective actions as necessaryIs familiar with the DOSH excavation standardsIs knowledgeable in soil analysis and classification as well as the erection, use, and precautions for the protective system on site
9DefinitionsExcavation – a man-made cut, cavity, trench, or depression formed by earth removal.Trench – a narrow excavation. The depth is greater than the width, but not wider than 15 feet.Shield - a structure able to withstand a cave-in and protect employeesShoring - a structure that supports the sides of an excavation and protects against cave-insSloping - a technique that employs a specific angle of incline on the sides of the excavation. The angle varies based on assessment of impacting site factors.Cave-in – The separation of soil or rock material from the side of an excavation.ReferenceShield (shield system) -- a structure able to withstand a cave-in and protect employees with the structure. Shields can be permanent structure or can be designed to be portable and moved along as work progresses. Also known as trench box or trench shield.Shoring (shoring system) -- a structure such as a metal hydraulic, mechanical or timber shoring system that supports the sides of an excavation and which is designed to prevent cave-ins.Sloping (sloping system) -- protects employees from cave-ins by excavating to form sides of an excavation that are inclined away from the excavation to prevent cave-ins. The angle of incline varies with differences in such factors as the soil type, environmental conditions of exposure, and application of surcharge loads.
10Design of Protective Systems The employer shall select and construct :slopes and configurations of sloping and benching systemssupport systems, shield systems, and other protective systemsShield - can be permanent or portable. Also known as trench box or trench shield.Shoring - such as metal hydraulic, mechanical or timber shoring system that supports the sidesSloping - form sides of an excavation that are inclined away from the excavationReference , (b), (c)Benching -- excavating the sides of an excavation to form one or a series of horizontal levels or steps, usually with vertical or near-vertical surfaces between levels.Shoring or shielding is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical. There are two basic types of shoring, timber and aluminum hydraulic.Trench boxes (shielding) are different from shoring because instead of supporting the trench face, they are mostly serve to protect workers from cave-ins. The excavated area between the outside of the trench box and the face of the trench should be as small as possible. The space between the trench box and the excavation side may be backfilled (or other means may be used) to prevent lateral movement of the box. Shields may not be subjected to loads exceeding those which the system was designed to withstand. Trench boxes may be used in combination with sloping and benching.
11Materials and Equipment Equipment used for protective systems must not have damage or defects that impair function.If equipment is damaged, the competent person must examine it to see if it is suitable for continued use.If not suitable, remove it from service until a professional engineer approves it for use.Reference (d)Materials and equipment used for protective systems shall be free from damage or defects that might impair their proper function.Manufactured materials and equipment used for protective systems shall be used and maintained in a manner that is consistent with the recommendations of the manufacturer, and in a manner that will prevent employee exposure to hazards.When material or equipment that is used for protective systems is damaged, a competent person shall examine the material or equipment and evaluate its suitability for continued use. If the competent person cannot assure the material or equipment is able to support the intended loads or is otherwise suitable for safe use, then such material or equipment shall be removed from service, and shall be evaluated and approved by a registered professional engineer before being returned to service.
12Benching Benching can be used in conjunction with sloping. Benching is NOT allowed in Type C soil.The bottom vertical height of the trench must not exceed 4 feet.Benches must be below the maximum allowable slope for that soil type.(example: A 10-foot deep trench in Type B soil must be benched back 10 feet in each direction, with the maximum of a 45 degree angle.)
13SlopingMaximum allowable slopes for excavations less than 20 feet based on soil type and angle to the horizontal are as follows:Soil Type Height/Depth Ratio Slope AngleType A ¾ : degreesType B 1 : degreesType C 1½ : degrees
14ShoringA support system for trench faces used to prevent movement of soil, underground utilities, roadways, and foundations.Three types of shoring:Aluminum HydraulicTimberPneumatic
15ShieldingShielding also known as Trench Boxes focus on protecting from cave-ins.Workers must enter and leave the shield in a protective manner (ladder or ramp)Workers may NOT remain in the shield while the shield is being moved.
16Inadequate Protective System This worker is in a trench with no protective system, that is not sloped or benched and has no means of egressThis excavation has inadequate support posts and egress access
17Hazardous ConditionsThe weight and vibrations of the crane makes this a very hazardous condition.They should not be working under this crane.In addition to the unprotected trench, a cave-in hazard is increased by machinery which gets too close.Even normal vehicular traffic, such as that along an adjacent interstate or road through an industrial part may impact an excavation. The vibrations from continuous or heavy traffic may undermine the soil and cause a cave-in.
18Warning SystemsThe following steps should be taken to prevent vehicles or people from fallingBarricades must be installed where necessaryHand or mechanical signals must be used as requiredTrenches left open overnight shall be fenced and barricaded
19Ingress / EgressAccess to and exit from the trench requires the following conditions:Trenches 4 feet or more in depth should be provided with a fixed means of egressSpacing between ladders or others means of egress must be that the worker will not travel more than 25 feet laterally to the nearest egressLadders must be secure extending a minimum of 36 inches above the landingMetal ladders should not be used when electrical utilities are present
20Improper Means of Egress The ladder should extend 3ft above the excavationReference (c(1)Structural ramps- Structural ramps that are used solely by employees as a means of access or egress from excavations shall be designed by a competent person. Structural ramps used for access or egress of equipment shall be designed by a competent person qualified in structural design, and shall be constructed in accordance with the design.- Ramps and runways constructed of two or more structural members shall have the structural members connected together to prevent displacement.- Structural members used for ramps and runways shall be of uniform thickness.- Cleats or other appropriate means used to connect runway structural members shall be attached to the bottom of the runway or shall be attached in a manner to prevent tripping.- Structural ramps used in lieu of steps shall be provided with cleats or other surface treatments o the top surface to prevent slipping.Two ladders lashed together are not an adequate means of egressA stairway, ladder, or ramp must be present in excavations that are 4 or more feet deep, and within 25 feet of the employees
21Hazardous Atmospheres If there is any possibility that the excavation could contain a hazardous atmosphere, testing must be conducted prior to entry. (example: Natural gas line may warrant this)Test excavations more than 4 feet before an employee enters the excavation for:Oxygen deficiencyHigh combustible gas concentrationHigh levels of other hazardous substancesAll operations involving atmospheric testing will require Confined Space Entry procedures to be used. Continuous monitoring may be required.Oxygen should be between 19.5% %
22Water is HazardousWhen water is present in an excavation it is extremely hazardous to enter(h)Employees shall not work in excavations in which there is accumulated water, or in excavations in which water is accumulating, unless adequate precautions have been taken to protect employees against the hazards posed by water accumulation. The precautions necessary to protect employees adequately vary with each situation, but could include special support or shield systems to protect from cave-ins, water removal to control the level of accumulating water, or use of a safety harness and lifeline.If water is controlled or prevented from accumulating by the use of water removal equipment, the water removal equipment and operations shall be monitored by a competent person to ensure proper operation.If excavation work interrupts the natural drainage of surface water (such as streams), diversion ditches, dikes, or other suitable means shall be used to prevent surface water from entering the excavation and to provide adequate drainage of the area adjacent to the excavation.Methods for controlling standing water and water accumulation must be provided
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