Excavation and Trenching Procedures

Transcription

1 Purpose Excavation and Trenching Procedures It is the policy of K.R. Miller Contractors, Inc. to permit only trained and authorized personnel to create or work in excavations, and or trenches. These procedures are applicable to both daily workers working in excavations and those who only occasionally work with excavations. All contractors working on any of our sites must have a designated competent person present while any work is being performed. The excavation competent person is one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them. The affected contractor on site is in charge of all Excavation Procedures, and must ascertain that all employees have been trained to the level of competence for the types of excavations with which they work. Before Excavating Before anyone on any of our job sites begins excavating, it is standard procedure to: 1. Contact the utility companies, (the one-call service must be called),including property owners (for private facilities), and ask the utility companies or owners to find the exact location of the underground installations in the area. If the utility companies, or owners cannot establish the location of the utility lines, the excavation may proceed with caution (in accordance with state law). In this situation, the excavator provides employees with detection equipment or other safe and acceptable means to locate utility installations. In no instance will any excavation proceed until a locator has been to the site and attempted to locate all possible underground utilities. 2. Remove or adequately support objects in the excavation area that could create a hazard to employees. These may include trees, rocks, sidewalks, and other objects. 3. Classify the type of soil and rock deposits at the site as either stable rock, Type A, Type B, or Type C soil. The soil classification is based on the results of at least one visual and at least one manual analysis conducted by an excavation competent person. Details of the acceptable visual and manual analyses are to be found in Appendix A of the OSHA excavation standard. Page 1

2 4. Have the excavation competent person choose the appropriate method for protective support systems, as necessary. Protective Support Systems Each affected contractor shall follow the standard operating procedures regarding protective support systems for excavations, in accordance with safe practices and procedures and OSHA excavation regulations. 1. Each employee in an trench equal to or greater than 5 foot depth must be protected from cave-ins during by an adequate protective system designed in accordance with OSHA standards. Protective system options include proper sloping or benching of the sides of the excavation; supporting the sides of the excavation with timber shoring or aluminum hydraulic shoring; or placing a shield between the side of the excavation and the work area. The excavation competent person chooses the most practical design approach for the particular circumstance. The system approach selected must meet the required performance criteria. 2. No protective system is necessary if the excavation is made entirely in stable rock, or the excavation is less than 5 feet (1.52 m) in depth (provided there is no indication of a potential cave-in). 3. Protective systems for use in excavations more than 20 feet in depth must be designed by a registered professional engineer. Sloping And Benching 1. When sloping or benching is used to protect against cave-ins, there are four basic options that can be chosen for designing sloping or benching systems. First, if soil classification is not made, then the sides of the excavation can be sloped to an angle not steeper than one and one-half horizontal to one vertical (34 degrees). A slope of this gradation or less is considered safe for any type of soil. 2. The second option for designing a sloping or benching system is to use Appendices A and B of the excavation standard to determine the maximum allowable slope and allowable configurations for sloping and benching systems. These requirements are summarized in Table 1 in the Appendix. The soil type must be determined in order to use this option. 3. Sloping and benching systems can also be designed using other tabulated data approved by a registered professional engineer or by having an engineer design and approve the system to be used. Page 2

3 4. The excavation competent person will choose the best option for sloping and benching for the job at hand. 5. There are a number of exceptions or special cases to these general sloping and benching guidelines, which will be utilized by the excavation competent person if the conditions meet the exception's requirements. The exceptions and conditions are outlined below: In Type A soil, simple slope excavations which are open 24 hours or less (short term) and which are 12 feet high or less in depth may have a maximum allowable slope of 1/2 horizontal to 1 vertical. In Type A soil, all excavations 8 feet or less in depth which have unsupported vertically sided lower portions must have a maximum vertical side of 3.5 feet. In Type A soil, excavations over 8 feet but less than 12 feet in depth with unsupported vertically sided lower portions must have a maximum allowable slope of 1H:1V and a maximum vertical side of 3.5 feet. In Type A soil, excavations 20 feet or less with vertically sided lower portions that are supported or shielded shall have a maximum allowable slope of 3/4H:1V. The support or shield system must extend at least 18 inches above the top of the vertical side. In Type B soil, all excavations 20 feet or less which have vertically sided lower portions shall be shielded or supported to a height at least 18 inches above the top of the vertical side. The excavation shall have a maximum allowable slope of 1H:1V. In Type C soil, all excavations 20 feet or less which have vertically sided lower portions shall be shielded or supported to a height at least 18 inches above the top of the vertical side. The excavation shall have a maximum allowable slope of 1-1/2H:1V. 6. When an excavation contains layers of different types of soils, the general sloping requirements do not apply. The excavation must be sloped according to Table 2 in the Appendix. Timber Shoring 1. Designs for timber shoring in trenches for company work sites are determined using one of four methods: using the requirements set forth by OSHA in Appendices A and C of the excavation standard; using data provided by the manufacturer of the support system; using other tabulated data approved by an engineer; or having a registered professional engineer design the system. The excavation competent person chooses from among these options. 2. The design specifications for timber shoring provided by OSHA may be found in Tables 3, 4, and 5 in the Appendix. These tables refer to the actual dimensions and not nominal dimensions of the timber. If the company Page 3

4 chooses to use nominal size shoring, we use the additional tables found in Appendix C of the standard. 3. These OSHA design specifications apply only to trenches that do not exceed 20 feet. The soil type in which the excavation is made must be determined in order to use the OSHA data. The specifications do not apply in every situation experienced in the field; the data were developed to apply to most common trenching situations. If the specifications do not apply to the situation encountered in the field, the competent person will make a determination of what approach to use to allow safe protective support of the excavation. Aluminum Hydraulic Shoring 1. Designs for aluminum hydraulic shoring are based upon manufacturer's tabulated data and are in accordance with the manufacturer's specifications, recommendations, and limitations. Deviations from the manufacturer's specifications, recommendations, or limitations are only allowed upon written approval of the manufacturer. The written approval is kept at the job site during construction of the protective system. 2. If the manufacturer's tabulated data cannot be utilized, the aluminum hydraulic shoring is designed using the OSHA specifications found in Appendix D of the excavation standard. Before using the OSHA data, the soil type must be determined. Other options for the design of aluminum hydraulic shoring systems include using other tabulated data approved by an engineer or having a registered professional engineer design the system. General Requirements for Excavations and trenching: The following rules are to be followed at all times by all employees, and or subcontractors working on, in or near excavations, as applicable: 1. Employees exposed to public vehicular traffic must wear properly rated warning vests or other suitable garments made of retro-reflective or other high-visibility material. All employees are required to also wear hard hats. 2. The excavation competent person inspects the excavation and the adjacent areas on a daily basis for possible cave-ins, failure of protective systems and equipment, hazardous atmospheres, or other hazardous conditions. Inspections are also required after the occurrence of any natural (such as rain) or manmade events (such as blasting) that could increase the potential for hazards. Employees may not begin work until after being informed by the excavation competent person that these inspections are complete. 3. A warning system should be used to alert operators of heavy equipment and other employees at the work site of the edge of an excavation. Page 4

5 4. Adequate protection should be provided to protect employees from falling rock, soil, or other materials and equipment. Protection is provided by placing and keeping such materials or equipment at least 2 feet from the edge of excavations, or by the use of retaining devices that are sufficient to prevent materials or equipment from falling or rolling into excavations, or by a combination of both if necessary. 5. Employees are not permitted under loads that are handled by lifting or digging equipment. Employees are not allowed to work in the excavation above other employees unless the lower level employees are adequately protected. 6. While the excavation is open, underground installations should be protected, supported, or removed as necessary to safeguard employees. Adjacent structures are supported to prevent possible collapse. 7. Employees are not permitted to work in excavations where water has accumulated or is accumulating unless adequate precautions have been taken. Diversion ditches, dikes, or other means are used to prevent surface water from entering an excavation and to provide drainage to the adjacent area. 8. Before an employee enters an excavation greater than 4 feet in depth, the excavation competent person or other excavation competent person must test the atmosphere where oxygen deficiency or a hazardous atmosphere exists or could reasonably exist. Emergency rescue equipment is readily available and attended when hazardous atmospheric conditions exist or may develop. 9. Sufficient means for exiting excavations 4 feet deep or more, must be provided and must be within 25 feet of lateral travel for employees. When ladders are used they are to extend 36 above the landing area. 10. Guardrails must be provided if there are walkways or bridges crossing over an excavation. 11. Trench boxes, when used shall extend 18 above grade, to prevent material from rolling in. 12. Trench boxes when used may not be higher than 2 feet off the bottom of the trench. 13. All unprotected sides of a trench must be protected. This means that a protective system must be utilized at the ends of a trench box to prevent cave-ins for that area also. Training Under no circumstances shall any worker be allowed on or in excavations, until he/she has successfully completed an excavation and trenching training program. This includes all new employees regardless of claimed previous experience. Page 5

6 The training program should include classroom instruction and hands-on training on each specific type of protective support system to be implemented by the worker, or sub-contractor in his/ her work area. The excavation competent person must identify all new employees, and ascertain that they have been trained. Classroom training may consist of- 1. Review of handbook by employee. 2. Review of safety training video, and classroom instruction. Protective support system training consists of hands-on instruction in design, and use of the protective support systems, which the employee will be implementing in excavations. Appendix "Stable rock" refers to natural solid mineral matter which can be excavated with vertical sides and remain intact while exposed. "Type A soil" is cohesive with an unconfined compressive strength of 1.5 tons per square foot (tsf). Type A soils include clay, silty clay, sandy clay, clay loam, caliche, hardpan, and sometimes silty clay loam and sandy clay loam. No soil should be classified as Type A if it is fissured; subject to vibration from traffic, pile driving, or similar effects; previously disturbed; or part of a sloped, layered system where the slope is four horizontal to one vertical or greater. "Type B soil" is cohesive soil with an unconfined compressive strength greater than.5 tsf but less than 1.5 tsf. Type B soils include granular cohesionless soils like angular gravel, silt, silt loam, sandy loam, and sometimes silty clay loam and sandy clay loam; previously disturbed soils that are not type C; fissured soils and soils subject to vibration that would otherwise be classified as 'Type A; dry rock that is not stable; and material that is part of a sloped, layered system where the layers dip on a slope less steep than four horizontal to one vertical. "Type C soil" is cohesive soil with an unconfined compressive strength of.5 tsf or less. 'I'ype C soils include granular soils such as gravel, sand, and loamy sand; submerged soil; soil from which water is freely seeping; submerged rock that is not stable; or material in a sloped, layered system where the layers dip into the excavation at a slope of four horizontal to one vertical or steeper. Page 6

7 Confined space hazardous atmospheres Where oxygen deficiency or a hazardous atmosphere exists or could reasonably be expected to exist, such as in excavations in landfill areas or excavations in areas where hazardous substances are stored nearby, the atmospheres in the excavation shall be tested before employees enter excavations greater than 4 feet in depth. Table I Maximum Allowable Slopes SOIL OR ROCK TYPE MAXIMUM ALLOWABLE SLOPES (H:V) I FOR EXCAVATIONS LESS THAN 20 FEET DEEP 3 STABLE ROCK VERTICAL (90 degrees) TYPE A 2 3/4:1 (53 degrees) TYPE B 1:1 (45degrees) TYPE C 1-1/2:1 (34degrees) Table 2 Sloping Requirements for Layered Soils Slope Required For Each Soil Layer Layered Soil Type A Layer Type B Layer Type C Layer Type B over A 3/4:1 1:1 C over A 3/4:1 1-1/2:1 C over B /2:1 A over B 1:1 1:1 A over C 1-1/2:1 1-1/2:1 B over C 1-1/2:1 1-1/2:1 Page 7

8 Slope Configurations (All slopes stated below are in the horizontal to vertical ratio) A 1.1 Excavations made in Type A soil. 1. All simple slope excavation 20 feet or less in depth shall have a maximum allowable slope of 3/4:1. SIMPLE SLOPE - GENERAL Exception: Simple slope excavations which are open 24 hours or less (short term) and which are 12 feet or less in depth shall have a maximum allowable slope of ½:1. Page 8

9 SIMPLE SLOPE - SHORT TERM 2. All benched excavations 20 feet or less in depth shall have a maximum allowable slope of 3/4 to 1 and maximum bench dimensions as follows: SIMPLE BENCH Page 9

10 MULTIPLE BENCH 3. All excavations 8 feet or less in depth which have unsupported vertically sided lower portions shall have a maximum vertical side of 3 ½ feet. UNSUPPORTED VERTICALLY SIDED LOWER PORTION - MAXIMUM 8 FEET IN DEPTH All excavations more than 8 feet but not more than 12 feet in depth with unsupported vertically sided lower portions shall have a maximum allowable slope of 1:1 and a maximum vertical side of 3 ½ feet. Page 10

11 UNSUPPORTED VERTICALLY SIDED LOWER PORTION - MAXIMUM 12 FEET IN DEPTH All excavations 20 feet or less in depth which have vertically sided lower portions that are supported or shielded shall have a maximum allowable slope of 3/4:1. The support or shield system must extend at least 18 inches above the top of the vertical side. SUPPORTED OR SHIELDED VERTICALLY SIDED LOWER PORTION) 4. All other simple slope, compound slope, and vertically sided lower portion excavations shall be in accordance with the other options permitted under (b). Page 11

12 B Excavations Made in Type B Soil 1. All simple slope excavations 20 feet or less in depth shall have a maximum allowable slope of 1:1. SIMPLE SLOPE 2. All benched excavations 20 feet or less in depth shall have a maximum allowable slope of 1:1 and maximum bench dimensions as follows: Page 12

13 SINGLE BENCH MULTIPLE BENCH 3. All excavations 20 feet or less in depth which have vertically sided lower portions shall be shielded or supported to a height at least 18 inches above the top of the vertical side. All such excavations shall have a maximum allowable slope of 1:1. Page 13

14 VERTICALLY SIDED LOWER PORTION 4. All other sloped excavations shall be in accordance with the other options permitted in (b). C Excavations Made in Type C Soil 1. All simple slope excavations 20 feet or less in depth shall have a maximum allowable slope of 1 ½:1. SIMPLE SLOPE 2. All excavations 20 feet or less in depth which have vertically sided lower portions shall be shielded or supported to a height at least 18 inches above the top of the vertical side. All such excavations shall have a maximum allowable slope of 1 ½:1. Page 14

15 VERTICAL SIDED LOWER PORTION 3. All other sloped excavations shall be in accordance with the other options permitted in (b). D Excavations Made in Layered Soils 1. All excavations 20 feet or less in depth made in layered soils shall have a maximum allowable slope for each layer as set forth below. Page 15

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18 2. All other sloped excavations shall be in accordance with the other options permitted in (b). Page 18