TRENCHING AND SHORING EXCAVATIONS PROGRAM

Transcription

1 TRENCHING AND SHORING EXCAVATIONS PROGRAM

2 TRENCHING AND SHORING EXCAVATIONS PROGRAM The purpose of this program is to provide information to our company employees and to interested persons that Northern Clearing, Inc. is complying with the OSHA Excavations Standard 29 CFR , 65, and 652. This program applies to all of our personnel involved in excavations. The Health and Safety Director is the program coordinator for this program and will ensure that the program is reviewed and updated as necessary. Copies of the written program may be obtained form from Personal Administrator in the Corporate Headquarters. All employees, or their designated representatives, can obtain further information on this written program, the excavation standard and applicable company operating procedures. If after reading this program, you find that improvements can be made or you have comments, please contact your Supervisor or the Health and Safety Director. We encourage all suggestions because we are committed to the success of our written excavation program. We strive for clear understanding, safe behavior, and involvement in the program from every level of the company. GENERAL DEFINITIONS COMPETENT PERSON - 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 the authorization to take prompt corrective measures to eliminate them. HAZARDOUS ATMOSPHERE an atmosphere which by reason of being explosive flammable; poisonous, corrosive, oxidizing irritating, oxygen deficient, toxic, or otherwise harmful, may cause death, illness, or injury. PROTECTIVE SYSTEM a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation or from the collapse of adjacent structures. Protective systems include support systems, sloping and benching systems, shield systems, and other systems that provide the necessary protection. TRENCH a narrow excavation (in relation to its length) made below the surface of the ground. In general, its depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 5 feet. If forms or other structures are installed or constructed in an excavation so as to reduce the dimension measured from the forms or structure to the side of the excavation to 5 feet or less (measured at the bottom of the excavation), the excavation is also considered to be a trench. RESPONSIBILITIES The Job Superintendent, as designated by each project, functions as the designated competent person with the authority to shut down the job if he deems it necessary. The competent person on the excavation site has the following abilities/responsibilities: Ability to detect hazardous conditions such as hazardous atmospheres potential cave-ins, and the potential for protective system failures. 2

3 Experience and knowledge of soil analysis. Knowledgeable in the requirements of 29 CFR 926, Subpart P. Perform excavation pre-planning and daily excavation inspections. Knowledgeable in appropriate protective systems. All employees are responsible for performing their work in a safe manner, for utilizing the protective equipment available, following company procedures, and safety-related work directions given by the work site safety supervisor. EXCAVATION REQUIREMENTS / HAZARDS The requirements of this program apply to all open excavations made in the earth s surface and are defined to include trenches. Underground Utilities Utility companies and/or the work site host employer shall be contacted within the prescribed time allotted by such company (ies) prior to the start of any excavation; in order to locate any underground installations. In the event that company (ies) is/are unavailable for identification of utility location, the excavation will proceed with caution only after Northern Clearing, Inc. performs their own underground utility location procedures. Excavations are never performed unless, as a minimum the estimated location(s) of utility installations can be determined. Please refer to Appendix A for First Call information. Once the estimated location of an underground installation is reached, then the exact location will be determined prior to proceeding with the excavation. While the excavation is open, underground installations will be protected, supported or removed as necessary for employee safety. EXCAVATION ACCESS/EGRESS Access The competent person shall design structural ramps used by employees for entering the excavation. Ramps used for equipment access into and out of the excavation shall only be those that have been designed and approved for use by a competent person qualified in structural design. Structural ramps shall be constructed in accordance with the design and when two or more ramps used for access or egress are used, they shall be uniform thickness and shall be connected in order to prevent displacement. Any ramp connection obstructions shall be located so as not to create a tripping hazard. When structural ramps are used in lieu of steps, there shall be cleats or other surface treatments on the top surface to prevent slipping. Egress Stairways ladders, ramps, or other appropriate means of egress from excavations shall be used in excavations shall be used in excavations that are 4 feet or more in depth and shall be located not more than 25 feet from any employee working in the excavation. HAZARD PROTECTIONS Vehicle traffic all employees working at or near the excavation that may be exposed to vehicle traffic will be provided with and required to wear reflective or high visibility vests or garments. 3

4 Mobile equipment mobile equipment that is operated at or in the vicinity of the excavation shall use the following appropriate warning and safety precautions: Mechanical signals, hand signals, stop logs or barricades when the equipment operator s view of the excavation edge is limited or obstructed. When possible, the grade should be away from excavation Falling loads employees are not allowed to stand underneath loads handled by lifting or digging equipment. All employees must stand a safe distance away form any vehicle being loaded or unloaded; vehicle operators will either vacate to a safe distance from the vehicle being loaded or unloaded or may remain in the vehicle if the vehicle is equipped to provide adequate protection for the operator. Water accumulation in the excavation employees are not allowed to work in excavation where there is accumulated water or the potential for accumulation of water unless the appropriate following precaution(s) are used: Special support or shield systems are used to protect from cave-ins Water removal to control the level of accumulating water, Use of a safety harness and lifeline The competent person shall monitor the use of water removal equipment to ensure proper operation. If trench work interrupts the natural drainage of surface water, diversion ditches, dikes, or other suitable means to prevent surface water from entering the excavation and to provide adequate drainage of the area adjacent to the excavation. The competent person for water accumulation hazards shall inspect excavation subject to heavy rain runoff. Adjacent structures Here the stability of adjoining structures is endangered by trench operations, the stability of such structures is ensured by providing a support system such as shoring, bracing, or underpinning Loose rock or soil employees are protected from falling rock or soil by adhering to the following precautions and work practices: Scaling to remove loose material when necessary Installation of protective barricades on the face to stop and contain falling material when necessary All excavation materials and equipment shall be kept at least 2 feet from the edge of the excavation Use of retaining devices when necessary that are sufficient to prevent materials or equipment from falling or rolling into the excavation Fall protection where employees need to crossover excavations, walkways will be constructed and will have guardrails when the walkway is 6 feet or more above lower levels. All wells, pits, and shafts that need to be left open shall be sufficiently barricaded or covered to prevent accidental falls. Upon completion of an excavation project, it will be filed promptly. 4

5 Hazardous atmospheres where an oxygen deficient or a hazardous atmosphere could reasonably be expected to exist, such as in landfill areas or where hazardous substances are stored nearby, the atmosphere will be tested before employees enter excavations greater than 4 feet deep. Testing shall be done regularly to ensure that the excavation remains safe. The frequency of testing shall be increased if equipment is operating in the excavation or welding, cutting, or burning is done in the excavation. If the excavation qualifies as a confined space, Northern Clearing, Inc. will comply with the Confined Space standard and any requirements that the Host site employer may have. Please reference the Confined Space chapter of this manual. Employees must use respiratory protection in oxygen deficient or hazardous atmosphere unless there is adequate ventilation provided, as determined by the competent person. All employees shall comply with the company Respiratory Protective program, also found in this manual. Emergency rescue equipment, such as self-contained breathing apparatus, a safety harness, line, and retrieval device shall be readily available where hazardous atmospheric conditions may reasonably be expected to develop during work in an excavation. Employees entering bell-bottom pier holes, or other similar deep and confined footing excavations shall wear a harness with an individually attended separate lifeline securely attached to it. PROTECTIVE SYSTEMS Employees in an excavation shall be protected from cave-ins by: Sloping or benching the sides of the excavation Use of trench shields (i.e., boxes) or Construction of trench supports The competent person shall determine the type of protection used. These protections are not required if: Excavations are made entirely in stable rock (as determined by the competent person, or Excavations are less than 5 feet deep, and the competent person has inspected the excavation and found no sign of a potential cave-in. SOIL CLASSIFICATION Definitions Cemented soil a soil in which a chemical agent such as calcium carbonate holds the particles, together, such that a hand-size sample cannot be crushed into powder or individual soil particles by finger pressure. Cohesive soil clay (fine grained soil), or soil with a high clay content which has cohesive strength. Cohesive soil does not crumble, can be excavated with the vertical side slopes, and is plastic when moist. Cohesive soil is hard to break up when dry and exhibits significant cohesion when submerged. Cohesive soils include clayey silt, sandy clay, silty clay, clay and organic clay. 5

6 Dry soil soil that does not exhibit visible signs of moisture content. Fissured a soil material that has a tendency to break along definite planes of fracture with little resistance, or a material that exhibits open cracks, such as tension cracks, in an exposed surface. Granular soil gravel, sands, or silt (coarse-grained soil,) with little or no clay content. Granular soil has no cohesive strength. Some moist granular soils exhibit apparent cohesion. Granular soil cannot be molded when moist and crumbles easily when dry. Layered system two or more distinctly different soil or rock types arranged in layers. Micaceous seams or weakened planes in rock or shale are considered layered. Moist soil a condition in that a soil looks and feels damp. Moist cohesive soil can easily be shaped into a ball and rolled into small diameter threads before crumbling. Plastic a property of soil, which allows the soil to be deformed or molded without cracking. Saturated soil a soil in which the voids are filled with water. Saturation does not require flow. Soil Classification System a method of categorizing soil and rock deposits in decreasing order of stability (Stable Rock, Type A, Type B, and Type C). The categories are determined based on an analysis of the properties and performance characteristics of the deposits and the environmental conditions of exposure. Stable Rock a natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed. Submerged soil soil, which is under water or is free seeping Type A soil means cohesive soils with an unconfined compressive strength of.5 tons per square foot or greater. Examples of cohesive soils are clay, silty clay, sandy clay, and clay loam and, in some cases, silty clay loam and sandy clay loam. Cemented soils such as hardpan are also considered Type A. No soil is considered Type A if:. The soil is fissured, or 2. The soil is subject to vibration from heavy traffic, pile driving, or similar effects; or 3. The soil has been previously disturbed; or 4. The soil is part of a sloped, layered system where the layers dip into the excavation on a slope of four horizontal to one vertical or greater; or 6

7 5. The material is subject to other factors that would require fit to be classified as a less stable material Type B soil is:. Cohesive soil with an unconfined compressive strength greater than 0.5 tons per square foot (tsf) but less than.5 tsf, or 2. Granular cohesionless soils including: angular gravel (similar to crushed rock), silt, silt loam, sandy loam and, in some cases silty clay loam and sandy clay loam 3. Previously disturbed soils except those which would otherwise be classified as Type C soil 4. Soil that meets the unconfined compressive strength or cementation requirements for Type A but is fissured or subject to vibration; or 5. Dry rock that is not stable; or 6. Material that is part of a sloped system where the layers dip into the excavation on a slope less steep than four horizontal to one vertical, but only if the material would otherwise be classified as Type B. Type C soil is:. Cohesive soil with an unconfined compressive strength of 0.5 tsf or less; or 2. Granular soils including gravel, sand, and loamy sand; or 3. Submerged soil or soil from which water is freely seeping; or 4. Submerged rock that is not stable; or 5. Material in a sloped, layered system where the layers dip into the excavation or a slope of four horizontal to one vertical or steeper. CLASSIFICATION REQUIREMENTS A competent person must classify each soil and rock deposit. The classification of the deposits shall be made based on the results of at least one visual and at least one manual analysis. Such analysis shall be conducted by a competent person using tests described in this section, or other recognized methods of soil classification and testing such as those adopted by the American Society for Testing Materials, or the U. S. Department of Agriculture textural classification system. In a layered system, the system shall be classified in accordance with its weakest layer. However, each layer may be classified individually where a more stable layer lies under a less stable layer. If, after classifying a deposit, the properties, factors, or conditions affecting its classification change in any way, a competent person shall evaluate the changes. The deposit shall be reclassified as necessary to reflect the changed circumstances. VISUAL TESTS Visual analysis is conducted to determine information regarding the excavation site in general, the soil, adjacent to the excavation, the soil scorning the sides of the open excavation, and the soil taken as samples from the excavated material. As a minimum, the following procedures are used for visual tests: 7

8 . Observe samples of soil that are excavated and so in the sides of the excavation. Estimate the range of particle size and the relative amounts of the particle sizes. (Soil that is primarily composed of fine-grained material is cohesive. Soil composed primarily of coarse-grained sand or gravel is granular material) 2. Observe soil as it is excavated. (Soil that remains in clumps when excavated is cohesive. Soil that breaks up easily and does not stay in clumps is granular). 3. Observe the side of the opened excavation and the surface area adjacent to the excavation. (Crack-like openings such as tension cracks could indicate fissured material. If chunks of soil spall off a vertical side, the soil could be fissured. Small spalls are evidence of moving ground and are indications of potentially hazardous situations.) 4. Observe the area adjacent to the excavation and the excavation itself for evidence of existing utility and other underground structures, and to identify previously disturbed soil. 5. Observe the opened side of the excavation to identify layered systems. Examine layered systems to identify if the layers slope toward the excavation. Estimate the degree of slope of the layers. 6. Observe the area adjacent to the excavation and the sides of the opened excavation for evidence of surface water, water seeping from the sides of the excavation, or the location of the level of the water table. 7. Observe the area adjacent to the excavation and the area within the excavation for sources of vibration that may affect the stability of the excavation face. MANUAL TESTS Manual analysis of soil samples is conducted to determine quantitative as well as qualitative properties of soil and to provide more information in order to classify soil properly Plasticity Mold a moist or wet sample of soil into a ball and attempt to roll it into threads as thin as /8 inch in diameter. Cohesive material can be successfully rolled into threads without crumbling. (Example if at least a 2 inch length of /8 inch thread can be held on one end without tearing, the soil is cohesive.) Dry strength If the soil is dry and crumbles on its own or with moderate pressure into individual grains or fine powder, it is granular. If the soil is dry and falls into clumps that break up into smaller clumps, but the smaller clumps can only be broken up with difficulty, it may be clay in any combination with gravel, sand, or silt. If the dry soil breaks into clumps, which do not break into, small clumps and which can only be broken with difficulty, and there is no indication the soil is fissured, the soil may be considered unfissured. Thumb penetration The thumb penetration test can be used to estimate the unconfined compressive strength of cohesive soils The thumb only with very great effort can readily indent type A soils with an unconfined compressive strength of.5 tons per square foot. 8

9 Type C soils with an unconfined compressive strength of 0.5 tons per square foot can be easily penetrated several inches by the thumb, and can be molded by light finger pressure. This test should be conducted on an undisturbed soil sample, such as a large clump of soil, as soon as practicable after excavation to keep to a minimum the effects of exposure to drying influences. If the excavation is later exposed to wetting influences (rain, flooding), the classification of the soil must be changed accordingly. Other strength tests Estimates of unconfined compressive strength of soils can also be obtained by use of a pocket penetrometer or by using a handoperated shear vane. Drying test The basic purpose of the drying test is to differentiate between cohesive material with fissures, unfissured cohesive material, and granular material. The procedure for the drying test involves drying a sample of soil that is approximately inch thick and 6 inches in diameter until it is thoroughly dry. If the sample develops cracks as it dries, significant fissures are indicated. Samples that dry without cracking are to be broken by hand. If considerable force is necessary to break a sample, the soil has significant cohesive material content. The soil can be classified as an unfissured cohesive material and the unconfined compressive strength should be determined. If a sample breaks easily by hands it is either a fissured cohesive material or a granular material. To distinguish between the two pulverize the dried clumps of the sample by hand or by stepping on them. If the clumps do not pulverize easily, the material is cohesive. If they pulverize easily into very small fragments, the material is granular. SELECTION OF PROTECTIVE SYSTEMS The angle used for sloping or benching is a ratio based on the soil classification and site restrictions. SLOPING Maximum 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 Angle Stable Rock Vertical 90 degrees Type A ¾ : 53 degrees Type B : 45 degrees Type C.5 : 34 degrees Type A short term (max 2 ft.) ½ : 63 degrees 9

10 BENCHING There are two basic types of benching, simple and multiple. The type of soil determines the horizontal to vertical ratio of the benched side. The bottom vertical height of the trench must not exceed 4 feet for the first bench. Subsequent benches may be up to a maximum of 5 feet vertical in Type A soil and 4 feet in Type B soil to a total trench depth of 20 feet. All subsequent benches must be below the maximum allowable slope for that soil type. Benching ratio for Type A soil is ¾ :, for Type B (cohesive soils only) :, and Type C soil may not be benched. SHORING AND SHIELDING The following general rules and guidelines shall be adhered to when utilizing shielding and shoring systems:. No employee is allowed in a trench box while it is being raised or lowered into place. 2. Use of steel sheeting to extend the height of a trench box is not allowed. 3. Any shoring or shielding used with a sloped trench must extend at least 8 inches above the sloped part of the excavation. 4. Individual shores will be installed and released slowly to prevent failure of the remaining protection 5. Tabulated data on shores and shields provided by the manufacturer or a professional engineer will be followed regardless of soil classification. Any deviations must be approved in writing by the manufacturer 6. Excavations must be back-filled immediately after support systems are removed. SHORING Shoring is the provision of a support system for excavation faces used to prevent movement of soil, underground utilities, roadways, and foundations. 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. Shoring systems consist of posts, wales, struts, and sheeting. All shoring is to be installed from the top down and removed from the bottom up. Hydraulic shoring shall be checked at least once per shift for leaking hoses and/or cylinders, broken connections, cracked nipples, bent bases, and any other damaged or defective parts. SHIELDING The excavated area between the outside of a shield or trench box and the face of the excavation shall be as small as possible. This space is backfilled to prevent lateral movement of the box. Shields may not be subjected to loads exceeding those that the system was designed to withstand. Trench boxes may be used in combination with sloping and benching. The box shall extend at least 8 inches above the surrounding area if there is sloping toward the excavation. This is accomplished by providing a benched area adjacent to the box. The competent person to identify any problems that may exist with shoring or shielding shall perform careful visual inspections. 0

11 APPENDIX A TRENCHING AND SHORING ONE-CALL TELEPHONE NUMBERS

12 2

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16 APPENDIX B TRENCHING AND SHORING EXAMPLES 6

17 UNSUPPORTED VERTICALLY SIDED LOWER PORTION MAXIMUM 2 FEET IN DEPTH All excavation 20 feet or less in depth which have vertically sided lower portions that are supported or shielded shall have a maximum allowable slope of ¾ :. The support or shield system must extend at least 8 inches above the top of the vertical side. Support or shield system 20 Max. ¾ 8 Min. Total height of 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 sec (b). B.2 Excavations Made in Type B Soil. All simple slope excavations 20 feet or less in depth shall have a maximum allowable slope of :. 20 Max. SIMPLE SLOPE 2. All benched excavations 20 feet or less in depth shall have a maximum allowable slope of : and maximum bench dimension as follows VERTICALLY SIDED LOWER PORTION. All other sloped excavations shall be in accordance with the other options permitted in (b). B.3 Excavations Made in Type C Soil. All simple slope excavation 20 feet or less in depth shall have a maximum allowable slope of ½ :. 20 Max. SIMPLE SLOPE ½ 7

18 2. All excavation 20 feet or less in depth which have vertically sided lower portions shall be shielded or supported to a height at least 8 inches above the top of the vertical side. All such excavations shall have a maximum allowable slope of ½ :. 20 Max. ½ AL SIDED LOWER PORTION 8 Min. Total height of vertical side 3. All other sloped excavations shall be in accordance with the other options permitted in (b). B.4 Excavation Made in Layered soils. 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. 20 Max. 4 Max. SINGLE BENCH 20 Max. 4 Max 4 Max 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 8 inches above the top of the vertical side. All such excavations shall have a maximum allowable slope of :. Support or shield system 20 Max. 8 Min. Total height of vertical side 8

19 B A 3/4 B OVER A C ½ A ¾ C OVER A C ½ B C OVER B A B A OVER B A ½ C ½ 9

20 A OVER C A ½ C ½ B OVER C 2. All other sloped excavations shall be in accordance with the other options permitted in (b). EXCAVATION CHECKLIST (29 CFR ). FACILITY DATE LOCATION COMPETENT PERSON ACKWLEDGE BY / 20

21 SURFACE ENCUMBRANCES. Are surface encumbrances (Trees, Boulders, Buildings, Machinery) at a safe distance away from the excavation area or sufficiently supported for safe excavation? UNDERGROUND INSTALLATIONS. Have underground piping, utility lines and/or other installations been identified and located? (One Call) 2. Have workers been advised of the installation? 3. Have owners of underground installations been notified? Who? When? 4. Are underground installations properly supported or removed during excavation? OVERHEAD INSTALLATION. Has the area over the worksite been checked for power lines or other obstacles that would interfere with extendable equipment (Backhoe Booms, Cranes, Etc.)? EMERGENCY RESCUE EQUIPMENT. Is emergency rescue equipment necessary? 2. Equipment Necessary: SCBA HARNESSES WIND SOCK LIFELINE COMMUNICATION EQUIPMENT ADJACENT STRUCTURES AND LOOSE ROCK/SOIL. Are support systems necessary due to structures located near excavation? 2. Is excavated material or other material kept two feet or more away from the edge of the excavation? 3. Is some type of barrier or scaling necessary? If yes, what type? 4. Does system require registered professional engineer design? 2. Have workers been advised of the installations? FALL PROTECTION. Are handrails and/or barriers use where necessary? ACCESS AND EGRESS WATER ACCUMULATION. If the trench is four feet or more in depth, has a means of egress. Where water accumulation is present, are been provided? necessary precautions being used? 2. Is the means of egress properly spaced? (25 feet lateral SOIL TYPE travel/max). Are soil tests necessary? 3. What type of egress is provided? 2. Type test: SHEAR / PENETRATION / HAND Ladders Sloping walkways (Circle One) VEHICULAR TRAFFIC 3. Type soil: STABLE ROCK / A / B / C /. Is warning vest or high visibility clothing provided? (Circle One) 2. Are traffic warning signs provided? 4. Projected depth of excavation: FALLING LOADS AND MOBILE EQUIPMENT. Have workers been instructed that they are not permitted to work under loads? 2. Have workers been instructed concerning equipment operated near the edge of the excavation? HAZARDOUS ATMOSPHERE. If excavation is four feet or more in depth, is atmospheric testing necessary? 2. If atmospheric testing is necessary, complete the following: Gas % LEL Oxygen % H2S PPM Instrument Type Serial No. Conducted by Time 3. Is periodic testing necessary? INITIAL / PERIODIC / CONTINUOUS MONITORING REQUIRED. PERMITS Are other permits required for job? (Circle All That Apply) Safe Work / Confined Space / Hot Work TES: 2