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Subchapter 20. Tunnel Safety Orders
Article 13. Ground Control

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§8441. Tunnel and Shaft Support.

(a) All working places underground shall be kept securely supported with timber, steel sets, or otherwise protected by installing wire mesh, rock bolts, gunite, shotcrete, or other methods.

(b) All sets, including horseshoe-shaped or arched rib steel sets, shall be of adequate design and installed so that the bottoms will have sufficient anchorage to prevent pressures from pushing them inward. Adequate lateral bracing shall be provided between sets to stabilize the supports.

(c) After each blast, supports systems in the effected areas shall be checked, tightened, or rewedged by a qualified person. If so, necessary repairs shall be made before employees other than those assigned to make the repairs are allowed in or below the affected areas.

(d) Damaged or dislodged ground supports that create a hazardous condition shall be promptly repaired or replaced. When replacing supports, the new supports shall be installed before the damaged supports are removed.

(e) Rock bolt systems, when used, shall be installed in uniform patterns. These patterns shall be determined by qualified persons. Plans and specifications of the rock bolting installation shall be available to the Division at the job site. These plans shall include bolt spacing, diameter, length, type, tension in the bolts, angle of bolts to the supported surface, and type of washers and bearing plates. Additional rock bolts shall be installed as necessary to support the ground.

(1) Torque wrenches shall be used whenever bolts that depend on torsionally applied force are used for ground support.

(2) A competent person shall determine whether rock bolts meet the necessary torque, and shall determine the testing frequency in light of the bolt system, ground conditions and the distance from vibration sources.

(f) Adequate protection shall be provided for workers exposed to the hazard of loose ground while installing support systems.

(g) Portal openings and access areas shall be adequately protected by sloping, benching, installing extra sets, wire mesh and/or rock bolts, shotcreting, or equivalent methods to ensure safe access of employees and equipment.

(h) Shafts and wells over 5 feet (1.53 m) in depth that employees must enter shall be supported by a steel casing, concrete pipe, timber, solid rock or other suitable material.

NOTE: Authority cited: Sections 142.3 and 7997, Labor Code. Reference: Sections 142.3 and 7997, Labor Code.

HISTORY

1. Amendment of section heading and section and new Note filed 3-5-96; operative 4-4-96 (Register 96, No. 10).

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