49 CFR § 393.136 - What are the rules for securing large boulders?
(1) The rules in this section are applicable to the transportation of any large piece of natural, irregularly shaped rock weighing in excess of 5,000 kg (11,000 lb.) or with a volume in excess of 2 cubic-meters on an open vehicle, or in a vehicle whose sides are not designed and rated to contain such cargo.
(2) Pieces of rock weighing more than 100 kg (220 lb.), but less than 5,000 kg (11,000 lb.) must be secured, either in accordance with this section, or in accordance with the provisions of §§ 393.100 through 393.114, including:
(i) Rock contained within a vehicle which is designed to carry such cargo; or
(ii) Secured individually by tiedowns, provided each piece can be stabilized and adequately secured.
(3) Rock which has been formed or cut to a shape and which provides a stable base for securement must also be secured, either in accordance with the provisions of this section, or in accordance with the provisions of §§ 393.100 through 393.114.
(b) General requirements for the positioning of boulders on the vehicle.
(1) Each boulder must be placed with its flattest and/or largest side down.
(2) Each boulder must be supported on at least two pieces of hardwood blocking at least 10 cm × 10 cm (4 inches × 4 inches) side dimensions extending the full width of the boulder.
(3) Hardwood blocking pieces must be placed as symmetrically as possible under the boulder and should support at least three-fourths of the length of the boulder.
(4) If the flattest side of a boulder is rounded or partially rounded, so that the boulder may roll, it must be placed in a crib made of hardwood timber fixed to the deck of the vehicle so that the boulder rests on both the deck and the timber, with at least three well-separated points of contact that prevent its tendency to roll in any direction.
(5) If a boulder is tapered, the narrowest end must point towards the front of the vehicle.
(c) General tiedown requirements.
(1) Only chain may be used as tiedowns to secure large boulders.
(2) Tiedowns which are in direct contact with the boulder should, where possible, be located in valleys or notches across the top of the boulder, and must be arranged to prevent sliding across the rock surface.
(d) Securement of a cubic shaped boulder. In addition to the requirements of paragraphs (b) and (c) of this section, the following rules must be satisfied:
(1) Each boulder must be secured individually with at least two chain tiedowns placed transversely across the vehicle.
(e) Securement of a non-cubic shaped boulder - with a stable base. In addition to the requirements of paragraphs (b) and (c) of this section, the following rules must be satisfied:
(1) The boulder must be secured individually with at least two chain tiedowns forming an “X” pattern over the boulder.
(3) The tiedowns must pass over the center of the boulder and must be attached to each other at the intersection by a shackle or other connecting device.
(f) Securement of a non-cubic shaped boulder - with an unstable base. In addition to the requirements of paragraphs (b) and (c) of this section, each boulder must be secured by a combination of chain tiedowns as follows:
(1) One chain must surround the top of the boulder (at a point between one-half and two-thirds of its height). The working load limit of the chain must be at least half the weight of the boulder.
(2) Four chains must be attached to the surrounding chain and the vehicle to form a blocking mechanism which prevents any horizontal movement. Each chain must have a working load limit of at least one-fourth the weight of the boulder. Whenever practicable, the angle of the chains must not exceed 45 degrees from the horizontal.
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