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南非土木工程施工标准 LB: 垫层(管) 英文原文节选 20100079 1-27 |
SELECTION
Suitable Material Available from Trench Excavation The excavation of a pipe trench
shall comply with the requirements of Subclause 5.4 of SABS 1200 DB, and the provisions of Subclause 3.7
of SABS 1200 DB (in terms of which, for the purpose of providing bedding materials, the Contractor is not
required to use selective methods of excavating) shall apply.
not required) to screen, wash, or otherwise treat excavated material in order to produce material
suitable for bedding or covering the pipeline.
avoid burying or contaminating material that is suitable and is required for bedding or covering the
pipe1 ine.
Suitable Material not Available from Trench Excavation (See also 8.1.2). When material suitable for use
as selected fill material or selected granular material is not readily available from trench excavation
within a distance not exceeding 0,5 km, the Contractor shall, subject to the Engineer's approval for each
material, obtain suitable material to replace the shortfall
a) from other necessary excavations on the Site; or
b) by opening up borrow pits at approved areas located at intervals along the route of the pipeline;
c) by importing from commercial or other sources.
PLANT
PLACING, COMPACTING, AND TESTING EQUIPMENT
Placing and Compacting.
as specified in 5.1.3 and 5.1.4.
(See also 8.1.2).
The Contractor will be permitted (but is
The Contractor shall take every reasonable precaution to
or
Adequate equipment shall be provided for the placing and compacting of bedding
Testing.
referred to in 7.1 and 7.2.
The Contractor shall provide the necessary test equipment for performing on Site the tests
CONSTRUCTION
GENERAL
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Subclause 5.2 of SAES 1200 DE.
The Contractor shall so excavate each trench that the width conforms to the requirements of
Bottom.
5.5 of SABS 1200 DB.
The Contractor shall prepare the trench bottom in accordance with the requirements of Subclause
Details of Bedding.
a) Drawing LE-1, appropriate to the class of bedding scheduled or ordered for rigid pipes; and
b) Drawing LB-2 for flexible pipes.
Placing
No bedding shall be laid until the Engineer has approved the trench, measured the depth if necessary, and
authorised pipelaying to proceed.
Except in the case of Class A bedding, the joint holes shall be refilled with fine granular material and
lightly compacted to prevent the migration of adjacent pipe bedding material into the holes and to
obviate the production of hard spots under joints (see Drawing LE-2).
In the placing of bedding, all voids under the overhang of the pipes shall be filled and the compaction
shall be carried out uniformly on each side of the pipe so as not to cause any lateral or vertical
displacement of the pipe.
Bedding shall be carried out as pipelaying proceeds, and shall be completed before the acceptance test is
carried out.
Compacting. The degree of compaction attained for bedding (other than concrete and the material over the
top of the pipeline) shall be 90 % of modified AASHTO maximum density (see 6.1).
PLACING AND COMPACTING OF RIGID PIPES
Class A Bedding. In addition to complying with the applicable requirements of 5.1, the Contractor shall
construct Class A bedding in accordance with the following requirements:
a) The pipes shall be supported on a continuous cradle of concrete having a 28 d compressive strength of
at least 20 MPa.
During pipelaying and before the placing of the concrete bedding, the pipes shall be suitably supported
as shown on Drawing LE-3 (a).
Care shall be taken during the placing of the concrete to prevent movement or flotation of the line.
the case of pipes with flexible joints, concrete shall not be allowed to enter the joints during
construction of the bedding and a positive vertical expansion joint in the bedding cradle shall be formed
at each pipe joint.
b) The selected fill blanket shall not be placed in any section until a period of 24 h has elapsed after
placement of the bedding cradle in that section.
c) The main fill shall not be placed in any section until the bedding cradle in that section has achieved
a compressive strength of at least 15 MPa.
Class B and Class C Beddings.
Contractor shall construct Class B and Class C beddings in accordance with the following requirements:
The pipes shall be bedded on a continuous bed of selected granular material, the material being placed in
accordance with the details shown on Drawing LB-l(b) or (c), as relevant, and the bedding constructed in
the manner shown on Drawing LB-3(b) or (c), as relevant. To ensure that each pipe will be fully
supported throughout the length of its barrel on the bedding cradle, joint holes shall be formed in the
bedding cradle for pipe sockets and couplings.
Class D Bedding.
construct Class D bedding in accordance with the following requirements:
The pipes shall be placed directly on the trench bottom after this has been hand-trimmed to ensure that
each pipe will be fully supported throughout the length of its barrel. Joint holes shall be formed in
the trench bottom for pipe sockets and couplings.
Temporary Support Material (Class B, C, and D Beddings). Any material that is used to support a pipeline
temporarily during construction or that does not comply with the requirements for bedding cradle shall be
removed before the selected fill blanket for Class B, C, or D bedding is placed.原件下载： 
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