SANS 10120-3 LB-1983 Code of practice for use with standardized specifications for civil engineering construction and contract documents Part 3 Guidance for design Section LB Beddi.pdf

1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA

2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any

3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. SABS 0120 : Part 3 Section LB-1983 Bedding (pipes) PART 3 : GUIDANCE FOR DESIGN SECTION LB Clause 1 . 1.1 1.1.1 1.1.2 1.1.3 1.1.4 1.2 1.2.1 1.3 1.3.1 1.3

4、.2 1.3.3 1.3.4 2 . 2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.1.5 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.3 3 . 3.1 4 . 4.1 4.2 4.2.1 4.2.2 4.2.3 4.3 4.3.1 4.3.2 5 . 5.1 CONTENTS Page Number PRE-TENDER CONSIDERATIONS 1 . Investigations 1 . Physical characteristics and sources 1 . Test pits and bore holes 1 . Selected gran

5、ular material 1 Cost of postponing preliminary investigations 1 . Administration 1 Preliminary establishment of sources of bedding materials 1 Documentation 1 Information for tenderers 1 Where source of materials is at Contractors discretion 1 . Selection of bedding 2 Concrete Class A and encasement

6、 2 DESIGN REQUIREMENTS 2 Structural Design of Buried Pipelines 2 General . 2 Economy 3 . Relating class of pipe to class of bedding 3 . Load-carrying capacity of pipeline 3 Reinforced and unreinforced pipes 3 Bedding Classes and Bedding Factors 3 Rigid pipes 3 Elliptical reinforced pipes 3 . Flexibl

7、e pipes 3 Concrete encasement 3 Procedure . 3 . APPLICABILITY OF OTHER CODES 5 General . 5 TEST PROCEDURES 5 Grading . 5 Compactibility Test 5 Apparatus 5 Procedure 5 Evaluation of results 5 Test Results . 5 Durban area . 5 Cape Flats area 6 . QUALITY CONTROL AND OTHER CONSIDERATIONS 6 Lessons from

8、Design Failures . 6 First Revision March 1983 This section of the code supersedes SABS 0120 : Part 3 : Section LB-1980 Approved by the COUNCIL OF THE SOUTH AFRICAN BUREAU OF STANDARDS SABS 0120 : Part 3 Section LB-1983 Bedding (pipes) SABS 1200 LB : BEDDING (PIPES) NOTE: The clause number(s) at the

9、beginning or after the heading of a clause is/are unless otherwise stated, the number(s) of the relevant clause(s) of SABS 1200 LB. PRE-TENDER CONSIDERATIONS INVESTIGATIONS Physical Characteristics and Sources. SABS 1200 LB is based on the use of bedding materials that have physical characteristics

10、such that the materials can be compacted with relative ease, thus eliminating the risks associated with the use of mediocre compaction techniques. In practice, suitable materials are often found in the excavation of a pipe trench and will thus be readily available alongside the trench for use during

11、 pipelaying. Where this is not the case, it will be necessary either a) to import material from elsewhere? or b) to reduce the level of compactibility required for the granular bedding material (with a consequent increase required in compactive effort). Weigh the costs of these alternatives. Test Pi

12、ts and Bore Holes. Under the circumstances it becomes prudent, in the course of preliminary investigations along the route of the pipeline, to sink test pits or bore holes to the level at which the pipes will be bedded and, in addition to listing the nature of material discovered, to carry out tests

13、 on the grading and compactibility characteristics of material recovered from such test pits or boreholes. Oonot test particular layers of materials that appear to be suitable but rather test made-up samples that incorporate some material from each layer, because the normal excavation process will p

14、roduce a mixture of materials from the top to the bottom (see 1.3.3 below). Selected Granular Material. When searching for a material suitable for use as a selected granular material, bear in mind the following facts: The main requirement for this material is that it should be free-running so that i

15、t can easily take up the shape of the pipe to form a sound support. For this purpose a non-cohesive material that is neither too coarse nor too angular is the best, a pea-gravel (i.e. a gravel-like material consisting of particles similar in size and shape to a pea and most commonly found in river b

16、eds) being ideal. The function of the bed is to provide continuous uniform support to the lower segment of the barrel of the pipe, and also perhaps to allow some longitudinal drainage if the trench is situated in waterlogged ground. Select a local material or a blend of local materials such that it

17、resembles as closely as possible a dry non-plastic singularly graded rounded fine gravel or a medium sieved sand and, if such a material is not available, consider importing the material. NOTE: The terms fine gravel and medium sand have the meanings given in BS 59301), the grain sizes being between

18、0.6 mm - 6 mm for fine, 6 mm - 19,O mm for medium sand (see Subclause 3.1 of SABS 1200 LB). Cost of Postponing Preliminary Investigations; The cost of preliminary investigations can be justified and it is in the employers interest that they be carried out thoroughly. If they are not carried out, the

19、 contractors rate must cover the cost of the various risk factors and will, therefore, inevitably be on the high side. The engineer administering the contract will run the risk of having to make snap decisions in order to avoid delaying the contractors progress (and incurring claims for delays) or o

20、f having to carry out investigations while construction is in progress and being in the weak position of having to negotiate non-competitive rates for unscheduled items of work. ADMINISTRATION Preliminary Establishment of Sources of Bedding Materials. In terms of the fee scale given in the Model For

21、m of AgreementL), the cost of preliminary investigations must be borne by the client (i.e. the employer) as a disbursement. Draw his attention to the economic advantages (see 1.1.4 above) of incurring these costs in his budget for the project during the planning stage (See also 1.3.1 below.) DOCUMEN

22、TATION Information for Tenderers. In addition to any geological description of the strata on site, ensure that the information provided for tender purposes relates the physical properties of the materials likely to be excavated from trenches to the properties specified for bedding materials. Where S

23、ource of Materials is at Contractors Discretion. Where the contractor is permitted to choose the source of bedding materials, consider the merits of adopting a clause such as PSLB 1.2 given in Subclause 3.2.1.2 of Section LB of Part 2 of the code. (See also Subclause 3.2.2 of Section LB of Part 5 of

24、 the code. 1) Site investigations. 2) Published by the South African Association of Consulting Engineers in Johannesburg in 1979. SABS 0120 : Part 3 Section LB-1983 Bedding (pipes) Selection of Bedding using excavated materials (Subclause 3.4.1) a) In preparing information required in terms of 1.3.1

25、, take cognizance of the fact that most trench exavations are carried out by means of backactors or various types of trenchers, each of which operates most economically if it excavates to the full final depth as the machine progresses along the trench. b) It follows that the material excavated and p

26、laced alongside the trench by such machines will be a mixture of the various layers penetrated and that the material most readily (and cheaply) available for bedding will be that mixture. C) Thus, if it is required that particular strata be preserved for bedding, specify this requirement clearly and

27、 bear in mind that selective excavation and separate stockpiling on the side of the trench will necessitate a higher rate than would otherwise be quoted. Contractor to provide suitable equipment to excavate selectively (Subclause 3.2.1.2 of Section LB of Part 2 of the code). In areas where a) homoge

28、neous materials occur in the trench in one or more layers each exceeding 300 nun in thickness; b) where trenches are relatively short (as in a township or treatment works); and c) in situations where sophisticated plant of high productivity is unlikely to be used for trench excavation by the contrac

29、tor, the engineer may, without great risk of incurring higher prices, require the contractor to excavate selectively in terms of a clause such as PSLB 1.2 given in Subclause 3.2.1.2 of Section LB of Part 2 of the code. Where this aspect of the project is considered to be a borderline case, frame PSL

30、B 1.2 in such a manner that the engineer retains the right to order selective excavation and obtain prices for both alternatives by scheduling as follows: Item Payment NO. refers Short Description Quan- Rate Unit tity Amount SABS SECTION : 1200 LB .l PROVISION OF BEDDING Available without selection

31、from trench within 0.5 km (Subclause 3.4.1) (Provisional. Tenderer to state rate but not extend) .1.1 8.2.1 a) Selected granular material .1.2 b) Selected fill material 3 Rate only 2 (Give total quantities) Rate only Selected from trench within 0,s km (PSLR 1.2) .1.3 a) Selected granular material 3

32、b) Selected fill material m3 9 .1.4 m (Give total quantities) Port Elizabeth area. In the case of Port Elizabeth the sands are not coarse enough (see 1.1.3 above) and do not have the right compactibility factor (see 4.2.3 below). However, local engineers consider a) that where the trench is in dry g

33、round and the load is not critical, Arlington sand of which not more than 5 % passes through a sieve of nominal aperture size 0,075 mm is acceptable; and b) that under all other circumstances 7 mm quarry stone should be specified as the selected granolar material, because it is the cheapest product

34、available. Concrete Class A and Encasement (Subclause 5.4). Where concrete encasement is required (see 2.2.4 below) schedule an item in terms of Subclause 8.2.4 of SABS 1200 LB. Do not schedule working space for either Class A bedding or concrete encasement. DESIGN RENIREMENTS STRUCTURAL DESIGN OF B

35、URIED PIPELINES General. It is essential that the design of bedding and the design of the pipelines be carried out at the same time. Acceptable design criteria for pipelines intended to carry stormwater, sewage, and water in residential townships have been set out in Parts 111, IV, and V respectivel

36、y of Rational norms for engineering services for residential townships3), and additional guidance on design requirements may be had by reference to Clause 2 of each of Sections LE, LD, and L. Design requirements for the bedding are dealt with in 2.1.2 - 2.1.4 below. Structural design of buried pipel

37、ines is subject to many detailed considerations. Design engineers should be familiar with the parameters involved in the basic aspects of the theory of differential settlement. 3) In course of preparation for the Department of Community Development. SABS 0120 : Part 3 Section LB-1983 Bedding (pipes)

38、 In order to give effect to the requirements of SABS 1200 LB. in addition to the pipeline design procedure set out in 2.3 below, carry out preliminary investigations into the suitability of bedding materials using the tests set out in Clause 4 below. Economy. Carry out investigations during the pre-

39、tender period in order to establish whether bedding materials that comply with the relevant requirements of SABS 1200 LB are available within an economic distance of the areas in which pipelaying will be carried out. Decide which of the materials available within an economic distance of the pipeline

40、 is most suitable before specifying the compactibility factor or varying the specified grading for the bedding cradle or the selected fill blanket. Relating Class of Pipe to Class of Bedding. To meet the design load requirements, a particular pipe class and a bedding class to suit it must be specifi

41、ed. However, a change in the conditions at the trench bottom may necessitate a strengthening of the pipeline which should be achieved by changing the bedding class rather than,the pipe class, as a change in the pipe class usually involves the more costly delays. Therefore, where bedding of a high cl

42、ass is being contemplated, consider using, where possible, a higher strength (class) pipe on a lower class bedding so that, if required, the bedding class can be increased to provide improved support. (See also Subclause 3.2.1 of Section LE of Part 5 of the code.) Load-Carrying Capacity of Pipeline.

43、 As the load-carrying capacity of a pipeline depends largely on the way it is supported by its bedding. the selection, placing, and compaction of the bed is of great importance. The load-carrying capacity of the pipeline is related to the pipe strength (as determined in laboratory tests) by a beddin

44、g factor, as follows: Test strength X bedding (load) factor = load that buried pipe will sustain. For rigid pipes, four classes of bedding (designated A, B, C, and D) are used. Reinforced and Unreinforced Pipes. See Subclause 3.2.l(a) of Section LE of Part 2 of the code. BEING CLASSES AND BEDDING FA

45、CTORS Rigid Pipes Bedding Class A. Bedding of Class A is concrete bedding and is required for a pipeline designed for a bedding factor of 3,O. This bedding provides support for the pipe sides and spreads the reaction load. A bedding factor of 3.4 can be used in the design where the concrete bedding

46、is strengthened with reinforcement. Give details of the reinforcement. (See also 2.2.4 below.) Bedding Class B. Bedding of Class B is necessary for a pipeline designed for a bedding factor of 1,9. This bedding requires that the bedding cradle supports the bottom half of the pipe barrel. edding Class

47、 C. Bedding of Class C is necessary for a pipeline designed for a bedding factor of 1.5. This bedding requires that the bedding cradle supports the bottom quarter of the pipe barrel. Bedding Class D. Bedding of Class D is necessary for a pipeline designed for a bedding factor of 1.1. This bedding pe

48、rmits the pipe to be laid directly on the trench bottom and requires no bedding materials to be worked under the pipe. The pipe is therefore, in theory, subject to line loading. Such a bedding condition is generally acceptable for small diameter rigid pipes only, such as galvanized iron pipes of dia

49、meter up to 100 mm and subsoil drain pipes. Elliptical Reinforced Pipes. The bedding of elliptical reinforced concrete pipes differs from that of circular pipes and circular reinforced pipes. Never bed elliptical reinforced concrete pipes on concrete cradles. Design the bedding specially and so lay each pipe that the angle between the line joining the manufacturers marks indicating the top and bottom of the pipe and the vertical plane through the longitudinal axis of the pipe is not more than 5 O. Flexible Pipes. Generally steel pipes that are not coated or lined with concrete, all PV