SANS 10120-3 DB-1982 Code of practice for use with standardized specifications for civil engineering construction and contract documents Part 3 Guidance for design Section DB Earth.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. Clause PART 3 : GUIDANCE FOR DESICN SECTION UB CONTENTS SABS 0120 : Part 3 Section DB-1982 Earthworks (pipe trenches) (As amuiiticcl 1081) PRE-TENDER CON

4、SIDERATIONS . 1 . Investigations 1 . Preparation of trench bottom 1 . Administration 1 . Riqht to use ground throughout route of pipeline 1 Minimum width of servitudes/wayleaves 1 Site clearance and the reinstatement of lawns. gardens. etc l Backfilling 011 private property 1 Tenders 1 Documentation

5、 1 . Pipeline servitudes or wayleaves l Acconwodation of traffic . 2 . Disposal of surplus and unsuitable material 2 Methods of excavation. bedding. and backfilling 2 Other project specification requirements . 2 DESIGN REQUIREMENTS 2 Trench Widths 2 Maximum width 2 Minimum width 2 . Cover over Pipes

6、 2 APPLICABILITY OP OTHER CODES . 2 TEST PROCEDIJRES . 2 General 2 QUALITY CONTROL AND OTHER CONSIDERATIONS . 2 Lessons from Design Failures 2 Trench depths and structural design of buried pipelines 2 SABS 0120 : Part 3 Section DB-1982 Earthworks (pipe trenches) Amendment No. 1 : 27 February 1989 SA

7、BS 1200 DB : EARTHWORKS (PIPE TRENCHES) NOTE: The clause number(s) given at the beginning or after the heading of a clause is/are, unless otherwise stated, the number(s1 of the relevant clause(s) of SARS 1200 DD. PGE-TENDER CONSIDERATIONS INVESTIGATIONS Preparation of Trench Bottom (Subclause 5.5).

8、Where the preliminary investigations reveal a risk of difficult conditions at the bottom of a trench in any section of the work, ensure that sufficient items have been scheduled, on a provisional basis, to deal with situations that are likely to occur. The design engineers attention is drawn to the

9、following main types of situations that may arise: a) Where the trench bottom is coarse-grained, and reasonably dry, and variations in bearing qualities are insignificant, or where the bottom is fine-grained but dry, no prohlems are likely to atise and bedding can be constructed as specified. b) Whe

10、re water is present the contractor is responsible, in terms of Subclause 5.1.2.1 of SABS 1200 DB, for ensuring (by the sloping of the bottom, the provision of a channel on one side and the draining of water to low points, or the removal of water by pumping) that the bottom of the trench is always fr

11、ee from standing water. Where this has been achieved or is practicable, conditions on the trench hottom should be such that the situation given in (a) above is applicab3e. C) Where the steps outlined in (h) above are impracticable because ot the sloppy nature of the material in the bottom of the tre

12、nch, it will be necessary to stabilize the trench bottom and to avoid disturbance and further softening of the trench bottom. This situation will arise in wet fine-grained soils snch as soft clays, silts, and fine sands. Suitable granular material, crushed stone, crusher-run, or ash should be placed

13、 as necessary on the trench bottom immediately the excavation has been completed. Such a layer should become effective before its thickness exceeds 200 mm. Where such steps are inadequate, a concrete raft should be constructed on top of the stabilizing layer. Where the condition of the soil to a dep

14、th exceedinq 600 mm below the pipe invert level is poor, piles may be necessary to suppurt a reintorced concrete raft constructed on the bottom of the trench. Normal bedding as described in (a) above should be constructed on top of the concrete. Attention is drawn to Subclause 3.1.4 of Section DB of

15、 Part 5 of the code, where further aspects of the problem are outlined. Right to Use Ground ThroughoutRoute of Pipeline (Subclause 5.3). Ensure that the employer has the necessary authority to use the ground or wayleaves or servitudes over the whole of the route of the pipeline before tenders are in

16、vited. This is necessary to enable the contractor to carry out, in the most economical sequence, permanent works on property belonging to others from the date of award of the contract without let or hindrance. (See also Subclause 1.2.1 of Section D.) Minimum Width of Servitudes/Wayleaves (Subclause

17、5.3). Ensure that the servitude obtained for the works is wide enough to allow normal working conditions (bearing in wind the depth to invert of the pipe) both during construction of the pieline and during subsequent repair and maintenance work. Where this is not possible, negotiate temporary occupa

18、ncy of adjoining land (such occupancy being probably also of advantage to the employer). Alternatively, it may he possible to deal with the matter by way of a provision in the project specification such as that in Subclause PSDB 4.1 gjven in Subclause 3.2.5.2 of Section DH of Part 2 of the code. Sit

19、e Clearance dnd the Reinstatement of Lawns, Gardens, etc. (Subclause 5.3 and SABS 1200 C). Although it is common practice to specify that the contractor is to reinstate lawns, trees, etc. it must be appreciated that many shrubs, trees, and hedges cannot be transplanted temporarily and returned to th

20、eir oriyinal places. Explain the problems to the landowner and reach an equitable dnd practical arrangement with him before completing the documentation. Set out the details of such an arrangement in the project specification. Backfilling on Private Property (Subclause 5.9.2). Ascertain whether the

21、requirement that backfilling of a trench is to stand not more than 150 nun proud of the surrounding ground is acceptable to the property owner and, if it is not acceptable, include a clause in the project specification to amend Subclause 5.9.2 of SAW 1200 DB accordingly. Tenders. Ensure that before

22、the start of construction action has been taken in the matters set out in (a) and (b) of Subclause 3.1.2 of the Introduction to Part 3 of the rode. DOCUMENTATION Pipeline Servitudes or Wayleaves (Subclause 5.3 and see also 1.2.2 and 1.2.3 above) Where a pipeline is to be laid in a servitude or wayle

23、ave, state the width of the servitude or wayleave and state whether the contractor will be required to restrict his operations to the surface area of the servitude or wayleave. Where a servitude or wayleave is parallel to a public road (or nearly so), state clearly whether or where the servitude or

24、wayleave and road boundaries coincide. Set out details in Clause PS 2 (Description of site and access) of the project specification. SARS 0120 : Part 3 Section DB-1982 Earthworks (plpe trenches) Amendment No. 1 : 27 February 1989 Accommodation of Traffic (Subclauses 5.1.3, 5.9.3 and 5.9.4). Select f

25、rom Subclause 3.2.9 of Section DM of Part 2 of the code, such project specification clauses as are necessary to deal with services, majntenance of temporary onsurfac.ed and other road surfaces, fencing, gates, and other responsibilities of the contractor relevant to the project. Disposal of Surplus

26、and Unsuitable Material (Subclauses 3.5, 5.6, and 0.3.2). In many instances reduction of the freehaul to only 50 m warrants consideration because this is the maximum reasonable distance within which a contractor can distribute surplus material without incurring the cost of “loading it up“. Thus 50 m

27、 is a cheaper freehaul than 0.5 km . An analysis reveals that in the case of most pipe trench contracts in the Republic, surplus material is in fact heaped on top of trenches or distributed over the servitude in r-lose proximity to the source. In urban areas, over farm lands, and in other situations

28、 where it is required that all or part of the surplus material be moved to particular localities, state the requirements in the project specification, includjng the method of control of distances and measurement of quantities. Methods of Excavation, Bedding, and Rackfilling (Subclauses 5.4, 5.5, and

29、 5.6) . Jn addition to a geological description of the strata on the site, the information provided in the project specification (in Portion 1 or a PSDR or a PSLB clause) should relate the physical properties of the materials likely to he excavated from trenches to the properties specified for beddi

30、ng and backfillinq materials. See Subclause 1.3 of Section LB for action to be taken when framing the contract. Other Project Specification Requirements. See 1.2.2-1.2.4 above. DESIGN REQUIREMENTS TRENCH WIDTIIS (Subclause 4.1) Maximum width. The contractor can be held responsible only for the costs

31、 of strengthening a pipeline or its bedding to compensate for the additional design loads attributable to any excess of trench width over the maximum trench width that is stated on the drawing or required in terms of the project specification, provided that a separate item has been scheduled for the

32、 particular sectlorr of the pipeline that is subject to the “maximum trench width“ embargo. Minimum width. Each minimum trench width specified has been determined in practice as providing the minimum width between the sides of the pipe(s) and trench necessary for effective placing, working, ranming,

33、 and compaction of bedding under and around the pipecs). I COVER OVER PIPES. When specifying the earth cover over the pipeline tab into consideration the probable construction processes and make provision in the design of the pipeline for the earth- moving plant loads that may occur during construct

34、ion. See Subclause 3.1.3.3 of Section DB of Part 5 of the code. APPLICABILXTY OF OTHER CODES The requirements of SABS 1200 DB take precedence over any recommendations for trenching given in SAES 0102 The selection of pipes for buried pipelines. I TEST PROCEDURES GENERAL. Except where otherwise speci

35、fied, use the test procedures recornnended in the applicable TWI publication of the NITFR. QUALITY CONTROL AND OTHER CONSIDERATIONS LESSONS FROM DESIGN FAILURES Trench Depths and Structural Design of Buried Pipelines. Be alert to problem areas in the design of buried pipelines and particularly to th

36、e following reported cause of pipeline frilure: The regrading and reconstruction of roads in existing townships frequently reduce the cover to below the safe minimum value, thus necessitating the relaying of services or the provision of a special cover. Water mains and stormwater pipes are particularly vulnerable to this hazard. TSRN 0-626-08250-1