SANS 10120-3 DK-1996 Code of practice for use with standardized specifications for civil engineering construction and contract documents Part 3 Guidance for design Section DK Gabio.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 01 20-3 Section DK:1996 Gabions and pitching First revision Part 3 : Guidance for design Section DK Contents Page l Pre-tenderconsiderations 1 1.1 I

4、nvestigations 1 1 . 1 . 1 Need for geotextiles and geomembranes . 1 1.2 Administration l 1.2.1 Provision for alternativelextra work . 1 1.3 Documentation . l 1 . 3.1 Project specification clauses 1 1.3.2 Pitching . 1 1.3.3 Foundations for gabion walls and aprons . l 1.3.4 Founding conditions for pit

5、ching . 1 1.3.5 Scheduling 1 1.3.6 Tolerances 1 2 Designconsiderations 2 2.1 PVCcoating . 2 . 2.1.1 Where PVC coating should not be used 2 2.1.2 Where PVC coating has proved useful 2 2.1.3 Where the use of PVC coating should be considered 2 2.2 Maintenance and corrosion considerations in design 2 2.

6、3 Wiremeshforgabions 2 . 2.4 Firmness of lacing 2 2.5 Gabionmattresses . 3 2.6 Useofgeotextiles . 3 2.7 Examplesofdesign 3 2.7.1 Bridgeabutments . 3 2.7.2 Mountainside stabilization 4 2.8 Gabiontolerances . 4 3 Applicability of other codes . 4 . 4 Testprocedures 4 5 Quality control and other conside

7、rations . 4 Drawings DK.3.1 Examples of gabion structures . 5 First revision 24 June 1996 This section of the code supersedes SABS 0120-3 : Section DK:1984 Approved by the PRESIDENT OF THE SOUTH AFRICAN BUREAU OF STANDARDS CODE OF PRACTICE SABS 0120-3 : Section DK:1996 SABS 1200 DK : Gabions and pit

8、ching NOTE - The clause number) given in brackets at the beginning or after the heading of a clause islare, unless otherwise stated, the number(s) of the relevant clause(s) of SABS 1200 DK. 1 Pre-tender considerations 1 .l lnvestigations 1 .l .l Need for geotextiles and geomembranes In the case of g

9、abions, establish the need or otherwise for geotextiles or geomembranes by investigating foundation conditions before completing the documentation for the project. Investigate substrata and other conditions on the site of the proposed gabion construction sufficiently thoroughly to ensure the disclos

10、ure of a seasonal water table and of seepage or other water that might adversely affect the proposed gabion construction and its foundations. (See also 2.6 below.) 1.2 Administration 1.2.1 Provision for alternativelextra work Ensure that provision is made in the schedule for prices to be tendered fo

11、r alternative or extra work that might be ordered while the works are being constructed. (See 1.3.4 and 1.3.5 below for examples of such items.) 1.3 Documentation 1.3.1 Project specification clauses 1.3.1 .l General Ensure that the project specification includes requirements arising from such design

12、 decisions as might be made in the light of 2.1 to 2.5 below and to cover the applicable of the matters set out in section DK of SABS 0120-2. 1.3.1.2 Tests on firmness of lacing (5.1.2) Where the design requirements are such that the firmness of the lacing must be greater than that specified in 5.1.

13、2 of SABS 1200 DK, include in the project specification requirements for the use of heavier binding wire and the achievement of a firmer attachment. (See also 2.4 below.) 1.3.2 Pitching (3.2) Ensure that clear directives are given as to whether pitching is to be extra heavy, heavy, medium or light.

14、1.3.3 Foundations for gabion walls and aprons (5.2.1) Ensure that details of the foundation trench to be constructed along the toe of the revetment(s) are given, and that the dimensions of such revetment(s) are clearly shown on the drawings. 1.3.4 Founding conditions for pitching (5.3.1) Ensure that

15、 the contract document includes details as to the extent to which a surface is to be compacted before construction of the pitching starts. Where so required, give details of backing. (See also 2.l(e) of section DK of SABS 01 20-2.) 1.3.5 Scheduling (8.2.1, 8.2.2, and 8.2.5 to 8.2.7) Ensure that: a)

16、an item is provided for filling cavities in the foundations with concrete, if use of concrete for this purpose is likely to be ordered; b) in the case of gabions, detail items are provided in the schedule for each size of box or mattress, each mesh size and each diaphragm spacing; c) in the case of

17、pitching, separate items are provided in the schedule for each type of pitching, and that suitable items are provided for additional excavation where it is likely that the toelfooting trench will have to be excavated to a depth exceeding 1 m vertically; d) the schedule provides for different thickne

18、sses of backing where more than one thickness of backing is likely to be required in terms of the project specification; and e) the schedule contains suitable items to cover weepholes. 1.3.6 Tolerances (6.1 ) See 2.8 below and 3.1.3(b) of section DK of SABS 0120-5. SABS 0120-3 Section DK:1996 Gabion

19、s and pitching First revision 2 Design considerations 2.5 PVC coating (3.1.2) 2.6.1 Where PVC coating should not be used PVC coating will not stand up to mechanical damage caused by heavy beach shingle being thrown against a wall by continuous wave acton, or by a mountain stream carrying a heavy loa

20、d of large sharp rocks. 2.1.2 Where PVC coating has proved useful PVC-coated mesh has been found to stand up to sand abrasion better than uncoated galvanized mesh and, in the case of gabions used in a jetty on a coastline that has a hot climate and where the sea water is warm, it has been found acce

21、ptably resistant to the effects of high ambient temperatures, long hours of sunlight and alternate wetting and drying. 2.1.3 Where the use of PVC coatlng should be considered In addition to its use in circumstances such as those described in 2.1.2 above, consider specifying PVC coating where a) the

22、resistivity of the soil is below 5 000 n.m, b) water that has a Langelier Index of -0,5 or lower is present, c) suifate-reducing bacteria are present, d) there is a constant flow of water at velocities exceeding 2 m/s, and e) milder abrasive action than that described in 2.1.1 above is present. 2.2

23、Maintenance and corrosion considerations in design The wire mesh used for gabions is required in terms of SABS 1200 DK to have a class A (heavy) zinc coating used for fencing and, where PVC coating is required, the thickness of the PVC is to be at least 0,50 mm because, when constructed, a) the hidd

24、en sides of the gabions will generally be in corrosive soils, and b) the cost of repairing or rectifying a structure that has collapsed or moved owing to failure of gabion cages will generally greatly exceed the initial installation cost and will always be far greater than the difference between the

25、 costs of heavy and light zinc coatings. 2.3 Wire mesh for gabions (3.1.2) The diameters of wire given in SABS 1580) are suitable for most applications. Certain applications might, however, call for diameters other than those given and, in this regard, consider the following cases: a) In the case of

26、 gabions of depth less than 0,3 m and required for light duty only (such as for walls of height not exceeding 2 m or for controlling water that flows at a velocity of less than 2 m/s), a 2 mm mesh wire with a 2,7 mm selvage wire is acceptable. b) In the case of gabions required for heavy duty (such

27、as for retaining walls of height over 10 m and carrying road or rail traffic or for dam spillways for the control of fast flowing water), use, for gabions of depth exceeding 0,5 m, a wire mesh and selvage each of PVC-coated wire that has a core of diameter at least 3,O mm or a wire mesh and selvage

28、of plain galvanized wire of diameter at least 3,4 mm and 3,9 mm, respectively. However, consider the cost implications of such non-standard gabion wire sizes. 2.4 Firmness of lacing Take cognizance of the relationship given in table 1 between the diameter of binding wire and the firmness of lacing o

29、btained in practice during construction. 1 ) Steel wife gabion cages. 2 SABS 01 20-3 Section DK:1996 Gabions and pitching First revision Table 1 - Flrmness of lacing I Diameter of binding wire / Load at failure I Type of failure mm kN/m I 24 Mesh wire broken 24 Selvage mesh unravelled or mesh wire b

30、roken 22 Selvage unravelled or binding wire broken 2,o 2.5 Gabion mattresses Gabion mattresses are generally used only as single-layer aprons, in revetments, channel linings, etc. 2.6 Use of geotextiles Where the investigations carried out in terms of 1.1.1 above reveal a risk that water could have

31、an adverse effect upon the stability of a gabion construction, incorporate a layer of suitable geotextile into the design in such a way that the movement of water through the gabion does not leach out soil from behind and below, or that silt-laden water from the fill or foundations does not cause th

32、e gabion to become clogged with unacceptable quantities of silt. Filtering of water can also be achieved by means of a geotextile, which is permeable and can be of various thicknesses and gradings; alternatively, the movement of water through an area can be prevented by use of a geomembrane. 2.7 Exa

33、mples of design 2.7.1 Bridge abutments2) (See figure 3.l(a) in drawing DK.3.1) During the design stage for the construction of abutments and wing walls on mobile estuarine silt, borehole tests indicated that the soil was soft to very soft, comprising dark-grey very silty clay, with traces of both bl

34、ack sand and organic matter present at depths down to 7 m. Calculations indicated that a semi-rigid base, constructed from a foundation mattress of depth 1 m, filled with stone, would extend the zone of influence and would effectively reduce the intensity of the applied load on the subsoil. The desi

35、gn called for full loading of the embankment area to the rear of the abutment, before a planned piling operation took place. The use of a gabion-reinforced soil-retaining wall allowed a slope of 70 to be attained at the interface with the bridge, while the wing walls were designed in a similar manne

36、r to have a stepped slope with an effective gradient of 45. The gabion face is stated to have provided a permeable and permanent structure, avoiding the inducement of forces caused by differentiai hydraulic heads (awing to tidal movement) which would otherwise have occurred with a conventional reinf

37、orced concrete wall. The design system was also sufficiently flexible to allow adjustment in the height of the embankment should settlement have been less than anticipated. The front toe of the foundation mattress was protected from scour by a 300 mm deep mattress constructed from a mesh that gave e

38、nough flexibility to allow the mattress to rotate downwards, producing a self-regulating toe protector. The designers specified mesh manufactured from high density polyethylene, which is resistant to marine environments and provides longevity in marine constructions. The foundation mattress was so d

39、esigned as to create 2 m X 1 m cells within the overall structure. (See also 3.1.4.1 of section DK of SABS 0120-5.) NOTES 1 The high density polyethylene mesh reported to have been used in the example given above is not available in South Africa, nor is its use recommended, but the principles of the

40、 design and methods of construction of the wall are valid for South Africa and, subject to (2) below, the construction would, in fact, be improved if the available wire mesh gabions and mattresses were to be used. 2 The top edge of the toe mattress (as reported and as shown in figure 3.l(a) in drawi

41、ng DK.3.1) should preferably have been inserted for a distance of at least 0,3 m under, and securely joined to, the underside of the foundation mattress. 2) Abstracted from Geotechnical materials, published in Ground Engineering, Vol. 14 Number 14. October 1981. SABS 0120-3 Section DK:1996 Gabions a

42、nd pitching First revision 2.7.2 Mountainside stabilizatlon. Figure 3.1 (b) in drawing DK.3.1 illustrates an application of construction with medium- duty gabions to control cuttings into a mountainside by means of a stepped revetrnent. 2.8 Gablon tolerances (6.1 ) Take the following into account wh

43、en designing and, if necessary, when deciding on tolerances to be stated in the project specification for Degrees of Accuracy I, II or Ill, as appropriate: The alignment tolerances given in 6.1 (b) of SABS 1200 DK are the same as those specified for the top edge of terraces, embankments, etc., in cl

44、ause 6 of SABS 1200 D=). In practice, acceptable tolerances for gabions depend on the purpose of the gabion construction. Where faces of cuttings and of natural features such as mountain slopes, river banks and eroded areas are to be protected by gabions, adherence to natural contours and shapes is

45、more important than adherence to designated lines and levels (unless the linos and levels have been designated on site during construction). Where faces of bridge abutments, high retaining walls that follow smoothly aligned roads, and the Bike are to be constructed, straight lines are frequently req

46、uired. In such cases, relatively close tolerances are desirable and true faces are obtainable if the construction methods recommended in 3.1.3(b) of section DK of SABS 0120-5 and by the suppliers of the gabions are followed. Curved alignments are more appropriate for gabion walls than are straight a

47、lignments. Applicability of other codes There are no other SABS codes of practice that are applicable to gabions and pitching. 4 Test procedures See SABS 1580 and 7.3 to 7.5 of SABS 1200 DK. 5 Quality control and other considerations Apply the relevant recommendations of SABS IS0 9000) to the design

48、 of gabions and pitching. 3) Earthworks. 4) Quality management systems. SABS 01 20-3 Section DK:1996 Gabions and pitching First revision Mesh reinforcement integral with face h aaabion on each course Compacted fill Foundation ymattresses Preferred of toe ma YToe mattress Figure 3.1 (a) Use of Gabion

49、 Mattress to raise an embankment on estuarine silt (See Subclause 2.7.1 ) Vertical face Overhang Overhang section Backfill section Note - Dimensions in millimetres Figure 3.1 (b) Gabion stabilization on Table Mountain 1050 m3 of gabions each 2 m X 1 m X 1 m, PVC-coated wire diameter 2,7 mm in 100 mm X 120 mm mesh. Designed by City Engineer, Cape Town. Drawing DK.3.1 - Examples of gabion structures ISBN 0-626-10828-4 5 sabs pta