Desk Study and Field Assessment Report (02 Final, with MS review)

1、Client:Guangdong LNG Terminal and Trunkline Project Joint Executive OfficeProject:Guangdong LNG Terminal and Trunkline Project, ChinaTitle:Preliminary Landslide Risk Assessment of Proposed Pipeline Routes Based on Desk Study and Selected Field VisitsDocument Reference: 5001585/GTG.2001334/Desk Study

2、 and Field Assessment Report (02 Final)02FinalJHCEMLSPPPGFMS13/02/200301Draft for review by:Client,Prof. P.G. Fookes,Mr M. SweeneyJHCEMLSPPDTSDTS20/12/2002Revision/ StatusPurpose/ DescriptionOriginatedCheckedReviewedAuthorisedDateCONTENTS TOC o 1-3 h z u HYPERLINK l _Toc32991837 EXECUTIVE SUMMARY PA

3、GEREF _Toc32991837 h 1 HYPERLINK l _Toc32991838 1.INTRODUCTION PAGEREF _Toc32991838 h 3 HYPERLINK l _Toc32991839 Background PAGEREF _Toc32991839 h 3 HYPERLINK l _Toc32991840 Subsequent Work on Landslide Risk PAGEREF _Toc32991840 h 4 HYPERLINK l _Toc32991841 Scope of work PAGEREF _Toc32991841 h 5 HYP

4、ERLINK l _Toc32991842 Programme PAGEREF _Toc32991842 h 6 HYPERLINK l _Toc32991843 2.REGIONAL SETTING PAGEREF _Toc32991843 h 9 HYPERLINK l _Toc32991844 Geology and Terrain PAGEREF _Toc32991844 h 9 HYPERLINK l _Toc32991845 Climate and Weathering PAGEREF _Toc32991845 h 10 HYPERLINK l _Toc32991846 Key T

5、errain Issues PAGEREF _Toc32991846 h 10 HYPERLINK l _Toc32991847 Slope Processes PAGEREF _Toc32991847 h 10 HYPERLINK l _Toc32991848 Other issues PAGEREF _Toc32991848 h 11 HYPERLINK l _Toc32991849 3.LANDSLIDE HAZARD AND RISK PAGEREF _Toc32991849 h 13 HYPERLINK l _Toc32991850 Introduction PAGEREF _Toc

6、32991850 h 13 HYPERLINK l _Toc32991851 Natural Terrain Landsliding in Hong Kong PAGEREF _Toc32991851 h 15 HYPERLINK l _Toc32991852 Applicability of Hong Kong Landslide Statistics to the Guangdong Area PAGEREF _Toc32991852 h 17 HYPERLINK l _Toc32991853 Cut Slope Failures in Hong Kong PAGEREF _Toc3299

7、1853 h 18 HYPERLINK l _Toc32991854 4.Landslide Risk Assessment for the Proposed Pipeline Route PAGEREF _Toc32991854 h 21 HYPERLINK l _Toc32991855 Introduction PAGEREF _Toc32991855 h 21 HYPERLINK l _Toc32991856 Natural Terrain Landslides PAGEREF _Toc32991856 h 22 HYPERLINK l _Toc32991857 Overall Risk

8、 PAGEREF _Toc32991857 h 22 HYPERLINK l _Toc32991858 Relative Risk within Landslide Prone Lengths of the Route PAGEREF _Toc32991858 h 24 HYPERLINK l _Toc32991859 Man-made Cut Slopes PAGEREF _Toc32991859 h 26 HYPERLINK l _Toc32991860 Introduction PAGEREF _Toc32991860 h 26 HYPERLINK l _Toc32991861 Asse

9、ssment of the Proposed Pipeline Route PAGEREF _Toc32991861 h 26 HYPERLINK l _Toc32991862 Combined Natural Terrain and Cut Slopes PAGEREF _Toc32991862 h 30 HYPERLINK l _Toc32991863 Summary PAGEREF _Toc32991863 h 31 HYPERLINK l _Toc32991864 Comparison of Risk with Other Pipelines PAGEREF _Toc32991864

10、h 33 HYPERLINK l _Toc32991865 5.OPTIONS FOR THE MITIGATION OF LANDSLIDE RISK PAGEREF _Toc32991865 h 34 HYPERLINK l _Toc32991866 Introduction PAGEREF _Toc32991866 h 34 HYPERLINK l _Toc32991867 Ridge and Spur Alignments PAGEREF _Toc32991867 h 35 HYPERLINK l _Toc32991868 Engineering the pipeline to iso

11、late it from existing and potential landslide and erosion processes PAGEREF _Toc32991868 h 36 HYPERLINK l _Toc32991869 Management of Spoil PAGEREF _Toc32991869 h 36 HYPERLINK l _Toc32991870 Management of Surface Water PAGEREF _Toc32991870 h 37 HYPERLINK l _Toc32991871 Summary PAGEREF _Toc32991871 h

12、38 HYPERLINK l _Toc32991872 6.FIELD ASSESSMENT OF VISITED AREAS PAGEREF _Toc32991872 h 39 HYPERLINK l _Toc32991880 Stake Nos. B084 to C007-2 (see Terrain Map No. 11) PAGEREF _Toc32991880 h 43 HYPERLINK l _Toc32991881 Stake Nos. B072-1 to B083 (see Terrain Map No. 12) PAGEREF _Toc32991881 h 44 HYPERL

13、INK l _Toc32991882 Stake Nos. B048 to B055-1 (see Terrain Map No. 13) PAGEREF _Toc32991882 h 45 HYPERLINK l _Toc32991883 Stake Nos. B030-1 to B039 (see Terrain Map No. 13) PAGEREF _Toc32991883 h 46 HYPERLINK l _Toc32991884 Stake Nos. B002 to B012-1 (see terrain Map No. 14) PAGEREF _Toc32991884 h 47

14、HYPERLINK l _Toc32991885 Stake Nos. A001 to A016 (see Terrain Map No. 14) PAGEREF _Toc32991885 h 48 HYPERLINK l _Toc32991886 Stake Nos. A034-1 to A039-1 (note: no Terrain Map produced for this area) PAGEREF _Toc32991886 h 49 HYPERLINK l _Toc32991887 Stake Nos. 1001 to 1032 (see Terrain Map No. 15) P

15、AGEREF _Toc32991887 h 50 HYPERLINK l _Toc32991888 Stake Nos. 1123 to 1131 (see Terrain Map No. 16) PAGEREF _Toc32991888 h 51 HYPERLINK l _Toc32991889 Stake Nos. 2015 to 3006 (see Terrain Map No. 17) PAGEREF _Toc32991889 h 52 HYPERLINK l _Toc32991890 Stake Nos. 3031 to 3042 (see Terrain Map No. 18) P

16、AGEREF _Toc32991890 h 53 HYPERLINK l _Toc32991891 Stake Nos. 3060 to 3068 (see Terrain Map No. 18) PAGEREF _Toc32991891 h 54 HYPERLINK l _Toc32991892 7.CONCLUDING REMARKS PAGEREF _Toc32991892 h 55 HYPERLINK l _Toc32991893 Landslide Risk PAGEREF _Toc32991893 h 55 HYPERLINK l _Toc32991894 Other Terrai

17、n Issues PAGEREF _Toc32991894 h 58 HYPERLINK l _Toc32991895 The Way Forward PAGEREF _Toc32991895 h 58 HYPERLINK l _Toc32991896 8.References PAGEREF _Toc32991896 h 60TABLES (in the text)Table 1Field Visit Programme.Table 2Summary Geology of Guangdong Province.Table 3Risk Assessment Definitions (from

18、Royal Society, 1992; Cruden and Fell 1997).Table 4Rainfall Thresholds for Landslide Activity in Hong Kong (Evans, 1997; Evans et al., 1997).Table 5Width Classes of Relict and Recent Landslides in the Natural Terrain Landslide Inventory for Hong Kong (from Evans et al., 1997).Table 6Landslides in Hon

19、g Kong Recorded by the Geotechnical Engineering Office (from Fell et al., 1996).Table 7Slope Approach Classes (Orientation of the Pipeline Relative to the Slope).Table 8Natural Terrain Risk Assessment: Summary Statistics.Table 9Summary of Natural Terrain Landslide Susceptibility Classes for Selected

20、 Hong Kong Bedrocks (adapted from Evans and King, 1997).Table 10Natural Terrain Landslides: Relative Risk Classes.Table 11Natural Terrain Landslides: Summary of the Lengths Associated with each Relative Risk Class.Table 12Example 1, a Fully Engineered and Maintained Cut Slopes: Assessment of the Pro

21、bability of Cut Slope Failure (based on Findlay and Fell, 1995).Table 13Example 2, Minimally Engineered Cut Slopes: Assessment of the Probability of Cut Slope Failure (based on Findlay and Fell, 1995).Table 14Landslide Risk Assessment for the August 2002 Pipeline Route: Summary Statistics.APPENDICES

22、Appendix APreliminary Natural Terrain Landslide Risk AssessmentAppendix BPreliminary Cut Slope Landslide Risk AssessmentAppendix CPreliminary Combined Landslide Risk AssessmentAppendix DTechnical Paper: Framework for Assessing the Probability of Sliding of Cut Slope (from Fell et al., 1996)Appendix

23、ELocation of Waypoints and PhotographsAppendix FSummary of Geology of the Guangdong ProvinceFIGURESFigure 1Regional Context and Key Map of Guangdong ProvinceFigure 2Landslides Ruptures FrequenciesFigure 3aScale of Weathering Grades of Rock MassFigure 3bModels of Weathering in GraniteFigure 4Typical

24、Shallow Hillside FailureFigure 5Problems Associated with Routing Across Deep Gullys and SpursFigure 6Type of Landslides on Cut SlopesFigure 7Event Tree Illustrating Potential Pipe Rupture Scenarios Associated with Cut Slope FailuresFigure 8Flowchart for Cut Slope Instability Risk AssessmentFigure 9A

25、 Summary of the Combined Risk Assessment ApproachFigure 10Pipeline Construction on Side SlopesFigure 11Pipeline Construction along Narrow RidgesFigure 12Pipeline Construction on Steep SlopesFigure 13Securing the Pipeline on Narrow Ridge LinesFigure 14Earthworks on Mountain pipelines: Spoil Managemen

26、t StrategiesFigure 15Diversity of Restoration Works on Steep Slopes(Figure 2 and Figures 10 to 15 have been provided by BP).PLATESPlate 1Natural Terrain Landslides: Relative Landslide RiskPHOTOGRAPHSThe photographs are included in digital format on a CD at the end of this report.DRAWINGSAPreliminary

27、 Natural Terrain Landslide Risk Assessment Sheets 1 to 20AKey Map for Landslide Risk AreasATerrain Maps Sheets 1 to 9APreliminary Landslide Map of Areas Covered by the Terrain Maps Sheets 1 to 8Please note that all the drawings are reproduced in digital format on a CD included at the end of this rep

28、ort.EXECUTIVE SUMMARYThe proposed Guangdong LNG pipeline passes through approximately 60km of dissected, hilly terrain. These hills are particularly prone to landsliding because of the combination of long-term deep tropical weathering and the frequent high intensity rainstorms. The majority of these

29、 natural terrain landslides tend to occur within the weathered residual soils that mantle much of the terrain to depths of over 25m. As part of the November 2002 field visit we inspected around 30km of the most severe hilly terrain. Our observations during the visit have indicated that excavation of

30、 a 12m wide platform for the pipeline right-of-way is unlikely to expose indurated rock-like materials. As a result, the pipeline will be at risk from landslides that may occur within the weathered soils and rocks and overlying colluvium.Construction of the pipeline along the proposed alignment, whi

31、ch crosses significant lengths of sidelong ground, would require extensive cutting into the hillslopes to create a right-of-way platform. Failure of cut slopes also presents a significant hazard to the pipeline.The objective of the November 2002 field visit was to provide an indication of the nature

32、 and scale of the landslide risk to the proposed route (as of August 2002) and to advise on the options available for reducing these risks. The work presented in this Report provides an indication of the level of landslide risk that should be expected along the proposed route. A scenario has been as

33、sessed that considers the current route alignment with no landslide preventative measures or slope maintenance.The landslide risk reflects a combination of the threat presented by both natural terrain landslides and cut slope failures. These two issues have been considered separately in the Report.

34、Of particular note, the estimated risk associated with man-made cuttings can be higher than that resulting from natural terrain landslides. This is consistent with experience in neighbouring Hong Kong. Pipeline damage caused by landslides tends to involve catastrophic full-bore rupture.Our best esti

35、mate of the landslide-triggered rupture rate is in the range from 0.38 to 0.042 per year for the 300 km length of pipeline route. This is equivalent to 1.27 to 0.14 ruptures/1000km/year. Considering just the 60km total length of landslide prone (hilly) terrain, the equivalent figure becomes around 6

36、.4 to 0.7 ruptures/1000km/year.A number of options are available for managing the potential landslide problems, including:Adopting alignments that avoid sections where the pipe would be exposed to high levels of landslide risk i.e. avoid sidelong ground and steep-sided gullies or ravines;Ensuring th

37、at all cut slopes are designed, constructed and stabilised to a high standard. This option needs to be accompanied by a programme of on-going maintenance, repair and clean-up operations.A high standard of design and construction, including detailed stabilisation works for the cuttings, can probably

38、deliver significant risk reduction. However, it will be at a major cost and will require a long-term commitment to maintenance, repair and clean-up operations to ensure that when cut slope failures occur they are not allowed to deteriorate to a point where they can lead to pipe rupture. If these ope

39、rations are sub-standard or reduced, the landslide risk associated with cut slope failures would be increased.Experience has shown that the most cost-effective approach to reducing landslide risk is to adopt a routing strategy that minimises the necessity for construction on sidelong ground (side sl

40、opes) and crossings of steep catchments. Alternative routing can be based on the ridge and spur alignment principle and linking these lengths where necessary by running the pipe normal to the contours. The following approaches are needed to ensure the security of the pipeline along ridges and spurs:

41、Engineering the pipeline to isolate it from existing and potential landslide and erosion processes. The pipeline should be buried in a trench sufficiently deep to be within the bedrock and below the material subject to potential erosion or slope instability; or it should be protected by retaining st

42、ructures founded or anchored into such material.Construction must also be closely controlled to ensure that the environmental impact is minimised. Particular attention is needed to ensure that the operations do not lead to an increase in landsliding or erosion processes on the adjacent slopes.It is

43、recommended that the process of minimising landslide risks through the hilly sections of the route should involve the following steps:GDLNG-JEO and their contractors (CPPE) should undertake a further routing exercise that seeks to put the concepts presented in this report into practice. Revisions to

44、 the proposed route (as of August 2002) should be identified in the hilly sections that will help minimise the landslide risks.The accompanying set of 1:25,000 scale Terrain Maps, together with the aerial photographs, provide a basis for identifying potentially suitable ridge and spur alignments tha

45、t can be checked in the field.Costed comparisons should be made of alternative options, where appropriate. These costings should include the cost of long-term maintenance, repair and clean-up requirements along stretches of cut slopes, or the costs of securing the pipeline along ridge and spur align

46、ments.There should be an audit of the revised route, including a revised landslide risk assessment. This exercise could be desk-based, although some fieldwork might be necessary to resolve outstanding areas of concern.Although improved routing and careful construction practice can help ensure that t

47、he landslide risks are kept to a minimum, a level of residual landslide risk is the inevitable consequence of routing through hilly, landslide prone terrain. It is recommended, therefore, that an assessment of the residual landslide risk should be undertaken towards the end of the detailed engineeri

48、ng phase.Close geotechnical supervision must be provided during construction to ensure that:Previously identified landslides are avoided;The pipe is buried to sufficient depth in areas of shallow landsliding;Construction through areas of sidelong ground does not initiate new landslides or increase e

49、rosional processes.The sensitive nature of the terrain will present a number of other terrain issues that will need to be addressed as the project progresses and before the route can be finalised. These include:Areas of severe soil erosion hazard.Dynamic alluvial river channels within the floodplain

50、s and delta region.Flooding, either as a result of large river flows or tsunamis.The presence of geological faults and a history of earthquakes indicate a potential for ground rupture and liquefaction, and associated risk of pipe failure.1.INTRODUCTION1.1BackgroundIn March 2002 a reconnaissance terr

51、ain evaluation of the proposed Guangdong LNG pipeline routes (comprising a Trunkline, along with Eastern and Western Branchlines, see Figure 1) identified that significant lengths of the hill sections are routed across steep, sidelong ground. As a result, landsliding and the associated potential for

52、 pipeline rupture events were therefore reported as likely to be a major issue for the project (Reconnaissance Terrain Evaluation and Preliminary Landslide Risk Assessment; Atkins, 22 July 2002). The reconnaissance terrain evaluation concluded that:The combination of monsoonal tropical climate, deep

53、ly weathered rocks of different types and steep slopes generate a number of active surface processes that need to be taken into account in route selection, construction and operation within the mountainous and hilly parts of the landscape. These include:Widespread landslide activity and the associat

54、ed potential for pipeline rupture events. The preliminary landslide risk assessment (Atkins, 22 July 2002) extrapolated the data from studies in nearby Hong Kong (the Natural Terrain Landslide Inventory, NTLI, as reported by Evans and King, 1997; Evans et al., 1997; King 1997, 1999). The assessment

55、of the route was thus an as-if Hong Kong landslide scenario. Predicted landslide rupture rates were in the order of 2 to 20/1000km/year. These rates are up to 10 times the rates identified by BPs research for older pipelines in the Andes (i.e. pipelines built before routing studies were undertaken t

56、o avoid landslides and detailed attention was paid to earthworks and drainage management practices) (Figure 2).Areas of potential severe soil erosion hazard, especially if vegetation is removed prior to pipeline construction and spoil is side-tipped onto the slope during construction.The options ava

57、ilable to mitigate the risks are:Maintain the current route alignment and accept the high risk of pipeline rupture.Carry out detailed re-alignment studies to reduce the risk through upland areas by adopting “ridge and spine” or “ridge and spur” alignments.Even with re-alignment, the Guangdong enviro

58、nment is so dynamic that considerable earthworks and drainage management works will still be needed and unacceptable risks may still remain over certain sections.Future work to identify suitable “ridge and spine” or “ridge and spur” alignments through the mountainous and hilly areas should involveAe

59、rial photograph interpretation.Walk-over survey.1.2Subsequent Work on Landslide RiskFollowing the recommendations of the Reconnaissance Terrain Evaluation report (Atkins, 22 July 2002), a series of aerial photographs were flown covering the route and an adjacent corridor. Variable weather conditions

60、 prevented the whole route being flown in a single date and, as a result, batches of photographs became available at different times.A desk-based study of the landslide risk was undertaken in July 2002 and reported in Desk-based Study of Pipeline Routes, Atkins 6 August 2002. This study was based on