tANSPORT REMPACIK LABOWORY TITLE Indonesian s13pe inventory studies / J R Cookg P J Beaven and A Rachian 1-i/I -~7T Ch -19as ~r _,._.port ~ Lboratcery /, jo~home E ,-A l Jr! 11 -gdc mir by / 'n a %MY (
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X - COOK, J R, P J BEAVEN and A RACHLAN, 1992. Indonesian slope inventory studies. In: Proceedings of the Seventh REAAA Conference, Singapore, 22-26 June 1992. INDONESIAN SLOPE INVENTORY STUDIES J R Cook Geotechnical Specialist, Technical Assistance and Research Training Project, IRE, Indonesia P J Beaven Principal Scientific Officer, Transport and Road Research Laboratory United Kingdom Jr Alan Rachlan Geotechnical Division Head, IRE Indonesia ABSTRACT A slope stability research programme is currently being undertaken at the Institute of Road Engineering (IRE), Bandung. The fundamental practical objective of this programme is to develop further an understanding of the geotechnical performance of slopes. This paper outlines the initial research methodology which is based on the recovery of information from both stable and unstable slopes. The preliminary results of the IRE research is presented and discussed and examples of inventory data from Indonesia are used as an illustration of the practical usefulness of such work. 1.0 INTRODUCTION A slope stability research project is currently part of an IBRD funded Technical Assistance and Research Training Programme (TARP) being undertaken by TRRL- at the Institute of Road Engineering (IRE), Bandung. The main objective of this work is the establishment of geotechnical guidelines on the performance of natural and man-made slopes as it affects existing and proposed road links in Indonesia. The immediate objective of the current phase of work is to collate existing information on slope stability in Indonesia, to conduct pilot studies- into -slope inventory- methodologies-relevant to-Indonesian conditions and to examine the relationship between slope stability and terrain models. This paper outlines the work undertaken so far on the development of an Indonesian slope inventory methodology and presents data recovered from a recent survey of slopes collected as part of the design studies for a proposed toll road in West Java. 723 2.0 SLOPE INVENTORIES It became clear during the development phase of the TA~RP project that there was a need to assemble and collate basic information on Indonesian slopes. This information was available or obtainable in a number of forms: - -in existing technical reports - in existing slope inventories - as potential data from existing earthworks - as potential data from natural slopes/failures. The use of an inventory based methodology therefore seemed a logical means by which this information could best be utilised in the pursuit of the overall project objectives. As an initial step in the development of an Indonesian inventory methodology a brief review was made of the range of existing inventories and their relevance to the Indonesian situation. The types of data recovered from these inventories was examined and it was clear that the inventories varied widely in the slopes investigated, in the detail recovered and in their particular objectives. The methodology of approach was further influenced by the geological, geomorphological and climatic terrain in which the studies took place. A representative cross section of their data sets is presented as Table 1. From an examination of this previous work it was obvious that a clear understanding of the slope environment in combination with the project objectives was essential for the development of an effective IRE inventory methodology. 3.0 SLOPE STUDIES IN INDONESIA In general terms, slope instability in Indonesia has a very high significance with respect to the development of infrastructure in comparison to some other countries of S.E.Asia (Brand, 1984). The variety of slope instability environments stems from the large scale natural instability problem, resulting principally from a combination of volcanic activity, seismic activity and the tropical climate, combined with the growing need to utilise available land for agriculture and infrastructure (Jibson, 1988). Previous TRRLIIRE co-operation in slope stability research has extended over a period of ten years and has resulted in significant work being undertaken in the fields of natural slope instability processes, cut-slope monitoring and detailed investigations of particular situations (DP'MJ-TRRL, 1982; Heath et al, 1990). Some initial slope inventory studies were also undertaken in Java and Sumatera as part of this co-operation; information from this inventory work is included as reference 8 in Table 1. The utilisation of terrain evaluation techniques has also been part of the above research (Saroso et al, 1983) and the recently completed Land System mapping of Indonesia by Bakosurtanal was seen as providing a potentially powerful research tool for further slope work. Hence a major theme of the current TARP work is to relate existing slope-information in Indonesia to the. Land System mapping. TABLE 2: PRINCIPAL INDONESIAN SLOPE INSTABILITY SITUATIONS 1 active volcanic instability .2 large scale landslide instability 3 smaller scale natural slope erosion/development 4 cut-slope failure/degradation 5 embankment failure/degradation 6 combinations of 2 to 5; eg embankment on old landslide or landslide failure initiated by cutting. 724 TABLE 1 TYPICAL INVENTORY DATA SETS Recorded Inventory Reference Number Features 1 2 3 4 5 6 7 8 9 *1O II LOCATION Namne/number * District 99 Road chain. Map Co-ord ENVIRONMENTDrainage basin Geomorph./terrainHydrology 9* Land use Weather/rainfall SLOPE __ Material type 9 9 9* * * Material condition * Material structure Height above e/works Anple above c/works Slope type 9* Slope angle * ** Slope height 9* Slope %idth ** 9 Slope shape (Vertical) Slope shape (Horizontal) Cross profile VegetationFAILUREErosion9 999 9 Failure yes/no * Causes 99 Movement/ape ** Stability Thickness 9 Width9Total area9 Length9 9 Foot area Scarp Height9 Scarp angle RotationShear plane Cracking Debris volume Debris angle Damage 99 ENGINEERINGRoad description Existing measures 99 9 9 9 Proposed measures EffectsBenching9Drainage 9 99 GENERALNotes9 9 Photos 9 9 Sketches9 9 Desk studies Data sources 9 Investigations S Analysis Inventories 1 Carrara & Merenda 2MA-Dabbagh & Cripps 3 Heath 4 Perry 5 Anderson & Kemnp 631ICA -Phillipines 70Olarte et a] 8 DPMJ-TRRL 9CGSL(UK)10 Bulman 11 RGL (CPTR) 725 A general examination of stability affecting the existing road network revealed that slope instability should be considered as a number of related situations (Table 2). For the purposes of the project objective relating to slope performance and the road network, the study has not included item (1) from Table 2. To attempt to draw-up a single data recovery procedure to cover all the remaining situations would be cumbersome and impractical. The proposed approach was seen therefore as having to consist of a variable information collecting procedure allied to a flexible database. 4.0 THE PROPOSED TARP INVENTORY METHODOLOGY The first stage in development of the inventory methodology at IRE was to access the considerable amounts of slope information that were known to be available at the Institute. A desk study inventory was therefore initiated which first sought to identify data types and then to transfer the relevant information into a database. Figure 1 outlines the structure of this inventory. 1Access reports and enter Report Definition Report Definition Fields Report name Author Report type Ref. No. TARP Ref Subject Location Tech. content 1Slope data types Geotech. data types Illustrations Extract data from relevant reports after searching 1 ~~Report Definition file fEnter relevant data into Desk Study file Desk Study Fields Site No. Site name Road from Road to Chainage Link No. Eastings Northings Slope type Geology Material Land system Slope height Slope angle Failure Yes/No Failure type Report ref. Comment Data date Entry date FIGURE 1 TARP INITIAL DATA EXTRACTION PROCEDURE Previous TRRL/IRE joint research was the starting point for a data collection programme; this has now been extended to over 100 IRE reports concerning various aspects of slope stability. Preliminary data from this database, combined with information about other inventories and experience obtained from previous data gathering exercises in Indonesia, led to some basic project guidelines being drawn-up. 1 The proposed methodology should be built around a PC based database system capable of accommodating differing levels of information from a variety of sources and with different reliabilities. 2 It should be based on the existing infrastructure network and would include information on both stable and unstable slopes. 3 The procedures would be flexible enough to be adapted to variable project constraints in terms of time and manpower resources. 726 4 Field collection of data would be based on the completion of standard sheets designed and operated so as to reduce operator bias as much as possible. The current TARP inventory methodology is based round the definition of 'sites' ; the procedures for describing 'locations' within these sites is dependant on the nature of the relationship between the site and the locations. Site, for example, may consist of the following:- - single location, eg one large landslide - a group of locations, eg an area of instability - an existing road or section of road, eg earthwork inventory - a proposed road, eg, natural slope inventory. The data collecting procedures and field forms will be different for each major type of 'site' although the general principal of utilising such forms in conjunction with lists of standard options remains the same. Locations themselves may be either natural slopes, earthwork slopes or combinations of both; they are then also subdivided on the basis of being stable or having failed. The general data collecting procedure for the current database is outlined in Figure 2 and typical field forms are presented as Figure 3. FIGURE 2 OUTLINE TARP SLOPE INVENTORY PROCEDURE In the light of previous experience in Indonesia some data fields, not found in other similar inventories, were felt to be important. 727 SHEET 1 GENERAL DETAILS 1Province Isite Sie type Road from Road to Link No. Linki tc Chainage 1 Chainagc 2 Easting 1 Easting 2 Northing 1 Northing 2 T PO. m aps _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1G eology maPS -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ L S m op __ _ _ __ _ _ __ _ _ __ _ _ 1TerrainRainfall 1Date Comments SHEET 2 NATURAL SLOPE 1Province 1 Site No. [Location No. Sb51p type Chainage I Eastin ]Northing Geolog Land system 1 Slope angle I ISIope height Slop profilie Slope Facet 1Sbo ematerial ILand use Vegelation type 1Vegelation % Hydrolog Weather Sb ep condition Failure shce 1Earthworks Elwork sheets 1Photos 1 Sketches Inspectors 1 Date SHEET 3 EARTHWORK SLOPE .Province JSite No. Location No. ~~~Sb e typ e 1Chainsg eGcolo Lan~~~~~d system Overall angle Overall height Slope profile Slope plan Slope shape Slope length Road section Road profile Berm Nos. Bcrm widths ~Bench heights Bench angles 1Material]Structure 1 Favourability lUPSbope H 1 Upsiope angle D/slope H ID/slo cangle U/sbope condtn ID/slope condw n Drainage lEngineeringVegetation type 1Vegetation% Hydrabg 1Weather ISbo esheets 1jFa ibu.r.esheet lPhotos i Sket~ches Inspectors 1 Date Comments SHEET 4 FAILURE DETAILS lProvince %Site No. ILocation No. 1 Failure No. 1Chainage Fail tye Fail size Fail location Fail profile 8lscar H IB/scar angle Fail angle I IFai condition Fail causes Fail materials 1Dams e caused 1 Potential 1Remcdials 1 Effectiveness 1Photos 1 Skctches ' Ins ectors 1 Date 7 Comments FIGURE 3 .PRELIMINARY SLOPE-INVENTORY FIELD FORMS 728 Land system: the Bakosurtanial mapping units, to form part of the basic IRE research into the relationship between terrain and slope stability. Climate/weather; in recognition of the relationship between rainfall and slope failure in tropical environments. -.Land use; to study the relevance of land use, and in particular, irrigated crops on slope stability. This is seen as particularly important in large areas of Indonesia where irrigated rice growing (paddi) may influence slope performance. Vegetation cover: included to establish the importance of the correct vegetation, ic root pattern, on earthwork stability. 5.0 THE PRACTICAL APPLICATION OF SLOPE INVENTORY DATA ,During 1990 the Principal Author of this paper was involved in the Geotechnical Studies for the proposed Cikampek-Padalarang Toll Road (CPTR) in Java (R.GL, 1991). As part of this work a simple inventory was assembled of relevant slopes in the vicinity of the route corridor. The data sets for this inventory, involving both natural-and man-made slopes, are summarised as reference 11 in Table 1. SLOPEANGLE + Older volcanic profile M OB) ca Miocene mudstoneprofile( MDM) * a~~~~ Miocene claystone protile(MSC) 500 04 2O a a 120 0 1 jo~~~ 0 10 20 30 40 so 60 SLOPE H4EIGHT (M) Figure .* Slope Angles related to bedrock only The principal objective of this inventory was to assist in the outline design of cut-slopes for the CPTR. Very distinct slope angle patterns were obtained from differing bed-rock types (Figure 4). These patterns become more applicable to slope design when considered in conjunction with terrain. Figure 5 presents the slope/height plots for the low level hilly terrain at the northern end of the rouate. The inventory was put to practical use in the determination of likely cut-slope designs in this problem terrain by means of the following outline procedure: Ascertain typical maximum natural slope angles/height relationship. 2 Use standard slope charts (Bishop & Morgenstern or Hook & Bray) to establish a likely range of C and 0 values -assuming for this terrain a high water table and high rainfall (saturated conditions) with a Factor of Safety (F.O.S.) equal to 1. 3 Cross check these against index tests and the strictly limited strength testing. 729 4 Assume an improvement in drainage of. man-made- slopes together with a suitable F.O.S. and again use the standard charts and the crosschecked parameters to establish outline cut-slope designs. SLOPEANGLE SLOPE HEIGHT (M) Figure 5. Slope angles related to one terrain unit Table 4 summarises some of the results from this exercise, for the Miocene claysione soil profiles, which enabled reasonable outline slope designs to be derived. This was achieved without reliance on extensive laboratory testing which in this tropically weathered geotechnical environment would not have been cost-effective. TABLE 4: SUMMARY DATA FROM TYPICAL SLOPE DESIGN EXERCISE 6.0 SUMMARY The current slope research programme at IRE- is seeking to establish firmer guidelines on the engineering performance of Indonesian slopes. As a first step in this process an inventory of existing information is being assembled which will be related to available land system mapping. At the same time a methodology for collecting more slope data by inventory procedures has been drawn- up based on the recognition of the wide range of slope failure situations in Indonesia. This methodology is based around a microcomputer database using currently available commercial software. Data is being assembled by means of standard field forms designed to suit the relevant site and location situations. 730 0 6~~~~~~: Volcanic profile (QOS) ~~~0. ~~~~+ :~Claystone profile ( MSC) o: Volcanic/c laystone profile 30 ~ ~ ~ ~ 0 0~~~~~~~~ 0 200000 40so6 Natural Slope Derived C (kPa) Shear Box Results from limited H(m) Angles 0=15 0=20 near surface sam~ples 5 300 8 3 '15 -24" 10 130 8 3 C': 2.5 -10 kPa 15 100 7 2.5 Final Outline Design For Miocene Claystone cut-slopes; can be generally cut at 4.5h:1v with an adequate F.O.S. provided sufficient cut-off, face and toe drainage is installed. Slope inventories may be put to a number of research and practical engineering uses. A recent road investigation in West Java exemplified the practical uses by utilising a simple slope inventory as a cost effective aid to cut-slope design in a difficult geotechnical environment. 7.0 Acknowledgements The work described in this paper flormns part of the collaborative research project being undertaken by the Indonesian Institute of Road Engineering and the Transport and Road Research Laboratory (UK). This paper is published with the permission of the Chief Executive of TRRL- and the Director of IRE. The work described in Section 6.0 of this paper was supervised by the Principal Author while retained by Rendel Geotechnics Ltd who were commissioned by Rendel Palmer & Tritton, Consulting Engineers, to undertake-Geotechnical Studies for the Cikampek-Padalarang Toll Road Project. Crown Copyright. The views expressed in this paper are not necessarily those of the Department of Transport, UK. 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