1,000,000. Geological Survey of Vietnam. Geological map of Cambodia, by bfk20410

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									               Power System Planning Study in the MM, Lao PDR                                                       Final Report

I              Asian Development Bank T.A. No. 2583-LAO




I                                                   CHAPTER 7 : ENGINEERING GEOLOGY

I
               7.1             SOURCES OF INFORMATION
I                              The assessment of engineering geological conditions at project sites has been based on the
                               following sources of information:

I                               a          Topographic Maps:
                                           -         1:50,000: produced by the US A m y Map Service from 1963 to 1967. A
I                                                    20 metre contour interval is given where aerial photography coverage and
                                                     ground control was sufficient. Some sheets are no longer available.
                                           -
I                                                    1:100,000: compiled from 1975 by the Lao PDR National Mapping
                                                     Organisation with assistance from Russia and based on more recent aerial
                                                     photography. The contour interval of 40 m increases in frequency to 20 m

I                                                    in flatter areas.
                                           The maps were obtained from the National Geographic Department, Vientiane, Lao
                                           PDR.
I                                          It should be noted that the mapping projections and grid system of the two map
                                           series differ.
I                               a          Geological Maps:
                                           The following geological maps were made available:
I                                          -         1 :200,000. Geological Maps from Department of Geology & Mines, MIH.
                                                     (maps: F-48 XXXII, XXVII, 111, E-48 I1 and Vientiane area map). (For
I                                          -
                                                     reference only at the library of the Department of Geology & Mines, MIH)
                                                     1 :250,000Photogeological Maps of Northern Lao. Institute of Geological
                                                     Sciences, London. 1971-73.
I                                          -         1:500,000. Geographic Service of Vietnam. 1961. (maps: 4W, 4E, l l E ,
                                                     14W, 14E).
I                                          -         1: 1,000,000. Geological Survey of Vietnam. Geological map of Cambodia,
                                                     Laos and Vietnam. lstedition, Hanoi 1988.

I                                          -         1 :1,000,OOO. Mineral exploration & development plan, Lao PDR
                                                     1990 - 91. British Geological Survey / Department of Geology & Mines,
                                                     MIH. (For reference only at the library of the Department of Geology &
I                                                    Mines, MIH)
                                8          Previous reports/documentsfrom schemes in vicinity:
I                                          A number of previously published reports detailing hydroelectric studies in the
                                           vicinity of the potential projects considered under this Study were reviewed and are
                                           individually referenced in the Project Portfolio Report.
I                                          In addition, a number of continuing hydroelectric studies were being carried out by
                                           others in parallel with this Study and unpublished site specific.. geological
I                                          information was obtained and is referred to where appropriate in the Project
                                           Portfolio Report.


I
v:\repom\lI189\r10896\chapur7.Wp5(13january 1998)                              7- 1                             - Piesold
                                                                                                                Knight
                 Power System Planning Study in the MM, Lao PDR                                                                                         Final Report
                 Asian Development Bank T.A. NO. 2583-LAO




I                                                                                                                      Chapter 7 :Engineering Geology

1                                               Aerial Photographs:

I                                               1:30,000 scale photographs were obtained from the National Geographic
                                                Department, Vientiane, Lao PDR. These photographs where largely used for
                                                generation of the 1:100,000 topographic map series.

I                                               Seismic Event Data:
                                                A database detailing the location and magnitude of all recorded earthquake events
I                                               between 1900 and 1995 in Lao and surrounding regions was obtained from the
                                                International Seismological Centre, Berkshire, U.K.
                                                Site Inspection.
I                                               For the more attractive project sites (Refer to Chapter 4, Section 4.2), the
                                                identificationof the principal geological features was achieved through the following
I                                               activities:
                                                -        review of the data detailed above.
                                                -        overflying the site by helicopter.
I                                                        site visit and inspection (where accessible).
                                                The activities undertaken for the geotechnical review for each site are detailed in
I                                               Section 3 of the project workbooks for the various selected projects, as set out in
                                                the Project Portfolio Report.

I                7.2
                 7.2.1
                                   REGIONAL GEOLOGY
                                   Lithology and Stratigraphy

I                                  A summary of the varied lithological sequences found in Lao is given in Table 7.1 and 7.2
                                   below.


I                                                                Age
                                                             Precambrian
                                                                                                                              Description
                                                                                                      acid gneiss, arnphibolite.
                                                             Cambrian to Lower Devonian               schists, sandstone, shales, limestone, mark.

I                                        Palaeozoic
                                                             Silurian to Upper Devonian
                                                             Carboniferous
                                                                                                      shales, sandstones, siltstone, limestone, chert, schist.
                                                                                                      limestones, coal bearing formations.
                                                             Carboniferous to Permian                 Limestone.
I                                                            Permian
                                                             Permian to Triassic
                                                                                                      volcano-terrigenous, carbonates.
                                                                                                      volcanics.

I                                  I
                                   I
                                   I
                                                         I
                                                         k
                                                         I
                                                             Lower to Middle Triassic

                                                                 ~
                                                                     e Triassic
                                                                                       ~   ~
                                                                                                  I
                                                                                                      marine arenaceous & argillaceous sediments, volcanics.
                                                                                                            ~   ~~
                                                                                                                            -
                                                                                                                                   ~~




                                                                                               T o n g l o m e r a t e s , volcanics, siltstone, marl, limestone.
                                                                                                                                                                    I
                                                                                                                                                                    I
                                                                                                                                                                    I
                                                             Upper Triassic                           coal bearing sediments, limestone, marl, shale.

I
                                          Mesozoic
                                                             Lower to Middle Jurassic                continental siltstones, claystones & marine shales,
                                                                                                   I
                                                                                                     conglomerates, gritstones, sandstones.
                                                                                                        -             -                                             I
                                   I                     I
                                   I                                                              I red continental sandstones, siltstones, conglomerate.           I
                                                                              ~~                                                        ~   ~~




                                                         E _ _ r Jurassic to Cretaceous
I                                  I
                                   I                     I Upper Cretaceous        ~




                                                             Neogene to Lower Quaternary
                                                                                                  I Evaporites, siltstones, sandstones.
                                                                                                      conglomerates, gritstone, siltstone, claystone, basalts.
                                                                                                                                                                    I
                                                                                                                                                                    I
                                          Cainozoic

I                                                            Quaternary                               fluvial boulders, gravels, sands, silts. Basalis.

                                                                     Table 7.1: Lao PDR Lithological Sequence.


v:\repons\I I 189\r108%\chapptcr7.Wp5(13 januaty 1998)                                                7-2                                         - Piesold
                                                                                                                                                  Knight
                Power System Planning Study in the MM. Lao PDR                                                                             Final Report
I               Asian Development Bank T.A. No. 2583-LAO




I                                                                                                            Chapter 7 :Engineering Geology

I
                                                                                                         DescriDtion

1                                I &G        to Middle Palaeozoic      Widespread medium to coarse grained porphyry granites.
                                                                       - small. variable intrusions of diorite, granodiorite and granite composition.

1                                      Late Palaeozoic to early
                                              Mesozoic
                                                                       - medium to tine grained subvolcanic microgranites, granosienites, aplites,
                                                                       pegmatites, larnprophyres.

                                                                       - melanocratic eranites. eamet eranites. aolites, uegmatites.
I                                                              Table 7.2: Lao PDR Igneous Intrusive Rocks.

I               7.2.2             Geological Structure

                                  The principle structural zones found within Lao PDR are summarised in Table 7.3.
I                                          Age                Structural Zone                                 Description


I                                I
                                       Precambrian

                                     Early Palaeozoic
                                                          Baicanian

                                                        ICaledonian
                                                                                  Strongly folded metamorphic basement rocks found on the
                                                                                  Lao - Myanmar border. Largely intruded by granite.
                                                                                -1Folded volcano sedimentary formations in the Sekong area              I
                                 I                      I Hercinian             INorth west trending folds in central Vietnam, central & east Lao. I
I                                        Palaeozoic
                                     Late Permian to
                                      Early Triassic
                                                          ~




                                                         Indosinian
                                                                                     ~~




                                                                                  Extensive north north east trending folds in north west Lao.



I                                      Upper Mesozoic to Cainozoic fold
                                                 structures
                                                                                  Folding of Upper Mesozoic sedimentary and evaporitic deposits in
                                                                                  the Vientiane & Savanakhet basins. More intense tectonic
                                                                                  structures in the Boloven basin associated with volcanic activity.


I
                7.3               ENGINEERING GEOLOGY OF PROJECT COMPONENTS AND CONSTRUCTION

I                                 MATERIALS
                                  Detailed geological or geotechnical information specific to the project areas was not

I                                 available. Therefore identification of the principal geological features at the each site was
                                  by visual inspection (where accessible), overflying by helicopter and from a review of the
                                  data detailed above.

I                                 The assessment of the geological conditions at each site was based on assumptions regarding
                                  the engineering properties of the expected materials and experience of comparable geological

I                                 conditions that have been studied in detail elsewhere.

                                  Where possible the material strengths, geotechnical properties and rock mass characteristics
                                  have been estimated from visual observations and engineering judgment and used to
i                                 formulate an overall assessment of site conditions consistent with standard international
                                  practice.

I                                 Based on these assumptions, an appraisal has been made of the nature of foundation
                                  materials at the darddiversion weir sites, expected tunnelling conditions, power station
                                  foundations, slope stability criteria, reservoir leakage potential and location and suitability
I                                 of construction materials.


I
v:\reports\I 1189\r10896\chapter7.Wp5(l3 jammy 1998)                                        7-3                                        KniPht Resold
                 Power System Planning Study in the M M ,Lao PDR
I                Asian Development Bank T.A. No. 2583-LAO
                                                                                                                   Final Report




I                                                                                          Chapter 7 :Engineering Geology

1                                For each project, the conclusions of the geological assessment are detailed in the Project
                                 Portfolio Report.
I                                Given the conjectural nature of the geological assessment, the conclusions are to be regarded
                                 as tentative. However, it is considered that the approach adopted is entirely consistent with
I                                the objectives of the present level of project evaluation.

                                 Considerable investigative effort will be required to confirm these preliminary conclusions

I               7.4
                                 at any subsequent stages of study for the selected projects.

                                 MINERAL RESOURCES

I                                In order to determine the likelihood of there being significant mineral resources in the
                                 vicinity of the projects under study, discussions were held with representatives of the

I                                Department of Geology & Mines (DGM) of the Ministry of Industry and Handicraft at their
                                 office in Vientiane.

                                 With the assistance of the DGM geologists, reference was made to an unpublished
I                                1:1,000,000 plan detailing areas where the Ministry has issued Memoranda of
                                 Understanding (MoU) to potential developers for exploration and exploitation of mineral
                                 resources.
I                                Details of the proximity of mineral exploratiodexploitation MoU’s to the various projects
                                 are given in the Project Portfolio Report.
I               7.5              SEISMIC HAZARD

I                                In order to make a preliminary assessment of the likelihood of there being a significant
                                 seismic hazard at the project locations, reference was made to a seismic event database
                                 obtained from the International Seismological Centre, Berkshire, U.K.

I                                The database gives details of the location and magnitude of all recorded earthquake events
                                 between 1900 and 1995 in Lao and surrounding regions. An event distribution plot of the

I                                database is given in Figure 7.1.

                                 No specific seismic hazard assessment or attenuation relationship has been derived for Lao

I                                PDR. Much of the country is generally aseismic. However the northern regions, and those
                                 bordering more active zones in Vietnam, Southern China and Myanmar exhibit a greater
                                 frequency of earthquake occurrence.

I                                For each project under consideration, the relative influence of each recorded event at the
                                 project site was determined by applying a range of the more commonly used attenuation
                                 relationships. From this, the most significant event was determined and is detailed in the
i                                Project Portfolio Report. Whilst this exercise does not represent a seismic hazard analysis,
                                 it indicates that projects in the north of the country are situated closer to potential
                                 seismogenic sources and in an area with a higher earthquake recurrence rate.
I                                Whilst many of the project structures proposed in this Study are relatively small and
                                 therefore their susceptibility to the expected ground movements would be- low, it is
I                                recommended that a more detailed seismic hazard appraisal be undertaken during any
                                 subsequent stages of study for the selected projects.

I
v:\reports\lI189\r108%\chapter7.W~(l3 january 1998)                          7-4                               - Piesold
                                                                                                               Knight
                Power System Planning Study in the MM, Lao PDR                                                     Final Report
                Asian Development Bank T.A. No. 2583-LAO




                                                                                           Chapter 7 :Engineering Geology


                                In addition, the construction of a number of large hydro electric schemes are proposed in
                                many of the lower river basins in Lao and it is recommended that the effect of induced
                                seismicity from the these large reservoirs be considered where appropriate.

                7.6             FURTHER INVESTIGATION
                                Recommendations for investigation at each of the selected projects to confirm the
                                conclusions of this Study are given in the Project Portfolio Report. In addition, a number
                                of geological features requiring specific attention during subsequent stages of study are also
                                identified.




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v:\reports\ll189\r10896\chap(cr7.Wp5(13                                      7-5                               - Piisold
                                                                                                               Knight

								
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