Failures at slope cuts in clastic sedimentary bedrock in Malaysia


Author : J.K. RajPublication : Bulletin of the Geological Society of MalaysiaVolume : 48Page : 25-29Year : 2004


Description

Bulletin of the Geological Society of Malaysia, Volume 48, June 2004, pp. 25-29

 

Failures at slope cuts in clastic sedimentary bedrock in Malaysia

J.K. RAJ

Department of Geology, University of Malaya, 50603 Kuala Lumpur

 

Abstract: Interbedded sandstones, siltstones and shales are the dominant clastic sedimentary rocks of Malaysia and are exposed at slope cuts where an upper Zone I (residual soil) of completely weathered bedrock modified by pedological processes is seen. Zone I is up to 6 m thick and overlies the in situ, slightly to completely weathered bedrock of Zone II that preserves the minerals, textures and structures of the original strata; the degree of preservation increasing with depth. Low cuts and the top benches of high cuts in undulating to hilly and mountainous terrain expose Zone I and have experienced small earth falls and shallow slips during periods of continuous daily rainfall. Where the cuts intersect unconfined groundwater tables, slumps and compound slides are observed. In hilly to mountainous terrain, the lower benches of high cuts (> 10m high) expose Zone II and have experienced small to large, block and slab slides as well as wedge failures, during periods of continuous daily rainfall. At some very steep benches exposing indurated (hard) bedrock, toppling failures and rock falls have sometimes occurred during rainfall. Design of slope cuts in clastic sedimentary bedrock in Malaysia thus needs to take into consideration their geometry, topographic setting, exposed lithologies and structural discontinuity planes as well as weathering and rainfall patterns.

 

Abstrak: Batuan sedimen klastik utama di Malaysia adalah batupasir yang saling berlapis dengan batulodak dan syal. Batuan tersebut terdedah di cerun-cerun potongan di mana satu lapisan permukaan terdiri daripada batuan terluhuhawa sepenuhnya dapat dibezakan (Zon I - tanah baki). Zon I mempunyai ketebalan sampai 6 m dan menindih Zon II yang dicirikan oleh batuan terluluhawa secara in situ dengan mineral, tekstur dan struktur batuan asal. Di kawasan beralun sehingga bukit, cerun potongan rendah, dan bench atas cerun tinggi mendedahkan Zon I dan telah mengalami jatuhan tanah dan gelinciran cetek semasa tempoh hujan. Di mana cerun potongan merentasi air tanah tak terbatas, nendatan dan luncuran kompleks telah berlaku. Di kawasan berbukit, bench bawah cerun tinggi mendedahkan Zon II dan telah mengalami luncuran blok dan slab yang kecil ke besar dan kegagalan baji semasa tempoh hujan. Di cerun potongan curam yang mendedahkan batuan sedimen keras, kegagalan terbalik dan jatuhan batuan telah berlaku semasa hujan. Rekabentuk cerun potongan di kawasan batuan sedimen klastik di Malaysia perlu mengambil kira geometri, keadaan topografi, jenis litologi dan satah ketakselanjaran batuan, serta corak peluluhawaaan dan hujan.

https://doi.org/10.7186/bgsm48200406