Q n O l t - W ? MY1204093 THE USE OF GPR TECHNIQUE IN THE SLOPE STABILITY SURVEY AT RADAR DOPPLER TERMINAL, BUKIT TAMPOI, DENGKIL, SELANGOR Nurul Fairuz Diyana Binti Bahrudin2, Azmi Ismail, Amry Amin bin Abbas2 & Umar Hamzah1 ! Universiti Kebangsaan Malaysia 2Agensi Nuklear Malaysia Abstract A site investigation survey using GPR technique was carried out at Radar Doppler Terminal, Bukit Tampoi, Dengkil, Selangor. The Terminal is situated approximately 10 km to the North of Kuala Lumpur International Airport. Geologically, the study area is located in the Kenny Hill formation consisting of low grade metasedimentary rocks mainly of quarzitc and phyllite. A detailed geotechnical investigation at a cut slope of Kenny Hill formation in Selangor showed that the interbedded rock mass is dominated by relatively thick sandstone with thin shale of slightly to highly weathered materials. The objective of study is to investigate any fractured or weak zone in the study area using the GPR technique. In this survey, 100 MHz frequency antenna model RAMAC/GPR™ was used as a source to send the electromagnetic wave into the ground. A control unit (CUTI) was used in monitoring the antenna via a laptop, A total of 25 parallel and vertical lines with 3m-5m spacing between each line were traversed in the study area. The maximum subsurface depth investigated was approximately 12m. Reflected waves arrival between 0m to 5m depth in the radargram section shows discontinuous, subparallel and wavy patterns. These chaotic reflections patterns correspond to highly weathered silt with sandstone and gravel based on nearby borehole information as well as indicated by low SPT N-values of 0 to 13. For depth deeper than 5m, the reflection pattern is dominated by high frequency parallel waveform that could be associated with stiff mudstone of 28-34 SPT N-values. The radargram section also shows the presence of internal features in the metasedimcntary soils and rocks such as several small scale normal faults as well as sliding planes trending northwest-southeast in direction. Keywords: ground penetrating radar, site; investigation, sedimentary rocks, faults SURVEI KESTABILAN CERUN DENGAN TEKNIK GEORADAR DI STESEN RADAR KAJI CUACA , BUKIT TAMPOI, DENGKIL, SELANGOR Satu survei penyiasatan tapak menggunakan teknik georadar telah dijalankan di Stesen Radar Kaji Cuaca, Bukit Tampoi, Mukim Dengkil, Selangor, Terminal Radar Kaji Cuaca (Radar Doppler Terminal, TDR) dipasang di Bukit Tampoi, iaitu kira-kira 10 km ke utara Lapangan Terbang Antarabangsa Kuala Lumpur. Kawasan kajian tcrlctak dalam Formasi Bukit Kenny yang terdiri daripada batuan metasedimen iaitu kuarzit dan filit bergred metamorf rendah. Penyiasatan geoteknikal yang terperinci menunjukkan bahawa potongan cerun di Formasi Bukit Kenny di Selangor menujukkan perlapisan batuan yang didominasi oleh lapisan batu pasir yang tebal dengan lapisan syal yang nipis dan telah terluluhawa. Tujuan kajian ini adalah untuk mengenal pasti kedudukan kawasan rekahan, retakan dan zon Icmah. Teknik georadar menggunakan gelombang elektromagnet yang berfrekuensi 100 MHz yang di hantar dalam subpermukaan menggunakan antena model RAMAC/GPR™. Jumlah rentasan yang dilakukan di sekitar kawasan kajian adalah sebanyak 25 garis, dimana jarak antara setiap garis adalah 3m hingga 5m, Kedalaman penyiasatan iafah 12m. Berdasarkan rajah radagram, kedalaman 0m hingga 5m menunjukkan pantulan yang berbentuk putus-putus dan tidak lurus serta bcrgclombang. Bcrdasarkan data lubang gerudi, lapisan ini terdiri daripada batu lodak dengan bam pasir dengan sedikit kelikir. Lapisan ini dianggap terluluhawa tinggi dengan nilai SPT yang agak rendah; berjulat dari 0 hingga 13. Lapisan yang lebih dalam daripada 5m, menunjukkan pola pantulan yang lurus dan berfrekuensi tinggi dalam radargram georadar yang mewakili bam lodak keras (SPT 29 hingga 34). Radagram juga menunjukkan imej beberapa struktur dalam tanih dan batuan metasedimen seperti sesar normal kecil dan satah gelinciran beijurus kemiringan BL- TGA di beberapa garis rentasan. Katakunci: Radar penusukan bumi, penyiasatan tapak, batuan metasedimen, sesar INTRODUCTION Recently, various geophysical surveys were carried out in locating structures of landslide (Grasmueck 1996). Among these, the ground penetrating radar (GPR) and the electrical imaging techniques are frequently used in such investigation (Imai et al. 1987). Stevens et al. (1995) applied GPR technique in the Canadian Nuclear Fuel Waste Management Program to map structural features in granite and gneissic rock of the Canadian Shield as well as mapping the features in the tunnel and boreholes. In China, this technique has been applied in civil engineering exercises especially in the geotechnical aspects (Kong & By 1995). The GPR technique has proven to be very useful in solving engineering geological problems and detecting buried object in the ground especially faults and cavities (Benson 1995). Tn this study, the GPR technique was used to investigate fractured or weak zone in the meta-scdimentary soils and rocks. This study is part of a slope stability detailed investigation by IKRAM (2007) as appointed by the Malaysian Public Work Department after the incident of uncontrolled earthwork near the terminal which caused public awareness on the stability of the slope. LOCAL GEOLOGY According to IKRAM (2007), the study area is located in the Kenny Hill formation consisting of highly weathered outcrop of sandstone and mudstone. Thick Quaternary layers are deposited on the bedrock consisting of inter-bedded shale, mudstone and sandstone. This meta-sedimentary rock formation is of Upper Silurian to Devonian in age. Figure 1 and 2 show the map and the geological cross section of the study area while figure 3 shows the locality of the GPR traversing lines in the study area. According to Mohamed et al. (2004), the Kenny Hill formation consists of low grade metamorphic sandstone and shale known as quartzite and phyllite. Detailed geotechnical investigation at a Kenny Hill formation cut slope in Selangor showed that the inter-bedded rock mass is dominated by a relatively thick sandstone with thin shale of slightly to highly weathered in properties (Rosly 1980). Legend 7 n i —---- ------ " Road 2 ----- ----- - Rivec 3 ---------- - Geological boundary 4 Fault Sinclii) 5 ......... ■ m Description Formation Age Alfaviura- Marine and continental deposit Q uartem aiy □ • clay, silt, sand, peat and gravel L ........... SKD1MI.M UOf. ■ H H I Phylhe, slate, shale and sandstone; argillaceous Kenny Hill Middle Perm H i rocks. Locally prominent development Formation of limestone. Hawthordan ■ Schist with phylite in lamina Forrsatsola Middle Upper Silurian Figure 1: Geological map of study area Source: Laporan Analisis Kestabilan Cerun Bagi Stesen Radar di Bukit Tampoi, Dengkil oleh Institut Keija Raya Malaysia (2007) o o o CN a & & 03 ’P? <U o .£3<D 33 a 0 tcd H 1as a : 1 m : • Q Tc3 3 C* a Geological Cross Section At Bukit Tampoi, Dengkil <D ■p §!§ . <i> O Ilf <4h a > 0 § *c E l l 1 j a iai S b u* r i l i <1> (D PIp f 1 (ui) jq g p H J> S s a O §■ CN T"! i—te 8Jh S/iJ o3 Ph C A M ir, • ^ r*l f M CN r-jCN --------------------------------i 1 i 5. J V J ^ 1 . ____________ V™-111««i 11M«„i«in« ™111 iiLi.. ’"—__ _ 'T V." l — 1 > | .#................ ..... _ _ mm ms7 W * CN ... | m ■ ■ ' - ^ ■ j V ..... %­ ..... > £ < - o , Figure Figure 3: Locality map THEORY GERORADAR Ground Penetrating Radar (GPR) is one of the geophysical techniques basically utilizing electromagnetic wave as a source of input energy in investigating the physical properties of shallow earth materials. Recently, it is widely applied in solving problems encountered in civil engineering and geotcchnical disciplines especially in detecting and characterizing the subsurface structures. The GPR technique which was first introduced in 1937 is basically consisting of a portable device that produces high resolution image of any structure below the surface (Davis & Annan, 1989). Its use has now being extended into the application of environmental, geotechnical, and archaeological aspects especially in exploring the related features as given in table 1. Field Aplication Environmental Mapping of hazardous waste Mapping of underground storage tanks, Study of sedimentology, Bathymetry Geotechnical Stratigraphy mapping of sinkhole and cavity area Groundwater investigation, localizing the weak and fractured zone. Details study in tunnels and dams Archeology Mapping archeology features Table 1: The application of GPR This technique uses transmitter and receiver mounted at a fixed position in a box as. antenna (Figure 4). When an electromagnetic wave is transmitted into the ground, at any boundary separating two different media with different dielectric constants (£ ), part of the incoming or incident waves are reflected back to the surface with amplitudes proportional to the reflection coefficient. as calculated by <J — —s 2------- ~ e \ e2 +£] According to Mohamad Pauzi et al. (2004), the remaining waves will penetrate further down into the subsurface materials. Basically, this technique is similar to the seismic reflection and sonar in principle. An electromagnetic wave will be radiated into the ground via a transmitter antenna. When the radiated wave encounters different medium, part of the wave is reflected back to the antenna and part of it will be transmitted into the ground. The reflected waves will be recorded and saved by the receiver antenna as raw data. Tx: Transmitter antenna Rx: Receiver antenna Figure