M. M. Nordiana

Imaging Subsurface Characterization at Bukit Bunuh Using 2D Resistivity Method: The Effectiveness of Enhancing Horizontal Resolution (EHR) Technique

2D resistivity method is an indirect method to the shallow subsurface survey for maintaining the geo-environment. It is used to measure the apparent resistivity of subsurface. This study was conducted at Bukit Bunuh, Perak (Malaysia), where EHR resistivity technique was developed in order to get detail and deeper penetration for shallow subsurface study. The survey line for EHR technique was executed in West-East direction while South-North direction was covered without EHR technique. The 2D resistivity results were compared between the survey line, with and without EHR technique. The survey used Pole-dipole array with 5 m minimum electrode spacing. The results show the first zone with resistivity value of 10-800 ohm-m and thickness 5-60 m as alluvium consisting of boulders (weathered granite) with resistivity value of >6000 ohm-m. The second zone with resistivity value >20 000 ohm-m was granitic bedrock. The penetration depth for 2D resistivity without EHR technique is 70m and with EHR techniques is 140m with 5m electrode spacing.

2-D Electrical Resistivity Tomography (ERT) Assessment of Ground Failure in Urban Area

This study was carried out to assess the foundation defects around an urban area in Selangor, Malaysia using 2-D electrical resistivity tomography (ERT). The affected structure is a three storey houses and having severe foundation-based cracks. Six 2-D ERT survey lines with 5 m minimum electrode spacing using Pole-dipole array were executed parallel to buildings wall. Four boreholes were conducted to identify the depth to competent layer to verify the 2-D ERT results. Inversion model of 2-D resistivity show that the study area consists of two main zones. The first zone is a low resistivity value (<100 Ωm), which appears to be a zone that is fully saturated with sandy silt and this could be an influence factor the increasing water level because sandy silt is highly permeable in nature and alluvium (silt, sand and clay), boulder (1200-3500 Ωm) or highly weathered with the resistivity values of 100-1000 Ωm at 20-70 m depth. The second zone is the granite bedrock of more than 3500 Ωm with depth greater than 70 m. These results were complimented and confirmed by borehole records. The ERT and borehole record suggest that the clay, sand, saturated zone, highly weathered zone and boulders at foundation depths may lead to ground movements which affected the stability of the building.

Buried Man-made Structure Imaging using 2-D Resistivity Inversion

This study is carried out with the objective to determine the suitable resistivity inversion method for buried man-made structure (bunker). This study was carried out with two stages. The first stage is suitable array determination using 2-D computerized modeling method. One suitable array is used for the infield resistivity survey to determine the dimension and location of the target. The 2-D resistivity inversion results showed that robust inversion method is suitable to resolve the top and bottom part of the buried bunker as target. In addition, the dimension of the buried bunker is successfully determined with height of 7 m and length of 20 m. The location of this target is located at -10 m until 10 m of the infield resistivity survey line. The 2-D resistivity inversion results obtained in this study showed that the parameters selection is important in order to give the optimum results. These parameters are array type, survey geometry and inversion method used in data processing.

Geological Structures Mapping of Bukit Bunuh using 2-D Resistivity Imaging Method

The geological area of Bukit Bunuh is very complex due to the meteorite impact that has occurred millions years ago at Lenggong, Perak. The lithology of the study area consists of alluvium, tephra dust, and granitic rock. The geological contact, fault and fracture zone were found at the study area may indicate the geological process that undergoes at a place locally or regionally. These important features have led to the further research on 2-D resistivity imaging method (2-D RIM) to study the geological features. This method can provide the subsurface image that will delineate the geological structures. The surveys include three separate lines of different length which depend on the accessibility. The surveys were done by using Pole-Dipole array and 10 m of electrodes spacing. The objectives of this research are to determine the subsurface geological contact and to determine the existence of fault/fracture zones at the contact zone. The results from 2-D inversion profiles have successfully signified the types of geological structural such as fault, contact, and fractures. Hence, the results from 2-D RIM were used to draw the geological lineaments of Bukit Bunuh. The discontinuity of the lineaments may indicate the structures present.

Slope failures evaluation and landslides investigation using 2-D resistivity method

Abstract Slope failure is a complex phenomenon that may caused to landslides. Buildings and infrastructure such as transportation facilities and pipelines located within the boundaries of a landslide can be damaged or destroyed. Slope failure classification and various factors contributing to the instability using 2-D resistivity survey conducted in Selangor, Malaysia are described. Six 2-D resistivity survey lines with 5 m minimum electrode spacing using Pole-dipole array were performed. The data were processed using Res2Dinv and surfer10 software to evaluate the subsurface characteristics. The 2-D resistivity results show that the subsurface consist of two main zones. The first zone was alluvium or highly weathered with resistivity value of 100–1000 Ω m and depth of >30 m. This zone consists of saturated area with resistivity value of 1–100 Ω m and boulders with resistivity value of 1200–7000 Ω m. The second zone with resistivity value of >7000 Ω m was interpreted as granitic bedrock. The study area was characterized by saturated zones, highly weathered zone, highly contain of sand and boulders that will trigger slope failure in the survey area. This will cause to low strength of soil, debris flow and movement of earth. On the basis of the case examples described, 2-D resistivity method is categorized into desirable and useful method in determination of slope failure and future assessments.

3-D Resistivity Imaging on Archaeology Characterization at Sungai Batu area in Kedah, Malaysia

Electrical Resistivity Imaging (ERI) was conducted at the archaeological site of Sungai Batu, Lembah Bujang in Kedah, Malaysia and it is located between Gunung Jerai in the North and Muda River in the South, Kuala Muda, Kedah. This paper presents the geophysical results that aimed to identify the characterization at Sungai Batu, Kedah. ERI survey was performed at plot SB2ZZ, Sungai Batu with total of 15 survey lines using pole-dipole array with electrode spacing of 0.75 m. The ERI results were then processed with Res2DInv and Res3Dinv softwares. Resistivity contrast shows good variation to correlate well with lithology of the earth materials. To enhance the results, data were visualized using isosurface resistivity surface. The ERI shows interesting anomaly with resistivity of 400 - 500 Ωm varies from 0.34 – 1.17 m and few spotted anomalies detected at deeper depth which varies from 2 m - 4 m. Based on-site calibration at partly exhumed sites, anomalies were interpreted as baked clay bricks. The results obtained in this study area gives reliable interpretation for archaeological interest.

Correlation between Resistivity and Ground Penetrating Radar (GPR) Methods in Understanding the Signatures in Detecting Cavities

The research was conducted using Resistivity and Ground Penetrating Radar (GPR) methods in detecting in-filled cavities and air-filled cavities. The importance of this study is to see the difference in conductivity value of the in-filled and air-filled cavity. The first study location in which the known target is air-cavity located at School of Language, Literacies, and Translation (SoLLAT). The next study location is at Desasiswa Bakti Permai, which the known target is a bunker with both were located at Universiti Sains Malaysia, Penang and the last location is at Gua Musang, Kelantan with suspected in-filled cavity. The result from Gua Musang is compared with both of the results that have been done at Universiti Sains Malaysia. The resistivity value of the first location that indicates the possible tunnel is about 500 Ωm to 800 Ωm and the conductivity value is about 0.0017 S/m. The resistivity value for the second location located at Desasiswa Bakti Permai that indicates the bunker is about 50 Ωm to 250 Ωm and the conductivity value is about 0.1104 S/m. The resistivity value from Gua Musang is about 50 Ωm to 100 Ωm and the conductivity value is about 0.0101 S/m. The velocity of the in-filled cavities is much lower compared with the velocity of the air-filled cavities. Based on the characteristics, Gua Musang area was dominated with in-filled cavities.

Application of 2-D Resistivity Imaging and Seismic Refraction Method in Identifying the Structural Geological Contact of Sedimentary Lithologies

The interest of this study was to prove the existence of geological contact to field models with presences of outcrops as references. The physical relief of the outcrops can be determined by geological events of faulting, fracture, and folding. Geological contact plays important roles in environmental studies. 2-D resistivity imaging is the best method used for identifying the geological structures of study area located in Guar Jentik, Perlis and Bukit Kukus, Kedah. Besides that, seismic refraction method also applied at the study area. Results from both methods were integrated to get data correlation. There is good correlation produced which have successfully proved the existence of the faults and contact zones in study areas. Resistivity result shows that first study area has two main zones, red mudstone with resistivity value of 1 Ωm – 100 Ωm, sandstone with resistivity value of 2000 Ωm – 9000 Ωm, and Seismic refraction has provided the result on velocity of each zone, mudstone zone is 200 m/s -1800 m/s and sandstone zone is >2000 m/s. The geological contact of fault is determined between the red mudstone zone and sandstone zone. In the second study area, the fracture was found within chert zone and contact zone is located between the chert zone and mudstone zone. In addition, the fold is found to form in the chert zone. Mudstone zone has resistivity value of 1 Ωm – 1500 m/s and chert zone has resistivity value of 2600 Ωm – 35000 Ωm. The first layer of the seismic section is consisting of mudstone with a velocity of 1200 m/s is interpreted as chert zones.

Integration of Ground Penetrating Radar (GPR) and 2-D Resistivity Imaging methods for soil investigation

Rock lithology influences the electrical properties representing soils or rocks. Electrical conductivity value can be measured using geophysical methods like Ground Penetrating Radar (GPR) and 2-D resistivity imaging. The objective of this survey is to integrate GPR, 2-D resistivity imaging and borehole log based on the conductivity value with soil description and N-value from borehole. Borehole is conducted in the middle of the survey line at a distance of 20 m. GPR method used 250 MHz frequency antenna. The result was filtered using Band Pass, Time Varying Gain and DC removal. 2-D resistivity imaging used two arrays; Wenner-Schlumberger and pole-dipole with total distance of 40 m and 1 m minimum electrode spacing using ABEM SAS4000. The results of both arrays are represented in the form of inversion models. Electrical conductivity values for GPR are calculated based on the conductivity values obtained by 2-D resistivity imaging. The conductivity values calculated from GPR are in good agreement with the values from 2-D resistivity imaging method. Electrical conductivity for the top soil is 0.7 – 3.0 mS/m with no soil description and N-value due to imprecise sample of the loose soil condition. The results showed that soil composed of loose silty gravel with some sand at the depth of 1.81 – 2.99 m has higher value of conductivity (0.4 – 3.0 mS/m) while soil dominated by very stiff sandy silt with some rock fragment (gravel) at the depth of 3 – 3.5 m has lower conductivity values of 0.4 mS/m to 0.7 mS/m. Soil having low electrical conductivity is probably due to the stiff condition (minimum water content) confirmed by greater N-value. Integration of geophysical methods and geotechnical method is a success and the geophysical parameters can be used in understanding soil condition.

Evaluation of Semanggol Formation (Permian Facies) Using Electrical Resistivity Tomography and Seismic Refraction Tomography Parameter

Outcrop studies are a fascinating part of geology as it evidently shows the aftermath of how the earth forming processes billion years ago. Outcrops do not cover majority of the Earths land surface as it is covered by soils or vegetation thus cannot be seen clearly. In Kedah, Malaysia, there are many outcrops exposed in the state. The aim of this research studies was to correlate the parameters of geophysical survey with the properties of the Permian facies of Semanggol Formation in Kedah. The Permian facies consists of bedded chert and claystone. Two geophysical technique, electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) were applied at the same line on top of the outcrop at Bukit Kukus beside Kulim – Baling (Kedah) road. The arrays used for ERT are Pole–dipole and Wenner–Schlumberger. The spacing between electrodes for ERT is 1.5 m while the geophone spacing for SRT is 2 m. Both ERT and SRT line is 60 m and 46 m respectively. Based on the results of both geophysical techniques, relating the porosity and permeability (poroperm) with geophysical parameters, it can be concluded that the bedded chert of low poroperm having seismic velocity and resistivity values at range of 1500 m/s – 2500 m/s and 1400 Ωm – 45000 Ωm. Whereas for claystone, it is very soft and laminated, concluding having high poroperm with seismic velocity between 600 m/s – 1200 m/s and resistivity values between 400 Ωm – 1000 Ωm.