Tropical Clayey Sand Soil's Behaviour Analysis and Its Empirical Correlations via Geophysics Electrical Resistivity Method and Engineering Soil Characterizations

Soil is a heterogeneous medium which consist of liquid, solid, and gaseous phases. The solid and liquid phases play an essential role in soil spontaneous electrical phenomena and in behaviour of electrical fields, artificially created in soil. Soil electrical properties are the parameters of natural and artificially created electrical fields in soils and influenced by distribution of mobile electrical charges, mostly inorganic ions, in soils. Geophysical method of electrical resistivity was used for measuring soil electrical properties and tested in different soil studies. Laboratory tests were performed for the numbers of clayey sandy soil samples taken from Batu Uban area. The empirical correlations between electrical parameter, percentage of liquid limit, plastic limit, plasticity index, moisture content and effective soil cohesion were obtained via curvilinear models. The ranges of the soil samples are changed between 229 Ωm to 927 Ωm for resistivity (ρ), 6.01 kN/m2 to 14.27 kN/m2 for effective soil cohesion (C'), 35.08 kN/m2 to 51.47 kN/m2 for internal fiction angle (?'), 38% to 88% for moisture content (W), 33% to 78% for liquid limit (WL), 21% to 43% for plastic limit (Wp) and 11% to 35% for plasticity index (PI). These empirical correlations model developed in this study provides a very useful tool to relate electrical resistivity with effective cohesion, internal friction angle (strength), void ratio, porosity, degree of saturation, moisture content, liquid limit, plastic limit and plasticity index in context of medium-grained of clayey sandy soil that is, its fluid behaviours.

Clayey Sand Soil's Behaviour Analysis and Imaging Subsurface Structure via Engineering Characterizations and Integrated Geophysicals Tomography Modeling Methods

The geoelectrical resistivity and seismic refraction surveys which were used in this study on the test site, delivered a detailed image of the near-surface conditions in generally very good. Electrical resistivity and seismic refraction analysis proved that a combination of these integrated study of the physical environmental data provided a reasonable compromise between measurement time and image resolution. Quantitative interpretation of the resistivity and seismic models based on soil's parameters determined using laboratory practices and field survey could reproduce the range of resistivity and seismic values found on the site very well. The model explains the ambiguity in between resistivity and clayey sands found on the site and predict the dominant role of water saturation. Geophysical methods are used in this research in purpose to determine the internal structure of a soil mass. Various geophysical methods and their merits for imaging subsurface structures and condition are discussed. Seismic methods are often the most suitable because the measurements depend on the mechanical properties which are also important in the mechanical calculation of soil's behaviour analysis. Other geophysical method, such as geoelectric resistivity, is useful to determine the internal structure, but require a correlation of found boundaries with mechanical properties. This research was conducted to investigate the subsurface structures and conditions through geotechnical engineering properties and its geophysical characteristics. The computation analysis is used in this research in purpose to investigate clayey sand soil's behaviour. Electrical resistivity test and engineering laboratory practices such as soil strength test, liquid limit test, plastic limit test and grain size distribution test was also carried out to investigate clayey sand soil behaviour in Batu Uban, Penang area during monitoring period.

2-D Resistivity Study: The Horizontal Resolution Improvement by Introducing the Enhancing Horizontal Resolution (EHR) Technique

2-D 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. EHR technique was developed in order to get detail and deeper penetration for shallow subsurface study. In this study, 2-D resistivity with Enhancing Horizontal Resolution (EHR) technique is adopted to map and characterize the shallow subsurface (mineral exploration, geology, engineering and environment) using Pole-dipole array. The locations are Pagoh, Johor;Nusajaya, Johor and Puchong, Selangor (Malaysia). The study associated with mineral exploration is Pagoh, Johor while for Nusajaya, Johor is associated with geology and Puchong, Selangor is associated with engineering and environment. The 2-D resistivity and Induced polarization (IP) were employed at Pagoh, Johor to study and detect the subsurface variation of resistivity and chargeability of iron ore in the area. Result of the 2-D resistivity as well as the Induced Polarization (IP) shows that the area is underlain by a thick alluvium with resistivity value of 10 - 800 ohm-m iron which has chargeability rate of 0.1 - 3 msec. A sedimentary case study was executed at Nusajaya, Johor shows sandstone contains iron mineral (30 - 250 ohm-m) and weathered sandstone (500 -1000 ohm-m). Interpretation of 2-D resistivity data at Puchong, Selangor showed a low resistivity value (< 40 ohm-m), 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. The borehole, support the results of 2-D resistivity method relating a saturated zone in the survey area. There is a good correlation between the 2-D resistivity investigations and the results of borehole records. The stratigraphy and structure of the three case studies (mineral exploration, geology, engineering and environment) can be mapped effectively using 2-D resistivity with EHR technique.

Interpretation of Geological Structures Hosting Potential Gold Deposits in the Konongo Gold Mine Using Airborne Magnetic, Electromagnetic and Radiometric Datasets

The renewed interest in the reactivation of the defunct National Konongo Gold Mine located in the Ashanti Greenstone Belt, calls for a further probe into its geology and the associated mineral hosting structures to discover its mineralization potential. In order to achieve this, airborne magnetic, radiometric and electromagnetic datasets were interpreted to determine the potential gold hosting features in the studied area. The results show the area to consist of the metasediment, the metavolcanic, Tartwaian Formation and their associated granitoids. Results also show that the Tarkwaian sediments, observed largely in the north-eastern side of the site;widen out substantially and truncate in the south. The analysis of the structure lineaments using a rose diagram reveals three main tectonic structures trending in N-S, NNW-SSE, and third the structure trending in the NNE-SSW to NE-SW directions in the area. The dominant structures in the area, form 90% of all the delineated structures and trend in the NE-SW and NNE-SSW direction with the remaining 10% trending in the N-S and NNW-SSE. These structures are associated with the major shear and fracture zones located mainly at the contact between the basin sediments and volcanic belt and also associated with the Tarkwaian Formation. The mapped potential gold mineralization zones located mainly at the contact between the metasediment and the metavolcanic units of the Birimian Supergroup, as well as the Tarkwaian Formation, were mapped by integrating the structures, alteration zones as well as the complex dyke systems. This paper delineates the prominent geological structures with the potential of hosting economic gold mineralization in and around the Konongo Gold Mine.

High Resolution in Seismic Refraction Tomography for Environmental Study

Seismic refraction tomography (SRT) involves more complex mathematic algorithms to fit more flexible model. In the field procedure SRT in generally needs more shot points than standard seismic refraction survey to obtain high resolution profile. In this seismic refraction study, we have used 9 shot-points for inline and 10 shot-points for offset in purpose to obtaine high resolution of seismic refraction tomography. During a recent geophysical test site, the subsurface material was mapped along survey line using seismic refraction method. Analyses of the site investigation data revealed that the studied site was made up of two layers of the subsurface. The upper layer has velocity values with range of 500 m/s to1500 m/s which can be classified as unconsolidated surface deposits and mixtures of unsaturated sands and gravels. Meanwhile the lower layer has velocity values with range of2000 m/s to5500 m/s which is classified as compacted fine’s soil due to high pressure of the overburden. Analysis of seismic refraction data demonstrated that refraction tomography software systems are able to reveal subsurface material which represented by their seismic velocity value. Furthermore, the velocity model obtained in this study is agreed with its synthetic modelling result as initial model. This validity and reasonable results was able to assist in interpretation of the seismic refraction method for the environmental study.

Integration of Seismic Refraction and 2D Electrical Resistivity in Locating Geological Contact

The aim of this research is to locate the geological contact for engineering purpose applying seismic refraction and 2D electrical resistivity method. Resistivity and seismic refraction method was conducted on four survey lines with 3 lines running from NW to SE which about parallel to each other and 40 m apart while the fourth line was running from SW to NE. The 2D resistivity survey used minimum electrode spacing of 5 m and the survey used pole-dipole array with minimum current was 2 mA and maximum was 20 mA. The seismic refraction survey used 5 m geophone spacing with offset shot was + 30 m and - 30 m. Resistivity results generally show the area was divided into two main zones, alluvium with resistivity value of 10 - 800 ohm-m, and granite bedrock with resistivity value of > 2500 ohm-m. There is a geological contact between granite and alluvium. The seismic results show the area consists of two layers. The first layer (top layer) with velocity of 460 - 900 m/s which was alluvium mixed with boulders. The second layer with velocity of 2060 - 3140 m/s with depth 71 - 90 MSL. The thickness of the overburden is 5 - 15 m.

Geoelectrical Survey for Engineering Investigation

Water seepage erosion has been and remains one of the major engineering problems. However, most engineers will much depend on borehole data and soil test for designing and problem detection. By considering of the cost and destructive method, selection of geoelectrical prospecting would be appropriate. Therefore, two electrical geophysical surveys were carried out in Sekolah Menengah Kebangsaan Dato’ Haji Mohd Nor, Gelugor, Pulau Pinang to map the presence of the unknown underground water sources (saturated zones) and its movement. With the total of seven resistivity lines parallel to each other and self potential (SP) with 5 m × 5 m gridding survey were successfully done. The resistivity result from line 1 (R1) to line 6 (R6) shows the subsurface consist of saturated zones with range between 3 m up to 10 m depth, before it reaches the R7 which is believed as the accumulation zone. Meanwhile, as for SP result it shows the water flow from higher value (north-east) towards the lower value which is mostly at the south area. In conclusion, geoelectrical survey could assist in detecting and solving engineering problems as it proven by the result from each method.

Electrical Resistivity Survey in Bukit Bunuh, Malaysia for Subsurface Structure of Meteorite Impact Study

An electrical resistivity tomography (ERT) study was conducted at Bukit Bunuh, Lenggong Perak (Malaysia). The study is to justify the features and environmental subsurface geological structure which is due to the meteorite impact. The ERT survey used resistivity equipments comprises of 4 survey lines with 5 m electrode intervals, covering an area of approximately 64 km2. The survey lines were carried out using ‘roll-along’ technique. The data were processed and analysed using RES2DINV, Excel and Surfer software in order to produce electrical resistivity tomography for qualitative interpretations. The results show the variation of resistivity value and faults. The 2-D resistivity results generally show the study area was divided into two main zones, alluvium with resistivity value of 10 - 800 Ωm, and bedrock with resistivity value of > 1500 Ωm and depth of 20 - 40 m. There are lots of fractured zones which are different than normal, identified along the survey lines. The South-North line shows the fractured zones were identified at 760 - 3800 m and 4700 - 5900 m. The West-East line, the fractured zone was identified at 1545 - 6570 m and North-West to South-East line, the fractured zone was identified at 740 - 5850 m. Meanwhile, South-West to North-East line, the fractured zone was identified at 720 - 1520 m. These interesting results were indicated at position of longitude;100.965 - 100.978 and latitude;5.056 - 5.066 where the bedrock depth is 40 - 60 m MSL and highly fractured. The area was surrounded by high elevated bedrock. Integration of 2-D resistivity results with boreholes is successful give valid and reliable results. The results of the study indicate that these geophysical approaches have a capability of retrieving the meteorite impact subsurface of the studied area.

Geophysical Interpretation of Possible Gold Mineralization Zones in Kyerano, South-Western Ghana Using Aeromagnetic and Radiometric Datasets

Airborne magnetic and radiometric datasets are used to interpret the geology and geological structural patterns which serve as potential gold mineralization zones in the Kyerano area located at south-western boundary of the prospective Sefwi Gold Belt and the Kumasi Basin in south-western Ghana. The geophysical data processing approach adopted concentrated on mapping geological boundaries, geological structures and possible gold mineralization zones is link to hydrothermally altered zones. The application of the enhancement filtering algorithms such as the reduction to the pole and analytic signal to the magnetic data, as well as the ternary radiometric image aided in the mapping of the mafic metavolcanics, basin metasediments and the belt-type granitoid complexes. The first vertical derivative and tilt angle derivative filters helped to delineate fractures, folds, and the contact zones of the formations such as that of the metavolcanics-metasediments that host the main Bibiani Shear Zone. Lineament analysis of the structures using rose diagram, reveals two main tectonic episodes in the area. These are NE-SW and NNW-SSE trending regional structures which account for about 90% of the extracted structures and are associated with the D1 and D2 deformational episodes of the Birimian Formation respectively. These structures are major fracture systems and play a pivotal role in the localization of gold mineralization in the study area.

Advances in Microgeophysics for Engineering and Cultural Heritage

A large number of unconventional investigations have been implemented, tested, and validated in the field of microgeophysics, with the aim being to solve specific diagnostic and/or monitoring problems regarding civil engineering and cultural heritage studies. The investigations were carried out using different tomographic 2D and 3D approaches as well as different energy sources, namely sonic, ultrasonic and electromagnetic （radar） waves, electric potential fields, and infrared thermography. Many efforts have been made to modify instruments and procedures in order to improve the resolution of the surveys as well as to greatly reduce the time of the measurements without any loss of information. The main new methodologies here discussed are the sonic imprint, the global tomographic traveltime, the electrical resistivity tomography, and the control of external films （patinas） grown on stone monuments. The results seem to be very promising and suggest that it is the moment to dedicate time and effort to this new branch of geophysics, so that these methodologies can be used even more to diagnose, monitor, and safeguard not only engineering buildings and large structures but also ancient monuments and cultural artifacts, like pottery, statues, etc..