Mixi Resources

Old-dormant landslide is an inactive landslide that can be reactivated by its original causes or other causes that will trigger its mechanism. It is normally overshadowed by thick and densely forested, wet tropical hilly terrain and highlands. The older the landslide, the more difficult for it to be recognized although the causes of movement remain apparent. Due to these reasons, local geoscientists tend to ignore this type of landslide. Dormant landslide can be classified as a serious natural terrain geohazard and can cause very costly consequences. This is because it can re-collapse or still in the process of collapse without any significant trace. Besides human interventions such as deforestation and mining, it also can be triggered by extreme natural events such as earthquakes and heavy rainfall. These things will affect the structure and mechanical stability and make the soil vulnerable to oversaturation and erosion (Salleh et al., 2019).

MASW evaluates ground stiffness by measuring shear-wave velocity (Vs) of subsurface in 1-D, 2-D, and 3-D for various types of geotechnical engineering projects in the most common depth range of 0-30 meters. Shear-wave velocity (Vs) is one of the elastic constants and closely related to Young’s and shear moduli. Under most circumstances, Vs is a direct indicator of the ground strength (stiffness) and therefore commonly used to derive load-bearing capacity.

Seismic refraction determines depth to bedrock and bedrock structure. Due to the dependence of seismic velocity on the elasticity and density of the material through which the energy is passing, seismic refraction surveys provide a measure of material strengths and can consequently be used as an aid in assessing rippability and rock quality. The technique has been successfully applied to mapping depth to base of backfilled quarries, depth of landfills, thickness of overburden and the topography of groundwater.

Seismic reflection surveying is the most widely used geophysical technique, and has been since the 1930s. Its predominant applications are hydrocarbon exploration and research into crustal structure, with depths of penetration of many kilometres now being achieved routinely. Since around 1980, the method has been applied increasingly to engineering and environmental investigations where depths of penetration are typically less than 200 m. Applications of shallow high-resolution seismic reflection surveying include mapping Quaternary deposits, buried rock valleys and shallow faults; hydrogeological studies of aquifers; shallow coal exploration; and pre-construction ground investigations for pipe, cable and sewerage tunnel schemes, and offshore wind farms.

Electrical resistivity methods were developed in the early 1900s but have become very much more widely used since the 1970s, due primarily to the availability of computers to process and analyse the data. These techniques are used extensively in the search for suitable groundwater sources and also to monitor types of groundwater pollution; in engineering surveys to locate subsurface cavities, faults and fissures, permafrost, mine shafts, and so on; and in archaeology for mapping out the areal extent of remnants of buried foundations of ancient buildings, amongst many other applications. Electrical resistivity methods are also used extensively in downhole logging. For the purposes of this chapter, applications will be confined to the use of direct current (or very-low frequency alternating current) methods

The self-potential or spontaneous polarisation (SP) method was devised in 1830 by Robert Fox, who used copper-plate electrodes connected to a galvanometer to detect underground copper sulphide deposits in Cornwall, England. The method has been used since 1922, when Schlumberger introduced non-polarisable electrodes as a secondary tool in base metal exploration, characteristically to detect the presence of massive ore bodies, in contrast to the induced polarisation method (see Chapter 9) which is used predominantly to investigate disseminated ore bodies. The SP method has been extended to groundwater and geothermal investigations, and can also be used as an aid to geological mapping, for example, to delineate shear zones and near-surface faults. It has also been used in forecasting earthquakes (e.g. Corwin and Morrison, 1977; Varotsos and Alexopoulos, 1984) and volcanic eruptions (Zablocki, 1976), and investigating volcanic plumbing (Patella, 1997a; Lenat, 2007). The technique has also been used successfully in archaeological investigations (Wynn and Sherwood, 1984; Drahor, 2004). The method is increasingly being used in environmental studies such as in monitoring fluid contamination and bio-remediation. A useful general introduction to the method has been given by Corwin (1990).