Bulletin of the Geological Society of Malaysia, Volume 65, June 2018, pp. 69 – 76
1Program Geologi, Pusat Pengajian Sains Sekitaran & Sumber Alam, Fakulti Sains & Teknologi,
Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
2Program Geosains, Jabatan Geosains, Fakulti Sains Bumi, Universiti Malaysia Kelantan, 17600 Jeli, Kelantan, Malaysia
*Corresponding author email address: firstname.lastname@example.org
Abstract: A residential area in Puchong Selangor has been badly affected by multiple geohazards, i.e. sub-surface erosion, ground settlement and embankment slope failure. The multiple geohazards incident was first noticed by the residents when the retaining wall and the associated road which bordered the southern end of the area had collapsed in May 2011. The collapsed retaining wall and road have been rehabilitated and reinstated back in around August-September 2011. However, ground movement (lateral and vertical) continued to occur. As a result, new tension cracks emerged on the road pavements, side walks and propagated into the houses and other rigid structures. Other signs of distress include differential settlement of road surfaces, tilted lamp posts, leaked fish ponds and wide spreading cracks in the walls over the time. Geological and geophysical studies were carried out in February 2012 upon request by the residential association. Field mapping was carried out by “walk-over” survey and focused on the mapping of signs of movements and other structural damages. Based on the literatures and field observation, geology of the embankment materials comprised of chaotic mixture of soils and rock blocks/boulders of various sizes and shapes. The rock chunks resemble much to the quartzite, phyllite, meta-sandstones and meta-mudstones of the Kenny Hill Formation. An electrical resistivity survey was also conducted to investigate and to characterise the sub-surface geology. A total of six survey lines was carried out in the residential area. Interpretation of Google Earth’s satellite images, dated 2001, 2004, 2007, 2008 and 2009, has also been carried out to visualise and assess the geomorphological and topographical changes that took place during site preparation and construction works. Results of the studies showed that the residential area was actually built up in a valley that has been filled up and buried two stream channels. The existence of the buried channels is well-illustrated in the pseudo-sections of the electrical resistivity. In conclusion, the multiple geohazard incident in the residential area was largely attributed to human errors and blunders. Stable and flat platform for residential area or any other permanent engineering structures, shall not be constructed by simply dumping rocks and earth materials to fill up a stream-flowing valley. Natural stream flows should be properly diverted or provided with adequate sub-surface drainage system before hand to avoid unwanted risks of geohazard. This case study presents a great lesson on the importance of basic geological knowledge when dealing with earth materials, water, soils and rocks.
Keywords: Multiple geohazards, sub-surface erosion, ground settlement, slope failure