International Journal of Scientific & Engineering Research Volume 9, Issue 5, May-2018 999 ISSN 2229-5518 A Rock Slope Stability Analysis at West- Northwest (WNW) part of Barangay Cayumbay, Tanay, Rizal along the selected 5 stations of the 1.8km section of MARILAQUE Highway using in- puts from Structural, Geomorphologic and Rock Mass Classification System Vhon M. Barquilla, Ma. Patricia Bernadette A. Soliman Abstract— Marikina-Infanta Highway or MARILAQUE highway which stands for Marikina-Rizal-Laguna-Quezon, is a highway that starts in Marikina and goes all the way to the Sierra Madre Mountain Ranges of Rizal, Laguna, and, finally, to Infanta, Quezon. The overall resolution of this research is to conduct an engineering geological study on the area in Tanay, Rizal along MARILAQUE highway. The area traverses parts of Barangay Cayumbay where rockfalls are a major problem. The geological study includes reconnaissance survey in the area, rock mass classification using Bieniawski’s RMR and Barton’s Q-System, and recommendation of any engineering mitigating measure to lessen any geologic hazard imposed by rock failure. Given a very low value for Q, it means that the study area is prone to failure; thus, it can be concluded that the 1.8km WNW part of Tanay, Rizal along the MARILAQUE highway is very prone to impending geologic hazard of rockfall. The study area also comprises splay of faults from the Philippines Fault Zone, different kinds of igneous rocks, which came from the Laguna Caldera of the Laguna de Bay, and sedimentary rocks, which indicate that some parts of Rizal were once submerged in the waters. Keywords— MARILAQUE Highway, Bieniawski’s RMR, Barton’s Q-System Index Terms— MARILAQUE = Marikina-Rizal-Laguna-Quezon, Q = Barton’s Q-System, RMR = Rock Mass Rating, WNW = West Northwest —————————— —————————— 1 INTRODUCTION IJSER HE province of Rizal belongs to Region IV-A or more cal survey with regards to structural and geomorphology of T commonly known as the CALABARZON Region in the the area under study; (2) to implement Rock Mass Classifica- island of Luzon. It is one of the country’s first-class prov- tion (RMR) in the study area; (3) to perform a rock slope engi- inces that enjoys a natural beauty of nature and a perfect set- neering studies to identify any impending geologic hazard of ting for investments, business establishments and human set- rockfall along a section of MARILAQUE highway, which is tlements. The area is bounded by the mountain ranges of Sier- about 1.8km, and; (4) to generate the slope stability analysis ra Madre and Quezon Province in the east, the province of and assessment of the area using Barton’s Q-System. Laguna in the southwest, the province of Bulacan in the north, Metropolitan Manila in the WNW portion and by Laguna de 1.3 Scope Bay in SSW portion. Rizal is one of the neighboring provinces The purpose of this study is to identify discontinuities i.e. of Metro Manila. wedges of joints, beddings, fractures, and faults, that will in- duce rock slope failure or rockfall in the area along the 1.1 Background and problem motivation MARILAQUE Highway that traverses the WNW part of Ba- For this study, the chosen location is the MARILAQUE high- rangay Cayumbay, Tanay, Rizal. This study is only applicable way that traverses the WNW part of Barangay Cayumbay, on the said area because different areas have different soil and Tanay, Rizal. rock profile, composition, failure mechanism, weathering, etc. This particular study would like to address the query: How This research project will be based on the rock mass character- susceptible is the West-Northwest (WNW) part of Barangay ization by using Barton’s Q-system as input to the design of Cayumbay, Tanay, Rizal along 1.8km section of MARILAQUE any mitigating measure for rock slope failures. There is also Highway to slope instability particularly to any impending geologic limited published works on the chosen study area. hazard such as rockfall or planar rockslides along discontinuities? 2 REVIEW OF RELATED WORK 1.2 Overall aim The major objectives of this study are: (1) to conduct geologi- Studies conducted in the rock units of the Southern Sierra Ma- IJSER © 2018 http://www.ijser.org International Journal of Scientific & Engineering Research Volume 9, Issue 5, May-2018 1000 ISSN 2229-5518 dre Mountains contributed to the understanding of the under- stratigraphy of SSM, the age of the ophiolitic basement rocks lying stratigraphy, tectonics and petrology as well as the in- and the correlation of number of stratigraphic units remain terpretations of the geomorphology, rock mechanics, and geo- unresolved. As with the NSM, the SSM was a site where Eo- logic history of the area. Oligocene arc magmatism took place and this was marked by quartz diorite-granodiorite. 2.1 Geological Considerations The work of Peña [6] defined that on a regional scale, Tanay Tanay is part of the province of Rizal and is situated along the is said to be included in the stratigraphic columns of Northern eastern part of the island of Luzon. It is underlain by a north- Sierra Madre-Caraballo and Southern Sierra Madre. south to north-northeast strips of Paleocene rock units along Tanay, Rizal which is the location for this study is affected the length of the Sierra Madre Mountain Ranges. The munici- by four major earthquake generators which includes the pality of Tanay has a complete sequence of Paleogene sedi- Marikina Valley Fault System, the Infanta Segment of the Phil- mentary rocks which represents the Paleocene-Eocene- ippine Fault, and two unnamed faults which are 4.0 km and Oligocene sedimentation that is unique in the Philippine ar- 5.96 km from the study area. chipelago. Commonly, ophiolites or ophiolitic complexes Barrier [7], that the Infanta segment of the sinistral Philip- comprise the basement of East Luzon. pine Fault, which is approximately 54.0 km from the study The Kinabuan Formation was named by Melendres and area was relatively seismically quiet and was related with an- Versoza (1960) for the flysch-like sedimentary deposits along other seismic gap. This seismic gap is believed to indicate that Kinabuan Creek which is north of Santa Ines, Antipolo, Rizal stress is accumulating and is not being released which makes [1]. The basal part of the sedimentary sequence was said to be it a candidate site for major earthquake. associated with underlying pillow basalts and basaltic The researchers also believed that the province of Tanay is breccias. The basalts represented the volcanic carapace of the affected by the Marikina Valley Fault System (MVFS) that ophiolite, whereas the pelagic sedimentary sequence consti- transects parts of eastern Metro Manila and possibly extend tuted the sedimentary cover of the Montalban Ophiolitic southwards to Tagaytay Ridge. It also belongs to a system of Complex. faults and subduction zones that accommodates an oblique As described by Cruz [2], the general area of Tanay, Rizal convergence between the Philippine Sea Plate and Eurasian was underlain by intensely disturbed suite of sedimentary Plate. rocks presumed to be of Cretaceous age which are Rimando [8] discovered that the neotectonic features along unconformably overlain by Eocene sediments, non-cherty the MVFS indicated a dominantly dextral strike-slip motion limestone, and cherty limestone. Another unconformity during its most recent activity which was believed to be Late caused the generation for the deposition of Miocene sedimen- Pleistocene to Holocene in age. Also, the variations in the rati- tary sequences composed of agglomerate and massive volcan- os of vertical to horizontal displacements for the segments ic rocks. Quaternary alluvium represented the younger rock implied a dominantly dextral motion of the West Marikina unit found along riverbanks as fluviatile deposit. Valley fault (WMVF) and oblique dextral motion for the East The geomorphology of Sierra Madre was described by Marikina Valley fault (EMVF). Lateral advection of the block IJSERbounded by the MVFS and the Philippine fault zone (PFZ) Wernstedt [3] and indicated that Sierra Madre, which is very rugged and heavily forested, formed the eastern margin of the best explains the observed kinematics of the MVFS. This was Cagayan Valley. This mountain range was said to be com- the result of compression during the westward drift of the posed of essentially large uplifted and tilted block of land with Philippine Sea Plate and northern Luzon and occurs through an abrupt slope facing the Pacific Ocean and with a gentler slip along the WMVF and EMVF at rates of 5–7 mm/yr. descent to the Cagayan Valley. The resistant intrusive igneous Rodrigo [9] concluded that the slumps, olistoliths and core of the highlands was overlain by a mantle of Tertiary sed- olistostromes found on the western flanks of Southern Sierra imentary and basic extrusive igneous rocks. Madre are product of large earthquakes related on the colli- Encarnacion [4] stated that the ophiolitic rocks found in sion of the Palawan Microcontinental Block to that of the Phil- Southern Sierra Madre (SSM) was first reported by Karig ippine Mobile Belt during Middle Miocene. Hence, previously (1983). The Montalban ophiolite described the assemblage of Angat formation was considered in the Norzagaray quadran- contiguous Cretaceous pillow lavas, diabase dikes and gabbro gle to be incorporated as a lower member of the conformably found in the Southern Sierra Madre of Luzon which is situated overlying Middle Miocene Madlum Formation. He also said east of the East Marikina Valley Fault. These rocks along with that the deformation found in the area were manifested at the a sheeted dike and gabbro sequence just west–northwest (be- base of the former Angat Formation. tween the West and East Marikina Valley Faults) as well as 2.2 Geotechnical Considerations isolated pillow lavas to the east were all grouped together as In terms of the application of geotechnical engineering in the the Angat ophiolite by Karig (1983).