Characterization of Geotechnical Properties of Phnom Penh Bedrock: A Case Study in Chrouy Chongvar and Dangkao Districts
Authors: Boeut S. , Fujii Y. , Sieng P. , Kaing S. , Badrul Alam A. K. M. , Dzimunya N. Z. , Oudom S. , Boeut S. 
Published: August 2024

ABSTRACT:
Bedrock layers support large load structures, while Phnom Penh faces limitations in mechanical properties. This research conducted rock testing on sandstone from Chroy Changvar and Dankao districts, both strongly developed zones in Phnom Penh. The fine-grain sandstones were compressed under varying conditions of confining stress of 0 to 6 MPa and pore water pressure of 1 MPa. Permeability was assessed at pore water pressures of 1 MPa and confining stress of 3 MPa. Core rock samples, collected at depths of 43 to 50 m below the surface from both sites, revealed characteristics. The dry and wet density of Chroy Changvar sandstone existed at 2,503 kg/m3 and 2,574 kg/m3, with a permeability value of 1.43·10-14 m2 of pre-failure rock 1.87·10-14 m2 showing slightly increase. The maximum peak stress ranged from 11 to 75 MPa. Shear properties were estimated, indicating an internal friction angle of 57-degree, rupture plane angle of 16.5 degrees, and cohesion of 1.6 MPa. Dangkoa siltsotne showed the value of dry and wet densities of 2,682 kg/m3 and 2,699 kg/m3, respectively, with intact rock permeability of 8.63·10-15 m2 with highly increased in fractured rock permeability of 1.64·10-12 m2. This rock existed of high stress under compression with the peak stress of 100 MPa to 330 MPa exhibited a brittle-rock type even the increase in confining stress. The internal friction angle of 71-degree, rupture angle of 10 degree, and cohesion of 11.2 MPa. The study provides insights into the contrasting mechanical properties of bedrock of two districts in Phnom Penh. Chroy Chongvar sandstone displayed plasticity, while Dankoa sandstone exhibited brittleness. These findings contribute valuable information for understanding and managing subsurface conditions in urban environments.

1. INTRODUCTION
The rapid urbanization of Phnom Penh drives the growth of its infrastructure while also fostering the proliferation of towering high-rise constructions across the cityscape. This advancement elevates not only the foundation but also enhances the design and analysis of other projects supporting structures, making them more sophisticated. Regionally, Phnom Penh is mostly covered by the alluvial, floodplain, and water (Fig. 1), (MPWT and JICA, 2003). Rock is mostly reached at a depth of between 30 to 40 meters depth below the surface. Thus, the enhancement of rock support structures in high-load projects is applied. Bedrock layers support large load structures, while Phnom Penh faces limitations in mechanical properties. Understanding of the bedrock is getting more important as construction increases sharply. The constraints of rock properties, and rock behaviors are challenges in the design. Santi Pailoplee and Montri Choowong (2013) reported that the earthquake activity in Cambodia is quiescent with no reported active faults or earthquake source zones allowing the bedrock to be the only factor most considered in designing the foundation of high-rise buildings, especially in Phnom Penh city. This research became vital to understand the considerably suitable location on top of many other factors in decision-making. The research project was focused on the understanding of rock failure behaviors and the mechanical and physical properties of sandstone and siltstone. The selected study area was from two study locations, Chrouy Chongvar, the fast and in-progressed development region, and Dangkao districts, the limited space city in Phnom Penh (Fig. 1).