ABSTRACTS OF TECHNICAL PAPERS
Presented by MGB-V to the
 13th Annual Forum on Mineral Resources and Geosciences Development
 November 14-15, 2003 Crispin Hall Petrolab, MGB Q.C.

Engineering Geological Study on the Proposed Salvacion,
 Macawayan 1 and Macawayan 2 Farm-to-Market Roads, Bgy Manamrag, 
San Andres, Catanduanes
by Arlene E. Dayao, Senior Science Research Specialist 

An engineering geological assessment of the proposed Salvacion, Macawayan 1 and Macawayan 2 Farm-to-Market Roads was undertaken per request of the Chief Executive of San Andres, Catanduanes. The infrastructure project would involve the construction of a 100.40 m. multi-line spillway (RCPC) and a 6m. wide gravel road having an aggregate length of 3.36707 kilometers in Bgy. Manamrag.

The study involved sub-surface soil mapping using an Eijkelkamp hand auger. Drilling was done at an interval of 100 m. along the 3 road segments. Each soil layer in the profile was sampled, logged and submitted for complete grading, moisture content, Atterberg limits determination, compaction and CBR. Construction materials from prospective quarry sites for fill materials, like the Manamrag and Macawayan Rivers, were likewise sampled for compaction analysis and CBR. The type, origin and the nature of occurence of sub-surface soils as well as the geologic hazards that could possibly occur at the site were assessed. Underlying rocks were mapped from drill holes as well as from exposures along the proposed farm to market roads.

In addition, groundwater levels were measured from drill holes. Permeability and/or hydraulic conductivity of certain soil layers was measured using the slug test method. Surface water condition was also observed, particularly water levels along the swamp on the terminal end of the proposed Salvacion Farm-to-Market Road. Interviews were made along local residents regarding swamp water levels during regular high and low tide periods as well as maximum flood levels during typhoons.

Study reveals five different soils classified according to nature and origin. These are the footslope deposits, the beach sands, the coastal gravels, the alluvial plain deposits and the riverbed and floodplain deposits. Results of laboratory tests were used to further classify these soils according to the Unified Soil Classification System that showed that the footslope deposits sands (SM). The beach deposits largely consists of poorly graded gravelly sand (SP) and well-graded gravelly sands (SW). These sub-grade materials have excellent drainage characteristics, good bearing values and CBR values of 10-40%. Thus, "capping" maybe unnecessary. However, since the uppermost 20 cm. of these deposits are very loose, this topmost 20 cm. portion need to be scraped off or mixed with silts and gravels and be properly compacted before the final fill and gravel surfacing is made.

The riverbed and floodplain deposits along Macawayan River was tested to have CBR values of 30%. This would mean that sub-grade materials from traverse station 19 through 23 and traverse stations 26 and 27 are very good and 'capping' would be unnecessary for these portions of the Macawayan 2 FMR.

The rest of the soils were likewise characterized in terms of drainage characteristics, value for foundation, unit dry weight and California Bearing Ratios and appropriate recommendations were provided in the report submitted to the local government unit.