compaction tests and the prevailing humidities would not allow materials to dry out as rapidly as fills were being made. Much of this material had to be wasted that might otherwise have been used if excavated in the dry season.
The wind rose accompanying the contract plans, based upon a 16 year interval, indicates that the new NE-SW runway will have parallel or slight cross winds 35% of the time and the NW-SE runway extended will have parallel or slight cross winds 25% of the time. There is a 267 calm and the remaining 14 of winds, North and South, will be cross winds.
The lowest elevation on the runway is about 20 feet above mean sea level. Ground water was encountered in one trench only during drilling operations and caused some misfiring in the blasting.
Design
This airport, although housing part of the Philippine Air Force, is considered a commercial airport and designed to U.S. Civil Aeronautics Administration and the Inter- national Civil Aviation Organization standards. However the design for pavement widths and clearances is not materially different than that previously adopted by the U.S. Army for this site. The flexible pavement design is similar to U.S. Corps of Engineer standards except as to rated wheel loading.
The adopted flexible pavement cross section consists of a 3 inch bituminous concrete pavement on a 10 inch base having a 100% density as determined by CAA com- paction control test. The sand sub-base is 17 inches thick at the ends and intersections of the runways and 12 inches thick elsewhere, all having a 95% density except that the top 6 inches of sand has a 100% density. The sub grade was required to have a 95% density. The compaction test is the standard Proctor test as modified by U.S. Corps of Engineers for airports.
The pavement surface has a 1% transverse slope away from the center line. This cross-section was carried down through all courses to the sub grade. The maximum gradient from the edges of the runway to the ditches in the conditioned areas does not exceed 1-1.2%.
The longitudinal profile of the new runway does not exceed a 1% gradient and this is flattened to a quarter of 1% through the intersection of the two runways.
Materials
The major items of materials required to be assembled included 132,000 c.y. of sand for the subbase, 125,000 c.y. of crushed gravel for the base course and asphalt concrete wearing surface, and 4,200 tons of asphalt.
The asphalt was supplied by Standard Vacuum Oil Co. and shipped direct from the United States and furnished in accordance with CAA requirements for a cut back asphalt for the prime coat equivalent to MC-1, an asphaltic cement for the concrete, equivalent to 100-150 penetration and an emulsion for the seal coat. The loss of asphalt materials in shipment, stevedoring, and trucking to site were negligible.
The specifications for gravel in the base course and the wearing course were close enough alike so that only a change in screen and crusher setting were necessary to meet the requirements, without resorting to additional materials or appreciable wasting of the pit material. The only source of good gravel in quantity in the Manila Area occurs in the Marikina River valley. Marscon, Inc, had several pit sites under lease for a prior project, one of which was selected for this project. This pit is located about 18 miles by road from the airport.
The Cedar Rapids Stone Crusher with capacity of 100 tons per hour which was used on this project.
Excavating Drainage Ditch with Caterpillar D-8 Tractor and 12 cu. yd. Le Tourneau Scraper.
The logical approach to the airport site from the gravel pit was through the U.S. Army Reservation at Ft. McKinley. Army authorities would not permit heavy truck- ing over reservation roads so the contractor was forced to build a pioneer road about 3 miles in length to overcome this objection. As this road was in use through the dry season only, and as the road base was in most part on the weathered tuff similar to that at the site, the initial cost and maintenance of this pioneer road was comparative- ly inexpensive using modern pneumatic tired excavation and maintenance equipment.
During most of the hauling period, due to the rebuild- ing of a highway bridge, the haul from crusher to airport was about 23 miles. Most of the hauling was done by sub-contractors using trucks averaging about 5 cu. yds, per load. Over 100 trucks were utilized for some time and during peak operations more than 2000 cu. yds, was stock- piled at the airport daily.
Tournapull self emptying 12 cu. yd. scraper,
described in this article,
The sand for the subbase was furnished by C.A.A. from a stockpile, the predetermined location of which was about 1 mile from the intersection of the runways.
The location of the stockpile was not satisfactory to C.A.A. and a shift was made increasing the length of haul another half mile. C.A.A. had arranged with the Philippine Department of Public Works for a hydraulic dredge to pump the sand from Manila Bay to the stockpile. C.A.A. had further arranged with the National Airports Corpora- tion, a Philippine governmental agency, to prepare the site of the stockpile and to maintain the dikes.
Earth Moving Equipment
Stripping was accomplished during the latter stage of the rainy season-October to December 1948-using 6 crawler type tractors with 12 yard scrapers and 3 push tractors. The stripping was carried deep enough to remove all roots with the sod and this helped to speed up the dry- ing of the clay so that it could be excavated by the pneumatic tired equipment (tournapulls) and later used in the fill areas.
The bulk of the excavation was accomplished with an average force of 10 pneumatic tired Tournapulls with 12 yd. scrapers, 4 crawler type tractors with 12 yards scrapers and 4 push tractors. About 1,100,000 cubic yards were excavated and placed in fill or spoil in about 150 working
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