Paving train at work on section D
suffered intrusion from the underlying clay embankment material and had seldom received any maintenance att- ention.
It suffered annually from being over-topped by floods which damaged not only the asphalt surface, but the underlying material which was chiefly the heavy, dense, highly plastic local clay. The road was bordered by klongs (canals), which were water- filled either from rains or irrigation water most of the year, keeping much of the embankment in a saturated con- dition.
Investigations
It was necessary for the engineers to spend considerable time in bring- ing together the several local govern- ment agencies concerned in selecting the southern terminus of the highway in Bangkok. Several months were re- quired, in addition, awaiting issuance of a Royal Decree to establish the right-of-way for the portion of high- way which was to be on a new loca- tion between Bangkok and Don Muang Airport. Beginning 6 km. north of the airport the new align- ment joined the old road, and from there on, except for two short devia- tions to improve alignment, the new highway was within the right-of-way of the existing road.
The engineers used this waiting period to carry out a comprehensive traffic survey, both to help determine the best point for the southern ter- minus of the new highway, and to support the requirement that the new highway from Bangkok to Don Muang be built as a four-lane divided sec-
tion, and that a two-lane, 7-metre wide surface, with 2.5 metre shoulders on each side, would be adequate for the remainder of the route.
During the same waiting period TCI conducted a comprehensive soils survey over the entire route. It had been determined that the choice of roadbuilding materials would be one of the most important factors in the design and construction of the high- way.
The heavy clay which predominat- ed over most of the road showed excessive shrinkage in the dry season. and Time-Swell curves made in the laboratory, in connection with CBR tests on the soils, showed that the
clay continued to swell for more than 30 days. The soils sub-surface in- vestigation showed that there would be consolidation of the foundation under embankment loading, but that there would be small danger of foundation failure under fills less than 3 metres.
It was also determined that higher fills, most likely at bridge approaches which might be expected to exceed 3 metres, would be risky unless some provision was made to either con- solidate the underlying material, or to reduce the weight of the bridge ap- proach embankment.
Field testing, followed by laboratory experimentation, showed that it was both feasible and economical to make use of the Bangkok Clay, in the new highway embankment. by stabilizing the top 15 cm. of the clay embank- ment by the addition of hydrated lime.
Section D. from Bangkok past the Don Muang airport to km. 32, was designed to use 5 per cent by weight of lime in the top 15 cm. of the un- classified borrow embankment built of Bangkok Clay taken from the right- of-way contiguous with the fill sec- tion. The lime-stabilized layer was then covered with a 10 cm. thick layer of sand on which the 20 cm. thick concrete pavement was poured.
After the lime was spread evenly on the roadbed surface by hand, it was watered and cut into the preshap- ed subbase with a scarifier on a motor grader. The lime and scarified sub- base material were then thoroughly mixed with a Pulvamixer, brought to the proper moisture content, lightly shaped with a motor grader, then seal- ed with a roller, and moist-cured for from four to seven days.
After curing the treated layer was mixed again, by which time the clay had been chemically altered by the action of the lime. Instead of being cohesive the once sticky clay had be- come friable and easy to grade, shape and compact. After final grading. shaping and compaction the subbase layer was covered with about 5 cm. of sand to retard evaporation from the surface.
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Hand-belting of newly poured concrete slab
Far East Architect & Builder October, 1966
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