176. Owing to the urgency of the job no preliminary borings were taken but subsequent test piling and exploration by a 2" steel tube driven with a pneumatic hammer showed that very stiff greyish clay was encountered at depths of 10 feet to 21 feet below the level of Principal Datum and following generally the spur of a hill running from the south abutment toward the north. The piles were precast with 1:4 vibrated concrete using granite aggregates graded to 3" max., rapid hardening cement and a water cement ratio of 0.475. This was found to give average test cube results of 6,500 lbs. per square inch in 7 days and 7,800 lbs. per square inch in 28 days. They were handled in 7 days and driven in 14 days with a Vulcan No. 1 single acting steam hammer having a gross weight of 5 tons, striking part of 2 tons and a stroke of 3 feet to carry a safe load of 65 tons calculated from Hiley's Formula. A Lima crane was used for the handling and pitching of piles and also for suspending the lead and hammer. The bridge deck will comprise a 10" thick concrete slab with a " thick waterproofing coat of mastic asphalt on top; each section being separated with expansion joints of sand mixed with asphalt retained in galvanized iron cups. The surfacing of the carriageway is to be laid with a 11/2" bituminous macadam 4" thick covered with 1" of 3/8" bituminous tops while the footpaths are to be surfaced with 21/4" of granolithic paving.
177. Construction of Approach Roads. The approach road to the south of the bridge, through a cutting, was constructed with an 8-inch 1:6 vibrated concrete slab using granite aggregate graded to 11/2" max., ordinary Portland cement and a water cement of 0.450. This gave an average test cube result of 5,000 lbs. per square inch in 7 days and 7,000 lbs. per square inch in 28 days. The concrete was vibrated in three layers with vibrating plates and after finishing to the proper camber the surface was heavily scored to form keys for the carpet coat. After 7 days the concrete surface was cleaned, a tack coat applied and a carpet coat of 3/8" bituminous tops 11/2" thick laid by hand and consolidated with a mechanical roller.
178. The northern approach road was founded on swampy ground which has been settling continuously. Because of this it was decided to construct the road with a foundation of 9" bottoming, a base course of 11/2" bituminous macadam 4" thick and topped with a 3/8" bituminous carpet 1" thick.
179. The work of reconstruction commenced in August 1950 and the bridge will be completed by the end of 1951.
QUARRIES.
180. The demand for crushed aggregate and bituminous material generally remained at a high level throughout the year while that for the
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Page 44
176. Owing to the urgency of the job no preliminary borings were taken but subsequent test piling and exploration by a 2" steel tube driven with a pneumatic hammer showed that very stiff greyish clay was encoun- tered at depths of 10 feet to 21 feet below the level of Principal Datum and following generally the spur of a hill running from the south abut- ment toward the north. The piles were precast with 1:4 vibrated concrete using granite aggregates graded to 3" max., rapid hardening cement and a water cement ratio of 0.475. This was found to give average test cube results of 6,500 lbs. per square inch in 7 days and 7,800 lbs. per square inch in 28 days. They were handled in 7 days and driven in 14 days with a Vulcan No. 1 single acting steam hammer having a gross weight of 5 tons, striking part of 2 tons and a stroke of 3 feet to carry a safe load of 65 tons calculated from Hiley's Formula. A Lima crane was used for the handling and pitching of piles and also for suspending the lead and hammer. The bridge deck will comprise a 10" thick concrete slab with a " thick waterproofing coat of mastic asphalt on top; each section being separated with expansion joints of sand mixed with asphalt retained in galvanized iron cups. The surfacing of the carriageway is to be laid with a 11" bituminous macadam 4" thick covered with 1" of 3/8" bituminous tops while the footpaths are to be surfaced with 24" of granolithic paving.
3
177. Construction of Approach Roads. The approach road to the south of the bridge, through a cutting, was constructed with an 8-inch 1:6 vibrated concrete slab using granite aggregate graded to 11′′ max., ordinary Portland cement and a water cement of 0.450. This gave an average test cube result of 5,000 lbs. per square inch in 7 days and 7,000 lbs. per square inch in 28 days. The concrete was vibrated in three layers with vibrating plates and after finishing to the proper camber the surface was heavily scored to form keys for the carpet coat. After 7 days the concrete surface was cleaned, a tack coat applied and a carpet coat of 3/8′′ bituminous tops 14" thick laid by hand and consoli- dated with a mechanical roller.
178. The northern approach road was founded on swampy ground which has been settling continuously. Because of this it was decided to construct the road with a foundation of 9" bottoming, a base course of 14" bituminous macadam 4′′ thick and topped with a 3/8′′ bituminous carpet 1" thick.
179. The work of reconstruction commenced in August 1950 and the bridge will be completed by the end of 1951.
QUARRIES.
180. The demand for crushed aggregate and bituminous material generally remained at a high level throughout the year while that for the
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