38
Hong Kong Builder
VIBRO CONCRETE PILES
AS USED IN THE CENTRAL MARKET BUILDING
.1 OPERATION DRIVING THE TUBE
TO THE REQUIRED
DEPTH & RESISTANCE.
SUSPENSION ROPES
TO FRAME HEAD SHEAVES
AUTOMATIC EXTRACTING
GEAR FITTING FOR VALVE.
VALVE OPERATED TO ŠIVĖ
40 BLOWS PER MINUTE
2 TON HAMMER
WITH
EXTRACTING LINKS FITTED
WHEN DRIVING TUBE
•
IS STROKE WHEN EXTRACTING TUBE
WITH 30 INCH TOMS
BO BLOWS PER MINI.
2 TON VIBRO
4-6 STROKE
PILING HAMMER ENERGY- 100 INCH TONS
WITH
OPENING FOR
CONCRETE
CHARGING THE TUBE
FROM 7 CUB FT, SKIP
FOR DRIVING.
KINGE OF PILING FRAME.
ROLLER BASE
4 STEEL TUBE 16 Du
CAVITY FORMED IN THE BOOUND
AS
PRESSED OUT BY THE
ENLARGED END OF TUBE,
C. I. SHOE
Fig 1
I
Fig 2
TUBE FULL OF CONCRETE
WHEN 13 OF ITS LENGTH
15 ABOVE GROUND
RAMMING SURFACE
OF TUBE.
COMPLETED
CONCRETE PILE
OF 17* DIA.
Fig 3
The Vibro system of forming cast-in-situ concrete piles has now been firmly established for many years. Innumerable contracts in all parts of the world have been carried out, and the results obtained have shown that the Vibro system is suitable for almost any type of foundation requiring the use of bearing piles.
One of the most important features of the Vibro System is the tamping to which the concrete is subjected. This ensures that the concrete is dense, free from voids, and that the high compressive strength is maintained throughout the pile. Tests have shown that the density of the concrete in Vibro piles exceeds that of concrete deposited in moulds by hand.
The tamping action also forms a corrugated surface to the pile, thus increasing its frictional resistance. During the formation of the pile the smooth steel tube encounters comparatively little frictional resistance; but the friction on the rough sides of the finished pile in- creases the bearing capacity calculated from the final set per blow by at least 20 to 30 per cent.
the concrete being employed. As a result the piles formed by most systems often contained voids and were "waisted."
The efficient tamping action employed in the Vibro process ensures that the concrete is free from voids, and that the pile is rammed out at least to the outside diameter of the tamping rim. The Vibro system is now accepted as the most scientific and practical method of forming cast-in-situ piles.
The formation of a Standard Vibro concrete cast-in- situ pile is shown diagrammatically in Figures 1 to 5. Figure 1 shows the steel tube and 18 in. diameter cast iron shoe driven to the required set by the 2 or 21⁄2-ton Vibro piling hammer. The tube is then filled with con- crete and extracting links are fitted to it, as shown in Fig. 2. The extraction of the tube and the formation of the concrète pile are effected by upward and downward blows of the hammer, and Figs. 4 and 5 illustrate the nature of the tamping action during one upward and one downward blow of the hammer.
Fig. 4 shows the lower end of the tube after an upward blow has been delivered, the tube having risen a small distance and a layer of concrete having been
Before the introduction of the Vibro system the withdrawal of the tube in forming cast-in-situ piles was effected by a direct pull, no efficient method of tamping deposited; the force of the blow overcomes the friction