DEVELOPMENT AND APPLICATION OF THE LARGE-DIAMENTER

DRIVEN CAST-IN-PLACE CONCRETE THIN-WALL PIPE PILE

1: 1: ABSTRACT

A new form of driven Cast-in-place Concrete thin-wall Pipe pile (referred as PCC pile) developed independently by GeoHohai recently has been patented in China. PCC piles are rapidly increasing in popularity as one of the most cost-effective soft ground improvement techniques in China since its first application.

The field study has demonstrated that PCC pile composite foundation is a cost-effective way to enhance ground bearing capacity and reduce settlement. Compared with traditional piling practice, the paper concludes with the statement on the potential application value of PCC pile with regard to other traditional piling techniques as being high bearing capacity, easily controlled and reliable quality and low construction cost.

2: PURPROSE OF USE

PCC piles could significantly improve the bearing capacity of the road foundation, which could be 10 times greater than that treated by cement grouted piles. PCC piles together with the top geogrid gravel cushion, act as a rigid pile group, which could remarkably reduce the settlement.

3: CONSTRUCTION EQUIPMENTS AND TECHNOLOGY

Main technique requirements of the construction equipments are:

- Penetration depth up to 25m,

- Pile outer diameter 1000 to 1500mm,

- Wall thickness 100 to 15 0mm,

- Multiply concrete supplement,

- Pulling capacity up to 30t and pushing capacity (sum of overload and high requency vibratory force) up to 100t.

4: MECHANISMS INVOLVED IN PCC PILE 

(1) Casing. After driven into the design depth, the steel casing is extracted under vibration; in the meantime, concrete is poured from the concrete shunt. The annulus steel casing prevents the concrete wall from shrinkage and collapsing. The new technology allows a continuous accomplishment of void formation, temporary casing, concrete pouring, and wall expansion, which subsequently ensures the stability and fullness of the concrete in the void.

(2) Compaction of concrete. The concrete inside the annulus casing and the void is being fully compacted continuously while the casing being extracted under vibration. It is also being forced squeezing outside, which subsequently increases the concrete wall thickness.

(3) Compaction of soil. During driving of the steel casing under vibration, there is certain degree of compaction to the surrounding soil as well while the soil is displacement radially. The degree of compaction depends on the wall thickness and the soil properties.

5: CONSTRUCTION QUALITY CONTROL AND THE PILE INSPECTION

PCC pile employs a very simple construction technology, which is easy to handle and in good control of the concrete quality.

The quality inspection of PCC pile is normally carried out in following three ways:

(a) In situ excavation: to check the appearance of the pile around 14 days after pile formation.

(b) Low strain and high strain testing methods: to check the pile integrity by echo waves.

(c) Static load tests of single pile and composite foundation: to estimate the bearing capacities of single pile and composite foundation.

PCC pile employs low strain dynamic testing or hand excavation inspection methods, which are cheap, only 1 to 2% of the total cost, non destroyable, extensive, and short inspection period.