Depth of Secant Bored Pile in Rock

[steveyeung]

Does any foundation engineer know whether secant bored pile (wall) is able to be socketed down into "Porous Rock - Allowable Bearing Pressure = 1000 kN/m square" for say 3-5 metres?????

 

[VAD]

What load is to be carried by pile

 

[steveyeung]

The problem is an exam question.

The bored pile wall is designed to act as an abutment of a highway bridge.

Horizontal load:
1. 205 kN/m (from traffic)at the level of the bridge deck
2. It is an abutment so it has to support lateral earth pressure from backfill/retained soil of 6m deep and surcharge say 10 kN/m square.

Note that the elevation difference between the bridge deck and the road underneath is 6m so the length of pile should be at least 6m. In addition, the carriageway is assumed to be two lane (7.3m wide) single diection carriageway.

Vertical Load:

1. about 80kN/m

Other information:
The level of the porous rock is just 3m below the bridge deck but 3m higher than the road underneath. The problem is that if a big strip footing is adopted which rests on the rock surface, it will impose "high" bearing pressure on the rock and may destabilize the 3m high vertical "slope"