CUURENTLY I AM HANDLING A PROJECT WHERE 200X200 RC PRECAST PILES HAS BEEN CHOSEN. IT'S PREDICTED THAT THE FOUNDING DEPTH OF HARD LAYER IS AT ABOUT 45M. THEREFORE 200X200 PILE WITH 7 JOINTS IS TO BE USED SINCE THE SMALL PILE SIZE COMES ONLY WITH 6M LENGTH.
MY CONCERN IS 7 JOINTS IS A PILE SEEMS TOO MANY AND CAN ANYBODY LET ME KNOW HOW TO FIGURE OUT THE MAXIMUM ALLOWABLE NUMBER OF JOINT IN A PILE.
The current practice in Penang Island, Malaysia is a reduction of 5% (I normally practice 7%) for every joint in the structural axial capacity. As far as I know, there is no limit on the number of joints in a pile point and the key issue is the slenderness ratio. Please note that the slenderness ratio permissible for piles is different for above and below ground. In the ground, the pile can be assumed to be fully braced (somewhat) to the intensity relative to the stiffness and of the soil.
Where is your project site? Do you know that 9m piles are already currently available in Malaysia? API (maybe known now as MDC), Hume, SG and PKM all produce 9m 200x200 RC Sq. piles. In terms of quality Hume and PKM are the only real choices but PKM is quite different. Hume's quality is very good but the reinforcement cage is hand-tied and the concrete is only OPC but PKM's reinforcement cage is fully welded using a welding robot, their concrete is PFA cement (better durability and long term strength) and because of the welding effect, they are the only manufacturer in Malaysia able to produce 10m piles! I have witnessed pitching and driving of their 10m and 9m piles and they are surprisingly more rigid than compared to the conventional market's pile.
What's your project location? If in M'sia I can probably check my database for the suitablility of a foundation. Also what's your working load (and FOS)? With depth of 45m, I would recommend normally 250x250 mm piles as the smallest size. 200x200 mm piles are too small in dimension for such a depth. Maybe you can redesign the pilecap. You can contact me if you want to obtain contacts for PKM, Hume or/and Api (or MDC).
Cotherion, thanks for your reply. the site is located in Shah Alam, klang (westbound). the underlying soil i silty sand somehow. talking about the 5-7% reduction in structural capacity per joint, is there any literature to refer to? slenderless ratio for this case is for sure a concern as normally it'll be limited to 120. we are considering 230x 230 pile with 9m length.
Klang region in that type of soil. I remember some areas of Klang you must pile very deep to get to the hard strata, guess you got it.
I got the 5-7% reduction from many consultant mates of mine (they practice 5% I practice 7% for prudence). One said it is from the BS but I'm not too sure. I will find out further since I guess I need to know myself.
230x230 pile. Due to the SI system of measurement, most call it the 225x225 pile. Good idea since it is bigger in size and therefore slenderness is less important an issue but there is a problem. If your project is located in the central region of Malaysia, the existance of 225x225 or 230x230 moulds for casting this pile is quite few and manufacturers do not keep much of this uncommon size for stock. If your project is relatively small and is not too soon to provide a good lead time for casting, this is not a problem.
In Klang the bracing effect of the topsoil is not very good. In fact, the soil is very soft until it reaches the hard soil. Because of this the soil cannot provide good bracing to the pile. Meaning your pile size still too small mate. I advice you to seek information from other consultants familiar with klang region piling and pool information resource.
Perhaps you can redesign your required pile to maybe a larger pile with less steel (longitudinal and links)since it is not hard driving. I advice you to contact various RC pile manufacturers in the central region of Malaysia like PKM, Hume and Sejati (most others are plain shoddy) since they have experianced engineers who can advice you for free as well as having the required moulds in a decent quantity.