Hi,

My house is a double storey terrace, with a 5' land at the back. I'm planning to extend it for a wet kitchen, just single storey.

A few of the houses at my Taman has done their extension as well, and some is having cracking problem due to soil settlement.

I managed to see the SI report from the developer, info gathered as per the sketch below.

From here, I would like to know if it's require to do a RC piling to support the extension work? Or bakau piling is good enough? Else I also read about raft foundation, will it help in this type of soil?

Thanks




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Quite a classic situation of landed housing addition.

If the original building is on piles, quite likely in this case, best is to pile(RC) for the extension. The issue is that whether driven piles allowed by local authority. Jack in system might not be feasible due to space constraint.

Raft (spread the weight on ground as big as the structure footprint)might help in lessen the differential settlement (main culprit of cracking of extension works) but the risk is still considerably real.

Next workable approach is to make the existing building to 'carry' the extension. Can work well in your case as the extension is shallow and only single storey. Need a bit more engineering for this though and existing building structural as built will definitely help.

hey,

RC pile either by hammering or injection is not an option due to the close proximity of neighboring houses. As for raft foundation, it only works if it has a large span and not mere dimension of 20ft x 5ft. The idea is to decrease the downward pressure by increasing the surface contact area. Lastly, it is good to have a soil investigation report from developer as reference but it may not necessarily reflects the actual soil strata underneath your house. I would recommend that you engage a structural consultant to deal with your situation. This is to ensure that you make an informed decision on getting the right solution.

All the best buddy!

Thanks for the reply.

The original house is actually on pad footing, based on the info from my neighbours, but too bad the developer is not willing to disclose more details.

Also the developer is not willing to provide the as-built structure drawings. Any idea if the engineer is able to design without this info?

Thanks for the info.

May I know what's the reason that RC pile is not suitable in this case? Is it due to the hammering process will affect the neighbouring houses?

I see one of the houses at my Taman was doing RC piling few months ago, he used a small simple machine as per the picture below. Is this good enough?

Noted your advise on the structure consultant, may I know normally how much is their charges for this type of small reno? Provided if they are willing to take small jobs

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This post has been edited by jetzxp: Jan 7 2021, 11:23 PM

If the building is indeed founded on footings, the design would a lot simpler. But you did mention there is settlement problems in the neighbourhood and the soil profile in your sketch does not really warrant footing as suitable foundation solution. Is the information reliable?

Bring in an Engineer to manage the risk and advise you accordingly.

This post has been edited by concretemad: Jan 5 2021, 12:32 PM

This is boring rig for soil investigation works.

design standpoint the extension structure is just leaning on the existing structure to allow settlement. then it is a matter of just filling up the cracks. it does not join up with the existing structure as a whole as differential settlement might complicate matters. This kind of extension we usually recommend bakau piles ONLY if the water table is high as it is prone to rot if not covered by water. Your SI should indicate the water table. RC pile is not practical as the shockwave it generates will cause your neighbours problems. The A frame rig you assumed to be for piling is only good for bakau, not RC as the hammer is not heavy enough to drive the piles to set. The pic you used is NOT a piling rig. Even if used as friction, doubt it will go more than 3m and that might not generate enough friction for load bearing. This kind of reno is bread and butter job for C&S consultant so find one. Design fee used to be under 1k depending on locale, plus misc fees around 3-4k. Once you have your construction plan, you can find a contractor to do the work. My guess is it would be bakau piling with pad footing. Just in case the piles fails, the footing is still able to provide support. Cracks around the new and old building interface is normal.

The SI I attached above is the the SI done recently by the developer due to this settlement problem and a lot of ppl complained. I understood that before the construction period, since the project is quite large, the SI point was quite far away from our area.

Haha ok ok misunderstood this as this was there next to the house under reno, so i tot that it's by them

Noted thanks for the info. The neighbour who did the RC pile told me that the depth was quite deep, can't remember the figure but it's like 10 or 20ft.

i made a mistake. looking back at your drawing of level, noticed it is backfilled and using reduced level. Assume needs to go 3-5m below RL0 to get the sufficient friction. If your backfilled height is RL 8, then add another 5m means need a depth of 13m. Normal A frame rig uses less than 1 ton hammer while a proper one uses at least 2.5t. 1 ton hammer prob will not drive to that depth and can be misunderstood to be set. I think the settlement in your area is due to the backfill not compacted thoroughly. Your developer should have at least 3 borehole logs done for the SI and you are most probably using the closest.

Thanks for the reply and yes based on the drawings shown to us, there are a few bore holes by the developer, and I took note of the nearest one. Since the project site is quite big, the other points are quite far away, I think got a few hundred meters away

Based on your comments above, I guess need to ask the contractor about the piling machine and make sure it's at least 2.5ton right?

Also to drive a pile 13m depth, is it something considered normal or special case ya?

Thanks