Underpining size of foundations & type of concrete

Hi,

I'm about to underpin the front of rendered brick façade on a Californian bungalow. The existing/original foundations appears to be a few inches of gravel, a few inches below the ground at best. The corner columns are leaning outwards about 100-150mm so they need jacking, pads for jacking, and pads to pivot the jacking off etc. I've worked out where each excavations need to be.

The few commercial engineers that could be bothered quoting etc. wanted $2-3000 to design the foundations. Based on the existing foundations anything would be an improvement, specially given 90 years have passed so far. The soil is class M wit ha bed of clay about 500mm down. The depth will most likely be 1000m for the columns and 600mm for the walls to suit the soil report. I suspect there is no need for reinforcement as the pad will be pretty large.

I've been trawling the net for months researching the job for months and the 2 things I'm not sure are the size of the foundations for the columns and walls and what type of cement as I'm not familiar wit the types of cement you can get premixed. Any help suggestions would be appreciated.

Cheers
Ramoun

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