These concrete walls need to be strong and heavy.

We need concrete retaining walls around the perimeter of the house as well as interior structural concrete walls.  These walls must support the weight of the house (point loads) as well as provide shear strength.  Importantly, these walls must contribute to the 1.5 million pounds of dead weight that we require to offset the hydrostatic pressure (so our house doesn’t float).

Where are we going with this?  Yes Scott, you are correct – more rebar.

Placing rebar in the north-west part of the perimeter retaining wall.

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After completing the waterproofing, setting the rebar in place is next. 

Let’s pause for a moment …

Some people have asked us, ‘why is building your foundation so difficult?’  Let us explain.

Foundation Design, In Simple Terms

Given that our house is sitting on a ‘seasonal perched water table’, we need to have a completely watertight basement that is heavy enough to withstand hydrostatic pressures that can be up to 500 lbs per sq ft.  In simple terms, we need to build a:

Concrete boat that is heavy enough to sink
and
strong enough to resist cracking as it sinks.

The rough numbers go like this:

Building footprint      = 3,000 sq ft

Hydrostatic pressure  =  500 lbs per sq ft

Total building weight –> 1.5 million lbs

So, we need to have dead weight of 1.5 million lbs in our concrete boat and it has to be strong enough so it doesn’t break up or crack while it is sinking.

Sounds easy?  Yes.  And expensive.  Ouch!

The strength in the ‘concrete boat’ will come from the steel rebar placed in the concrete.  Thus, Bill Brown’s team is putting the rebar in place, per Duquette Engineerings’ design.  Yes, all to meet the soil engineer’s recommendations (JF Consulting).  What fun …

Placing Rebar

This was the first day of placing the rebar.  The rebar will cover the walls and go over the protection slab (which protects the waterproofing from being damaged by the rebar and construction activities).  The protection slab is 3 inches thick and adds weight to our ‘concrete boat’ so it sinks, even though it is completely waterproof.

Waterproofing completed on the east wall.

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Addressing water below grade is a difficult issue to address. And, when you have addressed it, the solution isn’t perceived to add any real value (as, after all, the ‘base case’ is for a dry house).

Today provided an opportunity to photograph the water that is in the excavation and show how we are addressing it.

Trench filled with water.

Water around the new sump pit.

As we get ready to waterproof, the drainboard must go in first. The drainboard goes against the earth to allow water to drain down to the collector drains that, in turn, go to the sump pit.

Putting up drain mat on perimter walls.

At the same time, the geotextile fabric was put in the excavation, then the crushed rock and pipe, and then the fabric wrapped the pipe, and then crushed rock on top.

Trenches with geotextile fabric, crushed rock and drain pipe.

End of the day …

Completed trenches in north-west corner.

An interesting point to note is that none of the infrastructure we are building will ever be seen again.  (Especially when the system works as planned!)

It was a cool dry day today – perfect for trenching the perimeter drains under the foundation.

The tarps were pulled back in the morning and the two machines on site cleaned up the ramp going to the excavation.

Starting perimeter drains for foundation.

After Jorge established the drain locations, they started digging the trenches. One truckload of dirt was removed as the void will be replaced with pipe and 3/4 inch crushed rock (over fabric).

Trench for perimeter drains under foundation.

All of the perimeter drains will lead to the sump pit. With the tarps pulled back, the 36 inch wide vertical sump pit in the south-east corner of the property was exposed, in all its glory. We’re loving the sump pit!

Sump pit (36 inch vertical culvert) in south-east corner of property.

Why?

On our property, we have a ‘seasonal perched water table,’ which creates a number of costly issues. First, we have to deal with almost 500 lbs per sq ft of hydrostatic pressure, which is why our house must weigh at least 1.5 million lbs. Second, the water encountered caused the drilling and pouring of our shoring piers to take longer than expected (and cost much, much more than anticipated). Finally, the water requires waterproofing of the foundation and sump pumps in several areas, which is causing design delays and controversy and, go figure, lengthening the construction timeline and corresponding costs.

So, anything that reduces the level of the seasonal perched water table reduces the hydrostatic pressures on the foundation and, in turn, reduces the risk of water entering our house. We don’t want any water inside the house.

Yeah, we can’t wait to ‘show off’ our beautiful new dual electric sump pumps, complete with independent back-up natural gas generator. Oh, did you see that the stairwell and window wells have large capacity 3 inch drains going to the sump pit? And, if those get blocked, there are 2 inch overflow drains going to the sump pit. Very cool … not.

Although I didn’t meet with Bill Brown today, we did sort out the drains from the stairwell and window well, and how that ties into the sump pit.

A bright spot in the day was the surprise visit by Sandra Ayllon, an estimator for Bill Brown Construction Company. She had a meeting only a block away so, being friendly, she stopped by our job site to monitor the progress and say hi to everyone.

Sandra monitoring progress at the end of the day.

Bill has a competent, dedicated team that work together extremely well. It is fun to work with his team.

The rains that were forecasted for today did, in fact, happen. There were several showers through the day.

First on the agenda today was picking up a power supply. We found one on CraigsList last night and went to Morgan Hill to look at it today. The unit looked great although the 100 ft. cord seemed small. A yellow flag but, no prob, we bought it anyway.

Portable power platform.

Then to the job site where the tarps were off – it looked good. It was the first time that we saw the sump pit in the south-east corner of the property. The 36 inch wide vertical pipe extends almost 18 ft below grade, so the sump can collect water from the entire site easily (once the perimeter drains are in place that go into the sump pit). Our plan is to take the water from the sump pit and have it pumped up into the cistern for irrigation. When the cistern is full, the water will go to the storm drain at street level.

Let's open the cover over the sump pit and see what it looks like ...

Approximately 18 ft deep to collect water and reduce the hydrostatic pressure.

With the sump pit in place, the waterproof design can be completed. We need to take the water from the stairwell and window well to the sump pit. As well, we need to have overflow from both the stairwell and window well going to the sump. It should work nicely.  We will finalize the design with Bill Brown tomorrow.

Oh, the white board cleaned up nicely with a little denatured alcohol and paper towel. Thank you for the tip, Andrew.

Clean white board - ready for project planning.

The power supply uses three-phase power and the temporary power pole uses two phase. A quick call to National Construction Rental to see if they can change the power at the pole. The power supply unit has some great functionality, stepping down to 110 so it would be good not to have to change anything with the unit itself (just the temporary power pole). Yes, the cord was only 50 ft. Another lesson learned – trust, but verify.

Male plug from portable power platform.

Female receptacle in portable power pole.

Our Panasonic network camera had some problems. We dusted it off and tried to get it working last night/today so it can be broadcasting on site and available 24/7. It wouldn’t allow access to the IP address so … off it went to the Panasonic service center in Illinois. More on this in a few weeks.

The other procurement chore for the site office was a shelf. We found an acceptable shelf at a liquidation sale at Eastridge Mall so that should happen tomorrow.

Yes, the detailed project plan is still on the list.

Jerry Freeman completed the soils report and gave me eight wet-signed copies.

His report describes the perched water table and a hydrostatic pressure of 500 lbs per square ft.

17509-geotechnical-report-08-05-01-final

This is what we were afraid of …

We signed the engagement letter from Steve Duquette and sent him the soils report.

We’re probably looking at a lot of concrete in our house to keep it from floating. Oh well.