Soil testing... a tale of dirt and mountains

Soil tests are a big deal. No, really.
Not only will the results of the soil test impact the driveway design and the foundation design, they will ultimately give us an idea of whether we will be digging through dirt or stone, and thus how much this whole extravaganza will cost. But there is a third thing. Because our land is rural, we don't have any connection to town sewerage. So the type of on-site wastewater treatment system we can are able to install is also dependant on the type of soil.
And that's before the building even gets out of the ground.
We engaged Sven Nielsen from Strata Consulting to perform both the soil testing and the on-site wastewater management plan for us. Following a meeting with Neal-the-Architect, Sven advised that he would...

...propose to drill three bore holes to 2.5 meters in depth (or refusal on rock) across the footprint of the proposed dwelling.  This will give us and understanding about soil depth and composition across the footprint which will help to inform the suitability of the site for cutting as per the current plan.  This will also allow sampling of clays which will be submitted to the laboratory for the Atterberg Limit test which will give us the site classification details.  Given that I cannot get vehicle access to this area to use my vehicle mounted drilling rig I will use a man-portable drilling rig for this. 

The engineers also require soil bearing capacity determinations for the foundations as well as CBR (Californian Bearing Ratio) determinations for the driveway.  I will gather this information using a dynamic cone penetrometer and present this information in my report - we will need to do a test at each borehole as well as at 4 locations along the driveway.

That all sounded very impressive, although it did leave The Android feeling he was slightly incomplete without a dynamic cone penetrometer of his own. 
As we have tried to prepare ourselves for this journey on the basis that there will be monsters hiding around every corner, and what can go wrong probably will, we were not completely surprised when we heard again from Sven shortly after he had conducted the site testing and...

...discovered some tunnel erosion near to your proposed house site.  This is caused by dispersive soils (soil which dissolve in water) and is nothing to be unduly worried about but it does have implications for the management of storm water runoff and wastewater from your house as concentration can lead to further erosion and instability.  

I suggest that we subject a soil sample to a dispersion test, which will quantify how dispersive your soils are. This will help to inform management strategies in terms of your storm and wastewater, including the treatment of disturbed areas.   

Let me know if you want me to commission this test or if you have any questions.

Naturally, we requested that Sven proceed with the additional tests, believing it would be prudent that we get as much information as possible. We don't want to end up with a wastewater system that is inappropriate any more than we want to have the house sliding down the mountain after the first downpour. 
On receipt of Sven's report, the structural engineers will be able to complete their costing estimates for the driveway, we will have an idea of the type and cost of wastewater treatment system we can install, and Neal will be able to determine where on the block we can finally settle the house.

TIP: When it comes to building in remote areas, patience is definitely a virtue.

Driveways.... an engineering extravaganza

My word! Who knew planning a driveway would be so complicated?! A driveway people!
We are currently traversing the strange "Driveway Neverland" inhabited by Civil and Geotechnical Engineers. Although slowly learning to speak their language, we are still largely confined to making hand-gestures to make ourselves understood.
What is all boils down to is us having two driveway options... the first is favoured by those from Clan Engineer, while the second is favoured by Viktoria and the Android and Neal-the-Architect.
Following are the untranslated comments regarding the two options from Gandy & Roberts Consulting Engineers (as an aside, it's worth clicking on their name to visit their website if only to read about their forays into experimental siege engine research...)

I have done a quick design for both options. Design constraints included a maximum grade of 25%. Batters slopes have been done at 1:1.5 - this may be steepened depending on the geological situation.

Road 1 - Is the shorter of the two options (therefore less costs) and cuts across the contours better to achieve a better balance between earthworks required  and maximum grades used.

Road 2 - I have used a batter slope of 1:1 for the first 40m (may need stabilised batters), otherwise we would be cutting into the existing road formation. It is much longer with a more complex geometry. The hard part with this road is the turn at around Ch 60. Trying to achieve grades of not more than 25% when cutting perpendicular to the contours presents much larger earthworks.

Road 1 would be the better option (cost and construction wise) but does not enter from the north as the client wanted.

Following are the two design options, as provided by Gandy & Roberts. Bear in mind there is about 50 metres of land (in a straight line) from the left hand side of the picture to where the house outline begins.



Road 1 leading to (outline of) house



Road 2 leading to (outline of) house

So do we go with practical and less costly, or prettier and a small ransom? We are yet to make a decision as we won't get an idea of costs until some more geotech information has been gathered.
Do you prefer one design over the other?
Let us know what you think.

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