Construction & Contractors/Hardrock Excavation

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Question
There are two items in BOQ for the payment:
1: Excavate Unsuitable Common Material
Specification: Any rock which can not be removed withRipper of a 200 H.P. Bulldozer and
constitutes a firm and continuous bed of rock only.
This includes firm and rigid igneous,metamorphic and sedimentary rocks.
Boulders larger than quarter (1/4) cubic meter in volume will also be
considered as "Rock Excavation", provided these are firm and stable lying in
continuous bed and constitute more than 50% by volume as compared to
other type of materials in the total mass.
All drilling and blasting shall be done in such a manner as will most nearly
complete the excavation to the required grade line, and produce the least
disturbance of the material to be left in place. Blasting by means of drill
holes or any other methods shall be performed at the entire risk and
responsibility of the contractor. Care shall be taken to ensure that no injury
be done to persons or properties or to the finished work.
2: Formation of Embankment With Rock Material.
Specification: Embankment formed of material consisting predominantly of rock fragment of such size that the material cannot be placed in layers of the thickness prescribed without crushing, pulverizing or further breaking down the pieces,such material may be placed in layers not exceeding in thickness than the approximate average size of the rocks except that no layer shall exceed eighty (80) centimeters of loose measurement and compacted by a vibratory
roller.
The material shall be carefully placed inlayers, so that all larger stones will be well distributed and voids completely filled with smaller stones, clean small spells, shale, earth, sand, gravel, to form a solid mass. After placing rock material, surface shall be covered with a layer of fine material having
thickness less than twenty (20) centimeters. Such fine material shall be reserved from roadway excavation by the Contractor. Should such material be available but not reserved, Contractor will supply and place borrow material for forming smooth grade without extra payment.
Each layer shall be bladed or leveled with motor grader, bulldozer or similar equipment capable of shifting and forming the layer into a neat and orderly condition. No rock larger than eight (8) centimeters in any dimension shall be placed in the top fifteen (15) centimeters of embankment unless otherwise allowed by the Engineer.

My question is that if the excavated rock boulders are larger in size than 60 cm then what we should do
i) Claim extra payment for breaking them in to small size, or
ii) Consider them unsuitable for the formation of embankment.

Answer
First, I think the 80 cm dimension refers to the thickness of the rock layer ("such material" -- rock -- "shall be placed in layers not exceeding the average".....)  I'm not sure why they  make the maximum lift thickness equal to the average size of the rock (up to 80 cm).  Half the rocks will be sticking up from the surface of the layer if this is true, making it very difficult to work.  It is more common to use the maximum size or the 80th percentile, or something like that.  Anyway, I don't think you have to subtract 20 cm from 80 cm to get the 60 cm rock layer thickness you ask about.  I think it's 80 cm.

As to whether you are eligible for additional payment to break down oversize, typically in these specs the answer is no.  If it were yes, that would mean the Owner would pay the Contractor for poor blast fragmentation if blasting is required to loosen the rock.  When they say the material "cannot be placed layers of the thickness prescribed without crushing, pulverizing or further breaking down the pieces" the layer thickness they are referring to is the one specified (usually 150-250 mm) for material whose compaction can be measured by means other than visual -- in other words, soil that can be compacted to a density that can be specified and measured with a nuclear gauge, sand cone, etc.  Rock is a different case; placement and compaction are largely visual.  

It is your cost to meet the size limitation, and is your choice to waste the oversize or break it down and incorporate it into embankment.

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Robert Cummings, P.E.

Expertise

I can answer questions related to rock blasting, rock and soil excavation (such as tunnels and highway cuts), stability of such excavations, and foundations in rock and soil. I can also answer questions related to geology and mining.

Experience

30+ years as a geotechnical engineer and minerals engineer. Active consulting practice in rock blasting, geotechnical engineering, and rock mechanics for mining and heavy construction.

Organizations
Society of Mining Engineers, Deep Foundations Institute, Association of Engineering Geologists, and International Society of Explosives Engineers.

Publications
Mining Engineering, AEG Bulletin.

Education/Credentials
BS and MS Geological Engineering

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