Hydrofracture Risk in HDD drilling

[mohamadibrawish]

Hey,

I am working on developing Hydro-fracture Risk analysis for a HDD project that runs below a levee and wide river. I never done this before, however, I will be using Cavity Expansion Model for the analysis.
The model seems to be strait foreword, but wanted to know couple of clarifications..

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1- R(Pmax) defined as (Radius of Plastic Zone in ft), is this actually the area where plastic zone around the pipe? most of the literature indicates it can be all the way to the surface, but it recommends to to apply a factor of safe of 1.5 in sand and 2 in clays. If this is the case, and if I am understanding this correctly, then if my HDD pipe is located at 20 feet of sand then R(Pmax)= [20 ft/1.5]= 13.3ft. Is this understanding correct?

2- Dose anyone have an example analysis I can review to understand how are the results are typically provided?

We are using a CPT rig to collect the data for the analysis and thus, feel comfortable about the accuracy of my G (Shear Modulus) and the rest of the data for my Pmax and Pmin.

thanks for helping on this matter
Mo
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[BigInch]

Mohamad I suggest that you do not do this. Evaluate risks on a theoretical level. Leave any and all calculations and details to the expert contractors. To do otherwise you will assume a substantial portion of the risk yourself.

Furthermore there is not enough practical field experience with the method. It is not proven in the field due to lack of ability to measure pressure when fractures have occurred. What's worse is that it is reported there is a pronounced negative correlation to shear modulus. Third, levees are especially sensitive things to screw up, ie a huge risk.

Leave the equations alone. Evaluate the positive and negative aspects of the drill. Evaluate what can go wrong and what mitigation procedures are available, the probabilities and potential costs of failures. That is a risk analysis, not trying to do the design yourself. Trying that without the prerequisite experience is the major risk I see so far.