To accurately design and cost a Horizontal Directional Drilling (HDD) crossing it is always suggested that a geotechnical investigation is carried out close to the prescribed bore route, preferably to a depth exceeding that of the initial bore design. It is always important to undertake the bore holes along the full length of the bore, not just at either end.
From the bore sample and geotechnical report the following information can be determined:
- SPT (Standard Penetration Test) – for unconsolidated geology
- UCS (Unconfined Compressive Strength) – rock samples
- Mohs hardness determined for the different rock samples encountered
The diagram below identifies the in rock formation hardness of different geological ground conditions and suggests the rock tooling required for drilling.