Plane of Equal Settlement above HDD’s Borehole before Operational Condition

Shokoufeh Sadeghifard

Phone: +603 202 66118 Fax: +603 202 60884

Brighton Petroleum Sdn. Bhd.

Email: shsadeghifard@brightonpetroleum.com

PROBLEM DESCRIPTION: Damage to

existence structures above the HDD borehole because of change in vertical pressure (soil resistance) and additional settlement during borehole drilling.

OBJECTIVE:

Determine the plane of equal settlement above the HDD borehole.

METHOD:

Arching theory investigation based on two below observations:

Plaxis software Vr. 12.0

• Expansion of disturbed area (settlement) around the HDD borehole.

• Distribution of the amount of vertical stress in top soil layer.

Half the geometry was modeled, as the geometry is symmetric.

RESULTS & CONCLUSION:

For typical range of HDD borehole in dry sandy soil, the plane of equal settlement is located at a depth of H/D= 4.0.

This conclusion is independent of the size and soil properties.

The results is well accordance with Terzaghi’s arching formulation

Fabrication of HDD borehole in case of adequate soil cover depth over the borehole does not have any risk for other probable structures above the borehole after H/D >4.0.