Report No. : GEO Report No. 245

Report Title : Soil-Nail Hole Measurements (2009), 98 p.

Author : B.L.S. Lui

Abstract

As part of the soil nail related studies, a project about the as-built geometry of drillholes has been carried out. Field data on alignment (inclination and bearing) and diameter of the drillholes have been collected in the course of soil nail installation at four sites under the Landslip Preventive Measures (LPM) Programme. Similar measurements carried out by Ove Arup & Partners Hong Kong Ltd. at six sites under the LPM Programme have also been incorporated in the present study.

The alignment of the holes were measured by four different devices, namely Eastman Camera, Reflex Maxibor, Reflex Ezshot and RG Verticality Probe. The hole diameters were measured by another device called Borehole Caliper.

The measurements indicate that the measured and design values of hole inclination, bearing and diameter are subject to different degrees of disparity. In particular, the disparity in hole inclination increases as the length of hole increases. It is not uncommon that the deviation of hole inclination exceeds the current specification of ± 2°, and practically such specification is found to be not always achievable, particularly when long soil nails are required or there is presence of relatively less dense geological materials. Based on these site measurements, a few improvement measures to the existing design and construction practices of soil nailing are recommended

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