The Application of Wassara Hammer and Mudmotor Steering Drilling Methods

Hallandsås Project, carried out by Skanska-Vinci, concerns the construction of two 8.7 km long railway tunnels in Southern Sweden. These tunnels have been excavated with the use of Tunnel Borring Machine(TBM). The excavation of the East Tunnel brought some significant delays due to high discharge water quantities within a Lya Zone.

Therefore, prior to the excavation through the Lya Zone within the West Tunnel, special pre-treatment was designed to avoid time and cost consuming grouting works from the TBM.

This pre-treatment concerned long-hole grouting, performed from Cross Tunnels no. 5 and 6, sealing the rock masses within specified pattern. This dissertation aims evaluation of two drilling methods used during the pre-treatment works in Lya Zone: Mudmotor and Wassara Hammer. The practical experience was gained during training period in the Hallandsås Project from September 2012 until February 2013. This knowledge was completed with studies about theoretical applying of the rock drilling methods.

Two parameters were used in order to compare these two rock drilling methods: drilling time and deviation of the boreholes. Drilling time was presented from two perspectives. Firstly, the evaluation of the rate of penetration assigned to the specified sections pointed that Wassara Hammer provides much higher rate than Mudmotor. Moreover comparison of drilling time within each borehole show significant increase of drilling speed during Wassara Hammer application. The rate of performance was calculated to be almost 4 time higher for Wassara.

Deviation was introduced in two different approaches as well. On the one hand, deviated boreholes were shown within particular sections, significant tendency in horizontal deviation towards left was shown. Deviation average values have been decreasing while advancing the steering proccess, however, some significant correction was observed only in case of horizontal deviation.

On another hand, evaluation of the deviation within borehole GH11 brought the assumption that the borehole’s steering did not performed exactly during Mudmotor application. Mudmotor gave a direction for further drilling, and due to this, correction of the borehole was observed during Wassara drilling. It was originally assumed that the use of these two rock drilling methods together may result in effective performance. This research attempted to evaluate Mudmotor and Wassara Hammer technologies and show the efficiency of such combination. Wassara Hammer provided fast drilling proccess while minimal deviation was possible due to the use of Mudmotor.
Source: Halmstad University
Author: Obuchowska, Katarzyna

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