Injection of A Collapsed Rock Mass and the Installation of 100 Ton Strand Anchors at the PHEP II Project-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes remedial works at the Punatsangchhu-II Hydroelectric Project in Bhutan after a major rock-mass collapse above the downstream surge chamber on 3 March 2016. The cavity measured approximately 140 m in length and height.<br /><br />Work began from confined chambers on the north and south sides. From January 2020, five drilling rigs created injection holes up to 70 m long through collapsed material containing large boulders and other obstacles.<br /><br />Grouting was completed in two phases. Phase I used gravity-fed grout to fill large voids; Phase II applied pressure grouting through sleeved pipes to consolidate the mass. The target was a homogeneous result with a 28-day unconfined compressive strength (UCS) of at least 10 MPa. In total, approximately 5,460 m³ of grout was injected—about 9% of the estimated collapsed-material volume. Quality testing reported an average UCS of 28.3 MPa and average permeability of 9.9 Lugeon units.<br /><br />The project also installed 359 permanent cable anchors, each with seven strands and lengths of 40–70 m. Most were tested to 1,000 kN, while others were tested to 1,500 kN; the lock-off load was 300 kN.<br /><br />The presentation concludes that the works were successful and thanks the site personnel involved.

Keywords

Punatsangchhu-II

hydroelectric project

Bhutan

rock-mass collapse

grouting

cable anchors

surge chamber

pressure grouting

unconfined compressive strength

permeability testing