Drilling and Grouting in Rock, Executed by BAUER Vietnam Limited

 

In order to meet the increasing electricity demand for the country, Song Bung 2 hydroelectric power project has been planned and constructed on Song Bung River, Nam Giang District, Quang Nam Province, with supply capacity of 100MW. The technical design of Song Bung 2 hydroelectric power project was approved by Vietnam Electricity, with following basic parameters:

 

• Main dam structure: Concrete Face Rockfill Dam (CFRD) with dam length: 477m
• Maximum dam height: 98m
• Full supply water level (FSL): 605m and Minimum water level (MOL): 565m

Addressing the problems related to the permeability of a soil or rock mass includes (a) reduction of the strength of foundation materials due to high seepage forces and thus possible reduction of dam safety; (b) loss of retained water from the reservoir, Therefore it was decided to install a grouting curtain. A grouting curtain usually consists of a series of vertically drilled holes, which are filled with agreed mortar under defined pressure. The holes are drilled at intervals and in such a way that they overlap to form a curtain. Before installing the grouting curtain, the most reliable means of obtaining a realistic answer to the questions regarding the grouting of the rock, as well as determining the most suitable mixes and the probable amount of work to be carried out, the trial grouting was decided upon.

 

 

BAUER Vietnam Limited, the Vietnamese subsidiary of BAUER Spezialtiefbau GmbH, was commissioned to execute test grouting works and installation of mass grouting (grout curtain).

Employer/Owner:       Viet Nam Electricity (EVN)

Client:                         The Agriculture & Irrigation Mechanization Electrification Construction Corporation (AGRIMECO)

Engineer:                    Power Engineering Consulting Joint Stock Company 3 (PECC3)

 

Scope of works

Test Drilling & Grouting Package: includes 655m drilling and grouting in rock up to depth of 45m including water pressure testing (Lugeon test).

Mass Drilling & Grouting Package: Installation of Grout curtain, including drilling diameter 90-110mm through rock of various strengths (up to 100MPa) and grouting. Total drilling length is 8106m.

 

Construction Period:

October 2012 to December 2012: Test Drilling & Grouting

July 2013 to December 2013: Grout Curtain (Mass Drilling & Grouting)

 

Geology

First 10 - 12m below ground level is mainly highly weathered schist rock  with quartz (IA2). From 12m to 20m is a moderately weathered schist rock (IB). Below 20m is the schist bedrock (IIA) with compressive strength of 100 MPa.

 

Construction works

As per the design, it was required to seal the voids in rock layer design as IB and the depth of borehole was calculated as ½ of maximum water level which vary from 3 to 45m. Based on the results of test grout, drill holes at spacing of 2m was adapted for grout curtain installation. The DTH drilling technique was applied to drill through such hard rock with high performance.

One of the biggest challenges was to set up the drilling equipment for the installation of the grout curtain for a terrain with a gradient between 20% and 56%. The BAUER UBW drilling rig was used for drilling in shallow areas and six (6) portable drilling rigs were mobilized for work in the slope area. 2nos KP60 pumps with an automatic recording system known as the "Obermann System" were used to archive the exact data related to the injection work.