Record-breaking shaft boring operation for Portuguese Somincor Mine
Published 2011-11-08 11:01:02
Two mining ventilations shafts at the Somincor copper ore mine in Portugal, each more than 600m deep and 4.0 m diameter, are being bored using shaft boring techniques by specialist contractor Drillcon Iberia SA using Sandvik reaming heads.
Shaft boring specialist Drillcon Iberia is currently boring its two deepest shafts to date at 615 and 630 m respectively, each with a 4.0m diameter at Portugal’s Somincor copper ore mine; using Sandvik reaming heads.
Located close to Castro Verde, some 58 km north of Portugal’s Algarve region, the mine open some 25 years ago and is today owned by Lundin Mining. The mine has been producing significant quantities of copper since then, peaking at 2.6 million tons of ore and 0. 8 million tons of waste in 2010.
It employs both bench and fill and drift and fill stopping methods underground. With the surface at 200m and designated + 1200 m by the mine, it has some 800 m of underground workings and 160km of tunnels.
The mine covers four established working areas, named after the villages of Graça, Corvo, Zambujal and Neves above. Development production also began last year on a fifth designated Lombador.
Shaft boring methods
Drillcon started working with Lundin mining some sixteen (16) years ago with a contract to drill shafts, introducing raised boring techniques initially with a single unit – fitted with a Sandvik reaming head.
Elected as the fastest shaft boring technique, the method is considerably faster and safer than conventional drill and blast methods; with no people required in the shaft during boring.
A pilot hole is initially drilled from the surface down to the tunnel below. A Sandvik reaming head is then fixed to the end of the drill string at the bottom of the drop shaft. The drill rig then rotates and pulls the reaming head upwards towards the rig, excavating the ground.
The excavated material falls to the bottom of the drop shaft and is trucked out by the mine company.
Contracts
This year the company was awarded a three year contract, and according to Product Director, Marco Macedo, the company expects to drill up to 6000 m in the first year, but he adds “I anticipate thereafter it will stabilise at between 3500-4000 m.”
He elaborated, “As the Lombador development increases throughout this year, we will be producing considerable numbers of shafts following the development workings.”
“For example, CPV (principal ventilation shaft)17 provided air ventilation for the initial development into the Lombador tunnels.”
“Shafts CPV22 at 615m and CPV21 initially at 630m will provide the main inlet and exit ventilation shafts for further Lombador production development down to 590m level to a collector for passing the gases to the surface.
Pilot hole
The pilot hole for CPV21 started at the end of October last year passing through a number of geological layers. Marco Rafael Macedo elaborates “We can experience five or six different layers in drilling, yet just 100m away we may only encounter one or two rock types.”
Rock can vary from black schales (Xistos), which in turn can be very hard or very soft, almost like clay; hard volcanic rock ;black quartz, ultra hard chert and very hard quartzite, In addition he adds it is frequently ‘faulty’ which can be a real problem.”
The pilot hole using a 12 ¼ inch diameter Sandvik bit, took three months including a section of grouting, through a very ‘broken’ area with clays and also using the RVDS system (Rotary Vertical Drilling System) in order to keep the hole straight. The Sandvik tungsten carbide type SCMH2 bit has been designed as a medium hard rock bit and Drillcon was able to achieve up to 250 drill metres per bit.
Reaming was started at the end of May and within six weeks Drillcon had completed almost 300 m. “At this level experience has taught us that whilst the cutters will bore for up to 450 m we opt to pause and fully refurbish the reaming head with new cutters on the surface,” explains Marco.
“This entails dismantling the reaming head at the bottom of the shaft and bringing it to the surface. In total we anticipate that it takes up to 15 days to refit the new head and reaming again.”
In addition to replacing the cutters it also provides the opportunity for the contractor to eliminate any risk of damage to the reamed drill rods in the bottom 300 m.
Drillcon is relying on a Sandvik CRH 10ED reaming head dressed with 22 cutters for the CVP21 and CVP22 shafts.
Depending on the type of rock being experienced determines the reaming progress. According to Marco Macedo, " Some days it can be 8 to 9 m per day, on very good days it can be up to 13 m and very bad days just 4-4.5 m per day.”
Early March also saw the start of the pilot hole of CVP22.1 and already completed to 600 m depth. “If we were to break through at the full 615 m depth, for example, it would cause damage to the internal instrumentation of the RVDS drill. We therefore opt to drill the final metreage conventionally using the raised boring rig. Once through, the bit is removed and the reaming head connected.”
Since starting at the Somincor mine, Drillcon has seen its fleet of Sandvik reaming heads increase from the original single unit to today’s 9 heads, comprising - 1 x 2.4 m dia; 3 x 2.1 m dia; 1 x 1.8 m dia; 1 x 1.5 m dia; 1 x 1 m dia; and 1 x 0.66 m dia; in addition to the 4.0 m dia head.
Latest order
To meet increasing demand for ever larger diameter shafts in both the mining and construction sectors, Drillcon will take delivery of a new Robbins 91R shaft boring rig, once again featuring a Sandvik reaming head designed for 5.5 m diameter at depths of 500 m.
“Depending on the type of rock and safety margin, with our experience and knowledge of ground conditions, I am sure that we will be able to increase this depth” said Marco Macedo.
The company anticipates being able to supply the new rig for forthcoming hydropower schemes projected for next year.
Drillcon Iberia SA is headquartered in Braga, Portugal and is currently undertaking jobs in Sweden, Norway, Bulgaria, Finland and Portugal.
