Advance & retreat Longwalls.

[colly0410]

All the faces at Hucknall were advance longwalls, yet even back then the general consensus was that the retreat system was better. So why did Hucknall & some other pits persist in the advance system, did they have some advantages over retreat? ie cost, ground conditions or some other reasons?

[John]

May 17, 2015 15:53:36 GMT -5 colly0410 said:

All the faces at Hucknall were advance longwalls, yet even back then the general consensus was that the retreat system was better. So why did Hucknall & some other pits persist in the advance system, did they have some advantages over retreat? ie cost, ground conditions or some other reasons?

That question you'd better put to the Mining Engineers and Hucknall's Manager Steve.

One of the big advantages of retreating, is when you drive the gate roads you usually find any mining problems you're likely to encounter.
Yet, on saying that, you won't find mid face faults until you're on your way outbye with the shearer.
Another minus to retreating, gate roads are standing for a while, what's the strata like??? Soft?? Will it weight heavily making retreating dangerous??
But on the plus side, you don't have to follow a face with back rippers and dinters if you've a soft floor.
Swings and roundabouts comes to mind Steve.

[colly0410]

66's face in the Waterloo seam at Moorgreen used a pre-existing main roadway as a main gate & a normal advancing tail gate, called it a 'semi-retreat face.' I'm wondering if they carried on with advancing faces because of a 'that's the way we've always done it!" attitude, I bet mine management were a very conservative lot & didn't like change..

[John]

May 18, 2015 16:00:56 GMT -5 colly0410 said:

66's face in the Waterloo seam at Moorgreen used a pre-existing main roadway as a main gate & a normal advancing tail gate, called it a 'semi-retreat face.' I'm wondering if they carried on with advancing faces because of a 'that's the way we've always done it!" attitude, I bet mine management were a very conservative lot & didn't like change..

My guess it was up to "Area" the method and equipment used Steve.
There are advantage's of advanced LWing in thinner seams, one, being you produce coal from day one, and two, a lot of the dirt ends up in roadside packs instead of the pit tip.
Faces I worked on in retreat produced all coal from the gate developments, no dirt, in fact we didn't even have a spoil heap!

[smshogun]

Waterloo was in poor coaling conditions at Moorgreen and was littered with faults, with this uncertainty and an additional subsidy it became an experimental face which could be abandoned at any time, and it was to prove a concept of an idea.

As for advance/retreat arguments it came down to money, or more specifically a return on investment. With retreat faces you have a finite length of face and you have to follow the coal seam with your gates, and following coal brings its own problems due to local geological conditions which of course was floor lift; Moorgreen stopped this practise of heading in coal, particularly for main roads, and adopted a practice of heading in the solid strata above the coal which stabilised roadways much better and prevented floor lift, in addition they drifted down to coal seams when they developed new faces. With a retreat face you have a fixed face length and you retreat, you also have the problems of floor lift and continual dinting before you even begin to get chocks down and as we all know, time costs money.

With advance systems you can extend the length of the face and increase your return on investment, Moorgreen proved this with their final faces being under Hucknall market place which meant they were mining coal closer to Hucknall and Linby shafts than Hucknall and Linby pits were, but why? in reality it was return on investment.

To explain this we need to look solely at this from an economic point of view, with an advance face your initial outlay is much lower, no driving of roadways and no continual dinting, and less time. Less time means coaling begins sooner and the return on the investment begins much sooner, Moorgreen had two major advantages which were bunkers and an adit, bunkers meant if the drift belts stopped coaling didn't as they just filled the bunker, and running drift belts and an adit belt was cheaper than winding coal to the surface and you removed the restrictions imposed on the quantities of coal you could wind per hour.

Moorgreen, Hucknall, and Linby coal costs per ton were evaluated and Moorgreen could produce more coal cheaper than Hucknall and Linby so some financial bod at Area HQ evaluated the figures and suddenly Moorgreen had its boundaries removed and mined nearly to the shaft pillar at Hucknall in Blackshale seam, hence why they mined coal closer to Hucknall's shaft that Hucknall pit. No further investment was needed as the face was already past the investment stages and was running solely on its running costs which are normal for any face, so returned a greater financial return (higher profit) on its original investment.

[colly0410]

Always wondered why Hucknall Black Shale workings were to the east/north east of the shafts, was the west left for Moorgreen to take? Deep Soft was mostly to the east as well with faces heading north & south off the main intake & return that went east. Mind you B1's, B2's, B4's, B6's & B8's were headed west off B's reused main & tail gates & doubled back past the shaft pillar. To get to the B faces you went round in a sort of big circle = you'd head east on the main intake, then turn right at 4 ways junction & head south on B's intake, (B's old main gate) then turn right heading west onto B6's main gate... Also you went round in a circle in Moorgreens Piper/Waterloo seam inset pit bottom IIRC...

[John]

Oct 1, 2019 9:46:09 GMT -5 colly0410 said:

Always wondered why Hucknall Black Shale workings were to the east/north east of the shafts, was the west left for Moorgreen to take? Deep Soft was mostly to the east as well with faces heading north & south off the main intake & return that went east. Mind you B1's, B2's, B4's, B6's & B8's were headed west off B's reused main & tail gates & doubled back past the shaft pillar. To get to the B faces you went round in a sort of big circle = you'd head east on the main intake, then turn right at 4 ways junction & head south on B's intake, (B's old main gate) then turn right heading west onto B6's main gate... Also you went round in a circle in Moorgreens Piper/Waterloo seam inset pit bottom IIRC...

You'd need to look at the abandonment plans to find where the collieries boundary was, that would tell you all you want to know.

[John]

My experience in retreat faces was in a thick seam, so all development was carried out in coal, and no dirt sent to the surface as there wasn't any. Each development was a production district from the outset. No steel work either, roof bolts, and hardwood props were set, but mainly to hang cables from, and as indicators for convergence.
Never saw any floor lift in either of the NSW collieries, but then we usually had sandstone roofs and floors.
During my time at Wongawilli Colliery, just south of Wollongong, I did work in a modified pillar extraction district. As pressure relieved itself in the lifts, we used to experience very loud "bumps" as the floor sandstone cracked under the immense pressure. Something we soon got used to, but made trainees with little mining experience very nervous...