Advancing and Retreating Longwall Faces.

[John]

Pro's and con's of both methods.
Debate!

[John]

My own experience on both methods of working are limited to me being a face electrician on them.

Firstly advancing faces required stable holes, which sometime in the 1960's were eliminated.
Another drawback to them was having to have a good roadside pack to reduce roadway damage from convergence.
Constant roadway maintenance was also required, floor "dinting" in softer floors too due to "heave"
Natural problems like dykes, sills and faults could be encountered which were not known before the face started advancing.

Retreating is done by driving two or more parallel roads to the boundery of the workings, so any geological phenomina would be found before the face was driven and installed. My experience of retreating faces was in NSW Oz, and roadway roofs were bolted, which had to be done as soon as the road was cut, this to prevent bed separation which could lead to falls of roof at a later date.
Road side packs are eliminated and so are stable holes as the roads allow the shearer to "turn around".
Reduction of manpower is also a bonus of retreat longwall mining, no waiting for roads to be advanced are another bonus, steady production can be achieved.
Roadway maintenance is reduced, due to less stress on roads as against constant convergence damage on advancing longwall faces.

I had no experience of retreat longwalling in the UK, closest I came was at Cotgrave the year I left, they were driving the main and tail gates of the first retreat face, from what I have been told it was a failure at Cotgrave for reasons I don't know.

[John]

There's nothing new about retreating Daz, just that the NCB had something against that method for some reason.
I first worked on retreat longwalls at Angus Place Colliery in NSW, they were using an Anderson Strathclyde AM400 shearer and Gullick chockshields.
LW1 had a "green" crew and within several weeks of starting had broken yardage cut, OMS and weekly world tonnage records.
I started there during LW5's time and the crews were fairly competent, we were earning very high production bonus's.

[Pete]

When UK coal mining began advancing coal faces were preferred. Sort of sinking a shaft and hacking away from the bottom - after leaving a suitable shaft pillar.

The mine plans for Warsop Top Hard show the traditional 'onion ring' approach to mining - the coal face being a circle ( will octagon first with more sides added as you go ) spreading outwards, only upset by faults or washouts as they were met. As the face got larger more persons could be employed until separate advancing districts were set off.

That way you get an immediate return on your investment. Best if the seam is 6' then you do not need to do any ripping.

However as advanding faces became mechanised it was clear that ripping / heading perfromance was holding back production. If you can separate the two your coal face can concentrate on producing - with the tricky development hapenning somewhere else.

High output coal faces are now 99% retreat. Advantages include - no hold up for the heading, no awaiting supplies ( belt, structure, pipes, rails etc etc ) less manpower, roadway problems left behind, supports available near to the main roadway when the face finishes ( rather than 3 miles out along poor roadways ).

In particular the damage inflicted on the roadway by the forward weight would not be with you for long, whearase with advancing faces, poor conditions were with you for the life of the face.

Downsides relate to the need to keep development well in front of production, coping with faults found in development rather than production, managing the gas in the waste and er flogging the face for all it was worth because it was the only decent (retreat face) you had ( and not developing the next one fast enough ).

so for UK mining retreat did not take off until heading performance improved dramatically. This it has, with the advent of roof bolting ( good support and less logistics - plus no steel legs to remove when coming back ) and decent machines. Even so most UK retreat faces are single entry - due to depth and cost - which causes problems in gassy seams - I wonder if Harworth are still all advancing faces?

Abroad? Well if you frive multiple headings with bolting you can make money driving the roadways and get payola on the way back.

All for now - for a brief reply.

FYI a set of coal face machinery in Mongolia produced 9 Million Tonnes of coal in one year 2002-3, and was trying to do 10 Million Tonnes next. All retreat minimg - and the coal face equipment transferred from face to face within a week. UK mining would struggle to compete with that, if China was not runnung an energy defecit.

[dazb]

Thick as I am I have to ask about Circular Longwalls, how is this possible? Is it a series of relatively "short longwalls" (The traditional 200 yards or so)? Double units or multiple adjacent face lengths, I am guessing that these are individual faces being worked in a radial pattern and if so does that mean the face lengths were continually extended, because if not and the gates are parallel what happens with the wedge of coal in between them. Please help me Pete, or anyone else that can clarify this description of a circular longwall to a dimwitted spanner handler.

[John]

I think you will find Daz, they were pre industrial age faces, slow advancing hand got faces.
I seem to recall from an old mate I worked with years back that Cotgrave Colliery, south of Nottingham, where I finished my apprenticeship, tried retreating faces. Main problem at Cotgrave were soft floors and heavy roof. Gate maintenance was an ongoing concern with full time crews in both gates at some time or another. It was decided it was cheaper to advance rather than retreat.
Because of the problem with floor lift, Cotgrave resorted to roof hung monorail haulage in the tailgates for supplies.
All main gate gate end boxes's and transformers were slung from a mono rail too. We had an exemption to have the m/g transformer mounted inbye of the GEB's within a few feet of the ripping lip with a shotfiring guard mounted on the inbye side of the transformer to protect it.

[Pete]

Daz - Admin is right - they were hand filled faces which formed an Octagon around the shaft pillar. As the faces moved away from the pit bottom they got longer, and the roadways split. Everything would have been hand filled into tubs and carted off to the nearest haulage.

[dazb]

Did Warsop continue to work later longwalls in the same radial pattern, or did they resort to block extraction as soon as the longwalls became seperated? I can just about grasp the initial benefits of a relatively small diameter circular face, but I can then envisage the problems of going to paralled gates from that, at the point of change over there would surely have been a triangle of coal left between the faces that was impractical to remove. Hope I'm not coming over as too pedantic, but I have never heard of this and the thoughts a circular face is something that has passed through my tiny mind in years past, the ultimate in potential production and engineering nightmares. A spoked wheel arrangement where modern shearers were able to cut in ever increasing diameters of circular Longwalls, loading onto extendable, curved belt type face conveyers, powered by a cable-less power supply to the shearer, 100% coal extraction based on a Hornby Dublo layout.
Pete, is that Outer Mongolia, the Datong area perhaps, where the fantastic tonnage was achieved? What section of coal and machinery set up were they working?

[Ragger]

Just noticed the post about the circular longwall faces. Prior to face teams being paid by the amount they advanced they were paid by the number of cuts/webs taken. So if they took 20 webs that’s what they were paid. It didn’t take the management long to realise the face was advancing more in the middle than at the face ends. Banana shaped faces were frequent if the stable holes weren’t ready for push-over when the machine arrived the chockers just pushed over where they could and the machine went for its next cut.

Paying by how much the face advanced, which was measured at the gate ends put a stop to the practice (well almost).
;D

[dazb]

Hya Ragger, and when they started paying the men by face advance the problem simply reversed, stable holes or face ends anyway, suddenly got that extra shove over each time and the faces went convex, face workers at Manvers were past masters at gaining yardage this way, the men then got another bite at the cherry by coming in over the weekend to take fly cuts in order to straighten the face up, so that it could all start again on Monday. It caused all sorts of problems with the AFC and shearer haulages, particularly dangerous on the chain hauled shearers.

[Pete]

Dazb
You have it right - the face lengths were continually extended.

Worksop dropped the 'circular or octaganal' face profile once they went over to mechanised mining. The first mechanisaed faces had conveyor belts. So from then on the layout would the usual two parallel as possible gates.

Re the 9 million tonnes of coal - I will ask the chap who sold the mining machinery - ( it is Joy equipment ) as to exactly where when I have a pint with him over the Xmas break.

[John]

Those haulage chains always made me nervous Daz, seen a few break and fly down the face. Must have been a lot worse when haulage ropes were in use though!
I wonder why someone didn't come up with the rack and pinion haulage for shearers when they were invented?

[dazb]

Haulage ropes were evil, and particularly so on the shearer, any fitter that had to tension one will shudder at their very mention, let alone the face workers that witnessed one breaking. I once and only once was on a face where the shearer haulage rope broke and once where the rope came through the banjo clamping device, luckily no one was hurt in either but I bet that ropes accounted for many injuries. A friend of mine was killed at a local colliery by a haulage chain breakage.
The first chainless haulage system that I worked on was the Pitcraft Rackatrack (Sp?) at Nostell Colliery I think in the late 1960's, a fantastic concept but at that time only a little less dangerous than the chain systems, the non retained horizontal rack pins were frequently fired into the direction of the goaf at the speed of cannon shells, not always easy to avoid in a yard thick seam. Pitcrafts second chainless system incorporated a different design in which the pins were postioned vertically which at least elimated the risk of being shot through the ribs by a 50mm hardened steel pin whilst crawling at the side of the shearer. I give credit to Pitcraft in pioneering chainless haulage and several other innovational face systems, contra rotating drums, cable-less and hose-less shearers.

[John]

Ropes were bad enough on undercutting machines let alone one over two hundred yards long hauling a shearer set with the "flit" pump running in cut!
Seen a few chains break in my time too Daz, was crossing one once when it gave a lurch and I got clear just in time! I'd have been minus me nuts if I hadn't moved rather quick and trusted instincts!
Used to make me cringe when the chain was being tensioned too, sprag the shearer and let it stall out near the main or tail gate, then drop the clevis in the back end of the springs, which were also spragged for max tension...OOOOO those fingers at risk!

[Clive]

In relation to the circular longwall faces I remember reading about a pit in the Wigan area whos face was a mile long and I think they were using the Iron man type cutters on them. The mind boggles

If you ever get the chamce to read the accident roport on the Gresford disaster in the 1930's just look atthe plans, the faces are all sorts of shapes.

Clive

[John]

When I was at British Gypsum, they worked bord and pillar and the middle bords were always kept in advance, so on the map the faces looked "arc" shaped, this was to get better ventilation throught the bords. It worked and they kept it that way.

[Ragger]

I haven't seen the plans of the pit re-Gresford Disaster Clive but the Manager Mr. William Bonsall who accepted full responsibility; the evidence clearly establishes that he was guilty of the following serious breaches of the General Regulations and of The Coal Mines Act 1911:-

Failure to keep book,copies thereof - Section 24
Failure to maintain adequate ventilation - Section 29 (1)
Failure to measure and enter quantity in every split - Section 29 (1)
Failure to supply separate means of egress in top end of 14's Section 36 (3)
Failure to cut off electric current in 14's face when over 1.25% of gas was present - Section 60 (2)
Failure to comply with requirement regarding telephone apparatus - Section 60
Failure to comply with sub-section 5 of Section 62 (4) dealing with coal dust
Failure to carry out instructions for withdrawal of workmen - Section 67
Failure to comply with Section 88 (b) to supply workmen with abstract
Failure to enforce General Regulations 2 part 1 dealing with wafting gas
Failure to observe Statutory Rules and Orders on Explosives Part 2
Failure to observe C.M.R. Limitations of hours etc 1908-32
He did not cause dust samples to be taken beyond 142's at any time
He left matters involving breaches of law to his under-officials, and never attempted to inculcate respect for the law among the officials appointed by him to supervise the day-to-day operations of the men
The under-manager and other subordinate officials, deputies and shotfirers have also been similarly guilty of flagrant and persistant breaches of The Coal Mines Act and The General Regulations, and all should be dealt with as the Law directs.

[John]

I was reading the other day with the present rates of extraction on retreating longwalls that it's getting impossible to keep up with development faces! I can understand not wanting to be too far ahead with developments as it will lead to roadway deteriation and having to employ full time maintenance crews, increasing production costs.

[limey]

Some mines over here have successfully used a "retreat/advance" system where they first develop a retreating panel - when it is mined out, they simply "slide" the entire face machinery into the next panel and advance it to the boundary. Makes for very quick and efficient changes. However, they still drive the gate headings ahead of the "advancing face" - usually with three headings - one is sacrificed as the panel advances so they don't have to put a pack on.

[John]

Three entry panels were used at Angus Place in NSW, two at what will become the M/G, eventually the second of those two will be the T/G of the next panel.

[Mick]

Hi all when i worked at Wheldale we did alot of retreat work.
But instead of driving 2 new roads,we tuck a face forward first then used one of the gates
as the tail gate of the retreat face.
So we only had one gate to drive for the new face.

[John]

mick said:

Hi all when i worked at Wheldale we did alot of retreat work.
But instead of driving 2 new roads,we tuck a face forward first then used one of the gates
as the tail gate of the retreat face.
So we only had one gate to drive for the new face.

That was standard NCB practice Mick, the law in NSW required two means of egress, hence twin headings being driven for a development, there were some exceptions allowed, but not many.
Due to stress relief, you can also find three and four heading entries in some countries depending on seam height too.
A bleeder heading is also driven parallel to the new face with a thick pillar between it and the face in many countries to help bleed off methane from the goaf area.

[John]

Let me rephrase and add to my post above.
Recall the NCB never or very rarely mined adjacent blocks of coal, so single entries were practiced in developments for retreat faces.
Most mining outside the UK goes for adjacent blocks of coal, so a series of roads, from double entry to many entries is practiced. The pillars are cross cut at regular intervals to recover more coal and also to provide access between the entries. So the resultant "chain pillars" provide extra egress in case of emergency, but also provide stability and support to the next longwall that will be extracted.

Now go back to the Cranwell Canyon accident in Utah last year. The company was extracting the very chain pillars that gave the old longwalls stability and the rest of the mine support. The outcome was widespread convergence spreading to the main outbye roadways.

[limey]

The reason for multiple entries in the States is twofold - firstly practical, so that they can use room & pillar techniques for driving the roadways for retreating faces. Since all roads are driven at seam height, this provides revenue coal. Secondly, the law requires an "intake free escapeway". This is a an intake airway that is free of all machinery - no belts or even rail tracks. Most mines use a three entry system to accomplish both goals, but it is possible to get away with dual entries at each gate.

[dazbt]

limey said:

The reason for multiple entries in the States is twofold - firstly practical, so that they can use room & pillar techniques for driving the roadways for retreating faces. Since all roads are driven at seam height, this provides revenue coal. Secondly, the law requires an "intake free escapeway". This is a an intake airway that is free of all machinery - no belts or even rail tracks. Most mines use a three entry system to accomplish both goals, but it is possible to get away with dual entries at each gate.

It's seems a lifetime now that I've been away from it all and although I knew that the international swing was well away from thin seam Longwall extraction, I would still be surprised to hear that the high quality thin seams of WV are no longer exploited. In the 1990s there seemed to be a great deal of interest from the USA in methods of extracting sections of coal even below the critical 1 metre section. Also at the time of my departure from the industry there was a concerted effort to establish a system of single entry shortwall / longwall system specifically to extract the betwixt-longwall pillars, it was used in the Selby area with some success and I believe that there was a great deal of interest from the US ..................... did it ever take off over there??

[cortonwood]

the single entry face system was used at wistow mine in the selby coalfield,,as far as i'm aware this was used because they had issues with water,single entry faces were used,I think 90m being the typical length..
it is mentioned in this thread that single entry faces were commonplace in uk coal mines,,i've worked all over yorkshire and the only place i heard of them being used all the time was wistow..
i'm not sure if the reference to single entry faces in the thread is getting confused with retreat faces that didnt actually cut into the tail gate..ie, where ventilation slits are made thru the tail gate rib ino the face,,,this practice is not the same as single entry faces..
single entry faces as far as i'm aware have just a main gate,the face is ventilated by auxillery fan with ducting running through the chocks.

[John]

I think the reason double entry's are used more commonly is it saves time and money. Thick seams with bolted roofs use what is known as "chain pillars" with cut throughs staggered so as not to leave too much unsupported roof at cut throughs. It's just more convenient to drive two roads at the same time as one road.
At Angus Place in NSW it was common practice, then the left hand heading would be for the M/G of the next development and the right would be for the following faces T/G. The first cut through was a rail turn for recovery of the present longwall face.

I downloaded a small map of Angus Place, I'll have to upload it to photobucket and post it here to show how we worked at that pit.

If you look at the maps of Crandall Canyon Mine in Utah where they had that accident a few years back, you can see all the old longwalls with their chain pillars, that's what the poor bastards were robbing when the area started converging on them.

[cortonwood]

most pits i've worked in were deep,,800m+,,,,at a couple of these pits we used retreat faces where the tail gate was a former gate to the last face worked,,it gave us nothing but trouble,within' 200-300m of retreating we were on our bellys in the tail gate,having to take supplies up the main gate and transport them through the face.,it was horse work at the tailgate making the vent slit thru into the gate..we used to have to dint down by boring and firing before we could even make a start on the slit.

[John]

Aug 28, 2012 17:52:29 GMT -5 cortonwood said:

most pits i've worked in were deep,,800m+,,,,at a couple of these pits we used retreat faces where the tail gate was a former gate to the last face worked,,it gave us nothing but trouble,within' 200-300m of retreating we were on our bellys in the tail gate,having to take supplies up the main gate and transport them through the face.,it was horse work at the tailgate making the vent slit thru into the gate..we used to have to dint down by boring and firing before we could even make a start on the slit.

That was the idea of chain pillars, to prevent weighting of the gate roads from the previous face.

I remember a face in the deep hard seam that converged from over five feet to closed up in minutes, the next face was developed very quickly adjacent to it and was very close to the water bearing Bunter strata, these were advancing. I'd never heard of retreating back then.
Everyone ended up traveling the M/G as the face advanced, all supplies went through the face on nightshifts!! The T/G was just too low and dangerous to travel.....Errrr where was HMI? ;D

We lost that face to water and weighting, our last high face. After that it was 3 feet to just over 3 feet.

[Wheldale]

Aug 28, 2012 17:07:39 GMT -5 cortonwood said:

the single entry face system was used at wistow mine in the selby coalfield,,as far as i'm aware this was used because they had issues with water,single entry faces were used,I think 90m being the typical length..
it is mentioned in this thread that single entry faces were commonplace in uk coal mines,,i've worked all over yorkshire and the only place i heard of them being used all the time was wistow..
i'm not sure if the reference to single entry faces in the thread is getting confused with retreat faces that didnt actually cut into the tail gate..ie, where ventilation slits are made thru the tail gate rib ino the face,,,this practice is not the same as single entry faces..
single entry faces as far as i'm aware have just a main gate,the face is ventilated by auxillery fan with ducting running through the chocks.

The single entry faces at Wistow were I think 15m in length. I knew an overman who worked them at wistow. The smaller normal retreat faces were 80 meters in length. These faces I believe were on the west side of the pit where the water problems were. These small faces were used to over come the water problems.