mining dump facility barrier loading

[bne_eng]

Looking at impact loading on a barrier where mining trucks reverse up and dump their load over the edge into hoppers. Big loads, big wheels, but the speeds are low because they're slowing down to a stop - they know the edge is there. Not like an accidental veering off a road on a highway. Perhaps more like a parking garage type scenario, but the vehicles are 250,000kg loaded and the tyres are over 3m diameter.

So my question is this: What do you think is a reasonable approach to calculating the appropriate loading on the barrier? We know the mass of vehicle, but need to know the starting speed and time to decelerate to work out a force. I've searched for some papers on this, but nothing I found covers the size and mass of vehicles we're looking into, so I'm concerned how applicable they are.

Thoughts?

Also appreciate thoughts on calculating appropriate braking forces to prevent the slab sliding on the subgrade - probably will need to implement anchor beams back some distance from the retaining wall.

 

[HTURKAK]

If I were in your shoes, i will try several approaches and envelope the results.

One approach, assume the truck wheels similar to the rubber fenders, a preliminary calc will be;

The mass of the truck m = 250X9810 /(9.81X1000)=250 N sec2/mm and approach velocty Va= 3kph =800 mm/ sec.
Energy of truck E= 0.5X 250X(800)**2=8.0 E7 N- mm. Look to the Energy absorption versus deflection curve, the expected deflection of tires for (4 tires ) 150 mm and the corresponding reaction force will be 4 X30 = 120 tons (1200 kN ).

Another approach ,the use of ship collision formula and one of them, assume V=3 Kph =1.7 knots
Ps=0.98* ((DWT)**0.5)*(ν/16 )

Ps =0.98*SQRT(250 )*(1.7/16)=1.646 (MN) =1600 kN.



Third approach, search the web for parking bumpers truck concrete, and scale the dimensions for the haul truck weight and tire size.
One of them ,

https://commercialconcreteproducts.com/parking-bumpers/

I will suggest you, provide a thick slab on grade (t=400 mm) with minimum width to cover the tire size with RC bumper at hopper side, having trapezoidal section top width 300 mm , height 450 mm and slope 1:1.

You may provide shear nib at far end of the slab to mobilize the friciton.

 

[Settingsun]

45% of weight * load factor is used by some. I used to work for a company that does a lot of mine work and that was in their standard mine design criteria document.

Edit in response to next post below: Mine was a concrete kerb (low wall) similar to the cross- section on this page:

http://www.retainingsolutions.com.au/case-studies/clermont-coal-mine-reco-terraclass-system

 

[LittleInch]

How "flexible" is the barrier?

Is this like a ships fender type thing or is all the flex taken by the tyres?

A drawing / photo would help.

A radar guage and some red, orange green lights might be a lot better in front of the driver?

Or a reversing camera?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bootlegend]

Similar to steveh49, I have used 50% of the loaded weight for design. For strength design of the barrier and slab I'd assume half of that to each rear tire, applied at top of barrier. I would distribute that out over 45 degrees or so to get an effective width.

As far as sliding of the slab I have used that same load as the sliding force. I make sure the pad is at least long enough to fit the front tires on before the back tires hit the barrier so that I can count on the vertical load there. I'd have to check to be sure but I think some of the cases the thickness of the pad has been controlled by the need for extra mass instead of the strength design.

I've anchored a few pads when sitting on a solid rock highwall, but many times they are on top of an MSE wall and the extra mass seemed easier than dealing with geogrid and critical backfill criteria.

I'm not an expert but I've designed several of these and they all have performed well to my knowledge.

 

[ldeem]

I did one of these 3 or 4 years ago (it is still working) and used energy method (truck speed times mass) vs energy absorption of the truck stop. I ignored the energy absorption of the tire deflection. In my case the truck stop was on steel beams spanning between the wall and top of the crusher dump hopper. I designed them to be like long springs.

I think I calculated impact energy at several speeds until the client and I arrived at one that would work in design and was reasonable for the operators.

The tricky part of this is if you make the stop too stiff it drives up the loading, you need to absorb energy which means deflection. Think of a crane runway stop or energy absorbing barriers along a highway.

On the slab question I think there are some brake force calculations that look at braking effectiveness based on friction between tire and ground. You might be able to take this information and assume the slab will need to transfer an equal amount of frictional force.

 

[bne_eng]

Thanks so much for the great replies everyone. To respond directly:

If I were in your shoes, i will try several approaches and envelope the results.
One approach, assume the truck wheels similar to the rubber fenders, a preliminary calc will be;
The mass of the truck m = 250X9810 /(9.81X1000)=250 N sec2/mm and approach velocty Va= 3kph =800 mm/ sec.
Energy of truck E= 0.5X 250X(800)**2=8.0 E7 N- mm. Look to the Energy absorption versus deflection curve, the expected deflection of tires for (4 tires ) 150 mm and the corresponding reaction force will be 4 X30 = 120 tons (1200 kN ).

Thanks mate. Yes - I agree about trying several approaches and enveloping results. Quick question - I'd like to be able to justify the assumptions you've made of 3km/h and 150mm deflection - are those figures from some reference, or were they just exemplar?

45% of weight * load factor is used by some. I used to work for a company that does a lot of mine work and that was in their standard mine design criteria document.

Edit in response to next post below: Mine was a concrete kerb (low wall) similar to the cross- section on this page:

http://www.retainingsolutions.com.au/case-studies/...

Thanks mate. That's along the lines of what I was thinking (50%) - and that link you posted is very similar to the one we're looking at.

How "flexible" is the barrier?
Is this like a ships fender type thing or is all the flex taken by the tyres?
A drawing / photo would help.
A radar guage and some red, orange green lights might be a lot better in front of the driver?
Or a reversing camera?

Very similar to the link steveh49 posted above - barrier is concrete (not flexible) so any flex and energy absorption taken by truck tyres. "Belts and braces" of signage and cameras are good idea, but need to have the last line of defence designed appropriately.

Similar to steveh49, I have used 50% of the loaded weight for design. For strength design of the barrier and slab I'd assume half of that to each rear tire, applied at top of barrier. I would distribute that out over 45 degrees or so to get an effective width.

As far as sliding of the slab I have used that same load as the sliding force. I make sure the pad is at least long enough to fit the front tires on before the back tires hit the barrier so that I can count on the vertical load there. I'd have to check to be sure but I think some of the cases the thickness of the pad has been controlled by the need for extra mass instead of the strength design.

I've anchored a few pads when sitting on a solid rock highwall, but many times they are on top of an MSE wall and the extra mass seemed easier than dealing with geogrid and critical backfill criteria.

I'm not an expert but I've designed several of these and they all have performed well to my knowledge.

Thanks mate. Exactly along the lines of our approach.

I did one of these 3 or 4 years ago (it is still working) and used energy method (truck speed times mass) vs energy absorption of the truck stop. I ignored the energy absorption of the tire deflection. In my case the truck stop was on steel beams spanning between the wall and top of the crusher dump hopper. I designed them to be like long springs.

I think I calculated impact energy at several speeds until the client and I arrived at one that would work in design and was reasonable for the operators.

The tricky part of this is if you make the stop too stiff it drives up the loading, you need to absorb energy which means deflection. Think of a crane runway stop or energy absorbing barriers along a highway.

On the slab question I think there are some brake force calculations that look at braking effectiveness based on friction between tire and ground. You might be able to take this information and assume the slab will need to transfer an equal amount of frictional force.

Thanks mate. Our barrier is concrete, but we'll certainly discuss with client assumptions regarding assumed speeds as per your recommendation.

 

[HTURKAK]

I only estimated the approach velocity 3km/h ( I think reasonable ) and the total energy is dissipated by only rubber tires (conservative but it is reasonable to assume the heavy offroad vehicle will not absorb energy ). I used the Energy absorption vs deflection curve and Reaction force vs deflection curve for rubber fenders which you can find at marine structural handbooks or manufacturer's data.

In past, i designed a similar stopper ( may be around 30 years ago for a coal washing plant ). I provided a thick pad which the rear axle will be supported with a RC stopper similar set up at my previous respond and i did not hear any negative respond.

 

[LittleInch]

Could you use a ramp instead to gradually increase the reversing force? That way you get rid of the impact loading which for a solid barrier will end up being rather large I suspect.

Or a solid block about 20% of the tyre height? Big enough to deflect the tyre but not to take the entire load?

Any sketches of ideas here?



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bne_eng]

Thanks again for the replies and clarifications. We can't have a ramp of any significance here, other than slight slope to shed storm runoff. The barrier will be about 1/3 of the wheel height, so as you suggested some energy will go into lifting the rear of truck. I think we're sorted. Thanks again for your thoughts all.