Conversion of Snow load to SURCHARGE LOAD on Soldier H Pile Retaining wall with Lagging 1

[EugeneNinnie]

We are designing a Soldier H Pile Retaining wall with Lagging to support 11 ft height of soil at its greatest to 2' at each of the ends of this 61 ft long wall. The wall also needs to have another 10 ft of extended H pile with steel lagging for avalanche control along its entire length. The analysis of the future avalanche is 400 psf along the 10 ft extension. We need to convert this to surcharge to be entered into our ENERCALC Retain Pro program.

How do you convert the snow load into surcharge at the top of the wall using the computer program ( not hand calculation) whereby the surcharge can be input.

Thanks in Advance

 

[dold]

Do you mean to apply the load as a lateral load on the top of the exposed 10ft extension? Or do you mean the surcharge due to the static weight of the snow just sitting there?

 

[EireChch]

I think the critical load condition will be an overturning moment from the avalanche, not the surcharge. Assume a unit weight of snow, (or take it as a soil to be conservative), and take the lever arm as 1/3 of 10ft.

 

[Craig_H]

This load case seems sufficiently different from what your software was designed for, warranting a detailed hand-calculation instead. A few thoughts:
- I hope you had an avalanche expert determine the impact pressure. It's a complicated field, and avalanche dynamics can impose unusual load distributions. The fastest moving snow is at an elevation above the ground, and the air blast preceeding the avalanche can impose larger impact pressures than the snow (in some specific cases).
- When determining the surcharge from an arrested avalanche (post-impact), I would consult with your avalanche expert regarding the density of that snow. It's not just the unit weight of snow on the ground; the snow has been through a high-energy event, has partially melted, and then been smashed into a wall. It could easily be in the range of 500 kg/cu.m
- In addition to post-impact surcharge, this wall will be exposed to snowpack creep/glide forces, which can be significant and long-term.

This is a complicated situation, and needs more consideration than merely adding a surcharge load to a generic retaining wall design program.

 

[BridgeSmith]

As Craig H noted, impact pressure from the dynamic loading during the avalanche event will be the controlling load case. Once that is determined by an avalanche expert, then I would think you would apply it according to the distribution the expert gives you. Most likely it will be a uniform surcharge or an increasing load as it goes up (similar to the application of stream force on a pier). The pressure of the snow sitting against the wall afterwards will likely be an order of magnitude smaller than the dynamic pressure produced by the avalanche.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[EugeneNinnie]

I should re-phrase my question....How do you convert the snow load into surcharge at the top of the wall??? and yes we have had an avalanche "expert" to provide all data. I need to convert this applied snow load to an equivalent soil height ABOVE the already 11 ft of soil we have to retain.

 

[dhengr]

EugeneNinnie:
Is the only loading you can input to that program the triangular, hydrostatic loading? Can’t you apply a trapezoidal load, the hydro. triangle, plus a uniform surcharge pressure loading block? Why not design the top 10’ in the fashion that your program allows, then apply the imaginary wall/ftg. loadings, moment, horiz. load (shear, outward) and any vert. loading at the top of the 11’ soldier pile wall, plus its own basic soil pressures. Similarly, apply the impacting avalanche loading to the top 10’ of wall, and then to the lower 11’. It kinda sounds like that software is getting in your way, rather than being a helpful means to a solution.

 

[BridgeSmith]

Oh, so you're looking for the vertical surcharge of the weight of the snow on top of the soil. In that case, you would just add the weight of the snow divided by whatever soil pressure coefficient you're applying (ka for active soil pressure condition or ko for at rest condition).

Alternately, the simpler approach may be to put the snow in as another 'soil' layer with the appropriate unit weight and angle of internal friction.

I'd still be surprised if the static load case was more critical than the dynamic case of the avalanche hitting the wall. I don't think you'd have to consider the case with the weight of the snow simultaneously with the impact loading. In bridge design, we don't consider vertical loading and impact simultaneously for vehicle impacts on traffic rails.

Rod Smith, P.E., The artist formerly known as HotRod10