Rockfill placement on bedrock with water 1

[Throstur]

Hi all,

I´m looking for helpful tips or comments on the placement of rockfill (-75mm) ontop of clean bedrock, which is quite uneven (+/- 1 m or so). Due to site conditions, water is covering much of the bedrock. Draining the "pond" is not working effectively due to groundwater flow.

The question is: does placing and compacting this rockfill "underwater" in lifts of around 300 mm have negative effects on the properties of the fill compared with if there was no water?

best regards,
Throstur

 

[BigH]

How deep is the water? If, say, the water is 2m deep, how are you going to place and "compact" the rock-fill in 300mm lifts? Best bet is to use, say, 25 to 75 stone, dump it in until you are out of the water, level, chink the surface and then place your normal fill atop. Indian Road standards permits tipping placement through the water of -75mm gravel and sand (with a uniformity coefficient of not less than 10) without compaction.

 

[Throstur]

Thanks for the input. Here are a bit more info to fill in the gap.

The water is not 2m deep. Maximum depth of around 600 mm meaning the compactor can easily operate on the layer in the water with vibration. The material that's being used is fixed and will not be altered, i.e. max size 75mm.

I'm just wondering whether the effect of the compaction is poor when the rockfill layer is completely saturated in water since foundations will be placed ontop in the near future. Do we absolutely need to drain the water before place the fill?

 

[BigH]

Throstur - okay the water is shallow - the material placed you call rockfill - 75mm max. What is, say the %passing #4? #200. If the rockfill is clean - as I indicated above, you won't get much compaction. In many places they use clear crushed stone for sewer fills to get away from compaction. How high will the foundations be above the current water level? Again, I would think that you would be putting in a granular pad to raise the grade to get the area out of the water. If, say, you are founding "at" current water table, then, the thin layer of stone should not have much settlement problems - how much will <1m of rockfill settle anyway? So not much worry there. All in all, I'd drop the fill through the water, get it out of the water by 300 to 500 and then compact the layer with your roller - staying out of the water. Big rollers will compact more than 200mm anyway. You'll get some compaction of the lower layers - enough I would think not to worry.

 

[Throstur]

The rockfill is blasted and crushed basalt. The gradation has approximately 30% passing the #4 sieve and approx. 2-3% passing the #200 sieve. The foundation will be around 2 m above the bedrock and are settlement sensitive.

The compactors are 15-19 (metric) tons so they actually compact to some depth - that´s true.

Thanks for your comments BigH,

 

[BigH]

I think that I would do a thicker first lift to get out of water, then as above. Good Luck!

 

[RCEJD]

Throstur: We recently performed a similiar type operation at the bottom of a canyon cleanout where future fill layers would be approximately 85 feet in thickness. We have done this on numerous occaissions. As in your case, the granular nature of the fill (low percentage < 200 sieve) with larger fragments permitted an effective placement of oversized materials (2 to 4 foot boulders) within a rockfill. Spacing of the oversized was ensured to prevent arching. We monitored the fill performance for 2 years with settlement monuments and have had excellent results. The granular nature of the fill is effective in allowing equipment movement under water. We made sure and spec'd select fill to prevent the fine content from increasing above acceptable levels.

Good luck.