Settlement / grade depression in a road 3

[fivestring]

I have been asked to come up with a solution to what looks like settlement in a road. This road is less than a year old and already has severe cracking and grade depressions in the majority of the 'fill side' of the road. My instinct tells me that the fill might not have been compacted properly, and we did receive a severe amount of rainfall a few months ago. What would be a good solution to this issue? I thought about removing the asphalt/aggregate and re-compact the subgrade; but to what depth? Would it be better to do something like specify a geotextile on the subgrade? Thanks.

 

[LukasJ]

Hello
It is a bit off-toppic, but I'd like to ask for something. I am in the UK as an abroad student and I am working on my masters project about geo-enginnering problems of road structures - taken generally, but I am also trying to collect different examples from practise, preferably those which weren't published yet. Because of lacking some cetral repository of geotechnical reports in the UK this is quite difficult.
Would you mind me to use this case in my work?

 

[LukasJ]

2:1 is a pretty steep for clay soil -in this case water may just triger the necessary. In aditional about compation - based what I know it might be problem with wrong moisture content in original fill during compation - this might couse local lesser compation and more permeable areas.

 

[LukasJ]

2:1 is a pretty steep for clay soil -in this case water may just triger the necessary. In aditional about compation - based what I know it might be problem with wrong moisture content in original fill during compaction - this might cause local lesser compaction and more permeable areas.

 

[fivestring]

LukasJ, if you are talking about the project I posted, unfortunately I don't have much more information other than what i have provided in this thread. Let me know if there is something else I could do.

 

[oldestguy]

One more item for possible consideration.

Year's back I heard about "California horizontal drains" and if you Google those words up comes info on them. Apparently it has been a successful way to stabilize sliding situations where water is doing the mischief in California.

They are drilled in from the toe of the slope and the hope is to tap sources of water.

I only used this procedure once. It was for a 30 ft, high lake laid clay bank that was sliding towards a valley.
First vertical holes were drilled and filled with sand. Then the horizontal drilling was done intersecting the vertical sand filled holes.
Vertical holes were 18 inches diameter and about 30 feet deep and the horizontal holes were 12 inches diameter maybe 60 feet long with sand blown in as casing was withdrawn.

Everything worked to stabilize the hill side, some 30 feet high, but in the winter the weeping drains caused a messy icy condition. I suppose we could have directed that discharge to a storm drain, but didn't think of that at the time.

Check out the references from Google and that may be an idea.

 

[LukasJ]

Fivestring: But this project has to be solved, right? I need to present my masters work in next June or later, so there is a lot of time during which project may be solved, or explored more deeply. This is a good chance for me to have a look at solution while it is made, not after.
Could you give me some email or so? I dont want to spam here...
Thank you a lot.

 

[fattdad]

For some reason (heat and humidity most likely), horizontal drains to relieve pore pressure buildup and the resulting instability do not work in the east. If this project is in the east, you'd need to reconsider this approach.

Heat and humidity have a way of fostering microbes that oxidize iron, which in turn clogs up the screens of the horizontal drains. They'll work for a spell, but after a few years, your on you own as they become clogged.

I considered this approach for a job in Georgia and that's what the contractors told me.

f-d

¡papá gordo ain’t no madre flaca!

 

[oldestguy]

On the subject of microbes and iron, take the situation with water supply wells where there is iron in the rock. To my knowledge there is no clogging. Iron in water softeners does clog things however.

Maybe those in the business of water supply wells might wade in here.

My single job use of the ideas did not clog.

The only problem with sub-drains that I have run into is use of galvanized perforated pipe in peat. Rather acid stuff. There the steel rusts out and leaves the galvanizing....Not much strength left.

 

[BigH]

horizontal drains work - in British Columbia we used vacuum horizontal drains to bring down pore-pressures faster - but these were for high ground water levels - in cuts. They have been used in Malibu too - a professor and his student (now a professor) at University of British Columbia did work (mid 1980s). We don't know how much traffic is on th road - is it a major road, a few cars/trucks an hour road or . . . how "big" are the half-moons. When one starts talking about horizontal drains and that - it comes to major bucks - now if Pres. Obama will give you some stimulus money . . . The solution has to match the importance - and if they are, in fact, translational slides due to rainy season water infiltration (infinite slope style analysis) it probably not necessary to use horizontal drains. One I didn't show a snap of (and it had "slid" some 4 times before), we just cut the slope put in a gabion wall and rock fill butress and made sure that we stepped into the sliding plane. Hasn't moved since - some 3 years now.

 

[Ltwine]

it is more cost effective if you can find ways to stabilize the toe of the sloping fill - with earth berm/stone wall,maybe, and suitable drainage system.

 

[fattdad]

Yeah, I'd like to find out whether the banjo player's (fivestring's) in the Carolinas, Georgia or such. You can design a horizontal drain (drilling methods), but I'd check with contractor's experiences first. It's not favorable from what I learned.

f-d

¡papá gordo ain’t no madre flaca!

 

[fivestring]

I am in Georgia and yes, I am a banjo player (paddle faster, I hear a banjo). Thanks for the valuable posts. I have learned that this issue might have happened for several reasons. I am planning to recommend further geotechnical testing to determine the cause. However the owner believes it was caused by a culvert from another street not working properly during the heavy rain back a few months ago. I don't believe this because we have this issue in several areas along the road. If the owner just wants to fix the road then I am recommending a full depth repair in the 'settled' areas as well as the sub-base where it has been undermined or not compacted correctly.

 

[fattdad]

Yes, it was Columbus, Georgia where I considered the use of horizontal drains to stabilize a slide. Contractors had already had bad experience and not willing to do the work (with any sort of warrantee or such). I did go to prominent contractors out of Atlanta (who had some backing) and figure you could find somebody with nothing to lose to attempt it.

I play the mandolin, but forever the amature.

f-d

¡papá gordo ain’t no madre flaca!

 

[emmgjld]

I have no idea what your conditions are. Fattdad had bad experience and probably most others who tried horizontal drains has noted the expense can be very high and risky.

I was at a Highway type conference in Denver several years ago and Dr. Paul Santi presented a short paper exhibiting Wick Drain Material inserted into short lengths of small pipe and pushed into a hillside. He had an article in Civil Engineering—ASCE, Vol. 71, No. 6, June 2001, pp. A10-A16.

In the Western Colorado area, I have had a fair amount of success with 'push drains' around residential structures and road cuts. Most of my experience has been pushing these into new to old slope failures, oftentimes with a significant amount of small to large boulders. The local county road & bridge has been using these fairly extensively in the higher elevations around Grand Mesa.
They are fairly inexpensive and if a boulder is encountered and more penetration is desired. The equipment moves a foot or two and tries again.

Here are a few links. The real long one is the basic presentation I heard. Hopefully this gives a few ideas.

http://inside.mines.edu/~psanti/

http://onlinepubs.trb.org/onlinepub...inalreports/highway/NCHRP076_Final_Report.pdf

http://www.sloperepair.com/news_developments.php

http://trb.metapress.com/content/g50265m5067558j9/

 

[BigH]

Thanks emmgjld!