Repair of Frost Heaved Sidewalk in Gravel

[rockchip]

We have been asked to evaluate the cause (and possible repair) of a sidewalk that has been damaged by frost heave or frost jacking. The soil below the slab consists of alluvial gravel with sand and silt. Silt content is less than 10 percent. However, the water table is reported by the client (a municipality) to sometimes reach the surface. We had a very dry winter in Eastern Washington this season and consequently very little snow on the ground. This combined with the usual below freezing temperatures and a high water table I believe caused the jacking of the sidewalk. Assuming these are the likely causes, we recommended drainage, combined with removal and replacement to at least 18 inches with imported clean gravel. I am interested in hearing from those of you in cold weather regions on how you typically handle this type of problem. Thanks!

 

[DRC1]

Drainage is the key, especially with a high water table. If yuo have area that are tough to drain, I reccomend using a frost resitant crushed stone, such as basallt for the sub base in those areas. Another option is to use asphalt or pavers, which are not as resistant to movement as concrete, but can be repaired cheaply. If you do use concrete, be generous with the mesh.

 

[rockchip]

Thanks DRC1. We are considering a shoulder ballast 2-1/2" minus crushed stone with 0-2 percent passing #100 sieve for the base. I appreciate the recommendation for additional reinforcing in the sidewalk. There is plenty of crushed basalt available in the area of the site so that sounds like the best approach so far combined with the drainage. The city did consider pavers but rejected them. Thanks for the feedback!

 

[CarlB]

How much sidewalk jacked? Did it return to original location/elevation after thawing? What was the maximum frost depth? Since there was damage there was obviously non-uniform heave, which is often the case. What is different betweeen the soils & water conditions in areas that didn't heave? You are correct in specifying non-frost susceptible material below the sidewalk, which is, for practical purposes, soil with less than 5% passing the #200 sieve. But 18" depth may not be enough if there is moderately to highly frost susceptible soil below the 18" depth. In the next cold/dry winter that deeper material could heave again. The damage may be less due to the 18" "cushion", but not necessarily eliminated.

 

[rockchip]

CarlB: It's been a busy month. Thanks for your comments. To respond to your questions, the sidewalk exhibited jacking by one end lifting up. Much of the sections return to nearly their original positions in summer. Over the years the cycles have resulted in typical uneven edges and cracking and spalling of the corners of the sidewalk sections where they get pinched or where traffic loads cross and crush them. We did not do enough testing to differentiate between areas that did not heave and those that did. We instead focused on areas that heaved. On next one we will explore the differences as these may be significant. We recommended drainage as being beneficial in reducing the potential for future damage as this removes the water in the first place. The drainage may not, however, remove the potential from moisture in the surface crushed rock though. Another good point. Thanks!