Details:

Creators:
Papanicolaou, A.N. Thanos ; Bressan, Filippo ; Wilson, Christopher ; Tsakiris, Achilles
Papanicolaou, A.N. Thanos ; Bressan, Filippo ; Wilson, Christopher ; Tsakiris, Achilles Less -
Corporate Creators:
University of Iowa. Civil and Environmental Engineering
Corporate Contributors:
Iowa. Highway Research Board
Subject/TRT Terms:
[+]
Evaluation Frost Damage Gravel Roads Permeability Coefficient Potholes (Pavements) Subgrade (Pavements) Subsoil Subsurface Drainage
Publication/ Report Number:
TR-654
Resource Type:
Tech Report
Geographical Coverage:
Iowa
Corporate Publisher:
Iowa. Dept. of Transportation. Highway Division
Abstract:
With over 68 thousand miles of gravel roads in Iowa and the importance of these roads within the farm-to-market

transportation system, proper water management becomes critical for maintaining the integrity of the roadway

materials. However, the build-up of water within the aggregate subbase can lead to frost boils and ultimately

potholes forming at the road surface. The aggregate subbase and subgrade soils under these gravel roads are

produced with material opportunistically chosen from local sources near the site and, many times, the

compositions of these sublayers are far from ideal in terms of proper water drainage with the full effects of this

shortcut not being fully understood.

The primary objective of this project was to provide a physically-based model for evaluating the drainability of

potential subbase and subgrade materials for gravel roads in Iowa. The Richards equation provided the

appropriate framework to study the transient unsaturated flow that usually occurs through the subbase and

subgrade of a gravel road. From which, we identified that the saturated hydraulic conductivity, Ks, was a key

parameter driving the time to drain of subgrade soils found in Iowa, thus being a good proxy variable for accessing

roadway drainability. Using Ks, derived from soil texture, we were able to identify potential problem areas in

terms of roadway drainage .

It was found that there is a threshold for Ks of 15 cm/day that determines if the roadway will drain efficiently,

based on the requirement that the time to drain, Td, the surface roadway layer does not exceed a 2-hr limit. Two

of the three highest abundant textures (loam and silty clay loam), which cover nearly 60% of the state of Iowa,

were found to have average Td values greater than the 2-hr limit.

With such a large percentage of the state at risk for the formation of boils due to the soil with relatively low

saturated hydraulic conductivity values, it seems pertinent that we propose alternative design and/or maintenance

practices to limit the expensive repair work in Iowa. The addition of drain tiles or French mattresses my help

address drainage problems. However, before pursuing this recommendation, a comprehensive cost-benefit

analysis is needed.


Format:
PDF
Collection(s):
US Transportation Collection
Main Document Checksum:
[+]
urn:sha256:d725eedd4aadd7e3922116cd72c10328dbe8454b074abb7e220fe7ffc12fc698
Download URL:
https://rosap.ntl.bts.gov/view/dot/29599/dot_29599_DS1.pdf
File Type:

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