Remediation Methods for Subgrade Settlements of Existing Roadways: Lifetime Cost-Benefit Analysis

Continual settlement of existing roadways can occur when a roadway is constructed over weak soils consisting of very loose/very soft compressible soils. These continual settlements typically increase the cost and frequency of maintenance that is required for a particular roadway segment. Other serious issues resulting from the settlement can occur such as regular flooding of the roadway, pavement deterioration causing a rougher riding surface, loss of design grade elevations on horizontal and vertical curves, dips in the roadway where water can pond and subsequently freeze, and other issues causing safety concerns. Remediation of these settlement issues include: 1) surficial treatments such as cement/lime stabilization or excavate and replace with or without geotextiles; 2) deep foundations to bridge the problem soils by transmitting loads to deeper more competent soil or rock; and, 3) ground improvement methods which can be utilized at sites with weak soils that are too deep for surficial treatment and where deep foundations aren\u27t a cost-effective solution. This study investigates the different types of remediation methods and their suitability for various subsurface conditions, particularly for sites where surficial treatment are not adequate and/or are prohibitively expensive. As part of the study, subsurface explorations were performed at a sites with continual settlement issues due to deep deposits of very weak soils Based on the results of the subsurface explorations, different ground improvement methods were evaluated for remediation of the ongoing settlements. Subsequently, a lifetime cost-benefit analysis was performed comparing the cost of construction of the selected ground improvement methods to the current typical practice of continual maintenance and overlay. Other costs associated with the current typical practice beyond the maintenance costs were examined including safety risk cost, societal cost, and cost to the road user due to the inferior pavement condition