This report summarizes the results of a literature research effort to assist the Minnesota Department of Transportation (Mn/DOT) in (1) evaluating methods and devices for reliably determining in-situ drainage characteristics of base and subgrade materials and (2) evaluating the specifics of the most promising options that are best suited to Mn/DOT's needs. This research effort is limited to existing information and studies. The primary goal of this effort is to identify a device or method that would be used by field inspectors to ensure that base and subgrade materials are capable of removing infiltrated water from pavement systems in order to prevent accelerated pavement deterioration. The device or method must be durable and easy to use by field personnel. The device or method must also be economical so that it can be distributed for state-wide use.
The research effort is being performed in two phases. Phase I (summarized in this report) is a comprehensive survey and review of existing literature to identify methods and devices for measuring in-situ drainage characteristics of aggregate base and granular subgrade materials and to summarize salient characteristics of these methods and/or devices. Phase II will focus on a more detailed evaluation and· analysis of the most promising methods and/or devices identified in Phase I. The selection of the methods and/or devices for the Phase II study will be performed in conjunction with Mn/DOT's review of the Phase I findings.
This report summarizes the devices from Phase I of this study, as well as Phase II results. In Phase II, researchers evaluated the inverse auger hole test, open single-ring infiltrometer test, and the direct velocity technique for measuring the in-situ drainage characteristics of aggregate base and granular sub grade materials.
According to research findings, the referenced methods of calculating hydraulic conductivity from the test measurements appear to be incorrect. The devices will have to be modified and the method of calculating hydraulic conductivity from the test measurements revised to obtain an appropriate value for hydraulic conductivity. The appropriate value for hydraulic conductivity calculated from modified tests can be used to estimate the drainage of the aggregate base and subgrade materials.
Another important finding from Phase II involves the characterization of flow within the aggregate base and granular subgrade material. As designed, the flow is primarily horizontal. Based on this finding flow normally will be in an unconfined flow regime. As such, it is critical that enough discharge capacity and storage capacity be provided within the aggregate base and granular subgrade material to prevent saturated confined conditions beneath the pavements during infiltration. The study also recommends continuing the investigation of drainage characteristics beneath pavements.
