Drainage

This research summary is part of the final deliverable for Report 2025-22, "Comparison of Compost and Proprietary Soil Amendments for Vegetation Establishment," Published in March 2025.

Post-construction roadside soils often suffer from compaction, low fertility, and poor structure, challenging vegetation establishment and stormwater management. This study evaluates the effectiveness of organic amendments (OAs) and proprietary amendments as alternatives to traditional methods. The study involves greenhouse experiments (pot and mesocosm) and field experiments to evaluate vegetation growth and water quality across different amendment and soil applications. Results show that compost amendments significantly improve vegetation growth, with yard-waste compost outperforming others. Biochar shows early growth potential but requires nutrient supplementation for sustained performance. Proprietary amendments support rapid vegetation establishment, enhanced root density, and reduced nutrient leaching, with Sustane 4-6-4 exhibiting consistent growth across application rates. The field study validates greenhouse findings and shows increased biomass and root density with compost amendments, while proprietary amendments result in high nutrient retention and runoff quality. This study highlights the potential use of OAs and PAs to reduce erosion and support long-term vegetation growth. The findings provide practical guidelines, benefits and implementation steps for managing roadside soils after construction activities.

The Minnesota Department of Transportation (MnDOT) recognizes the importance of subsurface drainage in pavements. Various studies have indicated that adequate drainage of pavement layers enhances performance of pavements in general. MnDOT thus uses various types of subsurface drainage in varying degrees of styles, frequency of use, and minor variation in construction practices in the various transportation districts of the state. The subsurface drainage technologies include Open Graded Aggregate Base (OGAB), Drainable Stable Base (DSB), Permeable Asphalt Stabilized Base (PASB), Geocomposite Joint Drain (GJD) and Class 5Q aggregate. This study examines the various drainable bases in the network and identifies their locations and limits. Using performance data from the pavement management system, the performance, measured via Ride Quality Index (RQI), of test sections with drainable base systems was compared to contiguous sections without the systems so that traffic and environmental factors as well as other variables were held constant. Reliability and logistic analysis were conducted to ascertain if there were performance advantages in the drainable systems. The difference between the systems was found to be advantageous in certain districts, and an operations research survey reflected advantages in the drainable systems where and when they were associated with proficiency in construction practice.

This study was initiated to examine the problem of plugging of geotextile/perforated pipe subsurface drainage systems by the precipitation of calcium carbonate.

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.

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 Implementation Summary relations to Report 2023RIC08, published April 2023.

The primary objective of this study was to determine whether concrete lug anchors retarded pavement movement on steep grades. Minnesota Department of Transportation's policy is that grades in the 3 to 5 percent and greater range are steep and may require lug anchors. Standard lug anchor spacing varies from 150 feet, center to center, for 3 percent grades to 75 feet, center to center, for 5 percent and greater grades. During the initial study of lug anchors on State Project 0702-49 it was observed that pavement settlement was occurring at these lug anchor locations. Settlement of up to 1 1/2 inches was observed. It was felt that this settlement was being caused by surface water entering the pavement structure, flowing in a down hill direction via the base aggregates, being trapped at the lug anchors and finally, due to traffic loads, being pumped out, thereby causing loss of base fines and some subgrade soil fines. End result was pavement settlement. Therefore, a second phase of this study, utilizing 2 inch perforated pipe to control surface water was initiated on S.P. 0702-51 This report covers both studies. Conclusions based on this study are: 1) that lug anchors do prevent the downhill movement of the concrete pavement; 2) that when lug anchors are used a perforated pipe system also be built to collect the surface water that enters the pavement structure thus eliminating the anticipated base pumping and pavement settlement.

This Implementation Summary pertains to Report 2023RIC01, “Best Practices for Improving Subgrade Drainage,” published June 2023.

Pervious pavement provides a solution for many highly developed urban areas where an excessive amount of contaminated water is diverted into storm and sewer systems and left untreated before entering natural water sources such as rivers and streams. By allowing water to flow through the pavement surface and infiltrate the underlying soil, pervious pavements can reduce the amount of this pollution. Test cells were constructed at MnROAD to be monitored for drainability to evaluate the possibility of using pervious pavements to mitigate this problem. Other important criteria influencing the performance of pervious concrete in pavements will also be monitored, including mechanical and structural properties, surface characteristics, noise, and durability. This document summarizes the research that went into Report 2011-23, "Pervious Concrete Test Cells on MnROAD Low-Volume Road.."