Mitigating Expansive Clay Soils in Kentucky

Case Study 

Application	Flexible Pavement Base Reinforcement	Engineer	Vision Engineering
Location	Lexington, KY	Date of Installation (m/y)	May 2018
Product	Mirafi® H2Ri

THE CHALLENGE 

Construction of a new Holiday Inn Express Hotel in Lexington, KY required engineered fill within the proposed parking lot area to achieve plan subgrade elevation. Fill thickness ranged from approximately 3 ft. to 6 ft. thick. The owner wanted to use available expansive soils (Unified Soil Classification System, CH), a.k.a., “fat clay,” for the engineered fill, as the material was readily available and would avoid the costs of trucking in imported fill. The geotechnical engineer clarified these soils are difficult to use for construction and are very sensitive to changes in moisture conditions, often leading to increased settlement or even swelling and expansion. Furthermore, the soils would require some type of modification to improve their water-resistant characteristics (volume changes with moisture variations) to render them suitable for construction.

THE DESIGN

Typically, CH soils are removed and replaced in proposed pavement areas. If left in place, chemical modification (addition of lime or cement) is implemented to treat the soil, modifying its characteristics and how it responds to moisture. Chemical modification was considered for this project but it was deemed too costly. The Geotechnical engineer opted for a more innovative approach and contacted TenCate Geosynthetics regarding the utilization of Mirafi® H2Ri- a reinforcing and robust moisture management system. Mirafi® H2Ri is a unique geosynthetic, integrating the performance functions of a geogrid and geotextile into a single product, plus moisture migration capability. By choosing Mirafi® H2Ri on this project, the Geotechnical engineer accomplished both of his main objectives: 1) Reinforcing the aggregate base course of the flexible pavement section to extend service life and performance, 2) Utilize the moisture migration technology to maintain a relatively consistent moisture content at the subgrade aggregate base interface. With minimal or no moisture content fluctuations, the expansive soils at the interface would be less likely to shrink or swell, thus remain more neutral and therefore not affect the overlying pavement.

THE CONSTRUCTION

The subgrade was brought up to plan elevation using the CH soils and then the Mirafi® H2Ri was deployed. A Mirafi® H2Ri “flat conduit” was installed along the edge of the new parking lot where it meets an existing parking lot. This conduit is used to carry the water away, as it is being wicked from beneath the pavement section. After the Mirafi® H2Ri was installed, the entire parking lot was saturated with water. Presoaking CH soils prior to covering is a very common construction practice, with the intent to cause the clays to swell prior to covering. Subsequently, the geosynthetic was covered with the 8-inch base course aggregate of the pavement section. The Mirafi® H2Ri immediately and rapidly began removing excess water from the interface, as well as any excess moisture within the aggregate base, while simultaneously reinforcing the aggregate base course, enhancing the resilient modulus (MR). Thus, providing a very resourceful solution that is more sustainable than conventional methods.

THE PERFORMANCE

The Mirafi® H2Ri was installed quickly and easily, allowing rapidity during construction and ultimately saving time and money. It is resilient and robust and contributes to a resourceful design. The parking lot was successfully paved without issue and is being monitored over time to observe the performance of Mirafi® H2Ri.