Gravel Loss Research Articles

Materials for Sealed Low-Volume Roads

Many unsealed roads carry relatively high traffic, which results in excessive maintenance requirements and costs. Sealing of these roads with a bituminous surfacing is typically cost-effective if minimal upgrading of the existing road needs to be done. An extensive evaluation of more than 50 roads that were constructed with base course materials of marginal quality, many with only a single layer of material over the subgrade, was carried out. Detailed evaluations of the in situ and laboratory properties as well as the performance of the roads indicated that good drainage and construction quality are the primary requisites for successful sealed low-volume roads. Provided these two criteria are met, current material standards and pavement designs can be significantly relaxed. The use of these light pavement structures results in significant environmental benefits compared with the construction of traditional pavement structures through conservation of higher quality materials, reduced energy usage through less haulage, and elimination of gravel loss and dust emission from the roads.

Earth Materials Catalyst Stabilization for Road Bases, Road Shoulders, Unpaved Roads, and Transportation Earthworks

Frequency of use of concentrated liquid stabilizers to improve stability of aggregate and soil materials in constructing roads and other transportation-related structures is increasing. Concentrated stabilizers are formulated specifically for modification, improvement, and stabilization of aggregate and soil materials and require dilution in a water solution before application to allow for adequate dispersion. Applied costs of treatment are generally much less than conventional chemical stabilization treatment, because application is much simpler and product and transportation costs are less. Treatments are applied to aggregate materials to reduce base course and subbase structural sections and to strengthen resistance to repetitive loading and environmental factors. Gravel loss and maintenance frequency have been greatly reduced for unpaved roads and road shoulders. A report of these findings is timely, because both public and private sectors are seeking cost-effective treatments to improve long-term performance of conventional pavements and to help use limited budgets to address environmental regulations mandating dust control and sediment control for road shoulders and unpaved surfaces. Representative case studies of federal and state agency projects that used an earth materials catalyst (a concentrated liquid stabilizer) document the benefits of appropriate application of concentrated liquid stabilizer technology.

The Flushing Flow Problem: Defining and Evaluating Objectives

Reservoir releases may be specified for the purpose of maintaining or improving the downstream channel and habitat. A wide variety of ecological or management objectives may be defined for such flushing flows (which may be broadly divided into sediment maintenance and channel maintenance flows). To specify a particular discharge and water volume for a flushing flow requires that the ecological or management objectives be translated into specific physical objectives for which flows can be specified. Flushing objectives that cannot be translated into definable flows are of little practical use, regardless of their intrinsic importance. Once defined, flushing flow objectives may be shown to conflict in some cases. For example, no flushing flow can satisfy the typical sediment maintenance objectives of maximizing sand removal and minimizing gravel loss. A discharge that mobilizes sediment throughout the channel cross section for channel maintenance purposes will often produce comparable transport rates of sand and gravel, thereby eliminating the selective transport of sand needed to reduce the sand content in the bed. Some nonflushing alternatives, such as artificial gravel replenishment and pool dredging, can be used to improve the performance of flushing flows. Selection among these alternatives and specification of a flushing flow discharge and volume depend directly on quantitative estimates of sand and gravel transport as a function of flow rate and volume.

Specification of Sediment Maintenance Flows for a Large Gravel‐Bed River

Reservoir releases may be specified to flush interstitial fine sediment from gravel beds in the river downstream. Choice of an effective flow depends on trade‐offs among discharge, flow duration, and pool dredging as they determine rates of bed mobilization, sand removal, and gravel loss. A basis for evaluating these trade‐offs is developed with an approximate method appropriate to the sparse data typically available. Sand and gravel transport are represented with rating curves. Approximate methods are introduced for estimating effective gravel entrainment, subsurface sand supply, and pool sediment trapping. These are combined in a sand routing algorithm to evaluate flushing alternatives for the Trinity River, California. A sediment maintenance flow of moderate size, just sufficient to entrain the bed surface over the duration of the release, limits gravel loss and maximizes sand trapping by pools. Larger discharges produce more fines removal but at the cost of greater gravel loss and reduced selective transport of fines. Dredged pools increase sand removal efficiency by providing multiple exits from the channel and minimize gravel loss if dredged sediment is screened and gravel returned to the river.