Quantifying Vegetation Effects On Soil Strength.

QUANTIFYING VEGETATION EFFECTS ON SOIL STRENGTH

S. A. Shoop*

ERDC-CRREL, Hanover, NH 03755-1290

603.646.432

Sally.a.shoop@usace.army.mil

T. Cary, ERDC-CRREL, Hanover, NH 03755-1290

H. Howard, ERDC-CERL, Champaign, IL 61826

ABSTRACT

Studies of vehicle impacts on soil compaction and soil influence on vehicle mobility are numerous; however, most often the soils involved are without vegetation or the amount of vegetation is not considered. This research aims to look at the effect of vegetated soils on vehicle performance, vehicle-terrain interaction, and trafficking impacts on training lands. The approach includes a series of experiments on the effects of above and below ground biomass on soil strength and trafficability.  Different types and stages of vegetation were subjected to combinations of training land stressors, such as trafficking, burning, and haying/cutting.  Biomass, soil strength and vehicle mobility parameters were collected during each experiment.  The measurements will be repeated during a multi-year recovery period, including additional combinations of land treatment.

Three experiments were completed in the field and in a controlled laboratory environment where full scale vehicle testing could be performed on vegetated soils. The experimental variables include the type of vegetation, soil type, vegetation treatment, and number of vehicle passes. Two indoor test sections were built, each containing a fine sand and a clayey silt soil. On the first test section a turf monoculture was grown and treatments simulated burning and cutting of the grass. The second test section was planted sequentially with Kentucky Bluegrass so that the amount of the vegetation biomass varied. The outdoor test section consisted of cut and uncut sections of a perennial rye grass mix. The test sections were characterized concentrating on strength measurements (drop cone, Clegg Impact Hammer, Trafficability, Cone Penetrometer, Pilcon shear strength, and others), traction and motion resistance mobility parameters (using the CRREL Instrumented Vehicle, CIV), and vegetation biomass.  The biomass measurements included above and below ground density as well as classification of root length and diameter. Test sections were trafficked with a Heavy Expanded Mobility Tactical Truck (HEMTT) and the disturbance effect on the soil strength and vegetation was also quantified. The experimental approach, overview trafficking experiments, and preliminary results are presented. Results will specifically address correlations between biomass measurements and the different soil strength measurements.