Reinforced Earth and Stone Columns for Weak Subsoil Conditions, HR-510, 1980

Reinforced Earth is a French development that has been used in the United States for approximately ten years. Virbro-Replacement, more commonly referred to as stone columns, is an outgrowth of deep densification of cohesionless soils originally developed in Germany. Reinforced Earth has applicability when wall height is greater than about twelve feet and deep seated foundation failure is not a concern. Stone columns are applicable when soft, cohesive subsoil conditions are encountered and bearing capacity and shearing resistance must be increased. The conditions in Sioux City on Wesley Way can be summarized as: (1) restricted right of way, (2) fill height in excess of 25 feet creating unstable conditions, (3) adjacent structures that could not be removed. After analyzing alternatives, it was decided that Reinforced Earth walls constructed on top of stone columns were the most practical approach.

Row Crop Response to Topsoil Restored on Borrow Areas, HR-186, Supplemental Report, 1982

Borrow areas are created where soil is needed to provide fill for construction projects. This research evaluated (1) the changes in row crop productivity resulting from removal of soil for highway construction in Iowa and (2) restoration methods which included: depth of topsoil, subsoil tillage, manure application, and two years of legume growth prior to row cropping. The research was carried out from 1977-1981 at four locations. Corn and soybean y1elds from borrow areas have been below, equal to; and greater than yields from undisturbed, neighboring farmland. Little or no yield increase was noted from restored topsoil at coarse textured sites. At finer textured sites, a marked yield increase of both crops occurred after the addition of 6 inches of topsoil but little added yield increase resulted from restoring 12 inches of topsoil. Subsoil tillage has shown little or no beneficial effect on crop yields. The manure treatment has resulted in a corn yield increase but only in the first year after application.

Row Crop Response to Topsoil Restored on Borrow Areas, HR-186, 1982

Borrow areas are created where soil is needed to provide fill for construction projects. The changes in row-crop productivity resulting from removal of soil for highway construction in Iowa and restoration methods, which included addition to topsoil, subsoil tillage, manure application, and 2 yr of legume growth before row cropping, were evaluated. The research was carried out from 1977 to 1981 at four locations. Corn and soybean yields from borrow areas have been below, equal to, and greater than yields from undisturbed neighboring farmland. Little or no yield increase was noted from restored topsoil at coarse-textured sites. At finer-textured sites, a marked yield increase of both crops occurred after the addition of 6 in. of topsoil but little added yield increase resulted from restoring 12 in. of topsoil. Subsoil tillage has shown little or no beneficial effect on crop yields. The manure treatment has resulted in a corn yield increase but only in the first year after application.

Soil Stabilization With Chemicals, Iowa Highway Research Board Bulletin No. 22, 1960

In the search for new soil stabilizing agents the effects of six organic cations on plastic limit, liquid limit, shrinkage limit, air-dry strength and rate of slaking of a highly plastic clay subsoil were studied. In all cases the plasticity index and shrinkage were reduced by the treatments. The air-dry strength was lowered in varying degree, which was the only undesirable effect noted. With one exception resistance to slaking was improved. It is concluded that large organic cations show promise as possible stabilizing agents for highly plastic fine-grained soils.