| Maintenance dredging is necessary to sustain navigability in some high traffic waterways such as the Houston Ship Channel in Galveston Bay in Texas. Construction of diked enclosures for storage of maintenance dredged material may be carried out by excavating suitable soil from an underwater location with a cutterhead dredge, then hydraulically transporting the soil through a dredge pipe, the length of which may vary from a few hundred feet to as much as seventy thousand feet. Loss of construction soil by disintegration during hydraulic transport is a concern since the supply of suitable material may be limited.; The purpose of this study is to devise a procedure to determine and quantify the disintegration loss of clay masses that are transported through a dredge pipe. Soil parameters that influence propensity to disintegrate are identified and evaluated. A program of laboratory tests was conducted to identify conditions that significantly influence degradation characteristics. Tests were performed on undisturbed soils in a laboratory device that was specially designed to simulate conditions inside a dredge pipe. A simple numerical model was devised to consider transport fluid density, viscosity, solids content and particle shape.; Results of degradation tests and model calculations are presented graphically as retention factor, or fractional clay mass remaining versus time or distance traveled through the dredge pipe. Survivability of materials in the dredge pipe is related to soil properties such as plasticity characteristics and overconsolidation, which is an index of the brittleness of the soil. Soils of low plasticity tend to disintegrate quickly and soils that are brittle tend to fragment into small pieces in spite of high density. An envelope of survivability is established on the well known soil plasticity chart. |
