SOIL-CONDUIT INTERACTION AND STRUCTURAL STABILITY OF MOLE DRAINS

The structural design of corrugated plastic conduits and mole drains is not adequate. Small diameter mole drains and plastic conduits buried in Lloyd clay were examined both experimentally in a laboratory soil bin and numerically by the finite element method, for various loading conditions.;Elastic finite element and elasto-plastic finite element models were both used to simulate the soil-mole and soil-conduit systems tested in the laboratory soil bin. The simulated results of the finite element analyses were compared to the laboratory test results. The results obtained using elastic and elasto-plastic material models were nearly identical. The laboratory deformations of the mole drains and plastic conduits agree well with the simulated deformations for strain levels less than 1.5 percent. At values above 1.5 percent vertical strain, the finite element method predicted vertical strain much lower than those measured in the laboratory.;Finite element analyses were next performed to simulate the soil-mole and soil-conduit system for field situations. The deformation of the mole drain and the plastic conduit for installations with depths of 1 m or more were found to be elastic for pressure levels generally occurring in the field situation.;In the laboratory study, mole drains were constructed and were subjected to live loads on the soil surface using a press. The resulting applied pressure-vertical strain relationships for mole drains were determined. Similarly, experiments were performed on 75-mm and 100-mm diameter plastic conduits in the soil bin.