Submitted to: Terramechanics Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/31/2009
Publication Date: 10/15/2009
Citation: Tekeste, M.Z., Tollner, E.W., Raper, R.L., Way, T.R., Johnson, C.E. 2009. Non-Linear finite element analysis of cone penetration in layered sandy loam soil-considering precompression stress state. Terramechanics Journal. 46(5):229-239. Interpretive Summary: Being able to predict the soil forces that are exerted on a tillage tool as it is pulled through the soil could enable better implements to be developed. A computer model was developed to simulate inserting a soil sampling device into the soil and compared against the actual force that was measured in laboratory experiments. Results indicated that the computer model reasonably predicted the location of a compacted layer within the soil profile. Future improvements on the computer model could enable reasonable estimations of the depth and degree of soil compaction within our compacted Southern soils.
Technical Abstract: Axisymmetric finite element (FE) method was developed using a commercial computer program to simulate cone penetration process in layered granular soil. Soil was considered as a non-linear elastic plastic material which was modeled using variable elastic parameters of Young’s Modulus and Poisson’s ratio and Drucker-Prager criterion with yield stress dependent material hardening property. The material hardening parameters of the model were estimated from the USDA-ARS National Soil Dynamics Laboratory - Auburn University (NSDL-AU) soil compaction model. The stress-strain relationship in the NSDL-AU compaction model was modified to account for the different soil moisture conditions and the influence of pre-compression stress states of the soil layers. The FE formulation was verified using cone penetration data collected on a soil chamber of Norfolk sandy loam soil which was prepared in two compaction treatments. The FE model successfully simulated cone penetration in layered soils indicating the location of the sub-soil compacted (hardpan) layer and peak cone penetration resistance. Modification of the NSDL-AU model to account for the actual soil moisture content and inclusion of the influence of pre-compression stress into the strain behavior of the NSDL-AU model improved the performance of FE in predicting the peak cone penetration resistance. Modification of the NSDL-AU model resulted in an improvement of about 42% in the finite element-predicted soil cone penetration forces compared with the FE results that used the NSDL-AU ‘virgin’ model.