Modeling soil-tine interactions in lateritic soil | |
| Author | Jayasuriya, Hemanatha Priyadarshana Warnarathna |
| Call Number | AIT Diss. no. AE-99-01 |
| Subject(s) | Soil-structure interaction Soil mechanics |
| Note | A dissertation submitted in partial fulfillments of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ;|vno. AE-99-01 |
| Abstract | This research study was comprised of the following major objectives. The first was to rearrange the research findings on soil-tool interaction models and the failure mechanisms into a logical order in a matrix form. Secondly to obtain three-dimensional soil failure models and to study the soil flow patterns for different tines using a new concept of superposition method. Thirdly to investigate the effect of soil particle size, change in tine speed under quasi-static range and the soil compaction level on soil failure mechanisms and soil reaction. Fourthly to investigate the effect of the presence of a sidewall on tine forces and soil failure patterns. Finally, to develop and validate models combining the results obtained in the previous steps of the study. All related research findings on soil-tool interactions, soil deformation and failure mechanisms were gathered and rearranged in a matrix form and tabulated for different soil type and conditions in order to highlight the remaining gaps and to identify the possible mechanisms. The experiments were conducted in laboratory glass-sided soil bins; narrow and wide, with varying test parameters such as soil particle size, tine forward speed, tine rake angle and soil compaction level etc. Three basic tine rake angles 50๐, 90๐ and 130๐ were selected for comparison considering previous results obtained for three major soils; sand clay and loam. Narrow tines were selected for major experiments. One wide tine condition and two depth conditions also were used for the comparison. Lateritic soils with two different gradations (screened at standard sieves No. 10 and 4) were selected and used in the experiments under dry condition mainly due to its compaction property and also to generalize the use of variety of soil types in the research are. The selected soil possessed the composition; 23% sand, 49% silt and 25% clay under field condition. The plastic limit and liquid limit of the soil were 17% and 26% respectively. The properties reflected the compressible and strength characteristics of the soil. Two-dimensional observations of soil failure mechanisms were obtained for different tines travelling alongside the glass and shifted away at selected distances from the glass. They were then superimposed to obtain three-dimensional geometrical models. This new concept led to obtain true shapes of three-dimensional soil failure models for different tines and it also helped to study the soil flow patterns in front of moving tines and the lateral failure boundaries. The study was further extended to observe the effect of the presence of a sidewall on tine forces and failure patterns. A narrow soil-bin was fabricated to investigate the condition of tine with sidewalls at both sides and hence a comparison was done for the tine moving without a sidewall, with one sidewall and with sidewalls in both the sides. Controlled soil compaction levels were obtained by hydraulic means in the narrow soil-bin to get uniform soil conditions. Using the results obtained in narrow soil-bin, a correction criterion was developed based on soil cone index measurements to adjust the tine forces in wider soil-bin and to simulate uniform soil condition for better correlation of results. The compaction levels in narrow soil-bin were maintained as steps between zero (loose soil) and 12kN of load at the actuator rod of the hydraulic jack. In wide soil-bin system it was achieved by using a light roller and layer compaction method during the soil-bin preparation time. Study on previous research finding revealed that the existence of four distinct failure mechanisms with the change of soil moisture content for major soil types. It was also found that the possibility of another failure mode in the range of sticky limit. It further showed that the invalidity of the numerical value of the soil moisture content, but the validity of consistency limits based on soil properties. The study identified four different zones in which different failure mechanisms could possible take place. In the experiments conducted for obtaining three-dimensional failure models and boundaries gave good results. The true shape and the soil flow mechanisms were useful in modeling the situation. Mathematical models were obtained for the failure boundaries with respect to all view directions. The failure boundary obtained by the superposition method, direct measurements and using tine force modeling approach were well correlated for all the test conditions. The effect of a sidewall or a solid boundary found to be increasing the tine force exponentially with the distance closer to the wall for all test conditions used. There was by over 300% increase in tine force under coarser soil at 8 mm/s speed by tines with rake angle greater than 90๐ (90๐ and 130๐) and 250% increase for the tines having the rake angle less than 90๐ (50๐). This is due to the resistance to the soil flow and the adhesive or cohesive effect due to the excessive side forces around the soil-wall interface. The correction criterion introduced for adjusting the tine force for uniform soil conditions showed good correlation with high regression coefficients. Based on the cone index values obtained and the other boundary conditions such as sidewall, hard soil patches, the above method can be used to simulate three-dimensional maps of tine forces or power for selected tines and soil conditions. The effect of soil particle size, tine speed on tine force and power found to be highly significant in all the test conditions used in the research. Future research work in the area is needed to investigate these parameters in order to obtain better prediction practice. Results obtained in the narrow soil-bin showed a good correlation with exponential relationship between tine force, tine power and applied soil compaction loads for all the test conditions used. Good linear correlations were also found for applied soil compaction load and the corresponding cone index values in the narrow soil-bin. The comparison and the performance evaluation of tines used in the experiments revealed useful trends and to identify some governing parameters leading to optimum tillage-tool design. Tine with 90 rake angle found with higher draft forces and exerting more power compare to the tine with 50 rake angle, and the later found most effective in soil tillage operation. Tine with 130 rake angle found ineffective in soil tillage as the vertical force component as well as power were very high compared to the other tines and that seemed to be invoking in more soil compaction work rather than pulverizing process. Above results could be effectively used in tillage implement design stage to obtain the best curvature on the plough surfaces for specific objectives, in which the optimization could lead to save the cost, time and energy during tillage. |
| Year | 1999 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AE-99-01 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Salokhe, V. M.; |
| Examination Committee(s) | Singh, G. ;Balasubramaniam, A. S ;Kitano, M. ; |
| Scholarship Donor(s) | The Government of Netherlands; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1999 |