Browsing by Author "Crossley, C. P."
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Item Open Access The economics of the provision of rural transport services in developing countries(Cranfield University, 1996-07) Ellis, S. D.; Crossley, C. P.Rural accessibility planning in developing countries over the last few decades has primarily focused on increasing rural communities access to rural roads. It has been considered that road building improves access to health, education, markets and employment opportunities, and hence promotes economic development. It is argued in this thesis that accessibility, particularly in Sub-Saharan Africa, has not improved to the desired extent because the problem of mobility, in terms of access to vehicle services, has not been addressed. The provision of rural roads and transport services have been taken as synonymous with each other, but in reality this has not proved to be the case. This thesis attempts to redress that balance by seeking to change the mindset of policy makers to think about mobility and increase the emphasis placed on the promotion of transport services, both motorised and non-motorised. The findings relate to surveys undertaken in Thailand, Sri Lanka, Ghana, Zimbabwe and Pakistan where data were collected on vehicle operating costs (VOC's) and performance for a wide range of commonly used rural vehicles. These included human porterage and non-motorised vehicles such as bicycles and animal transport, as well as motorised vehicles such as conventional trucks and pickups, agricultural tractors and simple engine-powered vehicles. Analysis of the data demonstrated large differences in the VOC's and transport charges for rural transport services between the generally efficient systems in the Asian countries and the inefficient ones in the African countries studied. These findings form the foundation for the development of the Rural Transport Planner (RTP) and the framework which identifies the relationships between transport charges, VOC's, and factors relating to the vehicles operating environment. The RTP provides the first known attempt at producing a model for rural vehicle selection and for recommending interventions to improve the operating environment for rural transport services.Item Open Access An investigation of tillage systems and implement design for water conservation in semi arid conditions in Botswana(Cranfield University, 2006-10) Kethobile, Elias; Crossley, C. P.Botswana, as a semi arid country, is faced with serious shortage of moisture for crop production. Its challenging climatic condition makes the little moisture received from summer rainfall insufficient. The development of appropriate tillage systems can assist with sustainable crop production. The aim of this project was to come up with a tillage system to improve the suitability of the physical conditions of soil for effective seeding in rain fed farming in Botswana. Strip, Reservoir (depression) and no tillage systems (control) were therefore investigated. Laboratory investigation of the tillage systems for soil water conservation and erosion was undertaken under different slopes (5 and 10°) and rainfall intensities (55 and 95 mm/hr). Energy requirements and work rates of the systems were analysed. The results showed that slope has effects on the capability of strip tillage to harvest water from rainfall of low intensity. It managed to harvest 69.12% of rainfall from 55mm/hr rainfall at a slope of 5° whereas at 10°slope it harvested about 49%. The effects of slope were not significant for the reservoir tillage and no tillage systems. Under a higher intensity rainfall of 95mm/hr the effects of slope were insignificant. The only source of variance was due soil disturbances and the strip soil disturbance performed better than the other treatments. When eroded soil was investigated under low intensity rainfall (55 mm/hr), there was no significant difference between strip and depression. Depression and strip soil disturbances reduced soil erosion similarly by 47 and 46 % respectively. Under high intensity rainfall eroded soil was still high under undisturbed soil disturbance. This is due to the fact that when the soil surface is bare, there is a higher risk of soil erosion. But when strips and depression are created, the risk of soil erosion is localised especially at high rainfall intensities. The evaporation analysis showed no significant difference among the tillage systems. This means that the power of water conservation in semi arid environment lies more on water harvesting than reduction of evaporation.The analysis of power and work rates showed big advantage of strip tillage system over reservoir tillage in the sense that it required less energy and power to complete a hectare of land. Its work rate is almost double of strip tillage. From the results it can be concluded that, at low slope and low rainfall intensity strip tillage harvest more water than reservoir tillage and zero tillage systems. When slope is elevated there is no difference between strip and reservoir tillage. The strip tillage system harvest more water than both reservoir tillage and zero tillage at high intensities. Strip and reservoir tillage reduce soil erosion similarly at both low rainfall and high rainfall intensity. The energy requirements and work rate were more positive for strip tillage that reservoir tillage. Therefore with these results a conceptual design of strip tillage system was developed.Item Open Access Otimizing the tractive performance of 4WD tractors operating on a frictional soil.(1996-10) Al-Hashem, Hasan Ahmed A.; Kilgour, John; Crossley, C. P.The present investigation aimed to develop a simple method of predicting the optimum performance of a medium size 4WD tractor performing a draught operation on a frictional soil in particular. The data obtained could provide an appropriate ballasting recommendation for the optimum combination of tractor power, weight and working speed on such soils taking account of minimizing the undesirable effect of soil compaction. A wheel torque/weight transducer system was developed to measure the forces applied on the tractor wheels. One side of a MF 3065 tractor was equipped and instrumented. The system fitted to each wheel consists of three link transducers, two modified wheel discs, wheel angular position measuring device and fifth wheel device together with a Datalogger and a portable computer. All transducers output were linear with a coefficient of determination, R² > 0.9994 and were repeatable. Field experiments were conducted on sandy loam soil condition to determine the peak tractive efficiency of the tractor in work. Three operating variables at three levels were considered including tractor ballast weight, working speed and implement pull setting. Soil compaction effect for a particular traction situation was assessed by three field measurement methods of soil dry density, penetration resistance and water infiltration rate. Five relationships of predicting tractor ballast recommendation proposed by Reece (1968), Brixius and Zoz (1976), Dwyer (1978), Gee-Clough et al. (1982) and Bloom et al. (1983) were chosen to present the existing ballast method. These relationships were modified to be at similar conditions of wheel slip, coefficient of traction and tractor power to describe the ballast recommendation as a non- dimensional number Rn and takes the form of: W/P* = Rn/V where W is the dynamic tractor weight, P* is the tractor axle power and V is the actual forward speed. The results of the study were compared with two concepts of existing work. Firstly, with the average ballast recommendation value used for all types of soil. The comparison showed that the ballast recommendation in terms of weight-power ratio is expected to be approximately 70 % of the amount of ballast recommended by the existing work for frictional-cohesive soil at a given speed operating at similar conditions of wheel slip and coefficient of traction. This means for the same pull at a particular power less weight is required because the soil under consideration has high angle of internal shearing resistance, φ than the average soil type. The ballast recommendation for a medium size 4WD tractor operating on a frictional soil (sandy loam) with optimum slip value of 10 % is determined as : W/P* = 1.3/V compared with the value suggested by the theory for all soil types which is generally accepted as : W/P* = 1.9/V when operating under similar conditions of 10 % wheel slip and 0.4 coefficient of traction. Secondly, the results were compared with an empirical approach of Dwyer et al. (1974), Gee-Clough et al. (1978) with the aim to extract the most related data to the tyre tractive performance operating on a sandy loam soil from all other types of soil. There was found to be a reasonable agreement between the two data sets which gave confidence to the accuracy of the modified equation to predict the ballast required when operating at maximum tractor efficiency. The recommended equation for relating maximum coefficient of traction (Ct)max and mobility number M for the frictional soil (sandy loam) becomes : (Cͭͭͭͭͭᵗ)max = 0.62- 0.82/M for rear wheel (Cᵗ)max = 0.42 - 0.52 /M for front wheel The measured tractor thrust force was also compared with the calculated using the classical theory of traction mechanics (Janosi and Hanamoto, 1961 and Reece, 1967) and the results showed no significant difference between the measured and calculated thrust values at 95% confidence level. The three methods of soil compaction measurement showed that there is a direct relationship between the tractor weight and /or wheel slip, and soil compaction effect. However, infiltration rate method seems to be the most sensitive one to demonstrate the compaction damage to the soil. The results obtained from this measurement indicated that under the optimum power conditions the tractor caused an acceptable level of soil compaction compared to the most serious effect that can occur. The optimum conditions in this soil type involved operating at 10 % wheel slip with mobility number of 6.5.