UNIVERSITY OF NAIROBI SCHOOL OF ENGINEERING DEPARTMENT OF ENVIRONMENTAL AND BIOSYSTEMS ENGINEERING OPTIMIZATION OF THE ANGLE OF CUT OF A FROG IN A MOULDBOARD PLOUGH: CASE OF A SANDY CLAY SOIL ANGELA WAMBUI HIUHU F56/69693/2013 A thesis submitted to the University of Nairobi in partial fulfilment of the requirements for the Degree of Master of Science in Environmental and Biosystems Engineering 2015