A Treatise On The Principles And Practice Of Dock Engineering

l8o DOCK ENGINEERING. from two consecutive corners. The intersection of the vertical lines through the points of suspension gives the centre of gravity of the figure. It is better to suspend from three points; the third line acts as a check against possible error. In all three instances the assumption has been made that the wall is homogeneous. When this is not the case, it will be necessary to deal with the weights of the different sections, instead of their areas. Thus, if two adjoining sections of a wall have areas A and B and unit weights, w± and w2 respectively, their common centre of gravity will be found by dividing the line joining their individual centres inversely in the ratio —l^. Typical Example. Fig. 105 is the profile of an actual dock wall, constructed at Liverpool, to which the methods of stress investigation just described have been applied, with the following results. The material of the wall is Portland cement concrete ; the foundation, sound rock ; the filling, selected earth and rock rubbish, moistened and well Consolidated. The wall is taken at unit length :— Area of section of wall (deducting pipe trench), . Weight of wall at 145 Ibs. per cubic ft., Area of section of filling resting upon wall, . Weight of filling at 112 Ibs. per cubic ft., Angle of repose assumed at .... . 90“ — 45° Angle of rupture to vertical - , . Area of hypothetically ruptured wedge, Weight of wedge at 112 Ibs. per cubic ft., Extent of surcharge, Amount of surcharge at | ton per sq. ft., Total vertical thrust at back of wall, Resolved horizontal thrust against wall, Total effective weight of wall and filling, Resultant thrust on foundation, .... Overturning moment about outer edge of toe, Moment of stability about ,, Factor of safety, Width of foundation, ...... Eccentricity of thrust, ......................... Average intensity of pressure on foundation per sq. ft., Maximum intensity, ...... Average intensity of shearing stress per sq. ft. at base, Maximum intensity, ...... 876 sq. ft. 56'7 tons. 310 sq. ft. 15’5 tons. 45“. 22“ 30'. 648 sq. ft. 32'4 tons. 23T8 lin. ft. 7'7 tons. 40'1 tons. 16'6 tons. 72-2 tons. 74 tons. 340'3 ft.-tons. 1101 ft.-tons. 3'2. 26-5 lin. ft. 2'66 ft. 2'7 tons. 3'8 tons. 0'6 ton. 0'8 ton. Practical Points. The two essential features of a well-designed dock wall are weight and grip on the foundation.* Without these qualifications even a high moment * Proc. Inst. C.E., vol. Ixv., p. 180.