320 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



[Skptkmber, 



Mr. Bull stated that the banks of the river Calder in Yorkshire had been 

 effectually secured from damage by means of stone pitching or setting, laid 

 at an angle of from 45° to 50° with the horizon, and resting on a mass of 

 stone thrown into the bed of the river below the level of the water in dry 

 seasons. These loose stones had generally been laid at an inclination of 

 about 25° or 30° where the depth at low-water was not great, but where the 

 water was deep the lower part of the slope had been made at about 45°, 

 returning at the upper part or near the surface of the water to the former 

 angle of 25° to 30°. The pitching, composed of oblong stones, was laid in 

 courses, with nearly vertical joints, having the least sectional area exposed to 

 the action of the flood-waters. The stones were from 15 to 20 inches long, 

 varying in their widths, and were laid on a bed of gravel, or soil, he preferred 

 coarse gravel, as it was less liable to be washed out from behind the stones, 

 which sometimes occurred with soil, unless it was of a strong clayey nature. 

 Several miles of facing done by him in this manner had now been standing 

 between seven and nine years without requiring any repairs. In a few 

 instances, when the loose stones at the foot had been either insufficient in 

 quantity, or so small as not to resist the action of the floods, and had been 

 washed away, the pitching has slid down into the bed of the river without 

 being otherwise disturbed ; after it had settled, the top part had been re- 

 newed, and the original line restored. The floods in the river Calder 

 frequently rose from 8 ft. to 12 ft., and flowed with a very rapid current, 

 consequently the pitching had to resist a powerful action, particularly at the 

 concave side of a bend in the river, where the action was both directly upon 

 and along the face of the work. The loose stones below the low-water mark 

 were seldom disturbed by the floods, and where they had been removed, no 

 damage had been sustained beyond the sliding down of the pitching as before 

 described ; such, however, had not been the case where from peculiar cir- 

 cumstances a perpendicular or nearly perpendicular wall had been built 

 instead of the pitching ; in such instances a slight disturbance of the loose 

 stones had frequently caused the destruction of the wall. Where the pitching 

 had been backed with light soil, which was easily washed out through the 

 joints, the stone-work had fallen into holes as might be expected, but where 

 a good strong gravel had been used for the backing, no such instances had 

 occurred. Mr. Bull differed from Colonel Jones's opinion as to breakwaters 

 ■with a vertical or nearly vertical face, beause any disturbance of the footing, 

 however slight, must have a tendency to overthrow the wall, and that ten- 

 dency would be in proportion as the angle of the wall diverged from the 

 angle of repose ; that is to say, if the wall was quite perpendicular a 

 comparatively smsll disturbance of the foundation or footing would destroy 

 the equilibrium, and the superstructure would be overthrown, but the nearer 

 the face approached the angle of repose, the greater would be the security. 

 He did not mean to assert that the angle of repose was the best for the face 

 of a breakwater, or that the same angle should be preserved from below low- 

 water mark to the top of the structure. On the contrary, he was inclined 

 to think that a curved section, commencing from a few feet below low-water 

 mark at an angle of 10° or 15° from the horizon, and terminating at the top 

 at an angle of 70° or 75° would be found a good form, and if the courses of 

 face stones were laid nearly vertically, should the footing below low-water 

 mark be removed by the action of the waves, the consequence woidd be a 

 Eliding down of the upper face, which could easily be replaced at the 

 top, as is done with respect to the river pitching. The proper angle for 

 the loose stones below low-water mark would, he had little doubt, be that of 

 repose, or nearly so, as Colonel Jones had shown to be the ease in several 

 existing breakwaters. The face stones shoidd be roughly squared on the beds 

 and joints, or what is called in the North "scappled" to the form of the 

 curve, and laid in equal courses not quite perpendicular, but inclining a little 

 from the direction of the prevailing wind, perhaps about 10° from the 

 vertical line. Mr. Bull was induced to offer these remarks, for the purpose 

 of recording a practice he had successfully applied to the protection of river 

 banks (of which he presented drawings) and his opinion as to its applicability 

 to the construction of breakwaters. 



April 19. — The President in the Chair. 



Flushing Apparatus for Sewers. 



" On the causes of accumulation of deposit in Seii'ers, and on the hitherto 



generally prevalent mode of removing the same ; with a description of a new 



Flushing Apparatus used for cteantiing the bewers in the Ilolbom and Finslury 



Divisions." By John Roe, Assoc. Inst. C. E. 



In the Holborn and Finsbury Divisions there are upwards of 80 miles of 

 covered sewers, in a large proportion of which there were accumulations of 

 deposit, which, by choking the side drains and causing effluvia, became 

 sources of much annoyance. The only remedy resorted to, was to raise the 

 deposit to the surface of the street and cart it away : this was for many 

 reasons an objectionable process, and a careful examination of the sewers 

 was ordered, when it was found that many causes of obstruction existed. In 

 sewers of the same form and inclination, different degrees of accumulation 

 existed : this was caused sometimes by a greater run of water in one than in 

 the other. In other cases, although the flow of water was equal, the deposit 

 was unequal : in some situations openings having been made to insert side 

 drains, bricks had been left in the sewer, against which considerable deposits 

 had formed. The admission of water from collateral sewers at right angles 

 and at different levels had also caused obstructions to the continuous flow 

 along the main line. An example is given, where, although the collatera 

 sewer was 3 ft. above the level of the main line, a deposit of a foot in depth 



was formed for several hundred feet up the stream, while below the'point of 

 junction the sewer was perfectly clear. The insertion of gully-necks fre- 

 quently caused obstructions, by permitting the access of dirt and rubbish 

 from the road. 



These facts being ascertained, the next consideration was how to remedy 

 the defects, as the locality would not permit an alteration of level, which 

 would give a flow through the sewers suflSciently strong to carry off the deposit. 

 After a long series of experiments (by the author, who is engineer to the 

 Commissioners) and trials upon several kinds of apparatus, the arrangement 

 shown by Fig. 1 was decided upon : — it consists of an iron frame set in the 



