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and the subsoil also water-tight, the fluid in one sewer would, by filtration and percolation, act and react upon the other sewer.
6. Earthenware pipes make good sewers and drains up to their capacity. The pipes must, however, be truly laid, and securely jointed. In ordinary ground they may be jointed with clay. In sandy ground, special means must be used, such as by bedding the joints in concrete. House-drains should, in all cases, be laid in concrete. If the subsoil is porous the trench should be lined with clay-puddle. Special care should be taken to prevent any contamination of wells by sewage when the water from the wells is to be used for domestic purposes. Earthenware pipes are rarely true in form, as the clay shrinks and becomes distorted in drying and burning. They should therefore be sorted for use so as to form one even line, and in laying, the joint should not bear in the socket in such manner as to be liable to fracture, but the pipes should bed evenly and solidly in the trench, the sockets being free from pressure, a grip, or small trench, being cut to receive the clay, or concrete, upon which the joint is to be made (a).
7. Brick sewers ought to be formed with bricks moulded to the radii (6).
8. Brick sewers should, in all cases, be set in
(a) Sanitary sewer-pipes, if more than eighteen inches in diameter, will be heavy to handle and difficult to joint, and may cost more than a brick sewer of similar dimensions set in cement and concrete, and not make such sound work.
(b) Power to trap drains : section 73, Metropolis Management Act, 1855.
“hydraulic mortar” or in cement. In no case should any sewer be formed with bricks set dry, to be subsequently grouted. When half-brick arches are used the top of such arch should be covered with concrete not less than three inches in depth, and made level over the top of the arch. Half-brick sewer arches are liable to damage if they are not protected by concrete, as a blow or undue pressure on any part or any joint may force a brick out of place; a covering or bedding of concrete will tend to prevent this form of damage and failure.
9. Main sewers may have flood-water overflows wherever practicable, to prevent such sewers being choked during thunderstorms or heavy rains. An overflow, to be of much use, should permit the sewer to be flowing full, and it should be so situated, formed, and protected, as to relieve the sewer by an opening formed like a bye-wash.
10. Sewers should not join at right angles. Tributary sewers should deliver sewage in the direction of the mainflow.
11. Sewers and drains at junctions and curves should have extra fall to compensate for friction.
12. Sewers of unequal sectional diameters should not join with level inverts, but the lesser, or tributary sewer, should have a fall into the main at least equal to the difference in the sectional diameter. The junctions of sewers and drains should be made with care, so as to permit of the delivery of sewage from side sewers and drains in such manner as shall not tend to impede the sewage of the main sewer in its flow. If the inverts of tributary sewers are not above, or, at the least, are not on the level of the ordinary flow of sewage in the main sewer, such tributary sewers, or drains, will be liable to be back-watered, in which case deposit will take place in the length of submerged invert, and so the tributary sewer, or drain, will become choked with its own silt. Many drains are so choked, where all the inverts in a flat district join upon the same level, because the sewage of the main sewer, which is in some degree constant, back-waters
the inverts of the tributaries as described, which tributaries are only in use intermittently.
13. Earthenware pipes of equal diameters should not be laid as branches or tributaries, that is, 9 in. leading into 9 in., or 6 in. into 6 in., but a lesser pipe should be joined on to the greater, as 12 in. to 15 in., 9 in. to 12 in., 6 in. to 9 in., and so on.
14. House-drains should not pass direct from sewers to the inside of houses, but all drains should end at an outside wall. House-drains, sink-pipes, and soil-pipes should have ample means of external ventilation. In towns where houses have to be drained from back to front through the basement the drain-pipes should have an effectual joint, and be bedded and covered in concrete, such drains being ventilated, back and front, on the outside of the house.
15. Sinks and water-closets should be against external walls, so that the refuse water, or soil, may be discharged into a ventilated trap and drain outside the main wall. Down-spouts may be used for ventilation, care being taken that the head of such spout is not near a window. Water-closets or sinks fixed within houses, and having no means of direct daylight and
external air ventilation, are liable to become nuisances, and may be injurious to health ; and if such sinks and. water-closets cannot be ventilated in an efficient manner they had better be removed.
16. Inlets to all pipe-drains should be properly protected; that is, no pipe-drain should have its upper end exposed so as to admit sticks, stones, or other solid materials being accidentally or mischievously passed in.
17. Side-junctions for house-drains should be pro-vided in all new sewers and drains.
The position should be sketched, and indicated by figures in a book or on a plan. Side-junctions not used at once should be carefully closed for subsequent use.
If side-junctions are not provided and put in as the sewers are being constructed or laid, the cost of subsequent provision and insertion will be much greater. It will be cheaper to insert extra side-junctions during construction rather than to have pipes to remove or brick sewers to cut after the trenches have been filled in and become consolidated, and the road or street surfaces made good.
18. A record should be kept by che surveyor of the character of the subsoil opened out in each street as it is being sewered or drained. A sketch-book may be used for the purpose, a section being drawn on a page to show the character and variety of the subsoil asexcavated in each street or road, the depths of the various layers, as of sand, gravel, clay, rock, or other material, being described in writing and also figured in the diagram; these books to be indexed, and preserved. with the plans for subsequent reference and use.
19. Sewers and drains should be set out true in line and in gradient. All the materials used should be sound, and the workmanship should be carefully attended to. Surveyors who have had but little practical experience in sewer construction do not at once perceive the necessity for straight lines, true gradients, with manholes, or lampholes, at the changes of line or gradient. The reasons will, however, become obvious when the works have been completed, as the surveyor will find that truth of line and of gradient can only be obtained by a use of good material and the best of workmanship; the sewer-trench must have been excavated carefully and must have been shored properly and strongly, the trench must also have been filled in carefully. The manholes and lampholes afford means for ready inspection, as also for flushing and cleansing; and, as previously stated, the line of the sewer can be readily and accurately indicated upon the surface of the street or road, and the exact position or depth of every side-junction be found. In main streets having much traffic, "side entrances” may have to be used instead of manholes. Each manhole may be a "flushing chamber,” and each manhole and lamphole may also be a sewer ventilator. Sewers and drains which have been set out and constructed true in line and in gradient are, for all subsequent time, under the ready inspection of the local surveyor.
20. “Sight-rails” should be put in each street kefore the ground is opened out, showing the centre line of each sewer and depth to the invert. The proper use of sight-rails in sewer and drain construction, when put up by the surveyor, will enable the