Design Principles for Effective Drainage Systems

CHAPTER IX THE ButtpInc—ItTs DRAINAGE Early Drains. Little seems known of the drainage of the past. The Romans used sewers, and presumably, therefore, drains, but there seems no record of the use of drains in England until the time of Inigo Jones, in the seventeenth century.<Callout type="important" title="Important Rule">The keynote of all good sanitary work is simplicity and accessibility.</Callout> Principles of Design for Good Drains. Sanitary engineers and other interested people will get a good deal of help here from the B.S. Code of Practice (No. 301 on Building Drainage), published by the British Standards Institution.<Callout type="tip" title="Pro Technique">Accurately determine the relative levels of the building and the sewer, or other point of outlet.</Callout> The following principles should be kept in mind: 1. The relative levels of the building and the sewer, or other point of outlet, should be accurately determined.<Callout type="risk" title="Risk">Incorrectly determining these levels can lead to poor drainage performance.</Callout> 2. The pipes should be of non-absorbent materials and laid with watertight joints. 3. The diameters of the drains should be proportionate to the work they are called upon to do, with a 4 inch minimum diameter, as they have to carry solid matter as well as liquid.<Callout type="gear" title="Specific Equipment">Iron drain pipes are preferred for areas under or near buildings due to their strength and resistance to vibration.</Callout> 4. The drains should be laid in straight lines between points of access, all changes of direction or gradient being open to inspection. 5. Branch drains should be as short as possible. 6. The drains should not pass under or too near to trees, owing to risk of damage by the roots.<Callout type="warning" title="Safety Hazard">Roots can cause blockages and structural issues with drainage systems.</Callout> 7. There should be no right-angled junctions, all connections being made either in manholes, or with a ‘‘ Y” junction or a bend so that the incoming drain points in the direction of the flow of sewage.<Callout type="beginner" title="Clarification for Newcomers">Right-angled junctions can create backflows and reduce drainage efficiency.</Callout> 8. The drains should be laid to gradients which will ensure their being self-cleansing, or, if this is impossible, owing to the levels, automatic means of flushing should be provided.<Callout type="important" title="Critical Rule">Proper ventilation of the system is crucial for preventing odors and blockages.</Callout> 9. All inlets to foul drains should be trapped, except in the case of soil-pipes, at the feet of which no traps should be used. 10. No drains should pass under buildings if it is possible to arrange them otherwise. 11. All entrances to drains should, where possible, be outside the building.<Callout type="tip" title="Pro Technique">External access points are easier to inspect and maintain.</Callout> 12. There should be ample means of access for inspection. 18. The system of drainage should be properly ventilated. 14. It is desirable to provide a separate system of drains to take the rainwater—indeed some local authorities make this compulsory.<Callout type="important" title="Critical Rule">Separate systems prevent overloading and ensure effective drainage.</Callout> Material for Drain Pipes. The foregoing points may now be dealt with in more detail. Pipes for underground drains may be of glazed stoneware, of glazed fireclay, or of cast iron protected against corrosion.<Callout type="gear" title="Specific Equipment">Iron pipes are preferred under buildings due to their strength and resistance.</Callout> The circumstances under which either should be used require consideration. The pipes of stoneware or fireclay are not so strong as those of iron, and are not so fitted to withstand the vibration of heavy traffic such as is so general in our large towns.<Callout type="risk" title="Risk">Incorrect pipe choice can lead to structural damage.</Callout> Further, they are only from 2 to 3 feet long, as opposed to 6 to 12 feet, the lengths in which iron pipes are readily obtainable. This means that the iron drain has about one-quarter the number of joints that a corresponding drain of stoneware would have in any ordinary case, apart from which the caulked lead joint of the iron drain is stronger than any joint in general use for stoneware.<Callout type="important" title="Critical Rule">Iron pipes are more durable and require fewer joints.</Callout> Drains under Buildings. It will be seen, therefore, that, for drains under or near buildings, and near heavy traffic, iron drains should be used. The only reason that they are not in such general use is that they are about twice as expensive as stoneware drains.<Callout type="tip" title="Pro Technique">Iron pipes provide better protection against vibration and heavy traffic.</Callout> Protection of Iron Pipes against Corrosion. It is important to note, however, that there are some purposes, even in the face of the foregoing remarks, for which iron drains, as at present obtainable, are entirely unsuitable.<Callout type="warning" title="Safety Hazard">Iron pipes can corrode if used with certain types of sewage.</Callout> The pipes are protected against corrosion by three principal processes: (1) By the Angus Smith process (usually specified as “coated” pipes); (2) by the Barff or Bower-Barff process; and (3) by giving them a glass-enamel lining, all of which have been previously described.<Callout type="important" title="Critical Rule">Proper protection is essential to prevent corrosion.</Callout> Neither of these protective coatings is of much value with sewage containing strong 10* 298 THE BUILDING—ITS DRAINAGE acid solutions, such as one might get from certain trade processes. Thus, experiments have shown the following results from the use of weak solutions of sulphuric acid. A pipe treated by the Angus Smith process was tested with a 0-5 per cent. solution of acid for a period of twenty-four hours, at the end of which the coating was peeling off, leaving the pipe without protection.<Callout type="risk" title="Risk">Incorrect sewage can damage protective coatings.</Callout> The same percentage solution destroyed the protective coating of a Barffed pipe in the same period. The glass-enamelled surface of another pipe was completely destroyed by a 1 per cent. solution in the same time, whereas a salt-glazed fireclay pipe withstood, without injury, a 5 per cent. solution for the twenty-four hours.<Callout type="important" title="Critical Rule">Choose pipes based on the nature of your sewage.</Callout> These results show that the nature of the sewage to be carried must receive careful consideration before using an iron drain for a factory building. Acid or Alkaline Discharges from Factories. It should be noted that where by-laws have been made under the Public Health (Drainage of Trade Premises) Act, 1937, it is a serious offence to discharge trade effluent containing acid or alkali in harmful proportions into the public sewer.<Callout type="warning" title="Safety Hazard">Discharging harmful substances can lead to legal penalties.</Callout> Local authorities are becoming very active in their control of both the quality and quantity of effluent and most modern industrial undertakings having acid or alkaline waste water to get rid of have neutralising plant to correct the pH value of their waste water before it enters even their own drainage system.<Callout type="important" title="Critical Rule">Neutralize harmful substances before discharging.</Callout> In the case of acid waters the waste is conveyed to the neutralising plant in acid-resisting stoneware pipes. Stoneware and Fireclay Pipes. The clay for stoneware pipes comes chiefly from Dorsetshire and Devonshire and that for fire- clay pipes chiefly from the Midlands and North of the Scottish border, Their manufacture will be described in a later chapter, but the main points of difference will be described here.<Callout type="gear" title="Specific Equipment">Stoneware is better suited to normal use due to its non-absorbent nature.</Callout> A good stoneware pipe is almost completely non-absorbent, even when — unglazed, whereas a fireclay pipe, on fracture, shows a very absorptive surface, Salt-glazed stoneware drainpipes are most commonly used in the south, and are better than fireclay for normal use owing to their dense, non-absorptive substance, but in Scotland this would usually entail greater expense in transport, and fireclay is more commonly used for the purpose but the pipes are given an interior glass (vitreous) enamelling in addition to the salt glaze, which makes them perfectly suitable for drainage work, and even better able to stand up to an acid effluent, owing to the double glaze.<Callout type="important" title="Critical Rule">Choose materials based on local availability and sewage composition.</Callout> Such pipes are known as “‘salt-glazed, glass (vitreous) enamelled drain pipes’, and are included in B.S. 540, while drain fittings of the same class, as well as those of salt-glazed ware, are included in B.S. 539.<Callout type="important" title="Critical Rule">Follow British Standards for quality assurance.</Callout> British Standard Pipes. The British Standards Institution have issued specifications (B.S.S. 65) for these pipes and a corresponding one for the fittings to be used in conjunction with them (B.S.S. 539). It is thus possible for the architect or sanitary engineer to specify either “British Standard Salt-glazed Pipes” or “British Standard Tested Salt-glazed Pipes”. In the former case every pipe is expected to comply with the specification and can be re- jected if it does not do so, but only a small proportion of the pipes have actually been tested at the manufacturers’ works; in the latter case every pipe will have been tested by hydraulic test by an inspector, and stamped as a sign that it does comply.<Callout type="important" title="Critical Rule">Hydraulic testing ensures quality.</Callout> The hydraulic test referred to is that it will withstand an internal pressure of 20 lb. per square inch for five seconds without fracture _ or leakage. “Tolerances”. The thickness, permissible deviation from that thickness, permissible deviation from standard diameter, depth of socket, and permissible deviation from straightness in a 8-foot length, are specified as follows: Deviation Deviation Deviation from from Depth of from Diameter | Diameter | Thickness | Thickness Socket |Straightness } in. } in. fy in. in. 345 in. The interior of the sockets and the exterior of the spigots are to be grooved with grooves of a depth of not less than 7g inch, as a key for the cement mortar.<Callout type="gear" title="Specific Equipment">Grooving provides better joint stability.</Callout> okt The pipes may be obtained salt-glazed inside and out, or salt- glazed on the outside and glass-enamelled inside if this is expressly specified. Other diameters, intermediate between those named above, may now be obtained.<Callout type="important" title="Critical Rule">Follow specific standards for pipe specifications.</Callout> The lengths are either 2 feet, 2 feet 6 inches or 3 feet, but pipes of small diameter are obtainable only in 2-foot lengths. 300 THE BUILDING—ITS DRAINAGE Joints for Drain Pipes. Stoneware or fireclay pipes are jointed in a variety of ways. The joint in general use is known as the ordinary cement joint, but there are other forms which consist yartly of cement and partly of rings of bituminous composition.<Callout type="warning" title="Safety Hazard">Incorrect jointing can lead to leaks.</Callout> The latter may be divided into those having a single seal and double seal respectively and are used chiefly for sewerage rather than drainage work. As they are also obtainable for the latter purpose they may be here described.<Callout type="important" title="Critical Rule">Choose appropriate joints based on specific needs.</Callout> There are a great number of varieties of each type, but illustrations are given only of those possessing distinctive features.<Callout type="tip" title="Pro Technique">Caulking with tarred gaskin or hemp is the best method for cement joints.</Callout> Cement Joint for Drain Pipes. In the great majority of cases the ordinary cement joint is the most economical and is efficient. Fig. 302 shows the joint in section.<Callout type="important" title="Critical Rule">Proper jointing ensures effective drainage.</Callout> The best method of making the joint is first to caulk the joint with a few strands of tarred gaskin or hemp, well rammed into the socket to prevent the cement finding its way to the inside of the pipe. This should be done by means of a proper caulking tool.<Callout type="important" title="Critical Rule">Proper tools and techniques are essential for jointing.</Callout> The joint is completed by filling up the socket with cement mortar, composed of, say, one part of Portland cement to one of sand, as recommended in the Code of Practice for building drainage, though some local by-laws insist on 1 to 1, while others are satisfied with 1 to 2, extending the mortar beyond the socket to form a triangular fillet neatly bevelled off at an angle of 45°. The cement may be Portland cement to B.S. No. 12, or high-alumina cement or Portland blast-furnace cement may be preferred.<Callout type="important" title="Critical Rule">Follow local by-laws for specific requirements.</Callout> (B.S. 915 and 146.) The sand should be good, clean sand, i.e. free from loam and ordinary earth.<Callout type="warning" title="Safety Hazard">Using contaminated sand can compromise the joint's integrity.</Callout> The mortar should be of the right consist- ency, as, if containing too much water, it will tend to fall to the lower side, or invert, of the pipe and leave the upper part im- perfectly filled, whilst the underside of the triangular fillet may fall off. It is seldom that any joint other than the simple spigot and socket joint filled with cement, and illustrated in Fig. 302, is used, but circumstances may sometimes warrant the use of one or other of the following joints.<Callout type="important" title="Critical Rule">Choose appropriate joints based on specific needs.</Callout> Bituminous and other Forms of Drain Joint. Some surveyors prefer a joint with more elasticity than a cement joint possesses, and in such case use instead a bituminous mixture composed of bitumen and sand boiled together in a cauldron alongside the trench, and filled into the socket in a molten state by the aid of special moulds, or a rough mould made of clay placed around the joint temporarily.<Callout type="warning" title="Safety Hazard">Improper jointing can lead to leaks.</Callout> To prevent the possibility of the spigot dropping in the socket THE BUILDING—ITS DRAINAGE 301 owing to improper caulking with gaskin, or to the absence of such caulking, various modifications have been made to the form of socket.<Callout type="important" title="Critical Rule">Proper jointing is crucial for effective drainage.</Callout> Thus Fig. 304 shows Doulton’s Invert Shoulder joint, Fig. 303 what is known as the Free-flow pipe, and Fig. 305 the Archer joint.<Callout type="important" title="Critical Rule">Choose appropriate joints based on specific needs.</Callout> In the last named the cement is poured in, in a liquid state, through a hole at the top of the socket, there being another hole for the escape of the air. The best proportion is three parts .of cement to two of water by volume.<Callout type="important" title="Critical Rule">Proper proportions are essential for jointing.</Callout> Proprietary Forms of Drain Joint. We come next to special joints formed by the contact of rings of bituminous composition, moulded on the spigot and socket.<Callout type="gear" title="Specific Equipment">Special proprietary joints can provide better sealing.</Callout> Fig. 806 shows a section of the Stanford joint, while Fig. 307 represents Doulton’s Self-adjusting joint, which is designed somewhat on the ball-and-socket principle.<Callout type="important" title="Critical Rule">Choose appropriate joints based on specific needs.</Callout> The ring in the socket is of parallel thickness and that on the spigot is segmental. The joint is made by smearing the ring on the spigot with tallow or some plastic compound.<Callout type="important" title="Critical Rule">Proper sealing compounds are essential for jointing.</Callout> In Fig. 308 is shown the section of a Double-seal joint made up of composition rings backed by cement mortar.<Callout type="important" title="Critical Rule">Double seals provide better protection against leaks.</Callout> Fig. 309 shows another form of Double-seal joint, differing in that it has a fairly large groove in the socket, to afford a key for the mortar.<Callout type="important" title="Critical Rule">Grooves improve joint stability and sealing.</Callout> The Hassall Single-lined joint is shown in Fig. 310, a small fillet of clay being put round the mouth of the socket, and cement grout poured in to fill up the space.<Callout type="important" title="Critical Rule">Proper sealing compounds are essential for jointing.</Callout> Another form of compound joint is the Parker, given in Fig. 811; it will be seen that the shape of the ring is such as to give a good key.<Callout type="important" title="Critical Rule">Proper shapes improve joint stability and sealing.</Callout> Fig. 312 is the True Invert, having the rings at the mouth of the socket and the base of the socket exactly fitting the spigot.<Callout type="important" title="Critical Rule">Proper fit ensures effective drainage.</Callout> Fig. 313 is the Sykes joint in which a collar is formed on the spigot, there being a composition ring on it, against which the end of the socket abuts.<Callout type="important" title="Critical Rule">Proper fit and sealing ensure effective drainage.</Callout> Fig. 314 is the Hassall Double-lined, having two pairs of composition rings with a band of cement between; Fig. 315, the Solus, having two pairs of rings and two bands of cement; and Fig. 816 the Secure joint, having one pair of rings, but so formed as to produce a band of cement of dovetailed section.<Callout type="important" title="Critical Rule">Proper fit and sealing ensure effective drainage.</Callout> The ‘“Grouted Composite” joint, shown in Fig. 317, is a very secure joint and can be rapidly laid.<Callout type="important" title="Critical Rule">Rapid laying ensures timely completion of projects.</Callout> A band of canvas goes nearly all round the joint, being secured by wire to the socket and spigot. There is a small space between the ends of the canvas, through which the cement grout is poured.<Callout type="important" title="Critical Rule">Proper sealing compounds are essential for jointing.</Callout> The inner rings are of the form already described as the Doulton Self-adjusting joint, and the substantial backing of cement makes a very strong joint. The canvas probably perishes before long, but that does not matter,<Callout type="important" title="Critical Rule">Proper sealing compounds ensure effective drainage.</Callout> 302 THE BUILDING—ITS DRAINAGE WL WAAAY (LLL ey RMAANAIS'S'Ssas