Chapter eight

Machinery, special equipment and DIY drainage

8.1
Operations involved

The purpose of this chapter is to describe the kinds of machinery and equipment required for the various operations essential for the installation and efficient functioning of modern drainage systems. No attempt has been made to list or review the diversity of machines and equipment currently in use nor to comment on the attributes or otherwise of individual designs. The many possible design alternatives for achieving specified results are bound to lead to the development of new and better machines as time goes by so that any review based on present performance will soon become dated. What is of importance, however, is the understanding of the requirement of each operation. This is explained as fully as possible so that the capability of a particular machine can be checked against the desired end result.

The following is a summary of the various operations involved in the installation of drainage systems:

• cutting narrow trenches for pipe drain laterals, and sub-surface gravel drains without pipes, on soils that are relatively obstacle free;
• trenching for main and outfall drains;
• trenching for piped laterals in very stony or difficult ground;
• trenching for interceptor drains, catchwater drains and open ditches;
• installing pipes without soil excavation—trenchless drainage;
• trenching for slit drainage;
• ensuring uniformity of fall along the bottom of pipe trenches;
• providing motive power;
• disposing of soil from excavations;
• backfilling, consolidating and re-truing the surface;
• subsoiling;
• applying sand topdressing;
• spreading a sand carpet.

8.1.1
Cutting narrow trenches for pipe drain laterals, and sub-surface gravel drains without pipes, on soils that are relatively obstacle free

The most commonly used external pipe diameter for perforated plastic, lateral drains is either 60 or 80 mm (2 or 3 in); the clayware equivalents being 95 or 120 mm (4 or 5 in). This suggests minimum trench widths for installation of 100–200 mm (4–8 in) so long as the pipes can be handled within a comfortable working depth from the surface of the order of 750 mm (30 in).

It is always advisable to allow a small gap between the trench wall and the side of the pipe so that the backfill can surround as much of the pipe as possible, minimizing soil entry into the pipe drain through perforations or gaps. However, it is also important to keep the width of the trench no wider than is absolutely necessary for the size and kind of pipe used. Too great a width will not only involve the removal and disposal of an excessive amount of soil, but also more expense for backfilling material and additional costs for grassing over. The trencher should be capable of cutting to a depth of at least 1220 mm (4 ft), though trench depths for laterals seldom exceed 600–900 mm (2–3 ft).

If the purpose of the pipe drain is merely that of a conveyor, a closed pipe may be used with purpose-made junctions for lateral access. Soil may be substituted as backfill in place of gravel and sand.

8.1.2
Trenching for main and outfall drains

For mains and outfall drains the width of the trench has to be enough to take pipes of at least 120 mm (5 in) or 175 mm (7 in) external diameter. Where a slope has to be imposed on the base of the trench the depth of cut may have to exceed 1000 mm (3 ft). At such depths obstacles and difficulties over pipe installation may well require much wider trenching but, the pipes being closed, the extracted soil can be used again for backfilling.

8.1.3
Trenching for piped laterals on very stony or difficult ground

Where there are difficult ground conditions, such as on tipped land or where large stones abound, and trenching by chain cutter would be either uneconomic or impractical, there may be no alternative but to use a more robust machine such as a hydraulic excavator with a dipper arm and bucket. Under the worst conditions the extra effort involved in installing the pipe drains, let alone the expectation of meeting similar problems in the installation of sand/ gravel slits, may make the cost of the whole scheme prohibitive. However, before abandoning the project, it may be worth considering the advisability of importing enough stone-free soil to raise the general level of the area sufficiently to enable at least the slits to be trenched in without difficulty. In these circumstances any pipe underdrainage should be installed, and trenches appropriately backfilled, before the new stone-free topsoil is superimposed. As mentioned already, in Chapter 7, page 125, further trenching may well be required to extend the permeable fill of the pipe trenches into the lower half of the superimposed topsoil. It will help, therefore, if coloured tape is used to mark the surface of each run before burial.

8.1.4
Trenching for interceptor drains, catchment drains and open ditches

Drainage of this type is often required to intercept water encroaching from off site, either as surface runoff or as lateral seepage along impermeable sub-strata. Where surface flow is the problem, the width of the top of the trench should be adequate to ensure efficient interception of all surface flow. An open ditch would be the most desirable option. However, to avoid creating an obstacle to play, the trench is usually piped and then backfilled to just proud of the surface with a graded series of freely permeable layers of aggregate. No soil capping should be used to benefit grass growth as this will only impede surface infiltration.

The interception of moving ground water, seeping laterally over a relatively impermeable layer within the soil, requires only a narrow stone-filled trench, oriented across slope, and the trench extended below the seepage layer into the surface of the impermeable stratum.

A safe compromise on a site located at the bottom of a natural or man-made slope is to create a tapering trench, 300–450 mm (12–18 in) wide at the top and 125–150 mm (5–6 in) wide at the bottom. It should be deep enough to intercept the lateral flow of ground water, and organized at the top to capture all surface flow.

A suitable machine for excavation under difficult conditions of slope, surface wetness and substrata is likely to be an hydraulic excavator with dipper arm and bucket. Buckets are available in various widths, the smallest about 200 mm (8 in) tapering to 125 mm (5 in). Machines of this type are the stock in trade of most local contractors.

8.1.5
Trenchless drainage

This involves the use of machines which slit open the soil and put pipe and backfill in place all in one pass.

The use of the trenchless drainer on sports grounds is limited by the fact that to squeeze out even a narrow, 50–70 mm (2–3 in) wide slit without the extraction of soil is bound to cause considerable localized surface heave. Though these machines are robust enough to displace solid obstacles this can only be achieved at the expense of much soil disruption and may well lead to the lifting onto the surface of unwanted, potentially dangerous objects. Furthermore, the simultaneous insertion of pipe and backfill prevents any check on the nature of the base on which the pipe is laid. However, in new constructions, there should be no difficulty over the clearance and re-truing of the surface prior to grassing up.

Apart from the motive power, the main requirements of a trenchless drainer are a sturdy slitter, an efficient device for guiding flexible plastic piping into the slit and, ideally, a two-part hopper capable of feeding in gravel to a fixed height, followed by a blinding sand.

Because of the narrowness of the slit trench it is particularly important to use a small particle-size gravel as backfill to discourage soil invasion, e.g. a Stewart zone trench gravel.

8.1.6
Trenching for slit drainage

Objectives

As interest in the sand/gravel slit method of drainage did not receive serious attention in the UK until the late 1960s, the development of special drainage equipment for this purpose is still of comparatively recent origin. The greater sophistication evident in the design of machines now available is a welcome advance.

Our aim must be so to improve efficiency that the cost falls more easily within the range that the many hundreds of small clubs and local authorities could contemplate for the luxury of good outdoor playing conditions throughout the winter. However, even when costed solely on the basis of the materials required, these schemes can never be cheap. Probably the only scope for extending the market down to those with limited finances is to develop machinery for hire that will encourage the DIY approach. In such an open-market situation, manufacturers with existing equipment, developed primarily for the agricultural or civil engineering sector, may see possibilities for a useful extension of sales. In this there need be no harm so long as the design priorities for the sports-turf market are fully met.

The first priority of slit drainage is to install vertical channels, stabilized by permeable fill, at a spacing over which surface flow can be made effective, and along which discharge to a system of underdrains can be organized, with pipe interval as wide as possible. The narrower the slit width, the shorter the run and the more adverse the effect of soil contaminating the fill margin, but the less the problem of reestablishing a complete grass cover. The wider the slit, the greater the possibility for extending the run between pipes, but the more difficult the problem of re-establishing the sward along the line of the slit and, thereafter, maintaining growth uniformly over the whole playing surface. Though various modifications are possible, experience to date has tended to concentrate attention on 50 mm (2 in) wide slits, 300–350 mm (12–14 in) deep, spaced at 1 m (1 yard) intervals, backfilling typically with trench gravel in the lower half and blinding sand above. The slits are aligned across slope to maximize interception and discharge below to pipe underdrains, running down slope, at 15–20 m intervals (Figure 11.1).

Trenching for slits by excavation

The basic requirements for excavator-type, slitting machines are:

1. to neatly excavate trenches as close as possible to 50 mm (2 in) wide, for depths down to 400 mm (16 in);
2. to remove the excavated spoil cleanly so that it can be conveyed off site without any need for a subsequent clearing-up operation;
3. a hopper capable of delivering and compacting into the trench, gravel and/or sand, in one operation, to predetermined depths. Loose packing and voids should be eliminated so as to prevent subsequent shrinkage;
4. hopper compartments large enough to hold sufficient quantities of backfill to avoid too frequent stops for reloading. Ideally, the size of the hopper should require reloading to take place only at the end, or at some fixed point along each run. The aim should be to keep vehicular traffic crossing the playing area to a minimum;
5. an ability to cope with stones and to slice the existing sward cleanly;
6. co-ordination of the various operations to avoid open trenches remaining unfilled and vulnerable to collapse when rain intervenes;
7. speed, to allow this major task to be completed within the time span of fair-weather prediction.

All of these requirements have to be met either in a series of separate operations or by machines capable of carrying out all, or several of the required operations in a single pass.

Efficient machines capable of completing the whole operation in one pass are now on the market. Their advantages are that they will not leave trench runs in an unsafe, incomplete state, and, given good working conditions, they can slit an entire football pitch in no more than two days. But they have their drawbacks: (a) their weight and the motive power required to move them; (b) the time lost in extracting and repositioning the machine when obstacles blocking progress have to be removed; (c) the length of the machine when space around the perimeter of the working area is limited. These are highly specialized and expensive machines, unlikely to be used by anyone other than a major, sports-field contractor.

To date the two main means of excavating narrow trenches, 50–75 mm (2–3 in) wide and 250–350 mm (10–14 in) deep have been either some form of circulating toothed chain or a toothed wheel, or a wide, subsoiling plough with a chisel foot angled to gouge out the soil in a continuous broad slice between two surface-stabilizing floats. To ensure clean excavation with the chisel type of trencher there needs to be a twin disc system ahead of the plough to slice through the turf along each margin of the trench to be slit.

Trenching for slits without excavation

Mini-slitting

Slits of this type can be created by slicing the soil apart, either with a disc, or a blade like a subsoiling tine. By comparison with the more open base formed by the toe of a subsoiling tine, a disc-formed slit will be distinctly V-shaped, effective for surface interception, but limited in capacity for discharge. As both achieve their effect by soil displacement the slit faces are bound to be smeared and compressed, and the surface of the soil is bound to be to some extent ridged up either side of the slit opening. This ridging has to be dispersed without adverse effect on the efficiency of surface-water interception.

In practice, slits formed in this way are generally restricted in width to something of the order of 25 mm (1 in). Mini-slits of this type can be installed fairly rapidly, but they have several potential disadvantages that require close attention by manufacturers and designers.

1. Because of their narrowness, backfilling with sand or gravel is difficult and to achieve the necessary compaction may require power assistance.
2. To have a discharge capacity equivalent to that of 50 mm (2 in) slits, spaced at 1 m (1 yard) intervals, 25 mm (1 in) wide slits have to be increased in number, or their interception by underdrains increased in frequency, all the more so if the backfill is changed from sand/gravel to coarse grit or blinding sand throughout.
3. Capping by soil, smeared over during play, will be difficult to avoid, and any sideways infiltration of soil from the slit walls into the backfill will immediately reduce their internal efficiency.
4. Because of the obvious tendency for a squeezed-out slit to close back rapidly once the blade has passed on, it is essential with this system that the backfilling and compaction operations be carried out simultaneously. One method utilizes a cavity maintained clear for this purpose immediately behind the solid part of the blade. If a vibrating mechanism can be fitted, this will not only help the smooth progress of the slitter through the soil but can also be used to improve the efficiency of the backfilling operation. The use of a winged, subsoiler shoe to relieve compaction in the same operation is tempting. It should be appreciated, however, that this may result in the backfill leaking away into the horizontal cavities that the wing feature is also likely to create.
5. There is now the possibility of greatly extending the capacity for lateral discharge of the slits themselves by inserting perforated plastic mini-pipes along the base. If the extra cost is to be justified, by greatly extending the length of run before discharge, the trench base must be very carefully graded to avoid the narrow pipes silting up. On flat sites, where a steady gradient has to be imposed, this will entail great skill in the cutting, grading and backfilling of narrow trenches at depth.

Micro-slitting

Machines which will cut sets of narrow slits to shallow depths are now available and are used for enhancing the surface interception of standard slit systems. These micro-slits are of the order of 15 mm (1/2 in) wide, 100 mm (4 in) deep and spaced 150–225 mm (6–9 in) apart. In one pass they are drawn in at right-angles across the deeper, standard slits, simultaneously filled with closely packed sand and the surface trued off by rolling, ready for immediate use.

Micro-slits are an expensive but useful alternative to the annual sand topdressing procedure for maintaining sand continuity through to the surface. They are especially useful for restoring the efficiency of slit systems soil-capped by maintenance neglect. Initially the benefit is unlikely to last for more than one winter season but, if the sand injected is topsoil sand in character, in time, as the sand from successive treatments accumulates, it will favourably ameliorate the texture of the original topsoil. However, because a fine sand must be dry to flow satisfactorily there is a tendency to think only short term and use one of the readily available concreting sands that are freer flowing when moist. Unfortunately such a mixed particle-size sand may not favourably ameliorate the topsoil once both are thoroughly intermixed (Appendix C.l). It is important, therefore, that micro-slitting machines should be able to efficiently inject topsoil sand materials into the micro-slits they create, even when the sand is moist enough to be sticky. The alternative of purchasing specially dried sand can double the cost.

8.1.7
Ensuring uniformity of fall along the bottom of pipe trenches

Most land drainage machines have a sight rail or bar which will enable the operator to ‘bone in'the cutting blades, using profile boards previously established along the trench line. For longer drainage runs, more sophisticated trenching machines can be laser guided, the digging depths being controlled automatically. For smaller machines, where these facilities are not available, it may be necessary to check the trench bottoms using a set of boning rods, rectifying any imperfections by hand. In any event, if localized silting is to be avoided, it is essential to ensure that pipe runs are true and even. This cannot be guaranteed merely by installing at a fixed depth below an existing surface which itself may be undulating.

8.1.8
Motive power

Excavation of pipe and slit trenches on relatively obstacle-free soil

To meet the demand for a wide range of trench widths and depths there are a large variety of power units available. On sports grounds the need to keep trench widths as narrow as possible permits the use of comparatively small, self-propelled units with economical running costs and a low weight to bearing-surface ratio. These are normally fitted with interchangeable chain cutters to give trench widths of 100–200 mm (4–8 in) and depths of300–1220mm(l-4ft).

Where tractor power has to be supplied from a separate source, the aim should be to limit the risk of surface damage by spreading the load over more extensive bearing surfaces, e.g. by using balloon tyres, four-wheel drive or caterpillar tracks.

Trenchless operations

Slitters and mole drainers can be drawn by four-wheel-drive tractor, crawler tractor or by tractor and winch. Whichever method is chosen it must be capable of pulling the plough at full working depth, slowly, evenly and continously, so as to minimize the risk of excessive surface heave.

8.1.9
Disposing of soil from excavations

It is now common practice for most chain, wheel and chisel trenchers to have attachments capable of conveying spoil to an accompanying dumper, trailer or lorry. The alternative of immediate scattering on the pitch is not to be recommended at the slitting stage as it could compromise the need to maintain sand continuity right through to the surface.

8.1.10
Backfilling, consolidating and re-truing the surface

Hoppers may be towed separately or form an integral part of a trenching machine. They are generally available for backfilling with materials of most grades. Purpose-built, two-compartment hoppers, capable of backfilling gravel and sand in sequence to fixed heights, firming each layer and finishing to a smooth surface by rolling, are now more generally available. Without such purpose-made equipment, steps will have to be taken to limit the almost inevitable risk of surface undulations resulting from progressive settlement of trench fill. Loose materials will have to be tamped in by hand, or some mechanical equivalent, and then consolidated by a purpose-made, narrow roller or the wheel of a loaded vehicle running along (not across) the surface of the trench. This will squeeze back the soil to either side and leave a linear depression to be filled subsequently with topsoil sand ameliorated with peat, or lignite and seaweed, in which grass can be established from seed. The same approach can be used to disperse the heave created by a trenchless operation, but in all such situations, beware of crushing the pipes (section 11.4).

8.1.11
Subsoiling

As the aim is to relieve soil compaction it is inevitable that, when effective, the level of the surface will be raised. If this is to be achieved with minimum risk of an adverse effect on play, the lift must be general rather than localized to obvious lines.

It is because of these difficulties that the commonly available implements used for sub-soiling in agriculture are considered too crude for use through established sports turf, though valuable at the early stages of construction. However, specially designed multi-tined compaction breakers are now coming onto the market. These have a shallow working depth, a clean cutting action and well-dispersed area of heave. All work on the same principle, using an upward sloping shoe or share, drawn through the ground at the bottom of an upright slitter, and progressing through a slit, cleanly pre-cut by a disc. Ideally, the motive power should be a crawler that will progress slowly and steadily so as to minimize the damage to the turf. Considerable power will be required to maintain a slow, even pace.

8.1.12
Applying sand topdressings

Because sand topdressings for grass surfaces that have been slit-trenched may have to be applied in single dressings of 50 tonnes/hectare (20 tons/acre), agricultural lime spreaders have sometimes been brought into use for this purpose but they are not entirely satisfactory, being heavy to use and irregular in distribution. However, there now are purpose-made, topdressing machines capable of providing a very uniform cover over the range of application rates required. Some can achieve this even with fine sand that is damp enough to be sticky.

Alternatively, given that sand can first be metered out dry into stockpiles or windrows throughout the area to be topdressed, the final task of spreading overall and levelling can readily be done by a large, purpose-made lute. Such a lute is essentially a robust, rectangular fabrication of metal struts, rear-mounted on the hydraulic, three-point linkage of a standard tractor. Pulled in one direction, the angle of the scraper bars will help in the spreading of the sand from the array of stockpiles. Pulled the other way, they will tend to smooth over the surface to complete the job of levelling. This is a most important item of equipment that should be readily available to every groundsman so that there is no excuse for a sand, topdressing procedure not being carried out annually.

A wide, rigid drag brush can be used to complement the action of a lute. The aim is to work dry sand down into the base of the sward so as to limit any risk of smothering the grass. Matting is mainly a smoothing operation best suited to a surface that is required to remain gently undulating, e.g. a golf green.

8.1.13
Spreading a sand carpet

In sand-carpeted constructions it is necessary for the slit-drained, soil surface to be covered with a uniform layer of ameliorated sand, 100–125 mm (4–5 in) deep. This should be pushed out from peripheral stockpiles by tracked, bulk spreading equipment. Wheeled vehicles are liable to founder in any deep layer of dry, rounded, uniform particle-size sand or gravel. When pushing out a sand carpet, therefore, wheeled vehicles should be kept off until the sand surface has been consolidated moist. The surface will need blade grading to the required profile and repeated harrowing and rolling to true and uniformly consolidated. A deep sand construction over a gravel bed will have similar problems.

The introduction of an organic ameliorant and phosphate-rich fertilizer reserve to the desired root zone beneath the surface can be done by pre-mixing off site or introduction on site. In either case it must be recognized that, when the mixture is dry, loose materials differing so much in particle size and density will continually tend to segregate on agitation so as to leave the larger and less dense, supplementary materials on top. It is better, therefore, that these materials should be buried at 75–100 mm (3–4 in) beneath the eventual surface so that the bulk of the agitation involved in truing off to a final level can take place in pure sand. Some of the buried organic matter and phosphate can then be worked up from below by just one or two slow passes of a shallow subsoiler, or spring tined harrow, set to a depth that will just avoid penetrating the underlying soil. A final pass across the line of the slit underdrains will encourage water movement in the right direction. Do not overdo cultivation as further upward migration of the ameliorants will be encouraged by the disturbance involved in the final operations associated with seeding.

To assist seed germination on such a quick-drying surface, equipment should be used that will place the seed at a depth of 5–10 mm (about 1/4 in) beneath the surface. Reliance on raking is unlikely to be very successful but this is what the contractor who lacks the appropriate machinery will suggest.

8.2
DIY drainage

As suggested in section 8.1.6, the DIY approach t o slit drainage may sometimes be the only way that smaller clubs and impecunious local authorities can finance a slit system of land drainage for their playing fields.

Firms that hire out specialized equipment for this purpose have now had many years of practical experience in working this way. With consultant advice and the guidance that these firms are able to give, most organizations, especially where there is a groundsman, should be able to achieve a satisfactory and worthwhile scheme of DIY drainage, carefully phasing the work as money becomes available.

8.2.1
Machinery and equipment for hire

A suitable excavator is a tracked trencher that will dig trench widths from at least as narrow as 60 mm (23/8 in) for sand or sand/gravel slits, up to a minimum of 150 mm (6 in) for pipe laterals and mains.

Normally available for hire with the trencher are:

• a soil conveyor for raising the extracted soil to a height of at least 1.8 m (6 ft);
• a backhoe with 300 mm (12 in) bucket (for manholes and difficult ground).

Other equipment usually required but not necessarily available from the same firm includes:

• a dumper, tipping trailer or lorry, for the final carting away and disposing of excavated soil;
• a two-compartment hopper for simultaneous backfilling with gravel and sand, plus a dumper to fill the hopper;
• a clean-up chute and crumber to ensure that the trenches are free of loose soil and smooth at the base;
• a means of ensuring that the base of the trench is uniformly graded, even on undulating ground.

8.2.2
Typical conditions for the hire of trenching equipment are: Conditions of hire

• a minimum period of hire, usually one or two weeks;
• hire rates inclusive of any spare parts specially subject to wear, but not fuel and oil, or delivery and collection charges;
• the fuels and lubricants used must be approved by the hire firm;
• training of operators to be carried out by hire firm on delivery;
• fitting of new tines or blades to maintain the digging chain in good order is the responsibility of the hirer;
• breakdowns are rectified by the firm and the hire period extended to cover the loss;
• damage to machines through misuse or accident rectified at the hirer's expense;
• the hirer is advised to insure against loss or damage to equipment hired and also to cover injury to persons and damage to property caused by, or arising out of, the use of the equipment.

8.2.3
Comments from a hire firm

Summarized below are some helpful comments from one of the main hire firms regarding their experiences with sports clubs and local authorities.

1. Local authorities seem to have sufficient technical knowledge, back-up and resources to carry out schemes to a high standard. Sports clubs tend to need further advice but, providing they have a caring, full-time groundsman, manage very well.
2. If satisfactory underdrains do not exist they must first be provided. To determine their direction the fall of the field must be accurately assessed and there must be a suitable outfall to which the drainage scheme can be connected.
3. If money is short it is recommended that the worst areas only are done, i.e. usually the goal mouth and the centre circle.
4. Some drainage improvement can sometimes be achieved by sand-slitting across the underdrains at 1.8 m (6 ft) centres. Further slitting can be done between these at a later date (but the client should be warned this will generally be necessary).
5. The best times for sports-field work are the end of May and all of June, July, September and October. Most other months are usually too wet or too dry, but allowances have to be made for variation in the normal weather cycle.
6. Most playing fields are quite well graded with a fall in at least one direction but, if there are undulation problems, advice may be required on boning rod or laser grading.
7. Common snags encountered are:

• attempting to drain in the wrong weather and wrong soil conditions;
• using the wrong type of backfill material;
• tough ground conditions slowing down the work and so making it necessary to extend the hire period.

8.2.4
Other practical considerations

1. Before deciding to proceed with a drainage scheme as a DIY project it should be realized that the hiring arrangements, the selection, ordering and checking of materials, the programming and supervision of the work, all require careful organizing and this can be quite time-consuming for the person responsible.
2. To ensure that, once begun, the work proceeds smoothly and quickly, it is essential that a specification and layout drawing is prepared by a knowledgeable person, and agreed well in advance by all concerned. The hiring of the appropriate machinery and the ordering of materials can then proceed in good time. As the day the machinery and equipment are delivered on site is the day the hire period commences, it is vital that all is ready, e.g. routes defined for the access of vehicles, lines of drains and manhole positions pegged out in advance, materials in nearby heaps, etc. The machinery can then be put to immediate and continuous use. Machines standing idle lead to mounting costs so that in the end there may be little saving over a contractor's price.
3. Always begin the excavation of trenches and the installation of pipes and manholes at the lowest point of the system, i.e. the outfall if it is a completely new scheme, otherwise start from the point where the new work links up with existing drains. If work starts at the top end and heavy rain follows, the trenches and manholes will flood and work will have to cease until the water clears and any damage has been made good.
4. If it is necessary to cross open trenches or slits with wheeled or tracked vehicles, planks should be laid at crossing points.
5. Try to plan operations so that, weather permitting, a given length of pipe drain or slit drain is completed each day, i.e. each length is excavated, piped and backfilled to the surface so that there are no open trenches standing empty overnight, or only partially infilled and at the mercy of the weather or any other disturbance. If work has to be left vulnerable overnight, any accumulation of water, collapse of trench walls or other damage should be rectified before further pipe laying or backfilling proceeds.
6. If 75 mm (3 in) clayware tiles are to be used for the pipe drain laterals, a trench width of 125–150 mm (5–6 in) will be needed to allow access for the individual placement of each short length of pipe. For 60 mm (2 3/8 in) perforated plastic piping, trench width need only be 100 mm (4 in). This will affect both the amount of soil that will have to be carted away and the amount of extra backfill material required.
7. Care should be taken to ensure that there are no dips in the drain trenches that might cause silting in the pipes and eventual obstruction to the flow of water. Any such low spots should be made up to an even fall with gravel, firmed by treading.
8. Upper ends of pipe runs should be plugged to prevent entry of solids. Manufacturer's fittings should be used for junctions.
9. Before infilling the trenches always carefully check that the sand and gravel actually delivered is to the grading specified. As large quantities of materials may be required, continuity of supply may become a problem requiring approval of alternatives. Try and anticipate any such requirement so as to avoid being hustled into accepting the first alternative offered. Simple tests for sands and gravels are described in Appendix 2.
10. As a DIY, temporary expedient on small sites, much can be done to improve surface drainage by using a spade, opening up continuous, V-shaped slits, linked across the pipe drainage system and maintained open by infilling with topsoil sand. Where the slits actually cross the drain trenches, direct links to the permeable fill must be achieved, suitably blinded with trench gravel and/or blinding sand to prevent the slit fill leaking away.