3. Active vocabulary:

4. Answer the questions:

1. What are the most common materials for drainpipes? 2. What materials are used for rigid pipes? flexible pipes? 3. What is the main disadvantage of a rigid joint? How can it be overcome? 4. What methods can be used to joint PVC pipes?

Text 4 (2500)

1.Study the meanings of the following misleading words:

Procedure – порядок работы, порядок действий, метод;

project (v) – выдаваться, выступать;

aggregate – заполнитель (бетона);

check – проверять, контролировать;

extra – дополнительный

2.Read and translate the text: Excavating the drain layout

Table 3 shows you the basic procedure for excavating the drain layout.

Table 3 How to excavate the drain positions

Step	Action
1	Mark out the positions of the drain runs on the ground and mark the manhole positions.
2	Calculate the depth of the inverts at the highest positions.
3	Set up sight rails on the first straight drain run using a levelling instrument. The difference between the sight rails divided by 80 is the difference in level.
4	Calculate the depth of the excavation and add 100 mm for bedding if required.
5	Measure the height of the upper sight rail above the datum. Make a boning rod which stretches from the sight line to the bottom of the excavation. Example: if the sight line is 1500 mm above the datum, then the length of the boning rod will be 1500 + 775 mm (for depth of excavation) = 2275 mm.
6		Excavate the trench until you reach the correct level and line up the boning rod with the line between the sight rails. As you move the boning rod you will dig the correct level for the slope.
7		Insert some pegs in the bottom of the trench that project 100 mm off the bottom.
8		Fill the bottom of the trench with 100 mm granular material (until it covers the pegs).
9		Shorten the boning rod so that it reaches from the highest sight rail to the invert of the drain. Attach a batten to the bottom of the rod so that it can sit on the bottom of the trench.
10		Lay the drains on the bedding and keep checking the levels with the boning rod. Joint the pipes so that the socket faces the flow.
11		Test the drains and backfill.
12		Repeat procedure for the next drain run.

Bedding drainpipes. The best pipe bedding is a granular material such as concrete aggregate. You should lay a 100 mm layer of bedding in the bottom of the trench to provide firm support for rigid pipes. If you trim and level the bottom of the trench carefully, then the pipes can be laid in the ground without adding infill material. You should pack and level the bed­ding firmly along the entire length of the pipes and scoop out holes to give extra space around the sockets.

When you lay the pipes in the bedding, then you need to check and test the support for the pipes and the gradient. After your inspection you can pack in more bedding so that it comes about half way up the pipe. The bedding that covers the top of the pipe can contain small stones less than 40 mm in diameter in 100 mm layers until there is at least 300 mm cover over the pipes in the trench. Figure 17.4 shows the difference between bedding rigid and flexible drainpipes.

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Figure1 Bedding rigid and flexible drainpipes: (a) rigid drainpipe; b) flexible drainpipe

Laying drains near buildings. Drains for domestic buildings are usually above the level of the foundations, except for raft founda­tions. If they are lower than strip foundations, then you should follow this procedure:

1. Backfill the trench around the drain up to the level of the foundation if the drain excavation is closer than 1 metre to the edge of the concrete strip.

2. Fill the trench with 150 mm of concrete if the angle of the drain excavation is less than a 45° angle from a bottom corner of the foun­dation.

Notes:

1. so that the socket faces the flow -