It has been found that the sphere of utilization of quarry
compounds can be broadened: the filter material heterogeneity
ratio which protects loose soil is 7¢ << 35. Up to 10 per cent oi
of fine particles may be present in the compound.

Synthetic mineral fibre has been found to be a promising
filter material. The regularities have been found in the develop-
ment of seepage deformation for various types of soil depending
on the material of the artificial filter. Various types of felt (1-F;
MRTU 7—1968) and fabrics (TSF b-7, mats MC-50) have been
recommended as filter material.

In order to increase the water intake capacity of the drainage
it is necessary to provide additional filling of natural quarry
compounds with a heterogeneity ratio of up to 35 and also dune
sand particularly at the seepage ratio of 1 m per day.

The use of pipe-filters makes it possible to utilize local buil-
ding materials and to reduce requirements towards the granu-
lar composition of the filter. Recommendations have been wor-
ked out for the seepage calculation of pipe-filters laid into
various types of ground. If the average size ol the pores is be-
low the rated value the pipe-filters may be laid without screens
IT this is not the case then filter packing is essential. Fine sand,
particularly sand taken from dunes, can be used as filling ma-
terial around the pipe-filters.

The most important section of any vertical drainage well is
its water intake made up of filters of various designs. High-
debit wells require filters with a gravel packing around the pipe
which possesses minimum resistance. All types of removable
filters have great resistance and are subjected to quick silting
which reduces the debit and the specific debit of the well 10 а
half and even to a third of the debit maintained by a well with
gravel and sand filters. On the basis of field studies of the
operation of filters in over 300 drainage wells built in various
zones of Central Asia and also on the basis of laboratory expe-
riments we have outlined a method for the selection of gravel
fillings. We have recommended the optimum composition for
gravel fillings on the basis of the acquifer performance.

The best material for the development of a stable filter has
been found to be the vary-granular sand and gravel mixture
with a composilion as given in Fig. 1. The heterogeneity ratio
of such a mixture must be within the range of 10--15 for non-
suffosion ground апа 5--10 for suffosion ground.

The use of such sand and gravel compounds in experimen-
tal drainage wells has reduced the period ol construclion pum-
ping to 10—15 days and also reduced the amount of sand in
the drainage water. After a stop and repeated activation of the
pumps with maximum opening of the valves the period of sand
washing does not exceed 5 minutes and the sand content in the

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