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~. !, ~. i. l 1 ~~ ~I ,. is i• 1 I' i. 1 ~. ~~ 1 ~I~ II 1 I - 15 - inclined between 1 and 5 degress; 3 degrees inclination is indicated on Plate 13. The diameter of the holes is usually 4 to 4 ~ inches; the slotted casing has a diameter of 1 '~ inches. According to our recent experience,. the costs of the horizontal drains may range between $ 8 and $ 10 per linear foot of installed drain plus mobilization and demobilization costs of the rig. Maximum spacing of drains as indicated in the drawing is on the order of 30 feet; it should vary according to the per- meability of the soils to be dewatered. An alternate system of dewatering may consist of trenches which are excavated parallel with the slope gradient or per- pendicular to it. The trenches would be filled with pervious material such as clean gravel-sand mixtures; a perforated plastic pipe located close to the bottom of the trench provides a means of collecting and removing water from the trench. This drainage system might be used to dewater the cut slopes above entries 2, 3, and 4; the trenches could be in- stalled after the excavation of the cuts. Although our studies have not dealt with the tunnels which will be driven-from the prdposed bench, several important fac- tors should be mentioned. As it is shown in individual profiles along the entries, the first tunnel parts will be driven in soils of the slides before intact rock (coal seam) is reached. The overburden of the tunnels will be low; ground water will probably be encountered in some tunnels as the newly installed piezometers seem to indicate. Such tunnelling conditions are difficult and special driving methods will be required. This problem could be partly or totally eliminated if the tunnel ow+~ro.e mwaa~.w Nc