Sự chuyển động của nước thông qua khối lượng đất thường được gọi là "rò rỉ" Trong thực hành kỹ thuật, đất thoát nước tốt, đó là mong muốn để loại bỏ áp lực thấm hoặc để tăng sức mạnh cắt. Hệ thống thoát nước cũng là quan trọng khi nó là cần thiết để ngăn chặn rò rỉ vào đất từ các nguồn bên ngoài. | 4. The cut-off from moisture intrusion 5. The stabilization of slope 6. The subdrain around the basement METHODS OF DRAINAGE The movement of water through the soil mass is generally termed seepage. In engineering practice soil is drained where it is desirable to eliminate seepage pressure or to increase the shearing strength. Drainage also is important when it is necessary to prevent seepage into the soil from exterior sources. Some of the methods of drainage are Drainage by gravity Drainage by consolidation Drainage by desiccation Drainage by electro-osmosis Drainage by suction Of the above the interests of the consultants are obviously in drainage by gravity although soil suction on expansive soils has received increased attention. Permeability The method of drainage in an excavation of a construction project depends on the slope of the excavation the permeability of the soils the elevation of the water table and the available equipment. If the soil mass through which the seepage occurs is compacted fill such as a dam or an embankment the permeability can be reduced by the proper selection of material used. The classification of soils according to their coefficient of permeability is as shown in Table . TABLE Coefficient of Permeability of Various Types of Soils Degree of permeability Values of k cm s High coarse gravel Over 10-3 Medium sand fine sand 10-3 to 10-5 Low silty sand dry sand 10-5 to 10-7 Very Low silt 10-7 to 10-9 Impervious clay less than 10-9 In most soils the coefficient of permeability depends on the direction in which water is traveling. In the direction parallel to the bedding planes the value can be 2 to 20 times that in the direction perpendicular to the bedding stratification. 2000 CRC Press LLC In the Rocky Mountain area the claystone shale is generally impermeable. However it contains numerous seams and fissures through which water can flow easily. The effective permeability will be far greater than that of the intact
