Purpose: Calculated substantiation of cavityless drain structure that provides for effective draining of poorly permeable soils. Hydraulic calculation methodology of composite profile cavityless drain, laid with a slope but without inclusion thitherwards of a drainage pipe, was developed earlier. Drainage pipe reinforces drainage capability of cavityless drain with the preservation of all its other advantages. Methods: Known differential equation of liquid filtration in a soil is used. It’s of special importance that the calculation method may be used at all modes of water movement in a drainage: laminar, transient or turbulent. The dependencies substantiated with experiments, held by Northern Scientific-Research Institute of Hydrotechnique and Melioration, were applied for transient and turbulent modes. The complex form of drainage transection is taken into account with the help of special coefficient which leads it to equivalent by area rectangular section. It’s proved that such transfer doesn’t lead to significant inaccuracy of results obtained. Results: Dependencies have been obtained allowing to calculate consumptions, flowing along drain cavityless part and along drain pipe. If drain is long, it’s feasible to divert a water periodically from it in lateral direction by collectors. Dependencies are derived which according to, the distance between intermediary collectors, whereto a water comes from drains that’re laid with a slope, and the water depth in drain cavityless part in characteristic sections are defined. Practical significance: Cavityless drainage is applied in agriculture, in the systems of engineering protection from environmental sinking and pollution. Cavityless drains of composite profile have attracted railwaymen’s attention providing effective draining of subgrade, they simultaneously increase its bearing capacity. Its application is especially effective on poorly permeable soils when laying in the zone of seasonable freezing of soils.