Researches on ventilation properties of block stones layer

Block stones were used to protect permafrost from thawing by air convection effect in the embankment of Qinghai-Tibet Railway.The diameter,porosity and ventilating ability of the block stones pile had important influences on air convection effects.It was shown that the porosity increased with the block stone size.It was about 38%～48% for the block stones in the sizes of 0.10～0.25 m.And it was seen from the wind tunnel tests that the wind pressure gradient had a nonlinear relationship with the wind velocity.The resistance coefficient decreased with the increasing of block stone size.Based on the ventilation ability analysis of the block stone embankment in Qinghai-Tibet Plateau,the block stones layer had stronger ventilated effect.It was suggested to consider the effect of natural wind on thermal field under embankment with block stones layer.