The swell-shrinking stress of porous concrete base was also calculated and the predication method of critical temperature difference and the calculation method of joint space under base cracking were put forward.

The swell-shrink characteristic of expansion soils has very big bane to some engineering, so forecasting its swell-shrink deformation has the important realistic meaning.

According to the tests results,it is concluded that: the vertical swelling pressure is remarkably decreased with the increase of small swelling strain;the swelling pressure and dry density,initial moisture content and swelling strain present exponential relations.