Study Of Water Migration And Strength Of The Loess Under Freezing-thawing Action

The diseases of engineering such as loess slope, canal, roads in seasonal frozen arefrequent, which is closely related to water migration and strength change of loess. Atpresent the study of water migration and strength of loess under freeze-thaw action hasmany problems. The further research work is carried out based on the problems.The characteristics of freeze-thaw disease and laws of temperature field andmoisture field with climate change are obtained through field investigation and field test.The mechanism of disease is preliminary analyzed. It reveals that freeze-thaw diseasesare closely related to water migration and strength change of loess. It laid a foundationfor the further study on freeze-thaw diseases.The experimental study of freeze-thaw strength of unsaturated undisturbed loessunder freeze-thaw action is carried out. The test results show that cohesion decreasesexponentially with the increase of the times of freezing-thawing cycle for the samewater content. For soil samples of the same dry density, the higher the water content is,the more cohesive decrease after the freezing-thawing cycles. Freezing-thawing cycleshave little effect on internal friction angle of unsaturated loess and can be neglected forengineering. The cohesive deterioration model expression of unsaturated undisturbedloess is obtained based on the test data.Through water migration tests of unsaturated loess with the large size sampleunder freezing effect, the influence of density, water content, freezing temperatures andfreezing way on moisture migration of unsaturated loess is researched. Results showthat the higher dry density is, the greater the increase of water content at the frozen front,but the increase of water migration of moving to the frozen part is lower. For a certain dry density, the higher the initial water content is, the greater the amount of moisturemigration is. And the increase of water content of the frozen front is also the greater.From the cold end to the warm end in the unfrozen area, water content increase at first,then decrease. And, this phenomenon is the more obvious with lower the initial watercontent. That is the combined affect of the freezing interface suction force, temperaturegradient and the matric suction gradient. The water content distribution and the totalamount of moisture migration in frozen area are affected directly by the freezing way.Further water migration test of frozen loess shows that gaseous water migration andliquid water migration in frozen loess is negligible for engineering.The test results of water migration of unsaturated loess under the freezing actionreveal the phenomenon that water is migrated to the phase interface and the phaseinterface has suction to water. Using the concept of water head, the suction is definedphase interface head. Water migration test results show that amout of water migration atfreezing interface is closely related to the density and water content. Based on thenumerical analysis phase interface head expression of unsaturated loess is obtained. Theexpression reflects the main factors of water migration to freezing interface and fittingdegree with the test results is higher. It shows that the expression used for phaseinterface head is appropriate. Using the phase interface head expression, temperaturefield and moisture field numerical calculation results in site reflect the measured results.Further maximum frozen deep relationship with the air temperature water content isgiven in the loess area.Using the loess freeze-thaw strength research results, the loess slope surfacespalling and reliability problems of freeze horizontal static load test of single pile arestudied. Considering the effect of slope side mechanics simplified calculation model ofspalling disease of loess area is established. The correlativity between spalling diseaseand thaw depth，height of spalling is calculated and analyzed by the model. The pilefoundation engineering construction in winter is frequent in the loess area. Mechanicalparameters of shallow loess increase a lot after freezing so that bearing capacityobtained by static load test of single pile is biger, but pile foundation is without thepresence of permafrost during normal use. It makes bearing capacity of pile so largerthat there are engineering problems and need to be amended. By finite element numerical simulation influence on permafrost to lateral loaded piles in loess area,correction factor is proposed for lateral static load test in winter and can be referencedfor detecting pile lateral bearing capacity in Loess Plateau.