Moisture Transfer Characteristics Of Dry-wet Cycle Laterite

The topic of this paper comes from the National Natural Science Foundation Project"Re-search on the effect of dry and wet cycles on Yunnan laterite dam"(Project No.51568031).Many problems still exist in the study of soil moisture transfer.This paper aims at providing some reference for the solving of the problems of cracking,deformation and seepage of laterite dam under distinct climate of Yunnan Province.Yunnan laterite is taken as the re-search object,with soaking humidification and constant temperature dehumidification as the control conditions,and the influences of the number of dry and wet cycles,dry density,ponding height and dehumidification water content are also considered.Experiment on the vertical and horizontal water transfer in laterite were used to study the effect of dry wet cycle on the water transfer characteristics of laterite in Yunnan Province.This paper may provide some references for the study of the mechanism of water transfer in laterite.The results of experiment on the vertical migration of water in laterite show that:(1)with the increase of the times of dry and wet cycles,the fluctuation of water content in laterite de-creases;when the dry density is small,the fluctuation of water migration time increases,and the fluctuation of migration rate and migration coefficient decreases;when the dry density is large,the fluctuation of water migration time shortens,and the fluctuation of migration rate and migration coefficient increases.(2)With the increase of dry density,the moisture content of laterite decreased significantly,the time of water migration prolonged significantly,and the fluctuation of migration rate and migration coefficient decreased.(3)With the decrease of the height of water accumulation,the time of water migration increased significantly,and the fluc-tuation of migration rate and coefficient decreased.(4)With the decrease of dehumidification water content,the water content of laterite decreases slowly;after the first dry wet cycle,the fluctuation of water migration time increases,and the fluctuation of migration rate and migra-tion coefficient slows down.(5)With the increase of migration time,the migration coefficient decreases slowly.The results of experiment of horizontal migration of water in laterite show that:(1)with the increase of the times of dry and wet cycles,the fluctuation of water content in laterite de-creases;when the dry density is small,the fluctuation of water migration time increases,and the fluctuation of migration rate and migration coefficient decreases;when the dry density is large,the fluctuation of water migration time shortens,and the fluctuation of migration rate and migration coefficient increases.(2)With the increase of dry density,the fluctuation of moisture content of laterite decreases,while the fluctuation of water transfer time increases,and the fluc-tuation of transfer rate and transfer coefficient decreases.(3)With the decrease of the height of water accumulation,the time of water migration increases slowly,and the fluctuation of migra-tion rate and coefficient decreases.(4)With the decrease of dehumidification water content,the fluctuation of laterite water content decreases;when the dry density is 1.15g/cm~3 and the num-ber of cycles is less,the fluctuation of water transfer time increases,the fluctuation of migration coefficient decreases,and when the number of cycles is more,the fluctuation of water transfer time shortens and the fluctuation of migration coefficient increases.(5)With the increase of migration time,when the number of cycles is less,the migration coefficient decreases slowly,and when the number of cycles is more,the fluctuation of migration coefficient increases.The comparison of vertical and horizontal water transfer characteristics of laterite show that under the same influence factors,the vertical and horizontal water transfer characteristics of laterite have the same change trend and different change degree.(1)Under the same dry and wet cycle times,when the dry density is small,the vertical migration rate of water in laterite is generally lower than that in horizontal direction;when the dry density is large,the vertical migration rate is generally higher than that in horizontal direction.The vertical migration coef-ficient is smaller than the horizontal migration coefficient.(2)At the same height of water ac-cumulation,before and after circulation,when the dry density is small,the vertical migration rate is less than the horizontal migration rate;when the dry density is large,the vertical migra-tion rate is greater than the horizontal migration rate;the vertical migration coefficient is less than the horizontal migration coefficient.The regression analysis of water transfer characteristics in laterite shows that:(1)the re-gression fitting relationship between the moisture content and transfer coefficient of laterite and each influencing factor is consistent in the process of transfer,no matter the water is transferred along the lead or along the horizontal direction.(2)There is a single factor linear function fitting relationship between the moisture content of laterite and the number of dry and wet cycles or dry density,and a multiple factor regression relationship between the number of dry and wet cycles and dry density.(3)The transfer coefficient of laterite has a polynomial function fitting relationship with the number of dry and wet cycles or the transfer time,a linear function fitting relationship with the dry density,and a binomial function regression relationship with the num-ber of dry and wet cycles,the dry density,the transfer time and the height of water accumulation.(4)Under different migration directions,there is a binomial function regression relationship between the transfer coefficient of laterite and the number of dry and wet cycles,dry density,migration time,ponding height and migration direction.