| Joints are extremely developed in the loess and have an important effect on the way of water migration during the infiltration of the loess.Openness is an important factor used to describe joint permeability.At present,considering the different opening degree,the research work on the infiltration capacity of loess joints is still lacking.Existing problems such as unknown wet front migration law,difficult to measure infiltration amount,and difficult to test the distribution of the final state water field are the main factors restricting the research on the mechanism of infiltration of loess joints under different opening conditions.Based on this,the infiltration device is designed for the insitu test of loess bodies with different opening degrees and joints.The research on how the opening degree affects the seepage properties of the joint-developed loess.The main research contents are as follows:Based on the infiltration test of closed joints to develop loess bodies and homogeneous loess bodies,the effect of closed joints on water infiltration in the presence of closed joints was studied.The results show that the infiltration capacity of the homogeneous loess body is limited,and the presence of closed joints will significantly change the infiltration characteristics of the loess body;the closed joints in the loess body have a certain degree of water infiltration along the joint direction and the vertical joint direction.Promoting effect;the existence of closed joints will significantly change the distribution of the water field of the loess after infiltration;the loess with closed joints is more likely to seep than the homogeneous loess.The infiltration test of the developed loess bodies with different spreading joints revealed the infiltration rules of the jointed loess bodies with different spreading degrees(0.63 ~ 5mm).The results show that the openness of the loess joints promotes water infiltration more than the closed joints promotes the soil water infiltration.The infiltration methods of the open joints for the development of loess can be divided into small opening mode and medium opening.There are three different infiltration mechanisms: mode and large opening mode.During infiltration with small openings,due to the water absorption expansion of the joint side walls and the erosion of the particles of the side walls with the inflow of water,the infiltration tends to be blocked quickly,which makes the infiltration tend to be a jointless,large-pore,homogeneous loess infiltration method;Under the opening degree,the water absorption and expansion of the soil particles on the side walls of the joint have little effect on the infiltration.During the infiltration,the water directly passes through the joint and faces the vertical joint direction(horizontal direction).The vertical infiltration;between the small opening and the large opening.There is a transitional opening interval(medium opening)between different infiltrations.The range of this opening interval is the upper threshold of small openings and the lower threshold of large openings,and the infiltration form in the transition interval is between large and small openings.Among the infiltration forms,the promotion of water infiltration is better than a small opening and weaker than a large opening.Based on the results of the above experimental studies,a model of moisture infiltration in loess joints with different openings was established.Based on the theory of "equivalent porosity ratio" and saturated-unsaturated soil seepage theory,a moisture infiltration model for loess joints with small openings is established.The calculation results show that the model is more accurate than the parallel plate model.The "parallel plate model" is the theoretical basis.Darcy's law,Newtonian fluid,and Newton's second law establish the expressions of joint permeability coefficients under large openings.The calculation results show that the parallel plate model has good applicability under large openings. |
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