Research On Hydraulic Parameters For Silty Soil In The Yellow River Flood Area

In the Yellow River flooding area,mono-sized particle has poor fine filling,which is not easy to form a dense structure through the packing method.A large number of capillary pores,rainfall,and high water level are the basic conditions of subgrade soil moisture transmission.The Water transfer mode increasing the water content of subgrade soil includes saturated-unsaturated permeability coefficient and capillary water.Hydraulic characteristic parameters such as saturated-unsaturated permeability coefficient,water characteristic curve(WCC)and capillary water are the important basis and prerequisite of roadbed humidification.Up till now,the researchers have mainly focused on the packing degree,the relationship between the rising height and strength of capillary water and water content,while have not paid attention to the relationship of water characteristic parameters and water content,and the experience estimation method for silty in the Yellow River flooding area.From the published research literature,there are no such information,which directly affects the understanding and quantitative analysis for the pathogenesis of silty roadbed in the Yellow River area.In this paper,through theoretical analysis and experimental research,the saturated-unsaturated permeability coefficient,the water characteristic curve and the capillary water experiment are going to be carried out.Saturated-unsaturated permeability,capillary water and water characteristic curves will be studied,transfer of water characteristic parameters and pile-filled equivalent pore model are established,and the model is used to evaluate the water characteristic curve,and the water characteristic curve changes with dry density and compaction water content are explained.The main research content and results are listed as follows:1.The data collected proves that the Yellow River flooding area covers the Zhengzhou city,Kaifeng city,Puyang city and other regions in Henan province,Heze city(Dongming country),Jining city,Liaocheng city,Jinan city,Binzhou city,Dongying city and other regions in Shandong province,and Northern Jiangsu of the old Yellow River flooding area.The analysis of the composition of silt sample data in the Yellow River flooding area shows that,in general,the silt percentage in the region is over 60%.For the most part of sand particle size of silt is less than 0.25 mm.Clay content is between 5% and 15%.The Fredlund(F)model is suitable for describing the particle size distribution function.A regression analysis is conducted,and the model parameter regression shows: the parameter ? becomes greater with the increase of the sand content of the silt.The variation of the parameter n is segmented.When the content of powder is less than 75%,the parameter n decreases with the increase of the content of powder.When the content of powder is more than 75%,the parameter n rises with the increase of powder content.The parameter m decreases with the increase of the parameter n.When the parameter n is greater than 5.5,the parameter m is basically stable between 0.5 and 1.2.By simplifying the interaction of soil particles in the grain stacking and filling process,mono-sized particle stacking patterns is built,and the relation between the void ratio(radius)and the accumulation of soil grain number is obtained.There are no fine particles wedging effect in tightly packing state.On this basis,a more convenient method of soil particle accumulation pattern is preferred.When the ratio of fine particles to coarse particles is among the range of 0.05 to 0.5,if the mono-sized packing densities of coarse and fine particles are 0.6,the required fine particle size is about 0.325.According to the principle of equal total pore volume,the packing equivalent pore model of binary mix soil particle is established,and the expressions of void ratio and equivalent pore diameter for the fine and coarse particle skeleton model are obtained.The multi-component soil particles stacking including a variety mixed with unequal size particle are simplified to binary-mix with close packing mode and combination in pairs.Complex pores are divided into three categories,dominant particles pores,(non)dominant particles pores,and dominant–secondary dominant particles pores.The matching relationship and order of multi-component soil particles are determined,and the calculate steps and method of equivalent pore parameters is proposed.3.The saturated permeability coefficient is 10-4cm/s,which belongs to medium permeability soil,when the void ratio is located in the range of 0.51 to 0.71.The saturated permeability coefficient increases exponentially with the rise of the void ratio.The variation of saturated permeability coefficient is almost the same at low void ratio,when compressed water content is greater or less than optimal water content.The saturated permeability coefficient increases with the rise of compaction water content when w>0.14,and the saturated permeability coefficient decreases with the increase of compaction water content when w<0.14,and the saturated permeability coefficient is the smallest value when w=0.14,if the void ratio are relatively large.The saturated permeability coefficient decreases linearly with the increase of compaction water content.The saturation permeability coefficient is less sensitive to the void ratio for optimal water content.In other words,when the subgrade soil is compacted under the optimal water content,the adverse effect of the actual control porosity ratio on the saturated permeability coefficient is relatively small.4.The water characteristic curve of the Yellow River flooding area soil is divided into three zones: the boundary effect zone,the transition zone and the residual zone of unsaturation.(1)The water characteristic curve is approximately coincident in the transition zone and the mean slope is larger when w<0.14.The water characteristic curves tend to be scattered in the transition zone and the average slope is small when w>0.14.The water characteristic curve is parallel,and they are close to each other as the matrix suction increases when w=0.14.(2)Based on the experimental data points in the range of 0 to 500 kPa for matrix suction,the fitting curve of VG model is consistent with the experimental data,and the characteristic of water characteristic curve is expressed.VG model parameter regression function shows that the model parameters a and the saturated water content decrease linearly with increasing dry density and compaction water content.The residual water content decreases with increasing dry density,and increases with increasing compaction water content.The parameter n is determined by the dry density and the compaction water content.(3)The prediction value of water characteristic curve based on AP model agrees well with the experimental data when matric potential(h)is in the range of 0 to 100 kPa.The calculated value of water content is much smaller than the experimental value for h>100 kPa.(4)The calculation flow of water characteristic curve based on equivalent pore model is then proposed.The predicted values agree well with the experimental value in the range of matrix suction 0 to 500 kPa.But the predicted value is not complete,does not contain high water content of the water characteristics curve.5.According to the fitting curve,the water absorption process of the silt soil is roughly divided into two stages: rapid water absorption and uniform water absorption.And the trend of fast water absorption curve is similar to the quadratic function,and the uniform water absorption curve is similar to a straight line.The effects of different dry density and water content on the soil water absorption quantity were analyzed,as well as the water absorption characteristics of the test samples under different saturation.It was found that the dry density and water content had no independent effect on the water absorption of the test soil sample,but the interaction of the both two factors.Under the condition of the maximum water content and the maximum dry density,capillary absorption water is more significant.The rate of increase in capillary water was faster at the beginning of the experiment,and gradually decreased with the passage of time.The rising height and time of the capillary water show a quadratic function in the double logarithmic coordinates.After the capillary water rises and stabilizes the water content of the soil decreases linearly along the height.6.The drainage quantity decreases with the rise of dry density generally.With the decrease of soil saturation,the drainage rate goes down accordingly.In general,the unsaturated discharge decreases with increasing dry density,but does not decrease or increase monotonically as the dry density increases.When the dry density is small and the packing water content is the optimal water content,the self-weight discharge is the largest.When the dry density is large,the packing water content is larger than the optimal water content,and the matrix suction is more than 25 kPa,discharge rate is much more.The packing water content has a great influence on the curve shape and the discharge rate.By using the empirical formula based on Arya-Paris model,the results show: With the decrease of saturation,the unsaturated permeability coefficient decreases rapidly.When the saturation decreases from 0.9 to 0.1,the unsaturated permeability coefficient decreases rapidly from the order of 10-5 to the order of 10-10,Control,when the matrix suction continues to increase,the non-saturated permeability coefficient decreased significantly,and the reduction rate is also greatly reduced.