The Research On Deformation Characteristics Of Red-Mudstone Packing Of LeShan Airport

Since the 21 st century, a large number of airport construction, renovation and expansion projects have been carried out in the southwest region of China’s expansion, the main distribution of these projects lies in the red-bed areas of Sichuan province and C hongqing. Most of the high embankments in airport construction projects involve the problem of red- mudstone used as packing inevitably.At present, it has been widely used in the fields of highway and railway, but few examples show its application in the field of high embankments of airport projects. When red- mudstone is used as packing, it may causeproblems because of its bad engineering geological characteristics, such as lo ng-term settlement of filling bodies and seepage deformation damage of slopes.This thesis is based on the detailed investigation of geotechnical engineering of LeShan Airport, the distribution and development characteristics of red- mudstone in the filed area are firstly identified. Then the compaction characteristics of mudstone packing is studied, and the maximum dry density and the optimum moisture content are obtained. Based on the research results, the deformation characteristics of mudstone packing are studied, and the compression creep test and the seepage deformation test are carried out, the laws of creep deformation and seepage deformation are obtained, and the related index value of the deformation characteristics is proposed, which provides re ference for the design and construction of LeShan Airport. The main conclusions of this thesis are as follows:(1) The heavy compaction test indicates that there are two types of compaction curves of red- mudstone packing, including single peak type and Shuangfeng type. The dry density of the packing increases when the coarse to fine ratio increases, when the coarse to fine ratio is 9:1, the maximum dry density and the optimum moisture content are obtained, respectively 2.180g/cm3 and 10.61%.(2) The compression creep test indicates that an appropriate increase in the compaction degree or the dry filler or the coarse to fine ratio is 9:1 all can control the long-term settlement of high embankments under the same condition.(3)The study on creep co nstitutive model indicates tha under the action of one-dimention stress(50kPa~400kPa), the logarithmic curve model in the empirical creep model can better describe the attenuation creep characteristics of mudstone packing than the power function model, and the Burgers model in the element creep model do better than the logarithmic curve model. The Burgers model can better describe the characteristics such as transient elastic and viscous flow, it is the most accurate, reasonable and reliable creep constitut ive model which is used to describe the characteristics of compression creep of mudstone packing.(4) The seepage deformation test indicates that the permeability of mudstone packing is poor, the permeability coefficient is small, and it tends to be a stable numerical value under the condition of low hydraulic gradient. The seepage deformation characteristics are closely related to the degree of compaction, and the permeability coefficient decreases when the degree of compaction increases. The permeability coefficient tends to increase with the increase of the hydraulic gradient when the degree of compaction is certain. The seepage deformation characteristics are closely related to the coarse to fine ratio as well, the permeability coefficient tends to increase with the increase of the coarse to fine ratio. When the coarse to fine ratio is 7:3, the value of the permeability coefficient is the maxmum, when the coarse to fine ratio is 9:1, the value of the permeability coefficient is the s mallest under the same condition.(5) Errors of the critical hydraulic gradient of mudstone packing will be generated inevitably only from the observed experimental phenomema when the seepage deformation damage occurred. The evolution process of the permeab ility coefficient is objectively reflected by the relationship between the permeability coefficient and the hydraulic gradient, and the internal mechanism of seepage deformation damage of mudstone is clarified. Based on the experimental phenomema and the relationship between the permeability coefficient and the hydraulic gradient, the methoed to determine the critical hydraulic gradient is reasonable and reliable.The seepage deformation damage occurred in the specimen when the coarse to fine ratio is 9:1, the moisture conrent is 10.61%, and the compaction degree is 90%. The critical hydraulic gradient is 11.0.