Study On Collapsibility Evaluation Method Of Loess In Roadbed

The collapsibility is the significant characteristics of loess which is different fromother soils, so the collapsibility of loess is always the focus of the study about loess of the geotechnical engineering. As a result of loess mainly distributed in northwest and north china, the study about the nature of engineering geology of loess in these areas is more in depth and extensive, and little about loess in the Northeast especially in west of Liaoning relatively. Fuxin and Chaoyang district in west area of Liaoning are firstly listed in the marginal zone of loess by the national standard Architecture Criterion In Collapsible Loess Area (GB50025-2004), and With the development of economic in Liaoning, many projects start Correspondingly, it is our duty to deal with the problem about how to avoid the engineering accidents of loess inthe engineering construction especially in the highway Construction. Based on this,this paper will mainly study the collapsibility issues of loess in west of Liaoxi , explore the characteristics and evaluation methods of loess in west of Liaoxi in the course of moistening and drying,establish collapsibility deformation model correspondingly, provide reference for further study about loess in west of Liaoning.The existing criterion is specifically targeted at the construction in collapsible loess area, when applied to highway projects, can not be in line with the practical reality, leading to that the evaluation about the collapsible loess in highway engineering is biased, bringing about unnecessary profligacies and so on. Therefore this paper studies the evaluation about the collapsible loess which is in line with the highway projects. This paper is divided into six parts: the first part introduces the status of the research about loess,the purpose of the research about the collapsibility of loess in west of Liaoning and the practical significance about the study results. The second part introduces the geological features of the geological structure,the topography and so on of the loess region in west of Liaoning and the physical properties of loess, Doing a large number of laboratory test combined with the Chao-Fu highway construction and get the basic material composition, the mechanical properties, the collapsibility properties and the microstructure characteristics and so on of the Liaoxi loess in the study area. The third part introduces the sample preparation, the moistening and drying method about the sample, collapsibility test method, test data processing and the study about the test result. The fourth part studies the subgrade load combined with the actual work about the roadbed,and based on that studies the collapsible evaluation method about loess. The fifth part analyses the state of the collapsibility deformation when the Liaoxi loess is moistening. The sixth part summarizes the conclusion and results about the research of the collapsibility of Liaoxi loess and put forward the lacks and needs for improvement.There are the following main results through research and analysis:1. Loess collapsibility test:(1) the collapsibility coefficient increases with the increasing of the test pressure; In addition to the sample of the moisture content 1% outside, when the test pressure reaches a certain value, the collapsibility coefficient is to the peak, then collapsibility coefficient also increases with the increasing of the test pressure, but the test pressure decreases when the collapsibility coefficient reached its peak with the increasing of the moisture content of the sample. (2) It is a negative correlation between the collapsibility coefficient and initial moisture content of the sample under the same test pressure. The collapsibility coefficient will be smaller when the initial moisture content of the sample is greater. When the initial moisture content of the sample is near to the saturated moisture content, the collapsibility coefficient tends to zero. In short, the collapsibility coefficient of the sample decreases with the increasing of the initial moisture. (3) When the moisture content of the sample is smaller, at about 1% ,the collapsibility coefficient of the inundated samples and natural samples increases with the decreasing of the void ratio; the moisture content of sample is high, when the collapsibility coefficient is in the pre-peak, the collapsibility coefficient increases with the decreasing of the void ratio, but after the collapsibility coefficient is to the peak the collapsibility coefficient decreases with the decreasing of the void ratio. (4) Combining the characteristics of the working environment about the roadbed engineering and the timeliness about the changes of the moisture content of the soil, proposes the relative collapsibility coefficient. Whether the concept is accurate and whether is used in engineering practice, that needs further examined.2. The collapsibility of loess is not only in the case of complete soaking, but runs through the whole process of the increase of the sample moisture content. Give out the concept of the relative collapsibility coefficient and give the method of calculating the collapsibility settlement by relative collapsibility coefficient.3. The subgrade loads are divided three parts: the weight load of the road surface and cushion, the self-loading of subgrade soil, the vehicle dynamic load. The calculations about the collapsible settlement value of the loess roadbed are more accurate with the method of compression modulus and collapsiblity coefficient, and gives the correction formula about the collapsible settlement with the criterion method.Combined with the actual working condition about the roadbed, give the determination about the test pressure and collapsibility coefficient.4. Give the calculating model about the collapsible settlement with secant modulus method with the study about the loess collapsibility test.This paper launched a more comprehensive and systematic research and analysis about the collapsibility of Liaoxi loess, the research results will provide reference for further study about the geological engineering characteristics of Liaoxi loess and even the loess in the northeast area.