| With the fast development of China’s economic construction, massive engineering construction such as subways, tunnels, airports, docks and expressways are springing up like mushrooms. Accordingly, the long-term settlement problems of the buildings with expansive soil foundation become an serious problems due to expansive soil’s characteristics of long-term compressibility. In terms of the present research status, many valuable research results have been achieved in components, structural characters, strength and expansion mechanism of expansive soil expect long-term compressibility. Moreover, there is no constitutive model that reflects both characteristics of overconsolidation and characteristics of long-term compressibility of expansive soil at present. In this paper, long-term compressibility of Nanning expansive soil is described fully according to experiment results. Based on the theory of critical state and theory of subloading surface, a constitutive model that comprehensively reflects characteristics of overconsolidation and long-term compressibility of expansive soil are put forward. The rationality of this constitutive model have been validated by above-mentioned results of test. Therefore, this study has important theoretical significance and practical engineering value.Research results of this paper can be concluded as follows:(1) In this paper, the secondary compression behavior of a typical expansive soil in Nanning was investigated. A series of long-term compressibility tests were conducted. The influence of compression pressure and water content on compression index Cc and coefficient of secondary compression Ca is discussed respectively. The method of decreasing secondary compressibility of expansive soil is discussed. lime-added dispose and preloading is compared on the effect of decreasing secondary compressibility of expansive soil so as to seek the best measure to reduce secondary compressibility. Some useful conclusions are drawn. The compression index Cc and coefficient of secondary compression Ca substantially increase with consolidation pressure respectively which it is less than preconsolidation pressure. The compression index Cc and coefficient of secondary compression Ca remain fairly constant respectively When consolidation pressure is more than preconsolidation pressure. Nanning expansive soil belongs to lower compressibility clay. The relation between the compression index Cc and coefficient of secondary compression Ca is linear. The compression index Cc and coefficient of secondary compression Ca of Nanning expansive soil which has less water content and consolidation degree is lesser than compared with other clays. (2) Secondary compressibility can be decreased by lime-added dispose. the value of Ca of preloading appears less compared with that of lime-added dispose when consolidation pressure is less than preloading. The value of Ca of preloading assumes larger compared with that of lime-added dispose while consolidation pressure is larger than preloading. The subloading modified Cam-clay model is improved. It can both calculate the long-term deformation of expansive soil and describe the elastoplasticity during unloading and reloading. In order to consider expansive soil’s characteristics of long-term compressibility, compression index Cc and rebound index are described by coefficient of secondary compression Ca and coefficient of secondary compression Ca is defined as a variable changing with the change of consolidation pressure in this model. Meanwhile, the concept of subloading surface is introduced due to the consideration of Nanning expansive soil’s characteristics of overconsolidation. Based on the modified Cam-clay model, yield surface of modified Cam-clay model is replaced by subloading surface so that this model can calculate the plastic deformation of expansive soil during overconsolidation. Then, secondary development of the subloading modified Cam-clay model is made on the platform of finite element software ABAQUS. The rationality of this model is validated by long-term compressibility tests and applied on practical engineering..Finally, the research orientation of future work is discussed briefly. |
