Study Of Creep Characteristic And Long-term Strength For Grouted Anchor In Expansive Soil Based On Indoor Test

Expansive soil is widely distributed, a large number of high-steep expansive soil slope occur with the construction of highway. In order to maintain the long-term stability of these slopes, anchor-type retaining structures are usually preferred. The key of long-term stability for anchor-type retaining structure is the long-term strength and creep property of the anchoring system, and it is influenced by the moisture content and dry density of soil seriously. In order to investigate the long-term strength and shearing creep characteristic of the anchor-soil interface for grouted anchors in expansive soil under long-term load, shearing creep tests and theoretical analysises is carried out based on the indoor model test. In this paper, the following research work is accomplished:(1) The regular physical and mechanical properties of the expansive soil got from the Guangxi Baise is tested. Anchor samples of different moisture content and dry density are produced using the group-developed apparatus, then instantaneous shearing test is conducted in the anchor-soil interface frictional behavior testing system, the last is the shearing creep test of anchor-soil interface. The shearing creep curves of anchor-soil interface in multi-stage loading are obtained, and can be transformed into the creep curve at each specific loading level by employing “Chen’s method”.(2) Long-term strength is determined through two methods: isochronous curve and the transition creep law. The stress-placement isochronous curve is drawed according to the respective creep curve. The inflection point in isochronous curve between viscoelastic phase and viscoplastic phase corresponds to long-term strength; the creep rate is obtained by mathematical fitting method, and the range of long-term strength is determined according to the inflection point of the stress and creep rate curve. The differences of the two methods are analyzed. Based on the above results, draw the curve of instantaneous strength, long-term strength changing with moisture content, dry density. The changing rule and the ratio of long-term strength and instantaneous strength are studied.(3) Based on the results of the creep test at limited stress level, establish a more suitable empirical model for shear creep of anchor-soil interface. The creep curves at several other stress level can be predicted using this model, and verify the practicality of the model through the actual curves. Simultaneously, establish model and predict curves using the famous Singh-Mitchell creep model and Mesri creep model for comparison, and these two model are compared with proposed model in the fitting and predicting effects to justify the practicability of proposed model.(4) In considering the fact that the Burgers model fits not so well with the creep curve and can’t depict the accelerating stage, improve the Burges model through two measures. Firstly, the Newton body is replaced with the soft body based on fractional calculus theory. Secondly, the Kachanov damage evolution is introduced to reflect the damage characteristic of the element parameters to create a new improved Burgers model. This model can simulate the whole creep process including accelerated creep.