Study Of The Dynamic Characteristics Of Warm Frozen Soil Based On Permafrost Dynamic Direct Shear Apparatus

Permafrost is widely distributed in our country, most of them belong to the warm frozen soil. Meanwhile, the Tibetan Plateau has the highest level of seismic activity and the largest intensity. A number of major projects of strategic importance, such as the Qinghai-Tibet railway and the Qinghai-Tibet highway, are threatened by increased temperature permafrost, earthquakes and other factors. In response to this situation, a new instrument for measuring soil dynamic parameters was developed; dynamic parameters of warm frozen soil under low confining pressure were studied; and empirical formula under certain conditions were presented as well. These could provide important insights for embankment engineering seismic design and calculation, as well as safe operation of structures on Qinghai-Tibet Plateau.With the support of National Basic Research Program of China (No.2012CB026104), based on a review of status quo of research at home and abroad, study subjects were chosen as typical Tibetan Plateau silty clay. By means of site investigation and sampling, instrument development, laboratory testing, dynamic strength, dynamic shear modulus and damping ratio of warm frozen soil under low pressure were studied. The relationship between different affecting factors and dynamic parameters were given, and applicable parameters were provided for structures seismic design and calculation in warm frozen soil regions. Moreover, the applicability of the new instrument was verified. Some achievements were summarized as follows:(1) On the basis of the summary and analysis of status quo of research at home and abroad, current research deficiencies were pointed out:dynamic characteristics of warm frozen soil under low pressure is lack of systematic research.(2) Typical sites were selected and monitored, and related laboratory soil test were carried out to learn the basic soil properties of soil samples in order to further study the dynamical properties of warm frozen soil.(3) Various components of the dynamic direct shear apparatus for frozen soil were specified. Hydraulic power systems, temperature-controlled direct shear box, actuators and spliced work platforms and other aspects were analyzed. Through different verification test, the accuracy and applicability of the new instrument was verified. (4) According to the theory of dynamic strength of soil, dynamic strength of warm frozen soil were systematically researched. Through a series of experiments under different conditions, dynamic strength parameters of warm frozen soil were calculated. Factors of temperature and vibration times were analyzed emphatic. The similarities and differences of two test methods and test results were compared and analyzed.(5) By summarizing the soil dynamic constitutive model, and combining the results of the two dynamic tests, Hardin-Drnevich constitutive model was chosen for the study of the test results. Factors of temperature, confining pressure, vibration times were systematically researched. Dynamic shear modulus and damping ratio were measured by two test methods. Results are compared and analyzed, and the applicability of the new test instrument was further verified.