Research On Foundation Soil's Dynamic Characteristics Of Three Pagodas In Dali

With the progress of economy and social civilization, the industry of heritage preservation showed a trend of rapid development. Coupled with the promotion of the local economy and the needs of local culture, a wave of heritage preservation and restoration research in recent years rises from around the world. Ancient architectures exist in rock and soil environment, so they contact with geotechnical engineering closely. With the development of science and technology, geotechnical engineering technology is more and more widely used in heritage conservation areas, which accumulate a large number of successful experience, make some research and have a good social benefits.China, a country with an ancient civilization, has a long history with the world renowned ancient cultural heritage. The pagoda as one of the few existing ancient architecture, integrating the foreign culture and traditional Chinese architectural art, is an outstanding representative of ancient China high-rise building. Ancient building technology as a result of the restrictions and vicissitudes of life for thousands of years of destruction, coupled with high aspect ratio such buildings, and high center of gravity of the ground conditions are often very sensitive. In static and dynamic conditions, the foundation produced a gradual deformation, so many pagodas produce various degrees of tilt. In particular, ancient masonry structures have the major deadweight and low-intensity. Once the tilt, the side of the foundation is often caused by stress concentration, which further accelerates the building of the tilt. In order for the continuous long-term recovery and preservation of ancient pagodas which destruct but still may be reinforced, experts at home and abroad have made efforts to explore and practice.Chongsheng Temple in Dali of Yunnan province founded in the Tang Dynasty (823-859 AD), which is national monastery in Royal Dali of the period for Nanzhao, is famous pagodas in southwest of China. In March 4, 1961 the State Council announced it as the first batch of national key cultural relics protection unit. The study of the protection of Three Pagodas in Chongsheng Temple has great significance and scientific value for the construction process in Tang and Song Dynasty, Buddhist culture, astigmatic construction and Dali country's history. The tourism development in Yunnan is also significant. Dali is located in the northern section of Yuanjiang fault zone - Erhai fault zone. The fault block as the activities of the border is to draw the attention of the major earthquake occurred. Frequent earthquakes result in sustained damage of the Three Pagodas in Dali. As a result of the use of part of gravel fill for the soft clay and the way from the ground for tower foundation construction, historical earthquakes and heterogeneity of foundation soil affect the larger contribution on the tower's tilt. Therefore dynamic characteristics of foundation Soil of Three Pagodas have become a pressing research need to be addressed.Domestic and foreign scholars have been carried out a certain amount of research on the dynamic properties of saturated clay. Due to the differences in the test apparatus, soil samples and test methods, test results will also be some differences, which impact in the results of the analysis for calculating. Based on the importance of research on the dynamic properties of saturated clay, this article makes use of indoor dynamic triaxial apparatus to simulate the soil body force unit of the actual conditions. Dynamic shear modulus and damping ratio of saturation remodeling clay and the growth pattern of pore water pressure under different conditions are systematic studied. Numerical simulation software FLAC is applied in northern tower to simulate and analyze dynamic response. The changes of indicators are summed up, providing the basis for seismic design and reinforcement.The main contents of the full text include the followings:(1) Based on geotechnical engineering investigation and design of reinforced maintenance projects on the Three Pagodas of Dali, the formation conditions and characteristics of tilted tower are analyzed.the opinion that earthquakes are also a major factor lays a theoretical foundation for the indoor dynamic test of tower foundation soil; Through geotechnical engineering investigation, a large number of soil sample were collected. Then the clay has to be prepared into the nature of the sample as a homogeneous soil test samples required. The confining pressure and different dynamic stress is imposed in the dynamic triaxial samples to study their dynamic properties;(2) Dynamic shear modulus and damping ratio characteristics test is one of the fundamental basis for the analysis of dynamic response. These relations reflect the role of the non-linear characteristics and viscosity of the soil stress-strain relationship under dynamic load. Soil dynamic properties tests were carried out in the use of dynamic triaxial apparatus and dynamic modulus and damping ratio at different confining pressure were respectively measured. The test with consolidation pressure of respectively 100,200 and 300 kPa, consolidation ratio of1.0 and Poisson's ratio of 0.5 received the maximum dynamic shear modulus G_{d max} and therelationship between G/ G_{d max}-γandλ-γ_d by means of the laboratory test. Changes ofdynamic shear modulus and damping ratio are summed up by comparative analysis;(3) For soft clay, stress-controlled dynamic triaxial tests in undrained equal consolidation conditions are experienced to study the main factors affecting the pore pressure changes in saturated soft clay under cyclic loading. Then found a pore pressure model reflecting the correct factors effects based on tests and determine the model parameters. In this study, the pore pressure growth model is suitable for saturated clay in Dali region, can be used to analyze saturated clay characters of non-drainage cycle after loading and monotonic undrained loading to research the impact of cycle of disturbance on non-drainage;(4) Numerical simulation FLAC software is used for seismic modeling of tower foundation and calculate. Factors such as the calculating area, boundary conditions, damping settings, the non-linear of geotechnical material are considered in the modeling process. The calculation results are relatively more in line with the actuality by selection of Mohr-Coulomb elastic-plastic model and set El Centro earthquake wave;(5) On the basis of the above work, the calculation results of the FLAC analysis results show that the seismic effects of dynamic response factors such as displacement, acceleration and shear stress have a certain degree of regularity changes. These provide a theoretical basis for the foundation and structural seismic design and reinforcement.