Study On Evaluation Method Of Sand Liquefaction In Xi Xian New Area And The Preparation Of Distribution Class Diagram

Xi Xian New Area is not only the second one of national district on the northwest in our country, but also the first national district in the way of urban development of the national innovation, it has great potential for development, the construction of Xi Xian New Area unfolds as the State Council formally approved in2014. There are many rivers in this area, with dense river network in the region, the sedimentary environment is also complex, potential problems with construction engineering and geological pose a threat to economic development, the sand liquefaction problem is one of the more important problems. Xi Xian New Area set up late, once belonged to the city areas, town areas and rural areas of Xi’an City and Xianyang City, the construction degree is low, the reconnoiter materials are not rich. Based on the investigation of earthquake damage, seismic damage to the building structure itself is not very severe, in contrast, damage caused by sand liquefaction of foundation of building structure is more strong. So, it is very important to find out the sand liquefaction degree and partitions by liquefaction degree, it is also very necessary to provide information and scientific basis for future planning and construction in this area.In this paper, researches are relyed on the research of the sand liquefaction engineering problems in Xi Xian New Area, the liquefied sand in area is the main research object, based on a collection of geography data in Xi Xian New Area, reaserches are combined with the hydrogeological conditions, component distribution and stratigraphic structural features of the study area, the topography of the area affected by liquefaction was identified, by drilling on the district floodplain and terraces carried liquefied sand layer and the situ test works and laboratory test works, a detailed analysis of the liquefaction engineering problems has been made, author got a division of liquefied sand and an evaluation of liquefaction level, then combined with the application of neural network model to evaluation of the liquefaction in the study area, finished the maps of liquefaction level in Xi Xian New Area. Firstly, the liquefaction sites in this area are mainly distributed in the floodplain and terrace of Weihe River or Fenghe River. Combined with field data of liquefaction sites, The probability of liquefaction under a10%or2%probability of exceedance earthquake in50years were evaluated in this area, then we could know the liquefaction index corresponding drilling locations. Secondly, Through dynamic triaxial test results, the common law of two typical liquefiable sand Weihe fine sand and Fenghe fine sand in study area was found out, as follows: under the same consolidation pressure, the cyclic stress ratio with the greater consolidation ratio is also larger, Weihe fine sand under the condition of equalizing consolidation, consolidation pressure did not affect the cyclic stress ratio, under bias consolidation condition, affected; Fenghe fine sand, regardless under the condition of equalizing consolidation or bias consolidation cyclic stress ratio are all affected by consolidation pressure, with the same severe dry condition:15kN/m3, under condition of equalizing consolidation or bias consolidation condition the law is nearly the same, when consolidation pressure is100kPa, Weihe fine sand is more prone to liquefaction than Fenghe fine sand; when consolidation pressure is200kPa, both own almost the same liquefaction resistance. However, in case of bias consolidation, effect of particle size is less than the situation under condition of equalizing consolidation. Thirdly, based on346groups of liquefaction sites data, which will be70%(246groups) as train data,30%(120groups) as test data, a back-propagation neural network model was established to evaluate the possibility of liquefaction by using MATLAB-a mathematical software, In the process of establishing,8liquefaction factors were selected, they are overburden stress, effective overburden stress, magnitude, fine content, SPT counts, modified maximum acceleration, the effective stress ratio, the average particle size. Using the model to evaluate the study area, then compared with the method of using Seismic Design Code of Buildings, the results were basically the same. Fourthly, by using the Geographic Information System, added the borehole and terrain data, author used the DTM module of MAPGIS software to draw the maps of the distribution of liquefied sand and the liquefaction levels, the maps are contained the probability of liquefaction under a10%or2%probability of exceedance earthquake in50years, liquefied area in the maps was divided into severe, moderate, mild threehazardous area, in order to achieve the purposes of the liquefaction plane visualization. The data in this paper, the test results, method of sand liquefaction evaluation suitable for the study area and the maps of the distribution of liquefied sand and the liquefaction levels, can provide a reliable reference to construction and disaster reduction in Xi Xian New Area.