长持时强震下砂土液化沉降机制与评价方法研究
发布时间：2018-08-02 07:36
【摘要】：近年来全球范围内长持时强震频发,长持时强震液化后产生过大沉降变形异常严重,是导致强震区地下基础设施及生命线系统失效破坏的主要原因之一。本文针对长持时强震作用下场地液化后沉降机制问题,开展单元体固结试验、动三轴振动试验(包括液化工况和非液化工况)研究,了解砂土受振动荷载后的变形特性,并进一步提出了基于固结和循环应力历史的再固结排水模型和沉降简化计算方法。同时,开展了两个离心机模型试验(正弦波模型和地震波模型)模拟长持时强震后的液化沉降,对上述模型和计算方法加以验证。本文还针对液化场地的边值问题提出相应的累积剪应变比的计算方法,并做了现场实例沉降计算。具体内容包括： (1)动三轴振动(包括液化工况和非液化工况)研究中采用累积剪应变比作为砂土结构性损伤的表征指标,确定了单元体试样中临界累积剪应变作为液化判别的标准； (2)饱和砂土在振动非液化工况下排水体变仅由再固结机制控制,其再固结过程的规律与固结试验中的回弹段的规律相似,其再固结指数在e-logp曲线中的斜率随着有效应力的增大而增大,且再固结指数与相同条件下的回弹指数相当； (3)饱和砂土液化后体变由再沉积和再固结两种机制组成：其中再沉积部分与所受振动历史密切相关,土骨架累积剪应变比越大、再沉积体变越大；而再固结部分受先期固结历史影响显著,再固结曲线会沿原有正常固结曲线趋势发展,其稳定段再固结指数与相同条件下的压缩指数稍大,前者大约为后者的1.3-1.5倍之间,于是,压缩指数可以用于再固结指数的估算； (4)提出了考虑先期固结和振动历史的砂土再固结模型和简化算法,将再沉积和再固结两者统一表达成再固结体变,该简化后体变的规律可用累积剪应变比(γacm/γacm0)与假设起始应力比(σ1a：/σ1v0)的相关关系加以描述,并建议了再固结指数和假设初始应力的确定方法； (5)开展了系列水平场地地震液化离心机模型试验,监测模型固结和振动液化过程急排水过程的沉降,从模型尺度进一步揭示砂土在长持时强震作用下的液化工况下的体变规律,并初步验证了本文模型与简化算法在计算非液化工况和液化工况下沉降的有效性。 (6)根据模型场地累积剪应变数据给出了模型或现场等边值问题下的临界累积剪应变判别液化标准,提出了依据现场地表加速度记录计算地表下各土层的累积剪应变的方法,并针对东日本地震中Urayasu地区某液化场地的液化进行沉降计算。
[Abstract]:In recent years, the long-lasting strong earthquakes occur frequently in the world, and the excessive settlement and deformation caused by the liquefaction of long-lasting strong earthquakes are very serious, which is one of the main reasons leading to the failure of underground infrastructure and lifeline system in strong earthquake areas. Aiming at the settlement mechanism of site liquefaction under the action of long-lasting strong earthquake, the consolidation test and dynamic triaxial vibration test (including liquefaction condition and non-liquefaction condition) are carried out to understand the deformation characteristics of sand under vibration load. Furthermore, a reconsolidation drainage model based on consolidation and cyclic stress history and a simplified settlement calculation method are proposed. At the same time, two centrifuge model tests (sinusoidal wave model and seismic wave model) were carried out to simulate the liquefaction settlement after long duration strong earthquake. In this paper, the corresponding calculation method of cumulative shear strain ratio is proposed for the boundary value problem of liquefaction site, and the settlement calculation of site example is made. The main contents are as follows: (1) in the study of dynamic triaxial vibration (including liquefaction and non-liquefaction), the cumulative shear strain ratio is used as the index to characterize the structural damage of sand. The critical cumulative shear strain in the unit sample is determined as the criterion of liquefaction. (2) the deformation of saturated sand is controlled only by the mechanism of reconsolidation under the condition of vibration and non-liquefaction. The law of the reconsolidation process is similar to that of the springback section in the consolidation test. The slope of the reconsolidation index in the e-logp curve increases with the increase of the effective stress, and the re-consolidation index is similar to the springback index under the same conditions. (3) the liquefaction of saturated sand consists of two mechanisms: redeposition and reconsolidation. The redepositional part is closely related to the vibration history, and the larger the cumulative shear strain ratio of soil skeleton is, the larger the redepositional body is; However, the reconsolidation part is significantly affected by the preconsolidation history, and the reconsolidation curve will develop along the trend of the original normal consolidation curve. The reconsolidation index of the stable section is slightly larger than that of the compression index under the same conditions, and the former is about 1.3-1.5 times of the latter, so, Compression exponent can be used to estimate the reconsolidation index. (4) A sand soil reconsolidation model and a simplified algorithm considering the pre-consolidation and vibration history are proposed. The simplified law of body deformation can be described by the correlation between the cumulative shear strain ratio (纬 acm/ 纬 acm0) and the assumed initial stress ratio (蟽 1a:/ 蟽 1v0), and the method of determining the reconsolidation index and the hypothetical initial stress is suggested. (5) A series of horizontal site seismic liquefaction centrifuge model tests were carried out to monitor the settlement of the model during consolidation and vibration liquefaction. Based on the model scale, the body deformation law of sand under the condition of liquefaction under the action of long-lasting strong earthquake is further revealed. The validity of the proposed model and the simplified algorithm in the calculation of settlement under non-liquefaction and liquefaction conditions are preliminarily verified. (6) based on the cumulative shear strain data of the model site, the impending problem of model or field isobaric value is given. Boundary cumulative shear strain criterion for liquefaction, A method for calculating the accumulated shear strain of each soil layer under the ground surface based on the field acceleration records is proposed and the settlement of a liquefaction site in Urayasu area during the East Japan earthquake is calculated.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU441
本文编号：2158665
[Abstract]:In recent years, the long-lasting strong earthquakes occur frequently in the world, and the excessive settlement and deformation caused by the liquefaction of long-lasting strong earthquakes are very serious, which is one of the main reasons leading to the failure of underground infrastructure and lifeline system in strong earthquake areas. Aiming at the settlement mechanism of site liquefaction under the action of long-lasting strong earthquake, the consolidation test and dynamic triaxial vibration test (including liquefaction condition and non-liquefaction condition) are carried out to understand the deformation characteristics of sand under vibration load. Furthermore, a reconsolidation drainage model based on consolidation and cyclic stress history and a simplified settlement calculation method are proposed. At the same time, two centrifuge model tests (sinusoidal wave model and seismic wave model) were carried out to simulate the liquefaction settlement after long duration strong earthquake. In this paper, the corresponding calculation method of cumulative shear strain ratio is proposed for the boundary value problem of liquefaction site, and the settlement calculation of site example is made. The main contents are as follows: (1) in the study of dynamic triaxial vibration (including liquefaction and non-liquefaction), the cumulative shear strain ratio is used as the index to characterize the structural damage of sand. The critical cumulative shear strain in the unit sample is determined as the criterion of liquefaction. (2) the deformation of saturated sand is controlled only by the mechanism of reconsolidation under the condition of vibration and non-liquefaction. The law of the reconsolidation process is similar to that of the springback section in the consolidation test. The slope of the reconsolidation index in the e-logp curve increases with the increase of the effective stress, and the re-consolidation index is similar to the springback index under the same conditions. (3) the liquefaction of saturated sand consists of two mechanisms: redeposition and reconsolidation. The redepositional part is closely related to the vibration history, and the larger the cumulative shear strain ratio of soil skeleton is, the larger the redepositional body is; However, the reconsolidation part is significantly affected by the preconsolidation history, and the reconsolidation curve will develop along the trend of the original normal consolidation curve. The reconsolidation index of the stable section is slightly larger than that of the compression index under the same conditions, and the former is about 1.3-1.5 times of the latter, so, Compression exponent can be used to estimate the reconsolidation index. (4) A sand soil reconsolidation model and a simplified algorithm considering the pre-consolidation and vibration history are proposed. The simplified law of body deformation can be described by the correlation between the cumulative shear strain ratio (纬 acm/ 纬 acm0) and the assumed initial stress ratio (蟽 1a:/ 蟽 1v0), and the method of determining the reconsolidation index and the hypothetical initial stress is suggested. (5) A series of horizontal site seismic liquefaction centrifuge model tests were carried out to monitor the settlement of the model during consolidation and vibration liquefaction. Based on the model scale, the body deformation law of sand under the condition of liquefaction under the action of long-lasting strong earthquake is further revealed. The validity of the proposed model and the simplified algorithm in the calculation of settlement under non-liquefaction and liquefaction conditions are preliminarily verified. (6) based on the cumulative shear strain data of the model site, the impending problem of model or field isobaric value is given. Boundary cumulative shear strain criterion for liquefaction, A method for calculating the accumulated shear strain of each soil layer under the ground surface based on the field acceleration records is proposed and the settlement of a liquefaction site in Urayasu area during the East Japan earthquake is calculated.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU441
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