砂土液化时间效应的剪切波速表征研究
发布时间：2018-11-18 13:49
【摘要】：近年来全球强震频发,造成极为广泛的地震灾害,其中饱和砂土液化问题尤为突出。在场地液化判别方面,目前国内外大多以Seed简化方法为框架,基于土体抗液化强度(CRR)与原位测试指标经验相关性,判别一定地震剪应力比下场地液化可能性。大量测试结果表明,土体物理力学特性包括标贯锤击数N、静力触探端阻qc、小应变剪切波速Vs及砂土抗液化强度CRR等都会受时间效应影响得到发展,因此基于不同测试时间的原位指标建立的液化评价关系其可靠性存在重大改进空间。 针对时间效应对砂土场地抗液化性能影响,本文以波速指标为表征参数,开展单元体试验及物理模型试验,研究时间效应对砂土抗液化强度剪切波速表征关系影响,揭示工程时间尺度内时间效应主要影响机制,发展考虑时间效应的砂土液化剪切波速评价方法。具体内容包括： (1)针对时间效应对土体特性影响,对基督城强震台站分析,发现场地特性在地震期间产生损伤,并在震后逐渐恢复,传统液化判别关系未考虑时间效应的这种影响,存在不安全评价风险。 (2)开展系列单元体试验,研究工程时间尺度内时间效应影响因素。结果表明,含细粒砂土时间效应远比洁净砂显著；而应力水平对时间效应影响并不会以固定趋势发展,会在某一合适的应力水平下达到最佳；当砂土处于低应力水平下,松砂时间效应比密砂更为明显。 (3)基于理论推导及动三轴试验,建立了砂土抗液化强度(CRR)与剪切波速(Vs)的相关关系,揭示土体强度与刚度的内在联系。该理论相关性能表征时间效应对强度及刚度的不同步影响,可靠评价具有不同时间效应砂土的抗液化强度,是时间效应初期砂土抗液化强度剪切波速表征的本征关系。 (4)通过水平场地地震液化模型试验,从小应变剪切模量Gmax及贯入阻力qc两方面实现影响土性主要因素结构性、密实度及应力状态的分离,发现土体结构性伴演变随着固结过程同步进行,振动液化有助于改善土体结构性,增强其抵抗液化的能力； (5)针对土层沉积年代与实际物理力学特性变化并不对应这一问题,从土体力学特性出发,联合Gmax与qc场地测试指标,建立基于土性的砂土时间效应定量表征指标AI,为现场评估场地抗液化性能提供有效手段。
[Abstract]:The frequent occurrence of strong earthquakes in the world in recent years has caused a wide range of earthquake disasters, especially the liquefaction of saturated sand. In the field of site liquefaction, at present, the Seed simplified method is used as the frame at home and abroad, and based on the empirical correlation between soil liquefaction strength (CRR) and in-situ test index, the possibility of site liquefaction under a certain seismic shear stress ratio is judged. A large number of test results show that the physical and mechanical properties of the soil, including the standard hammer number N, the qc, small strain shear wave velocity Vs and the liquefaction resistance CRR of sandy soil, are all affected by the time effect. Therefore, there is great room for improvement of the reliability of liquefaction evaluation based on in situ index of different test time. Aiming at the effect of time effect on the liquefaction resistance of sandy soil, this paper takes the wave velocity index as the characterization parameter, carries out the unit body test and physical model test, and studies the influence of time effect on the characterization of shear wave velocity of sand liquefaction strength. The main influence mechanism of time effect in engineering time scale is revealed, and the evaluation method of sand liquefaction shear wave velocity considering time effect is developed. The main contents are as follows: (1) according to the influence of time effect on soil properties and the analysis of strong earthquake stations in Christchurch, it is found that the site characteristics are damaged during the earthquake and gradually recovered after the earthquake. The traditional liquefaction discriminant relation does not consider this kind of influence of time effect, and there is the risk of unsafe evaluation. (2) A series of unit tests were carried out to study the influence factors of time effect in engineering time scale. The results show that the time effect of fine grained sand is much more significant than that of clean sand, but the effect of stress level on time effect will not develop in a fixed trend and will reach the best at a suitable stress level. When sand is at low stress level, the time effect of sand loosening is more obvious than that of dense sand. (3) based on theoretical derivation and dynamic triaxial test, the relationship between shear wave velocity (Vs) and liquefaction resistance strength (CRR) of sandy soil is established, and the relationship between soil strength and stiffness is revealed. The related properties of this theory indicate the asynchronous effect of time effect on strength and stiffness, and the reliable evaluation of the liquefaction resistance of sand with different time effect is the intrinsic relation of shear wave velocity characterization of sand liquefaction strength in the early stage of time effect. (4) through the seismic liquefaction model test of horizontal site, the main factors affecting soil properties, such as structure, compactness and stress state, can be separated from strain shear modulus (Gmax) and penetration resistance (qc) from small strain shear modulus (Gmax). It is found that the evolution of soil structure is synchronized with the consolidation process, and vibration liquefaction is helpful to improve the soil structure and enhance its ability to resist liquefaction. (5) aiming at the problem that the time of soil deposition does not correspond to the change of physical and mechanical properties of soil, starting from the mechanical properties of soil, combining Gmax and qc site testing indexes, a quantitative characterization index of sand time effect based on soil properties, AI, is established. It provides an effective method for site evaluation of site liquefaction resistance.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU435
本文编号：2340202
[Abstract]:The frequent occurrence of strong earthquakes in the world in recent years has caused a wide range of earthquake disasters, especially the liquefaction of saturated sand. In the field of site liquefaction, at present, the Seed simplified method is used as the frame at home and abroad, and based on the empirical correlation between soil liquefaction strength (CRR) and in-situ test index, the possibility of site liquefaction under a certain seismic shear stress ratio is judged. A large number of test results show that the physical and mechanical properties of the soil, including the standard hammer number N, the qc, small strain shear wave velocity Vs and the liquefaction resistance CRR of sandy soil, are all affected by the time effect. Therefore, there is great room for improvement of the reliability of liquefaction evaluation based on in situ index of different test time. Aiming at the effect of time effect on the liquefaction resistance of sandy soil, this paper takes the wave velocity index as the characterization parameter, carries out the unit body test and physical model test, and studies the influence of time effect on the characterization of shear wave velocity of sand liquefaction strength. The main influence mechanism of time effect in engineering time scale is revealed, and the evaluation method of sand liquefaction shear wave velocity considering time effect is developed. The main contents are as follows: (1) according to the influence of time effect on soil properties and the analysis of strong earthquake stations in Christchurch, it is found that the site characteristics are damaged during the earthquake and gradually recovered after the earthquake. The traditional liquefaction discriminant relation does not consider this kind of influence of time effect, and there is the risk of unsafe evaluation. (2) A series of unit tests were carried out to study the influence factors of time effect in engineering time scale. The results show that the time effect of fine grained sand is much more significant than that of clean sand, but the effect of stress level on time effect will not develop in a fixed trend and will reach the best at a suitable stress level. When sand is at low stress level, the time effect of sand loosening is more obvious than that of dense sand. (3) based on theoretical derivation and dynamic triaxial test, the relationship between shear wave velocity (Vs) and liquefaction resistance strength (CRR) of sandy soil is established, and the relationship between soil strength and stiffness is revealed. The related properties of this theory indicate the asynchronous effect of time effect on strength and stiffness, and the reliable evaluation of the liquefaction resistance of sand with different time effect is the intrinsic relation of shear wave velocity characterization of sand liquefaction strength in the early stage of time effect. (4) through the seismic liquefaction model test of horizontal site, the main factors affecting soil properties, such as structure, compactness and stress state, can be separated from strain shear modulus (Gmax) and penetration resistance (qc) from small strain shear modulus (Gmax). It is found that the evolution of soil structure is synchronized with the consolidation process, and vibration liquefaction is helpful to improve the soil structure and enhance its ability to resist liquefaction. (5) aiming at the problem that the time of soil deposition does not correspond to the change of physical and mechanical properties of soil, starting from the mechanical properties of soil, combining Gmax and qc site testing indexes, a quantitative characterization index of sand time effect based on soil properties, AI, is established. It provides an effective method for site evaluation of site liquefaction resistance.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU435
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