吹沙型填海地块场地卓越周期演化特征及预测模型

In recent years, it is happened occasionally that strong far-field earthquake causes long-period engineering seismic damages in soft soil areas. Located in the earthquake-prone coastal region, marine hydraulic reclamation areas, in which there exist layered strata with thick soft soil sandwich, are similar to above areas with thick or thicker soft soil. However, the difference is that there is artificial reclaimed sand overlying on the littoral sediment on the sea-bed rock in reclamation areas. These thick marine soft soil or reclaimed sand formations were formed more recently and they are still in an original and constantly changing consolidation state. Large numbers of engineering structures with a long-period of natural vibration are distributed usually on reclamation areas, but it is still lack of systematic research currently on the seismic characteristics and the resistance against strong far-field earthquake of such newly construction areas. The project aims to study on dynamic characteristics of these artificial lands with the large areas of soft substratum in the view of geotechnical engineering, to analyse the evolutionary trend of predominant period, to stimulate the influence factors resulting in the "predominant period drifting" of layered strata with thick soft soil sandwich. The study results will play an urgent and realistic role on the Seismic Safety of coastal petrochemical industry built on the reclamation areas in our country.

近年来关于在有软土分布的场区由远场强震造成长周期破坏的工程震害时有发生。处于地震活动相对频繁的滨海区域且具有夹持厚层软土的层状结构体的吹沙填海地块与这些场区有相似之处，即具有厚层至巨厚层的软土层；而不同之处在于填海地块是叠加在滨海沉积物上的人造岩土体：具有厚层的海相软土及砂土，土层形成时间短促，固结状态处于初始且持续的变动阶段，软土直接触及海底基岩。在这类地块的场地上分布有大量的自振周期较长的工程结构体。对这一新兴建设场地的地震动特征及岩土体结构对远场强震震害抵御能力目前尚缺乏深入系统的研究。本项目拟从岩土工程的角度研究这种人造的有大面积软弱下卧层的陆域的动力特性，剖析地块场地卓越周期的演化趋势，模拟诱导夹持厚层软土的层状结构体的卓越周期发生"漂移"的影响因素。研究成果对于建立在填海地块上的我国沿海石油重化工业的地震安全具有紧迫性和现实性。

近年来关于软土分布场区由远场强震造成长周期破坏的工程震害时有发生。本项目以广西北部湾夹持厚层软土层状结构体的吹沙填海地块为研究对象。在对吹填地块场地自振特性参数和土的动力特性参数进行量测分析的基础上，利用“浸泡-加载”试验装置制备一批不同固结度的海积软土样和不同密实度的吹填砂样，通过动三轴试验量测土的动力特性参数；在分析遴选近、中、远场基岩地震波的基础上，利用振动台土箱试验装置，对研究场地进行振动台地震模拟试验，并采用孔压计、加速度计、压汞仪、扫描电镜、光纳仪等量测手段和数值模拟技术，量测和分析在具有不同频谱特性的三种地震波作用下场地的地震动响应与场地卓越周期。通过上述试验方法和手段研究：(1)吹填地块夹持厚层软土的层状结构体的动力特性参数及其发展演化规律；(2)场地卓越周期的各主要因素及其内在作用机理；(3)各主要影响因素在变动态势下吹填地块场地卓越周期的演化模型。.项目研究主要取得了以下进展：.①设计了能将赋存环境变化要素“印记”到海积软土中的“浸泡—加载”联动试验装置，和可控制土层固结度及地下水位的振动台土箱模型试验装置。.②通过对不同固结度或密实度的制备土样进行动三轴试验，获得了土层固结度或密实度在变动态势下固结压力、固结比、动荷载频率等因素与动剪切模量和阻尼比的关系方程。.③通过振动台地震模拟试验，获得了海积软土固结度、地下水位、输入波周期成分等因素变化下场地的动力响应特征与卓越周期演化规律，建立了场地卓越周期随软土固结度变化的数学模型。.④运用ABAQUS软件，构建用于吹填地块场地卓越周期演化研究的数值分析模型，获得输入波周期成分、土层固结度、地下水位、地基处理、基础类型等因素变化下场地动力响应特征与卓越周期演化规律。.⑤对土工试验数据、计算机模拟成果和振动台地震模拟成果进行综合分析，获得在各影响因素变动态势下场地卓越周期演化规律，为完善吹填地块建设场地抗震救灾技术提供理论支持。