基于地震黄土滑坡反演地震动研究

The reasonable of ground motion input is one of the key conditions for the study of the slope seismic stability. In view of the current situation that the unreasonable and arbitrary input of ground motion in the study of slope dynamic stability, based on the 1920 Haiyuan great earthquake triggered loess landslides, this project constructs the database of earthquake landslides by making use of the remote sensing interpretation and field survey results, selects the typical earthquake landslides according to the developmental characteristics of landslide, set up the original landform model of the typical landslide by using the numerical fitting method, and build the geological mechanics model of the slope in combination with the results of exploration and test, explore the characteristics of the frequency spectrum of the micro vibration of the slope, and compare the results of the ground fluctuation test and establish a modified geomechanics model of the slope by using the excitation of the white noise of the micro vibration, deduct and determine the peak acceleration of the critical seismic motion under the limiting conditions of the instability of the slope via the pseudo-static method; using the standard spectrum of slope site as the target spectrum, combined with the slope vibration characteristic and synthetic ground motion; based on the dynamic time history method to investigate the dynamic instability process of the slope, combined with the development characteristics of the landslide, test and determine the ground motion input of the slope instability; Based on the all research results, a set of criteria for restoring the original landform of landslide is set up, and a method for inversion of ground motion based on the loess landslide is proposed. The results not only provide reasonable ground motion input for the slope seismic stability, but also establish a way to invert the ground motion based on relics of earthquake induced landslides.

合理的地震动输入是准确评价斜坡地震稳定性的关键条件之一。针对斜坡动力稳定性研究中地震动输入不合理、随意性强的现状，以1920年海原特大地震诱发黄土滑坡为依托，利用遥感解译和实地调查成果，构建地震滑坡数据库；依据滑坡发育特征，选定典型地震滑坡；采用数值拟合方法，建立滑坡原始地形模型，结合勘探、试验成果，构建斜坡地质力学模型；利用微振白噪声激励，探究斜坡微振频谱特性，对比地脉动测试结果，建立修正的斜坡地质力学模型；采用拟静力法，确定斜坡失稳临界地震动峰值加速度；以斜坡场地规范谱为目标谱，结合斜坡自振特性，人工合成地震动；基于动力时程法，探究斜坡地震动力失稳过程，结合滑坡发育特征，检验并确定斜坡失稳的地震动输入；基于研究成果，建立一套恢复滑坡原始地形准则，提出一种基于地震黄土滑坡反演地震动的方法。该成果不仅为斜坡地震稳定性研究提供了合理的地震动输入，也开辟了一条基于地震滑坡遗迹反演地震动的途径。

合理的地震动输入是准确评价斜坡地震稳定性的关键条件之一。针对斜坡动力稳定性研究中地震动输入不合理、随意性强的现状，本项目以1920年海原特大地震诱发黄土滑坡为依托，基于遥感解译和实地调查成果，利用ACCESS 2019平台构建了包含568个1920年海原特大地震诱发黄土滑坡的数据库，数据库除具有数据、图像的储存、查询、更新和调用功能外，还具有一定的工程应用价值。依据典型古（老）滑坡现存地形资料，基于滑体滑动前后体积相等原则，采用三维曲面插值等技术研究了黄土古（老）滑坡原始地形恢复方法，提出了一套复原黄土古（老）滑坡原始地形准则，并对其合理性进行了验证。以苏堡滑坡为例，基于在滑坡周界外的未滑动斜坡、滑坡体和滑坡后缘地表出露处测试的地脉动数据，采用HVNR法和HVIP法，利用Geopsy计算平台，探讨了滑坡场地不同部位土体动力响应的频谱特征和方向性特征，认为滑坡两侧未滑动斜坡的卓越频段和优势方向是开展滑坡场地动力稳定性研究的可靠参数，为一定地震动作用下斜坡失稳初始方向和运动过程的合理确定提供了理论基础。基于地形测绘、钻探取样、地脉动测试以及土工试验等成果，结合提出的黄土古（老）滑坡原始地形恢复方法，构建了苏堡滑坡修正的斜坡地质力学模型；利用FLAC 2D 开展数值模拟分析，确定了拟静力作用下苏堡滑坡滑动的临界地震动峰值加速度；基于获取的临界地震动峰值加速度，结合《建筑抗震设计规范》（GB50011 - 2010）（2016年版）、《中国地震动参数区划图》（GB18306 - 2015）中的规定，获取了基本地震动（50年超越概率10%）作用下滑坡场地的峰值加速度，并以滑坡场地规范谱为目标谱，人工合成输入地震动；采用动力时程法，在人工合成地震动作用下，利用FLAC 2D 开展苏堡滑坡动力失稳过程分析，通过塑性区位移变化特征与滑坡现有发育特征的对比，检验了人工地震动输入的合理性，提出了一种基于黄土地震滑坡反演地震动的方法。本项目研究成果开辟了一条合理确定地震动输入的新途径，可为开展古（老）滑坡动力稳定性研究提供参考。