兰州大学机构库 >土木工程与力学学院
震损黄土斜坡稳定性演化机制与应急评价方法研究
Alternative TitleStudy on stability evolution mechanism and emergency evaluation method of earthquake-damaged loess slope
蒲小武
Subtype博士
Thesis Advisor王兰民
2023-09-02
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name工学博士
Degree Discipline地质工程
Keyword震损黄土斜坡 earthquake-damaged loess slope 破坏等级 earthquake-damaged grade 稳定性 stability 耦合 coupling of earthquake and rainfall 应急评价 emergency evaluation 处置措施 prevention measure
Abstract

强地震不仅会诱发大量的滑坡、崩塌等同震次生岩土灾害,还会产生数量更为庞大的震裂损伤山体斜坡,在后续强余震、降雨作用下又将孕育出新的滑坡、崩塌灾害。黄土高原是我国地震活动最为强烈的地区之一,强震频发的构造环境、沟壑纵横的地形地貌,加之黄土较差的力学性能,多因素耦合、多因果轮回,使得滑坡、崩塌历来为黄土高原区最为突出的岩土灾害。震损黄土斜坡,在余震(后续地震)、降雨及其耦合作用下失稳风险很高,而关于震损黄土斜坡稳定性演化机制研究开展较少,其应急评价方法体系尚未形成,开展相关研究对提高黄土区应急救援与灾害防御能力、保障生命财产安全具有重要意义。

本文通过收集研究黄土震害资料,结合地质调查与测绘、岩土勘察、三轴试验、振动台模型试验,研究揭示了黄土斜坡地震损伤破坏机制,建立了黄土斜坡震损等级评价方法;基于人工降雨渗透试验,并结合斜坡土体物性参数测试,研究了黄土斜坡降雨渗透规律;通过振动台模型试验、数值模拟和理论分析计算,研究了天然状态、不同强度降雨后黄土斜坡的震损特征,揭示震损黄土斜坡在后续地震、降雨及其交互作用下的稳定性演化机制;建立了震损黄土斜坡稳定性应急评价方法,给出不同震损等级黄土斜坡应急处置措施建议。主要研究成果如下:

(1)基于近几十年黄土震害调查资料,总结了震损黄土斜坡的主要类型及其特征,建立了黄土斜坡震损等级评价方法。广义上,震损黄土斜坡可划分为:滑坡崩塌堆积体、震裂损伤斜坡两类,第一类包括松散堆积体、块状滑坡体两小类,第二类包括滑坡后缘陡坡、震裂未错动斜坡和震裂下错斜坡三个小类。根据震裂损伤斜坡主要破坏特征,考虑震后应急期滑坡风险快速评估需要,主要依据裂隙长、宽、深等指标将震损斜坡划分为轻度、中度、重度3种等级,滑坡崩塌堆积体作为一种特殊的震损斜坡划分为重度震损等级。

(2)基于振动台模型试验,结合数值模拟与理论计算,研究揭示了震损黄土斜坡在后续地震作用下的稳定性演化规律与机制。轻度和中度震损的天然黄土斜坡,当遭受到强度小于或等于先期的后续地震作用时,斜坡裂隙尺度、震损程度不发生显著变化,其稳定性不会显著降低;当遭受到更强的后期地震作用时,斜坡震损等级增大、稳定性大幅度降低乃至会发生失稳破坏;对于出现了失稳下错但并未发生滑坡的重度震损斜坡,潜在滑体的粘聚强度基本丧失,坡体因摩擦抗滑阻力而处于欠稳定状态,此时较小的后期地震作用该类震损斜坡就会发生失稳滑动,因此余震触发滑坡危险性很高,该类重度震损斜坡是震后应急期需重点关注的对象。

(3)通过测试斜坡不同部位土体物性参数并结合斜坡原位降雨渗透试验,揭示了黄土斜坡的渗透特性和降雨入渗规律。黄土斜坡因长期降雨渗透、干湿循环作用,在深度55-75 cm处形成了一个低渗透带。该带对降雨入渗有一定阻隔作用,加之降雨入渗过程中随渗透深度增大雨水入渗率会显著降低,故一般降雨条件下斜坡降雨入渗深度在1 m左右,若有长持时、大暴雨等极端事件,才会达到2 m左右的深度;但如有节理、裂隙等特殊渗透通道时,雨水会直接入渗至坡体内部,因此震损斜坡地质调查的重点是查明地震裂隙的深度及其发育分布范围。

(4)通过地震和降雨不同耦合模式的振动台模型试验,明晰了地震和降雨耦合交互作用下震损黄土斜坡稳定性演化机制。先期降雨后的黄土斜坡,相较于天然状态黄土斜坡在地震作用下产生的裂隙更多,在后续逐级增大的地震动作用下,裂隙增大、增深、增多,湿润锋下移,损伤范围持续扩大、损伤程度持续加剧;若前期地震后还有后续降雨作用,雨水会顺着裂隙渗透至坡体深部区域,导致后续地震作用下的临界失稳加速度显著降低,且失稳滑动致灾范围会更大,因此地震和降雨耦合交互作用下滑坡的危险性更大,危害性更高。

(5)综合本文以及相关最新研究成果,建立了涵盖了场地地震动预测、斜坡放大效应估算、震损斜坡地质力学模型构建和稳定系数简化计算在内的震损黄土斜坡应急评价方法。震损黄土斜坡震后稳定性计算模型设定潜在滑动面为张裂隙段、剪切段和抗滑段三段组成,对于在坡顶平台处产生了张裂隙的震损斜坡,潜在滑体简化为3块体模型,对于在坡面上产生了主张裂隙的震损斜坡,潜在滑体可简化为2块体模型;基于上述假定,参考了刚体极限平衡理论,构建了震损斜坡稳定系数计算模型。

(6)借鉴滑坡防治研究成果,考虑黄土斜坡地震破坏特征,提出了不同震损等级黄土斜坡的应急处置措施建议。轻度与中度震损黄土斜坡,其危险性较低,主要措施是填埋裂缝、夯实酥土;无贯通性破裂面的重度震损斜坡,需考虑余震和降雨耦合诱发滑坡可能,在填缝夯实的基础,需设专人开展定期巡查并对斜坡稳定状态进行及时研判;对于有贯通破裂面的重度震损斜坡,余震触发滑坡危险性很大,危险区内人员第一时间需紧急撤离、需架设监测系统设专人专班开展监测预警,并对滑坡风险进行动态预测评估。

Other Abstract

Strong earthquakes would not only induce a large number of secondary disasters such as landslides and collapses, but also produce a large number of earthquake-damaged slopes. Therefore, under the action of subsequent strong aftershocks and rainfall, new landslides and collapses would be induced. The Loess Plateau is one of the regions with the strongest seismic activity in China. Landslides and collapses have always been the most prominent geotechnical disasters in the Loess Plateau due to seismic tectonic environment with frequent strong earthquakes, the topography of the ravines, the weak mechanical properties of loess, multi-factor coupling and multi-causal cycle. Damaged loess slopes after earthquake have a high risk of instability under aftershocks (subsequent earthquakes), rainfall and their coupling effects. However, there are few studies on the stability evolution mechanism of earthquake-damaged loess slopes and the emergency evaluation method system has not yet been formed. Therefore, it is of great significance to carry out relevant research to improve the emergency rescue and disaster defense capabilities and ensure the safety of life and property in the Loess Plateau.

In this paper, the seismic damage mechanism of loess slope is revealed by collecting and studying the seismic damage data, combining with geological survey and mapping, geotechnical exploration, triaxial test and shaking table model test, and the seismic damage grade evaluation standard of loess slope is established. Based on the artificial rainfall infiltration test and the physical parameter test of slope loess, the rainfall infiltration law of loess slope was studied. Through shaking table model test, numerical simulation and theoretical calculation analysis, the seismic damage characteristics of loess slopes under natural conditions and different rainfall conditions were studied, and the stability evolution mechanism of earthquake-damaged loess slopes under subsequent earthquakes, rainfall and their interactions was revealed. Based on the above research results and the latest research results at home and abroad, an emergency evaluation method system for earthquake-damaged loess slopes is established, which includes site ground motion prediction, slope amplification effect estimation, geomechanical model construction and stability coefficient calculation of post-earthquake slope. Suggestions on emergency disposal measures for loess slopes with different earthquake damage levels are given. The main results are as follows :

(1) Through geological survey, mapping, geotechnical investigation, triaxial shear test of deformation and strength of earthquake-damaged loess, shaking table model test of earthquake-damaged slope, the seismic damage mechanism of loess slope is revealed, the evaluation standard of seismic damage grade of loess slope is established, and the main types and characteristics of earthquake damaged loess slopes are given. In a broad sense, earthquake-damaged loess slopes could be divided into two major categories: landslide and collapse accumulation, and seismic damage slope with cracks. The first category includes two sub categories: loose accumulation mass and bulk landslide mass, and the second major category includes three sub categories: steep slope at landslide trailing edge, earthquake-damaged slope without downward dislocation, and earthquake-damaged slope with downward dislocation; In a narrow sense, earthquake-damaged loess slope only include the second major category; According to the main damage characteristics of the second major category, and considering the need for rapid landslide risk assessment during the emergency period after an earthquake, the earthquake-damaged slopes are divided into three grades: light, moderate, and severe based on indexes such as crack length, width, and depth; As a special type of earthquake-damage slope, the landslide and collapse accumulation classifies as severe earthquake-damaged slope.

(2) Based on the shaking table model test, combined with numerical simulation and theoretical calculation, the stability evolution law and mechanism of earthquake-damaged loess slopes under subsequent earthquake actions were studied and revealed. For natural loess slopes with slight and moderate earthquake damage, when they are subjected to later earthquakes whose intensity is less than or equal to that of the previous period, the scale of slope cracks and the degree of earthquake damage would not change significantly, and the stability of the earthquake-damaged slope would not significantly decrease; When they are subjected to later earthquakes whose intensity is stronger than that of the previous period, the slope damage level would increase, the stability would greatly decrease, and even the instability and damage would occur. The severe earthquake-damaged slope of instability and downward dislocation but without landslide would maintain its basic stability due to friction and anti-sliding resistance under post-earthquake static condition, but the subsequent smaller ground motion would trigger the sliding of the earthquake-damaged slope. Therefore, the  landslide hazard of such earthquake-damaged slope under aftershocks is very high, and so it should be the focus of attention after earthquake of the main shock and aftershock type.

(3) By testing the physical parameters of soil in different parts of the slope and combining them with in-situ rainfall infiltration tests on the slope, the permeability characteristics of loess and the rainfall infiltration law of the slope were revealed. Due to long-term rainfall infiltration and dry-wet cycling, a low permeability zone is formed at a depth of 55-75cm of loess slope, which has a certain barrier effect on rainfall infiltration. In the process of slope rainfall infiltration, the infiltration rate would decrease significantly with the increase of rainwater infiltration depth, so the slope rainfall infiltration depth is usually within 1 meter under normal rainfall conditions. If there are extreme events such as long duration and great rainfall, rainfall infiltration would reach a depth of about 2 meters. When there are special infiltration channels such as joints and cracks, rainwater would directly infiltrate into the interior of slope. Therefore, the focus of geological survey of earthquake-damaged slopes is the depth and distribution range of seismic cracks.

(4) Through shaking table model tests with different coupling modes of earthquake and rainfall, the stability evolution mechanism of earthquake damaged loess slopes under the coupling interaction of earthquake and rainfall was clarified. The loess slope after initial rainfall, under the action of previous and subsequent gradually increasing seismic ground motion, the cracks gradually increase, deepen and enlarge, the wetting front moves down, the damage range continues to expand, and the damage degree continues to intensify. If there is subsequent rainfall after the previous earthquake, the rainwater would penetrate into the deep area of the slope along the cracks, so the critical instability acceleration of the subsequent earthquake of the earthquake-damaged slope would be significantly decreased, and the instability sliding range would be larger.

(5) Based on this article and the latest research results, a system of emergency evaluation methods for earthquake damaged loess slopes has been established, which includes prediction of site seismic motion, estimation of slope amplification effect, construction of post earthquake damaged slope geomechanical model, and simplified calculation of seismic stability coefficient. The potential sliding surface of loess slope damaged by earthquake could be assumed to be composed of three sections: tensile fracture section, shear section and anti-sliding section. For seismically damaged slopes with tension cracks at the top platform of the slope, the potential sliding body can be simplified into a three-block model. For the earthquake-damaged slopes with main tensile cracks on the slope surface, the potential sliding body can be simplified into a two-block model. Based on the above assumptions and rigid body limit equilibrium theory, the emergency evaluation method system of earthquake-damaged slope are established.

(6) Drawing on the research results of landslide prevention and control, taking into account the seismic damage characteristics of loess slopes, emergency response measures for loess slopes with different seismic damage levels were proposed. The hazard of loess slope with slight and moderate earthquake damage is low, the main measures are to fill cracks and compact loose soil; Severe earthquake-damaged slopes (no penetrating rupture surfaces) should consider the possibility of landslide induced by the coupling of aftershocks and rainfall. On the basis of filling cracks and tamping loose loess, it is necessary to set up special personnel to carry out regular inspections and timely research and judge the slope stability. For severe earthquake-damaged slopes with penetrating rupture surfaces, the possibility of aftershock triggering landslide is very high. People in the dangerous area need to evacuate urgently at the first time, and should set up professional monitoring equipment and assign special teams to carry out deformation monitoring, and need to dynamically predict and evaluate landslide hazard.

Subject Area岩土地震工程
MOST Discipline Catalogue工学 - 地质资源与地质工程 - 地质工程
URL查看原文
Language中文
Other Code262010_120180905561
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/538035
Collection土木工程与力学学院
Affiliation
兰州大学土木工程与力学学院
Recommended Citation
GB/T 7714
蒲小武. 震损黄土斜坡稳定性演化机制与应急评价方法研究[D]. 兰州. 兰州大学,2023.
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