【作者】 卢敦华；

【导师】 彭振斌；

【作者基本信息】 中南大学 ， 地质工程， 2007， 博士

【摘要】 自20世纪60年代始，特别是在1964年日本新泻大地震、美国阿拉斯加大地震造成广泛的饱和砂土地基液化失效、大规模结构破坏后，人们对地震破坏的严重性给予了更广泛的重视，对土体因地震而失稳破坏的原因、机理、土体的动力特性、饱和砂土液化等问题展开了广泛的研究。混凝土桩由于能较好地适应各种地质条件和各种荷载情况，并具有承载力大、稳定性好、沉降小等特点被广泛应用于高层建筑、重型厂房、桥梁、港口码头等深基础中。随着我国国民经济的快速发展，大规模基础设施的兴建，有关地震以及由此引发的土体液化诱发的侧向扩展对桩基础影响的研究，自然便成为现阶段岩土工程领域的一个重要研究方向。论文通过收集前人资料、理论分析以及计算机程序模拟，首先对土体液化诱发的侧向扩展对桩基影响的研究现状作了归纳和总结；并根据单桩或群桩对土体液化诱发的侧向扩展的响应主要取决于桩自身的特性、土体液化后的性能、桩土间的相互作用以及液化层内土的变形模式等因素，对砂土的液化及不排水抗剪特性、液化土体水平位移导致桩体变形的力学分析模型、桩的弯曲性能、单桩或群桩对土体液化诱发的侧向扩展的响应等方面进行了深入系统的研究，得出了一些有益的结论。以非线性旋转弹簧来模拟桩体弯曲时的非线性材料响应，以弹簧滑块单元来模拟桩土间的非线性相互作用，包括表面摩擦力和侧向压力，建立了一个数学分析模型以评价桩体因土体水平位移而产生的应力和应变。相关试验结果表明，砂土在单调荷载及循环荷载作用下将出现应变软化特性，表现为液化或有限液化。在砂土液化后施加循环荷载或静荷载，其变形特性是不一样的。砂土液化再固结体体变主要取决于循环荷载过程中试样结构的破坏程度，而其中的绝大部分发生在有效应力接近于零的阶段。通过对混凝土、钢筋的力学分析和钢筋混凝土的抗震性能分析，建立了一个模拟钢筋混凝土桩和预应力混凝土桩的抗弯强度和弯曲变形的模型，并对作用在桩上的侧向力特征、桩体的破坏机理加以阐述。通过分析桩体材料、桩径、轴向荷载、土体位移大小、桩土相对刚度对桩体响应的影响，对混凝土桩在侧向力作用下的破坏机理和响应特征进行了研究，并对造成桩体破坏所需的最大土体位移进行了量化确定。在给定桩的轴向荷载、桩土系统的特性长度、液化土层厚度的条件下，根据文中建立的分析模型，由程序模拟计算得出桩体破坏后的形状。模拟结果比较真实地的反映了地震过程中因土体液化侧向扩展而导致破坏的桩基特性，说明文中相关的分析、假设及模型的选择是合适的。对群桩在土体液化诱发的侧向扩展下的响应进行了初步分析讨论。根据一定的假设条件，建立了一个简化分析模型，对群桩间的土体剪切刚度变化对桩的影响进行阐述，对群桩桩帽连接对群桩的影响进行分析，并对群桩与单桩的性能进行了比较。对2×2、3×3、4×4群桩的分析结果表明，当群桩受到液化土体的侧向扩展作用时，桩间土体的刚度起着重要的作用，群桩内土体的剪切刚度的大小会影响到土体流动条件的形成。更多还原

【Abstract】 Much attention has been paid to the severe damages caused byearthquake, and then extensive researches have been carried out onfailure mechanism, soil dynamic characteristic, saturated sandliquefaction. For its proper accommodation to various deposit and loadcondition, characterized as large bearing capacity, high stability, lowsedimentation, reinforced concrete piles have been widely used in thedeep foundation of high building, heavy-loaded workshop, bridge, wharf,etc. With the rapid development of our national economy, studies on theeffect of liquefaction-induced lateral spreading on pile foundation willnaturally make it become an important research aspect in the fields ofpresent geotechnical engineering.By means of collecting previous information, theoretical analyzing,computer modeling, a summary was made on the research status ofliquefaction induced lateral spreading. Based on the fact that single pileor pile group’s response to lateral spreading mainly depends on its owncharacteristics, soil’s liquefied characteristics, soil-pile interaction, soil’sdeflection mode, systemic researches were carried out on soil’sliquefaction and undrained characteristics, mechanics analysis mode onpile deflection, pile’s bending performance, single pile and pile group’sresponse to lateral spreading. Some useful conclusions were reached afterthat.Using nonlinear rotational spring to model pile material’s nonlinearbending response, spring slider element to model nonlinear interactionbetween soil and pile, including superficial fraction and lateral pressure, amodel was established to evaluate the strain and stress caused byhorizontal displacement.Related experiments show that sand will exhibit its softeningcharacteristics under the monotonic load and cyclic load by liquefactionor limit liquefaction. Different properties will be obtained for liquefiedsoil under cyclic load and static load. Volume change due to thereconsolidation of liquefied soil will mainly depend on the structuraldamage degree, most was completed when effective stress is approaching zero.By analyzing concrete and steel mechanics, reinforced concreteaseismatic properties, a model was established to simulate reinforcedconcrete pile and prestressed pile’s bending capacity and deflection. Andthen lateral load’s characteristics acting on the pile failure mechanismwere specified.By analyzing the effect of pile’s material, diameter, axial load,magnitude of soil displacement, relative stiffness of soil-pile, the failuremechanism and response of pile to lateral force acting on the pile wereillustrated, the maximum soil displacement required to caused pile failurewas quantified. Under the given axial load, characteristic length of soilpile system, depth of liquefiable layer, pile’s damaged shape can bemodeled with the established model. The proper reflection of modelingresult to pile’s actual failure condition proved that the carried analysis,related assumption and the chosen model are correct.Primary study were carried out on the pile group’s response toliquefaction induced lateral spreading. Upon a simplified assumption, amodel was established, mainly to explain the effect of shear stiffness ofsoil, which lies within the piles, on pile group. Analysis were also carriedout on the effect of pile group’s cap connection. Results from analyzing 2×2, 3×3, 4×4 pile group indicate that stiffness of soil plays a veryimportant role when the pile group are subjected to the lateral spreading,its magnitude will affect the formation of soil flow condition.更多还原