模型桩低应变反射波法曲线研究

根据基桩低应变检测的基本原理,对于大型模拟缺陷桩低应变反射波法曲线进行了分析,以便在解释反射波法曲线时作为借鉴,提高基桩质量检测的可靠度。     

大直径钻孔灌注桩质量检测方法和存在的问题

阐述了大口径检测的重要意义,分析了目前大口质量检测的方法和存在的问题,并指出了解决这些问题的方法和途径。     

考虑环境效应的悬臂桩排支护结构优化设计

采用m法,控制桩身最大变形,通过对给定基坑外地表最大沉降量情况下的悬臂式桩排支护结构进行优化设计,来考虑基坑开挖的环境效应。经工程验证表明,效果明显。     

反射波法检测水泥搅拌桩的可行性和方法研究

水泥搅拌桩作为桩基础的一种特殊形式,在软土地基地区已被广泛应用。由于其桩身纵波波速远低于混凝土桩的波速,且长径比一般较小及桩身均质性等问题,所以应用于混凝土桩的小应变反射波检测方法是否可以应用于对水泥搅拌桩进行检测,在测桩界尚存在分歧意见。作者从理论上分析了反射波法的本质,指出波阻抗差异,分辨率和波长的关系是反射波法的要害。本文讨论了长径比的实际意义及其与一维波动理论的关系．提出了水泥搅拌桩“桩身质量“的新观点。从理论分析和实际检测结果资料的讨论出发．肯定了反射渡完全可以对水泥搅拌桩进行检测,并总结了实际检测过程中的方法技术。     

江苏海岸辐射沙洲地层中大直径钢管桩基础承载性能试验研究

江苏海岸辐射沙洲是江苏重要的海上风电规划区域,该海域的地层资料和试桩资料极为缺乏。通过钢管桩的现场静荷载试验,对江苏海岸辐射沙洲地层中大直径钢管桩基础承载性能进行研究,以揭示各地层的主要承载性能参数。试桩结果表明,江苏海岸辐射沙洲地层中钢管桩实际的轴向极限承载力明显小于高应变动测结果,只有高应变动测结果的79.09%。总侧摩擦阻力占总承载力的95.61%,而桩端阻力只占总承载力的4.39%。桩内土对管壁的侧摩阻力作用很小,主要是桩外土对管壁的侧摩阻力在发挥作用。辐射沙洲地层中粉土夹粉质黏土的承载性能一般,不适应作为钢管桩的持力层。轴向抗压静载试验得到的极限侧摩阻力高于静力触探的测试结果和API法的计算值。浅部砂层实际的极限水平土体抗力高于API法计算值,在水平荷载作用下上部砂层的p-y曲线具有明显软化效应,土体的软化效应在设计时需进行考虑。     

某桥梁桩基础的抗震计算研究

当前桩基础的抗震设计仅采取构造措施来保证其抗震性能,有可能会过高或过低地估计桩基础的抗震性能。针对某桥梁桩基础的抗震设计,建立全桥的三维有限元模型,计算在桩-土-结构共同工作情况下桩基础的地震响应,通过输入不同地震波来进行对比分析,并对结果进行复核,得出:(1)桩身内力响应与所输入地震动的频谱特性有关,桩身沿横桥方向的内力最大;(2)对于该场地的桥梁桩基础,桩-土-结构共同工作的有限元分析结果与m法结果差别不大;(3)当承台埋深为0时,桩身内力基本都偏大,要对承台侧土体做相应的加固处理。     

A lumped parameter model for time‐domain inertial soil‐structure interaction analysis of structures on pile foundations

The paper presents a lumped parameter model for the approximation of the frequency‐dependent dynamic stiffness of pile group foundations. The model can be implemented in commercial software to perform linear or nonlinear dynamic analyses of structures founded on piles taking into account the frequency‐dependent coupled roto‐translational, vertical, and torsional behaviour of the soil‐foundation system. Closed‐form formulas for estimating parameters of the model are proposed with reference to pile groups embedded in homogeneous soil deposits. These are calibrated with a nonlinear least square procedure, based on data provided by an extensive non‐dimensional parametric analysis performed with a model previously developed by the authors. Pile groups with square layout and different number of piles embedded in soft and stiff soils are considered. Formulas are overall well capable to reproduce parameters of the proposed lumped system that can be straightforwardly incorporated into inertial structural analyses to account for the dynamic behaviour of the soil‐foundation system. Some applications on typical bridge piers are finally presented to show examples of practical use of the proposed model. Results demonstrate the capability of the proposed lumped system as well as the formulas efficiency in approximating impedances of pile groups and the relevant effect on the response of the superstructure.     

黏性土桩间土拱效应计算与桩间距分析

土拱效应是安全经济地发挥抗滑桩等非连续支挡结构的支护功能的重要前提,桩间距与成拱作用密切相关。利用合理拱轴线几何特征与受压破裂角方位,通过力学概念分析,将黏性土土拱计算的平衡条件和强度条件综合简化为以拱脚处拱圈轴向压应力表达的形式。继而从最少且最易获得的土工材料参数（内聚力c、内摩擦角?）出发,根据轴向压应力与矢跨比函数关系,利用摩尔-库仑强度准则,推导了拱曲线与桩间距上下限的简便计算式,再以此进一步探讨了考虑土拱效应三维稳定的桩间距校核,并以工程实例验证,以对土拱效应的估算提供简便清晰的计算方法。     

Variations in the dynamic response of structures founded on piles induced by obliquely incident SV waves

Although the seismic actions generally consist of a combination of waves, which propagates with an angle of incidence not necessarily vertical, the common practice when analyzing the dynamic behavior of pile groups is based on the assumption of vertically incident wave fields. The aim of this paper is to analyze how the angle of incidence of SV waves affects the dynamic response of pile foundations and piled structures. A three-dimensional boundary element-finite element coupling formulation is used to compute impedances and kinematic interaction factors corresponding to several configurations of vertical pile groups embedded in an isotropic homogeneous linear viscoelastic half-space. These results, which are provided in ready-to-use dimensionless graphs, are used to determine the effective dynamic properties of an equivalent single-degree-of-freedom oscillator that reproduces, within the range where the peak response occurs, the response of slender and nonslender superstructures through a procedure based on a substructuring model. Results are expressed in terms of effective flexible-base period and damping as well as maximum shear force at the base of the structure. The relevance and main trends observed in the influence of the wavefront angle of incidence on the dynamic behavior of the superstructure are inferred from the presented results. It is found that effective damping is significantly affected by the variations of the wave angle of incidence. Furthermore, it comes out that the vertical incidence is not always the worst-case scenario.     

INTERPRETATION AND ANALYSIS OF THE FINE FAULT GEO-METRY BASED ON HIGH-RESOLUTION DEM DATA DERIVED FROM UAV PHOTOGRAMMETRIC TECHNIQUE: A CASE STUDY OF TANGJIAPO SITE ON THE HAIYUAN FAULT

Fault-related tectonic geomorphologic features are integrated expressions of multiple strong seismological events and long-term surface processes, including crucial information about strong earthquake behavior of a fault. It's of great significance to identify the strong seismic activity information from faulted landscapes, which include the date and sequence of the seismic activities, displacements, active fault features, for studying the seismic rupture process, predicting the future seismic recurrence behavior and evaluating the seismic hazard of the fault. However, due to the restriction of measuring techniques and the subsequent poor quality of the acquired data, it has been difficult to accurately extract such information from complex tectonic landforms to study active faults for a long time. Recently, "small Unmanned Aerial Vehicle(sUAV)" photogrammetric technique based on "Structure from Motion(SfM)" provides a cost-efficient and convenient access to high-resolution and high-accuracy "digital elevation models(DEMs)" of tectonic landforms. This paper selects the Tangjiapo area at the Haiyuan Fault to conduct data collection, in which the structural and geomorphic features are well preserved. Using a small quadrotor unmanned aerial vehicle(Inpire 2), we collect 1598 aerial photographs with a coverage area of 0.72km². For calibrating the accuracy of the aerial data, we set 10 ground control points and use differential-GPS to obtain the spatial coordinates of these control points. We use model software Agisoft PhotoScan to process these digital pictures, obtaining high-resolution and high-accuracy DEM data with the geographic information, in which data resolution is 2.6cm/pix and the average density of point cloud is 89.3 point/m². The data with these accuracy and resolution can fully show the real geomorphic features of the landform and meet the requirements for extracting specific structural geomorphic information on the surface. Through the detailed interpretation of the tectonic landforms, we identify a series of structures associated with the strike-slip fault and divide the alluvial fan into four stages, named s₁, s₂, s₃, and s₄, respectively.Wherein, the s₁ is the latest phase of the alluvial fan, which is in the extension direction of the Haiyuan Fault and there isn't any surface fracture, indicating that the s₁ was formed after the M8.5 Haiyuan earthquake in 1920. The rupture zone on the s₂ fan is composed of varied kinds of faulting geomorphologic landforms, such as a series of en echelon tension-shear fractures trending 270°~285°, fault scarps and seismic ridges caused by the left-lateral motion of the seismic fault. In addition, a number of field ridges on the s₂ fan were faulted by the 1920 Haiyuan M8.5 earthquake, recording the co-seismic displacements of the latest earthquake event. Relatively speaking, the surface rupture structure of the s₃ fan is simple, mainly manifested as linear fault scarp with a trend of 270°~285°, which may indicate that multiple earthquakes have connected the different secondary fractures. And a small part of s₄ fan is distributed in the southwest of the study area without fault crossing. Furthermore, we measured the horizontal displacements of river channels and vertical offsets of fault scarps. The faulted ridge on the s₂ fan and faulted gully on the s₃ fan provide good linear markers for obtaining the fault left-lateral dislocation. We used the graphical dislocation measurement software LaDiCaoz developed based on Matlab to restore the gully position before the earthquake by comparing the gully morphology on both sides of the fault, and then determined the horizontal offset of s₂, which is(4.3±0.4)m and that of s₃ is(8.6±0.6)m. In addition, based on the DEM data, we extracted the fault scarp densely along the fault strike, and obtained the vertical offset of s₂, which is(4.3±0.4)m and that of s₃ is(1.79±0.16)m. Moreover, we detect slope breaks in the fault scarp morphology. For compound fault scarps generated by multiple surface rupture earthquakes, there are multiple inflection points on the slope of the topographic section, and each inflection point represents a surface rupture event. Therefore, the slope break point on the scarp becomes an important symbol of multiple rupture of the fault. The statistical result shows that the slope breaks number of s₂ is 1 and that of s₃ is 2. Based on the analysis of horizontal displacements of river channels and vertical offsets of fault scarps as well as its slope breaks, two surface rupturing events can be confirmed along the Tangjiapo area of the Haiyuan Fault. Among them, the horizontal and vertical displacements of the older event are(4.3±0.95)m and(0.85±0.22)m, respectively, while that of the latest event are(4.3±0.4)m and(0.95±0.14)m, which are the coseismic horizontal and vertical offsets of the 1920 Haiyuan earthquake. These recognitions have improved our cognitive level of the fine structure of seismic surface rupture and ability to recognize paleoearthquake events. Therefore, the high-resolution topographic data obtained from the SfM photogrammetry method can be used for interpretation of fine structure and quantitative analysis of microgeomorphology. With the development of research on tectonic geomorphology and active tectonics toward refinement and quantification, this method will be of higher use value and practical significance.