Multivariate analysis of soil moisture history for a hillslope

In this study, the spatial distribution of measured soil moisture was analyzed on the platform of multivariate modeling. Soil moisture time series for two seasons were selected and used for analysis to reveal similarities and differences in soil moisture responses for a few rainfall events. The development of a soil moisture transport process that considers the representative element volume and uncertainty of soil media provides the hydrological basis for time series modeling. The systematic procedure of Box–Jenkins with noise modeling was used to delineate the final models for all monitoring points. The physical basis of mass balance and the continuity in inflow contribution, as well as statistical criteria, were used in the model selection procedure. Heuristic approaches provide the spatial distribution of selected models along the transect of a hillside. Comparative analysis for two different depths and seasons provide an understanding of the variation in soil moisture transfer processes at the hillslope scale. Differences in soil moisture models for both depths and seasons are associated with eco-hydrological processes. The relationships between distributed topographic features and modeling results were explored to configure dominant hydrological processes for each season.     

Damping coefficients for soil–structure systems and evaluation of FEMA 440 subjected to pulse-like near-fault earthquakes

In this study, attempts are made to investigate the effects of inertial soil–structure interaction (SSI) on damping coefficients subjected to pulse-like near-fault ground motions. To this end, a suit of 91 pulse-like near-fault ground motions is adopted. The soil and superstructure are idealized employing cone model and single-degree-of-freedom (SDOF) oscillator, respectively. The results demonstrate that soil flexibility reduces and amplifies the damping coefficients for structural viscous damping levels higher and lower than 5%, respectively. The coefficients reach one for both acceleration and displacement responses in cases of dominant SSI effects. The effect of structure dimensions on damping confidents are found insignificant. Moreover, damping coefficients of displacement responses are higher than those of acceleration responses for both fixed-base and flexible-base systems. Evaluation of damping correction factor introduced by FEMA 440 shows its inefficiency to predict acceleration response of soil–structure systems under pulse-like near-fault ground motions. Soil flexibility makes the damping correction factor of moderate earthquakes more pronounced and a distinctive peak value is reported for cases with dominant SSI effects.     

平面P-SV波入射时非均匀饱和土 自由场地的响应

基于Biot多孔介质波动模型,研究了非均匀饱和土层对平面P-SV波入射时的动力响应.考虑饱和土地基的物理力学特性沿厚度方向连续变化,利用亥姆霍兹矢量分解原理和动力刚度法,分析了平面入射P-SV波在非均匀饱和土层中的反射和透射,并给出了基岩表面和自由表面处反射系数和透射系数的计算表达式.基于理论推导结果,数值分析了平面SV波入射下非均匀饱和土自由场地的动力响应,其中假设饱和土地基的物理力学性质沿土层深度按幂律梯度变化.数值结果表明,平面SV波入射所引起的地面位移与基岩位移之比均随土层厚度和土体的非均匀程度、波的入射角和入射频率的增加而减小,且其竖向位移比的减小更为显著,厚土层对地震波的耗散作用尤为明显.      

Modal analysis of circular flexible foundations under vertical vibration

A methodology using modal analysis is presented to evaluate dynamic displacements of a circular flexible foundation on soil media subjected to vertical vibration. The interaction effects between the foundation and the underlying soil are represented using modal soil impedance functions determined by an efficient procedure developed. The displacements of the foundation can then be easily solved by modal superposition. Comparing with existing solutions, the presented method is found to provide accurate results with less computational effort using only a few vibration modes. In addition, parametric studies for modal responses of the flexible foundation indicate that the response of the foundation are significantly influenced by relative stiffness between the foundation and the soil medium, load distributions, vibration frequency range, and the foundation mass. Besides, justification for flexible foundations to be considered as rigid are investigated.     

Earthquake induced pounding between adjacent buildings considering soil-structure interaction

Many closely located adjacent buildings have suffered from pounding during past earthquakes because they vibrated out of phase.Furthermore,buildings are usually constructed on soil;hence,there are interactions between the buildings and the underlying soil that should also be considered.This paper examines both the interaction between adjacent buildings due to pounding and the interaction between the buildings through the soil as they affect the buildings’ seismic responses.The developed model consists of adjacent shear buildings resting on a discrete soil model and a linear viscoelastic contact force model that connects the buildings during pounding.The seismic responses of adjacent buildings due to ground accelerations are obtained for two conditions:fixed-based(FB) and structure-soil-structure interaction(SSSI).The results indicate that pounding worsens the buildings’ condition because their seismic responses are amplified after pounding.Moreover,the underlying soil negatively impacts the buildings’ seismic responses during pounding because the ratio of their seismic response under SSSI conditions with pounding to those without pounding is greater than that of the FB condition.     

Scattering of plane P waves by circular-arc alluvial valleys with saturated soil deposits

This paper presents an analytical solution for two-dimensional scattering and diffraction of plane P waves by circular-arc alluvial valleys with shallow saturated soil deposits. The solution is based on Biot's dynamic theory for saturated porous media, and derived by employing Fourier–Bessel series expansion technique. In this analysis, soil deposits in the circular-arc valley are modeled as saturated porous media based on Biot's dynamic theory, and the circular-arc valley is assumed to be imbedded in an infinite half-space, filled with elastic single-phase media. Numerical results from this solution show that the amplitudes of displacement at the surface of an alluvial valley are mainly relative to the angle of incidence, the dimensionless frequency of incident P wave, the degree of saturation and porosity of soil deposits, and the stiffness and Poisson's ratio of the solid skeleton of the soil deposits. Furthermore, the proposed solution is compared with the previous solution, in which the soil deposit was modeled as an elastic single-phase solid.     

地下综合管廊大型振动台模型试验研究

针对地下综合管廊缺乏抗震研究的现状,开展了地下综合管廊大型振动台模型试验研究。试验中除对通常的地下结构振动台试验中常规地震响应进行了测量外,还测量了模型场地水平位移、模型结构的层间位移、模型结构内钢筋应变。同时,通过自行设计的接触面土体滑移传感器测量了结构顶板接触面土体滑移。本文对模型结构的动力响应以及接触面和周围土体地震响应规律进行了分析。结果表明：在地震作用下地下综合管廊的地震加速度响应服从周围土体的地震响应,其响应幅值不会大于周围土体的加速度响应幅值;结构内力最大部位出现在结构的角部,并且内力随着地震动强度的增加而增大;地下综合管廊接触面土压总体上随着地震动强度的增加而增大,侧板和顶、底板的土压力分布模式不同;在水平地震作用下,地下综合管廊会产生顶、底板之间的相对位移,同时伴随着横截面内的刚体转动;地下综合管廊壁板与土接触面的作用力是结构产生内力的直接原因,其中侧壁土压起主要作用。     

Response of circular flexible foundations subjected to horizontal and rocking motions

A methodology using modal analysis is developed to evaluate dynamic vertical displacements of a circular flexible foundation resting on soil media subjected to horizontal and rocking motions. The influence of the soil reaction forces on the foundation is considered by introducing modal impedance functions, which can be determined by an efficient procedure with ring elements. The displacements of the foundation can then be easily solved by modal superposition. Parametric studies for modal responses of the flexible foundation indicate that the coupled response of the foundation is significantly influenced by relative stiffness among the foundation and the soil medium, vibration frequency range, foundation mass, and boundary contact conditions. The welded boundary condition should be considered to predict the coupling response while the relaxed boundary condition may be used to predict approximately the vertical displacements. As a foundation with a relative stiffness ratio more than three, it is found that the foundation can be considered as rigid to calculate coupling displacements. For a slightly flexible foundation, considerations of three modes are sufficient enough to obtain accurate foundation responses. Moreover, at low frequencies, the coupling effect due to higher mode can be neglected.     

土-地铁隧道动力相互作用的大型振动台试验——试验结果分析

在进行土-地铁隧道动力相互作用的大型振动台模型试验中,分别测出了模型地基的加速度反应、隧道结构的加速度反应、结构的侧向土压力反应和隧道结构的应变反应。本文首先对模型体系的加速度反应实测值进行整理,分析了模型地基的边界模拟效果、模型地基和隧道结构的加速度反应规律。其次,对模型隧道结构的应变实测结果进行了分析,给出了地铁区间隧道在水平向地震动作用下横截面的应变分布规律,分析了模型箱侧壁与地基土以及隧道结构与土体接触面上的动土压力实测结果及其反应的规律。最后,对试验中模型土的液化现象、地震裂缝和地下结构上浮等震害现象进行了描述。     

含地下水的土层对地震波传播的影响

本文综合地介绍了含地下水的土层对地震波传播的研究成果,并对一些普遍性的原则问题进行了讨论.在不变形介质的前提下详细研究了二维地下水的波动问题,应用和开发了线单元-特征线法、交替方向隐式差分法和伽辽金有限单元法,求解了一些边值问题.还研究了介质的不均匀性、地层的成层性等对地下水波动的影响以及地下水波在界面上的透射、反射现象,发现了一些新的规律.从普遍方程出发,论证了地下水波在可变形介质和不变形介质中的差别,导出了两者的换算关系.开辟了由不变形介质的解求可变形介质的解的一个间接途径. 在可变形介质的前提下,直接从两相介质动力方程组出发,对含水土层中的波动问题进行了详尽研究,考虑了弹塑性、非线性本构关系、剪胀性、刚度退化等各种因素的影响.通过计算对各种土壤刚度、渗阻条件、边界透水条件、荷载形式、本构关系和不均匀性等情况做了比较研究,发现一些新规律.在垂直地震荷载作用下发现了两种不同形态的孔隙水压反应--阶变形和振荡形的机制,并用间断波理论解释了孔压阶跃的原因.最后对发现的新现象做了一些讨论和总结.     

Influence of heterogeneity on unsaturated hydraulic properties (2) – percentage and shape of heterogeneity

In subsurface porous media, the soil water retention curve (WRC) and unsaturated hydraulic conductivity curve (UHC) are two important soil hydraulic property curves. Spatial heterogeneity is ubiquitous in nature, which may significantly affect soil hydraulic property curves. The main theme of this paper is to investigate how spatial heterogeneities, including their arrangements and amounts in soil flumes, affect soil hydraulic property curves. This paper uses a two‐dimensional variably saturated flow and solute transport finite element model to simulate variations of pressure and moisture content in soil flumes under a constant head boundary condition. To investigate the behavior of soil hydraulic property curves owing to variations of heterogeneities and their arrangements as well, cases with different proportions of heterogeneities are carried out. A quantitative evaluation of parameter variations in the van Genuchten model (VG model) resulting from heterogeneity is presented. Results show that the soil hydraulic properties are strongly affected by variations of heterogeneities and their arrangements. If the pressure head remains at a specific value, the soil moisture increases when heterogeneities increase in the soil flumes. On the other hand, the unsaturated hydraulic conductivity decreases when heterogeneities increase in the soil flumes under a constant pressure head. Moreover, results reveal that parameters estimated from both WRC and UHC also are affected by shapes of heterogeneity; this indicates that the parameters obtained from the WRC are not suitable for predicting the UHC of different shapes in heterogeneous media. Copyright © 2011 John Wiley & Sons, Ltd.     

Dynamic analysis of a layered half-space subjected to moving line loads

Using a thin-layer method enhanced by continued-fraction absorbing boundary conditions, dynamic responses of a layered half-space subjected to a series of constant and time-harmonic line loads moving at a constant speed are studied. The thin-layer method for moving line loads is formulated for plane-strain as well as antiplane-shear conditions and is verified by comparison of computed responses of a homogeneous half-space subjected to a single constant load on its surface against available analytical solutions. Next, time-harmonic loads on a homogeneous half-space are examined. The study continues with both constant and time-harmonic loads on a layered half-space. Finally, multiple constant and time-harmonic loads are considered. The formulation and results demonstrate the effectiveness and versatility of the method in problems of dynamic response of layered media to moving loads.     

Effects of pulse period of near‐field ground motions on the seismic demands of soil–MDOF structure systems using mathematical pulse models

In this paper, the effects of pulse period associated with near‐field ground motions on the seismic demands of soil–MDOF structure systems are investigated by using mathematical pulse models. Three non‐dimensional parameters are employed as the crucial parameters, which govern the responses of soil–structure systems: (1) non‐dimensional frequency as the structure‐to‐soil stiffness ratio; (2) aspect ratio of the superstructure; and (3) structural target ductility ratio. The soil beneath the superstructure is simulated on the basis of the Cone model concept. The superstructure is modeled as a nonlinear shear building. Interstory drift ratio is selected as the main engineering demand parameter for soil–structure systems. It is demonstrated that the contribution of higher modes to the response of soil–structure system depends on the pulse‐to‐interacting system period ratio instead of pulse‐to‐fixed‐base structure period ratio. Furthermore, results of the MDOF superstructures demonstrate that increasing structural target ductility ratio results in the first‐mode domination for both fixed‐base structure and soil–structure system. Additionally, increasing non‐dimensional frequency and aspect ratio of the superstructure respectively decrease and increase the structural responses. Moreover, comparison of the equivalent soil–SDOF structure system and the soil–MDOF structure system elucidates that higher‐mode effects are more significant, when soil–structure interaction is taken into account. In general, the effects of fling step and forward directivity pulses on activating higher modes of the superstructure are more sever in soil–structure systems, and in addition, the influences of forward directivity pulses are more considerable than fling step ones. Copyright © 2013 John Wiley & Sons, Ltd.     

成层地基一维土层对地震的随机反应分析

首先基于改进的一维剪切梁模型，对成层土层推导了确定自振频率、振型函数、参与系数及稳态动力响应的封闭型解析表达式，首次证明了成层土层振型函数的正交性，然后在此基础上，利用随机振动理论，研究了成层土层对地震的随机动力反应问题，关于基岩输入地震加速度的功率谱密度函数，考虑了两种形式：白噪声谱和过滤白噪声谱。数值计算结果表明：对这两种谱，土层的最大期望反应是不相同的；平稳输入与输出过高估计了土层的随机反应。     

无限长源二维各向异性地层中CSAMT有限元模拟

可控源音频大地电磁测深法(CSAMT)基本上是基于电性各向同性理论的假设,而实际地层普遍表现为电性各向异性现象,因此研究各向异性地层条件下CSAMT方法的电磁响应具有重要的理论意义和应用价值.本文从有源Maxwell方程出发,推导出了二维各向异性地层条件下无限长线源频率域的电磁场响应,得到了一组平行于线源方向的电场分量E_x和磁场分量H_x的偏微分方程,并采用有限元法进行求解.模型的计算结果表明:不论是对均匀半空间还是一维层状介质中的各向异性二维体模型的计算,均能从结果中明显地看出各向同性背景场和各向异性异常体的存在;在计算中通过改变各向异性系数或各向异性旋转角,其结果在视电阻率和相位曲线上均存在显著区别.计算结果表明了在各向异性地层中,仍然采用各向同性的假设进行CSAMT资料的处理与解释,可能会带来比较严重的误差,这种情况下必须采用基于各向异性的地质模型对CSAMT资料进行处理和解释.研究结果对于提高CSAMT方法的勘探效果和应用水平具有重要的指导意义.     

具有饱和土沉积层的充水河谷对平面瑞雷波的散射

针对具有饱和土沉积层的充水河谷对平面瑞雷波的散射问题,把半空间场地用单相弹性介质模拟,河谷中的饱和土沉积层用Biot饱和多孔介质动力理论模拟,河谷中的水假定为无黏性流体（理想流体）,利用波函数展开法在频域内给出了具有饱和土沉积层的圆弧形充水河谷对平面瑞雷波散射问题的解析解答.文中给出了算例,计算了不同输入频率和高宽比时河谷谷底的位移幅值.算例表明由于具有饱和土沉积层的充水河谷存在,使得河谷谷底的位移幅值放大4倍多,并且它的幅值随着河谷谷底位置的不同而产生较大的变化.     

黏弹性双相介质参数反演的同伦方法

本文以介质的动态时域响应（位移、速度、加速度）作为反演的依据,对黏弹性双相介质的材料参数进行了反分析研究.根据附加条件,并考虑到由于测量误差和测量数据的不充分造成的反演问题的不适定性,将黏弹性双相介质的参数反演问题转化为非线性泛函的极小值问题,然后应用大范围收敛的同伦方法求出使泛函极小的根作为反问题的解.最后,以二维半空间黏弹性双相介质模型为例进行了数值反演分析,数值结果表明本文方法在参数的反演过程中目标函数稳定收敛,且具有一定的抗“噪声”干扰性能;与利用速度和加速度信息反演的结果相比,利用位移信息反演的结果具有较高的精度和抗噪声能力.     

Quantifying hydrological responses to monsoon-controlled precipitation across the soil-groundwater-stream continuum with long-term high-frequency hydrometric monitoring

Stream water, groundwater and soil water in the riparian zone are closely linked. Their responses to rainfall events controlled by monsoon climate are variable and intertwined, which are still not well known. To address this knowledge gap, we established a monitoring transect adjacent to a headwater stream in Huashan Catchment, eastern China, with typical monsoon climate. We monitored precipitation, stream stage, groundwater level and soil moisture content at intervals of maximum 30 min. We then conducted an event-based analysis of rainfall event characteristics and diverse response metrics, and assessed their correlations and interrelationships through correlation and regression analysis. Our 2-year monitoring results show that water level responses occurred in most rainfall events. They had smaller threshold of rainfall amount and timing but longer time to peak response. Stream responses exhibited smaller response magnitude and intensities than groundwater responses. Rainfall amount and event duration were the most critical driving factors for groundwater responses. Soil moisture responses varied with depth. Only large storms could propagate into topsoil and generate rapid responses. Middle soil moisture responses had more frequent response occurrence and more variable response magnitude, while deep soil moisture responses had smaller response magnitude, longer time to peak response and larger wetting front movement velocity. Attenuated initial response timing with depth identified preferential flow, reflecting heterogeneity in the soil profile. Monsoon-controlled heavy rainfall improved hydrologic connectivity in the soil-groundwater-stream continuum (SGSC), mediating the influence of heterogeneity on soil moisture responses and potentially contributing more subsurface flow to catchment runoff. Overall, this study aimed to reveal the mechanism of hydrological responses to monsoon-controlled precipitation across the SGSC.     

基于流固耦合动力模型的饱和土体-隧道体系地震反应研究

基于ABAQUS软件平台,应用自行开发的流固耦合动力模型孔压单元模拟场地土体,并通过黏弹性人工边界方法实现地震动的输入,对饱和土体场地中的双孔隧道结构在地震荷载作用下的动力反应进行研究。计算结果表明:在地震反应结束时刻,场地土体位移幅值在两隧道之间以及两隧道的附近区域较大,而远离隧道的区域则较小;场地底部区域土体的孔压幅值较大,而场地顶部区域土体则较小;隧道左右两侧拱腰部位的衬砌的应力较大,而拱顶部位则较小。计算结果同时表明了流固耦合动力模型孔压单元在饱和土体-隧道体系地震反应研究中的适用性。     

Numerical analysis of simultaneous heat and mass transfer during infiltration into frozen ground

This paper concerns heat transfer and water infiltration into a homogeneous, unsaturated, frozen soil. A numerical analysis of the processes, which is based on the local volume averaging formulation of transport phenomena in porous media, is described. Simultaneous heat and mass transfers with phase changes are considered. The results of the simulations provide an insight into the mechanics of the infiltration process. They suggest that infiltration involves primarily two flow regimes, a transient regime and a quasi-steady-state regime. Once the quasi-steady-state regime is reached, the energy needed to increase soil temperature at depth is supplied by latent heat released from freezing of water in the upper layers of soil. The effects of surface saturation, initial soil saturation and initial soil temperature on infiltration are examined.