Lateral dynamic compliance of pile embedded in poroelastic half space

The time-harmonic response of a pile in a poroelastic half space and under lateral loadings is studied. By treating the pile as a one-dimensional structure and the half-space as a three-dimensional poroelastic continuum, the dynamic interaction between a pile and a poroelastic medium is formulated as a Fredholm integral equation of the second kind. Green's functions for a distributed lateral force field acting inside a poroelastic half space is an important ingredient of this paper. Numerical results for lateral dynamic compliance functions are presented to illustrate the dynamic characteristics of a pile in a poroelastic half space.     

Boundary shock waves in a conducting gas

Summary In this paper, we have postulated, in a conducting gas, the occurrence of a boundary shock wave, considered as a quick transition region in which the viscous effects are compressive and are confined to a thin layer adjacent to a surface. The analogues of the well known Rankine-Hugoniot jump relations, Prandtl relation, and other properties of a shock wave are derived and a discussion about the existence of a boundary shock wave is made.     

Radiating Vortices in Geophysical Fluid Dynamics

The dynamics of a single vortex on a beta-plane is discussed in this paper. A barotropic, an equivalent barotropic, one-and-a half and two-layer models are considered. The momentum and energy balances are used to describe the evolution of a vortex. A quasi-stationary balance of the Rossby, Zhukovsky-Kutta forces and the force induced by Rossby-wave radiation, describes the dynamics of the barotropic vortex. A net Coriolis force occurs if the fluid is stratified. The difference between the dynamics of cyclones and anticyclones results directly from the Coriolis force acting on a single vortex in a stratified fluid.All vortices radiate Rossby waves in the quasigeostrophic approximation but intense anticyclones propagate steadily in a one-and-a half layer model. A critical amplitude that bounds radiating and steadily propagating anticyclones is found. Steady propagation of anticyclones in general is impossible in a two-layer fluid due to the radiation of a barotropic Rossby-wave. Some solutions of solitary wave type which are known for a two-layer model, survive owing to wave interference.A single vortex can extract energy from a Rossby wave if synchronism conditions are satisfied. The wave interference again plays a crucial role in this case. The wave interference also determines the energy exchange of vortices located at larger distances. If the distance between the vortices is shorter than the length of the radiated waves, modon may be formed due to a small energy loss.The unbounded monotonic variation of the planetary vorticity is a characteristic feature of a beta-plane approximation. As a result, a single vortex propagates up to a 'rest latitude' where it disappears. The evolution of a single barotropic vortex over bottom topography provides another example of a background vorticity distribution with a local extremum above hills (valleys) or ridges (troughs). Physics of its movement differs from a beta-plane case, but if a vortex lies over broad topography, equations are similar and the evolution of a vortex manifests the same typical features. Particularly, a cyclonic vortex tends to drift to the top of a hill or a ridge. An anticyclonic vortex, on the contrary, slides to the bottom of a valley or a trough.An interaction of a barotropic vortex with a broad mean flow is tractable qualitatively on the basis of previous results. Numerical examples illustrating absorption of a small vortex by a larger one and a vortex movement across the flow, are direct analogies of the vortex evolution over a hill and a ridge, respectively. At the same time, strong influence of strain drastically changes the vortex structure.     

Impact of sensor measurement error on sensor positioning in water quality monitoring networks

This paper studies the impact of sensor measurement error on designing a water quality monitoring network for a river system, and shows that robust sensor locations can be obtained when an optimization algorithm is combined with a statistical process control (SPC) method. Specifically, we develop a possible probabilistic model of sensor measurement error and the measurement error model is embedded into a simulation model of a river system. An optimization algorithm is used to find the optimal sensor locations that minimize the expected time until a spill detection in the presence of a constraint on the probability of detecting a spill. The experimental results show that the optimal sensor locations are highly sensitive to the variability of measurement error and false alarm rates are often unacceptably high. An SPC method is useful in finding thresholds that guarantee a false alarm rate no more than a pre-specified target level, and an optimization algorithm combined with the thresholds finds a robust sensor network.     

西宁地区第四纪晚期孢粉组合及古环境

西宁地区位于黄土高原与青藏高原的接壤处,是环境和气候变迁的敏感地带。本文对西宁市北川河河谷地区黄土沉积的钻孔剖面进行了孢粉分析,获得了比较丰富的孢粉数据,结果呈现出以松、桦、蒿及藜等木本及草本植物花粉为主的孢粉组合。据各类植物花粉量在该剖面垂向上的明显变化,由下而上可划分为5个孢粉带。研究表明,该剖面的孢粉分析数据及资料不仅记录了75kaB.P以来大量的古地理及古环境的变迁,也揭示了西宁地区晚更新世以来古植被及古气候的演替及变化,其演变分别经历了5个阶段:第一阶段为森林型针叶林,反应了温爽轻湿的气候;第二阶段为针叶林,为温凉轻润的气候;第三阶段为针叶林夹稀树草原,属温和湿润夹温凉轻湿的气候;第四阶段为森林草原,反应了温凉轻爽的气候;第五阶段为针叶林,反应了温和湿润的气候。     

Dipping-interface Mapping Using Mode-separated Rayleigh Waves

Multichannel analysis of surface waves (MASW) method is a non-invasive geophysical technique that uses the dispersive characteristic of Rayleigh waves to estimate a vertical shear (S)-wave velocity profile. A pseudo-2D S-wave velocity section is constructed by aligning 1D S-wave velocity profiles at the midpoint of each receiver spread that are contoured using a spatial interpolation scheme. The horizontal resolution of the section is therefore most influenced by the receiver spread length and the source interval. Based on the assumption that a dipping-layer model can be regarded as stepped flat layers, high-resolution linear Radon transform (LRT) has been proposed to image Rayleigh-wave dispersive energy and separate modes of Rayleigh waves from a multichannel record. With the mode-separation technique, therefore, a dispersion curve that possesses satisfactory accuracy can be calculated using a pair of consecutive traces within a mode-separated shot gather. In this study, using synthetic models containing a dipping layer with a slope of 5, 10, 15, 20, or 30 degrees and a real-world example, we assess the ability of using high-resolution LRT to image and separate fundamental-mode Rayleigh waves from raw surface-wave data and accuracy of dispersion curves generated by a pair of consecutive traces within a mode-separated shot gather. Results of synthetic and real-world examples demonstrate that a dipping interface with a slope smaller than 15 degrees can be successfully mapped by separated fundamental waves using high-resolution LRT.     

SEQUENTIAL STIFFNESS DESIGN FOR SEISMIC DRIFT RANGES OF A SHEAR BUILDING–PILE–SOIL SYSTEM

A shear building supported by a prescribed pile–soil system is subjected to bedrock earthquake input. A new design procedure is presented for generating a sequence of stiffness designs satisfying the constraints on interstorey drifts. The mean peak interstorey drifts of the shear building subjected to a set of spectrum-compatible ground motions at the bedrock are evaluated by a modal combination rule. Tuning of the fundamental natural period of a shear building with a fixed base with that of a shear beam ground results in a non-monotonic sequence of stiffness designs with respect to a ground stiffness parameter and previous approaches cannot be applied to such a problem. This difficulty in finding such a non-monotonic sequence is overcome by utilizing the ground stiffness parameter and the superstructure stiffness parameter alternately in multiple design phases and by developing a new multi-phase perturbation technique. Fundamental characteristics of this sequence of stiffness designs and the effect of ground stiffnesses on the design of the shear building are disclosed. It is further shown that the stiffness contour method is also useful for the design procedure such that a scattering effect in the estimates of ground stiffnesses is taken into account. The usefulness of the proposed procedure of sequential stiffness design and contour line method is demonstrated through several sequential design examples.     

Capturing critical behaviour in soil moisture spatio-temporal dynamics

A physical system is subject to a phase transition process when it shows a discontinuous change of a macroscopic feature of the system under a continuous change of a system’s state variable.     

INTERPRETATION AND DEPTH OF INVESTIGATION OF GRADIENT MEASUREMENTS IN DIRECT CURRENT GEOELECTRICS*

Gradient measurements in a homogeneous electrical primary field can easily be interpreted for simple models. The simplified solution (conducting or resistant body in a homogeneous space in a homogeneous electrical field) is often sufficiently accurate, as comparisons with the exact solution (body of finite resistivity in a homogeneous half-space in a quasihomogeneous electrical field) show. The exact geometry of the body cannot be determined by gradient measurements; the same anomaly of apparent resistivity can be caused by different bodies. In particular, the similarity between a sphere and a cube of the same volume is very high. There is a distinct influence of the resistivity of the overburden: the higher this resistivity is, the stronger is the effect caused by a buried body. If a deviation of 10% of the apparent resistivity is assumed as the lower boundary at which a buried body can be detected by gradient measurements, the depth of investigation for a three-dimensional body is approximately equal to its width; in the two-dimensional case the thickness of the overburden can be twice the width. If the overburden has a resistivity which is higher than the resistivity of the substratum, these depths are greater. The greatest possible depth is approximately three times the width of the body.     

Holocene grassland vegetation, climate and human impact in central eastern Inner Mongolia

~~Holocene grassland vegetation, climate and human impact in central eastern Inner Mongolia1.Ye,D.Z.,Chou,J.E,Liu,J.Y.et al.,Causes of sand-stormy weather in northern China and control measures,Acta Geographica Sinica(in Chinese),2000,55(5):513-520. 2.Qiu,X.E,Zeng,Y.,Miao,Q.L.,Temporal spatial distribution as well as tracks and source areas of sand dust storms in China,Acta Geographica Sinica(in Chinese),2001,56(3):316-322. 3.Cui,H.T,Kong,Z.C,Preliminary analysis on the cli…     

Some consequences of the differences in seismic properties in old and young continental plates for isostatic compensation

We present a short review of seismological data and show that a difference of upper mantle structure is clearly resolved between old and young continental plates. An Archean plate is approximately 1 second faster than a Paleozoic plate for P waves. Such a change in plate structure implies that the density of an Archean lithosphere should be greater than the density of a Paleozoic lithosphere, if they have the same chemical composition. Applying isostasy, we would expect a Precambrian plate to sink and its surface to stand at a level 8 km beneath that of a Paleozoic plate. We first check that the weight of a crustal column is not smaller for a Precambrian crust than for a Paleozoic crust. Explosion seismology data show that isostatic equilibrium is nearly achieved in the crust. Therefore a compensating mechanism has to be acting in the subcrustal lithosphere. Two hypotheses are presented. Provided that the chemical composition of the lower lithosphere does not vary with time, a simple condition for a continental plate not to sink when aging, would be that the density of the lower lithosphere be ?0.1 g/cm³ smaller than the density of the asthenosphere. Another condition that would prevent plates to sink would be a lowering of the density of the lower lithosphere with age due for example to a variation of its chemical composition and to a reduction in the mean atomic weight. Both hypotheses imply that isostatic equilibrium of old continental plates is maintained by a geochemical mechanism. Although thermal evolution is a key factor for explaining the evolution of continents, it has to be complemented by a hypothesis on the change of the chemistry of the lower continental lithosphere with respect to the asthenosphere and/or with respect to age.     

A three-scale cracking criterion for drying soils

Cracking is a most unwanted development in soil structures undergoing periodic drying and wetting. Desiccation cracks arise in an apparent absence of external forces. Hence, either an internal, self-equilibrated stress pattern resulting from kinematic incompatibilities, or a stress resulting from reaction forces at the constraints appear as a cracking cause, when reaching tensile strength. At a meso-scale, tubular drying pores are considered in the vicinity of a random imperfection, inducing a stress concentration in the presence of significant pore suction. This approach allows one to use the effective stress analysis, which otherwise, away from the stress concentration, usually yields compressive effective stress and hence a physically incompatible criterion for a tensile crack. Recent experiments on idealized configurations of clusters of grains provide geometrical data suggesting that an imperfection as a result of air entry deep into the granular medium penetrates over 4 to 8 internal radii of a typical pore could yield a tensile effective stress sufficient for crack propagation.     

Shear wave velocities from down-hole measurements

Shear wave velocities of soils, which provide shear moduli for earthquake response calculations, can be measured clearly and accurately using the down-hole method. Such a method has been used at a number of sites in California with good results to depths of 200 ft. Seismic waves from hammer blows, delivered to the ends of a heavy plank loaded by the front wheels of a vehicle, are received by a three-component geophone in a carefully prepared vertical hole and recorded at 1 mm/ms with a six-channel seismograph. A series of records are obtained at various measured depths in the hole, allowing calculation of interval velocities. Shear waves are easily identified by a clear 180 degrees phase difference between waves generated by blows on the opposite ends of the plank. Compressional waves are routinely logged by a vertical hammer blow at each recording depth. Shear velocities are reproducible to about 5 per cent in surveys of neighbouring holes. The reading uncertainty of ± 1 msec for the S arrival gives a resolution sufficient to detect a buried layer 5–10 ft thick with a velocity contrast of only 20 per cent.     

DIKE FORMATION WITH SUBMERGED VANE

1 INTRODUCTION Increasing capital costs, emerging environmental concerns and rising maintenance expenses of conventional river training works around the world have led to the development of submerged vanes in practice. Submerged vanes are being favoured f…     

Late Quaternary Activity and Paleoearthquakes along the Nanyukou Segment of the Northern Piedmont Fault of Wutai Mountain

The northern piedmont fault of Wutai Mountain is located at the north of the Shanxi Graben system,which is the dominating fault of the south boundary of the Fanshi-Daixian depression. This paper discusses the fault activity and paleoearthquakes around the Nanyukou segment of the northern piedmont fault of Wutai Mountain during the late Quaternary through field investigation along the fault,measuring geomorphic deformation and excavating trenches at some important sites. From Nanyukou to the southwest of Shanhui,we find obviously dislocated alluvial fans,with strong neotectonic movement at these sites. Since nearly 20ka,the vertical average slip rate is 1. 55mm /a to 2. 0mm /a. However,since nearly 6ka,it has reached as high as 2. 3mm /a,which is twice that on other segments. 2 trenches were excavated around Nanyukou with 6 events discovered. The referenced ages of the events are before 7600a,6700a ～ 7600a,5321a ～ 5575a,4400a ～ 5400a,4200a ～ 4400a and after 1600a B. P. with approximate recurrence interval 1400a. The latest event is likely to be the earthquake occurring at 512 A. D. ,so it is necessary to do further work to verify this in the future.     

Note on the hypergeometric distribution as an invalidation test for binary forecasts

One mechanism giving rise to the hypergeometric distribution is the number of matches in a random reordering of a sequence of forecasts of binary events. This provides a simple means of invalidating a time series of binary forecasts if in fact the forecasting method has no skill. The hypergeometric distribution has a long history of application in this context but appears not to have a high profile in the environmental sciences. Attention is drawn to the utility of the distribution as a simple nonparametric test of the null hypothesis of no skill when forecasting binary environmental outcomes.     

Contamination of a well in a uniform background flow

In this paper we describe the transport of pollution in groundwater in the neighbourhood of a well in a uniform background flow. We compute the rate at which contaminated particles reach the well as a function of the place of the source of pollution. The motion of a particle in a dispersive flow is seen as a random walk process. The Fokker-Planck equation for the random motion of a particle is transformed using the complex potential for the advective flow field. The resulting equation is solved asymptotically after a stretching transformation. Finally, the analytical solution is compared with results from Monte Carlo simulations with the random walk model. The method can be extended to arbitrary flow fields. Then by a numerical coordinate transformation the analytical results can still be employed.     

不同深度鱼塘水温状况分析

滆湖位于江苏省常州市西南13km处,水面面积164km~2,平均水深1.26m,是太湖湖群的重要组成部分。其氮、磷平衡研究结果表明:①入湖氮、磷总量分别为4120.29t/a和270.03t/a;其中以河道入湖量最大,分别占入湖总量的71.9％和57.1％,其次是养殖投饵,分别占入湖总量的12.4％和29.9％;氮、磷的滞留系数分别为0.36和0.35,年滞留量分别为1481.6t和94.82t。②湖水的氮、磷负荷较大,但由于水草的吸收净化作用,湖水水质仍能保持较低水平。③网围养殖区底泥氮、磷释放强度大。非网围区水草根系的吸收对底泥氮、磷释放起到一定的抑制作用。     

The mechanism of basaltic explosions: Experimental modeling

An instrument package for simulating basaltic eruptions (IPSBE) with a height of 18 m has been developed for investigating the processes that occur during Strombolian eruptions. The device follows the geometrical ratio between the actual plumbing system of a volcano, with the ratio of conduit diameter to conduit height being 1 to 1000. For the first time in physical modeling studies, we created conditions in which a moving gas-saturated model liquid enters the conduit; this enabled us to study bubble nucleation, expansion, and coalescence, the generation and transformation of gas structures, and the kinetic features shown by the evolution of the gas phase. These experiments revealed a novel (previously unknown) flow pattern of two-phase mixtures in a vertical column, viz., a cluster flow that involves the regular alternation of compact clusters of gas bubbles that are separated by a fluid that does not involve a free gas phase. It is shown that the liquid, bubble, cluster, and slug flow patterns are mutually transformed under certain conditions; they are polymorphous modifications of a gas-saturated liquid moving in a vertical pipe. The data thus acquired suggested a new model for the gas-liquid movement of a magma melt in a conduit: depending on the type of gas-liquid flow behavior at the vent, the crater will exhibit different types of explosive activity, including actual explosions.     

Dynamic response of single-span beam bridges to a series of moving loads

The paper makes a contribution to the problem of a stream of loads crossing a single-span beam bridge. There are considered the basic load models, in the form of a stream of fixed amplitude forces, unsprung masses and viscoelastic oscillators. The matrix equations of motion of the system are formulated and discussed. The problem of dynamic stability and steady-state response of a bridge carrying a periodic stream of inertial loads is formulated and solved. The paper also includes a vibration study of a beam bridge subjected to a uniform stream of moving loads, of a limited or unlimited number of load cycles.