摄动随机有限元法在土坡可靠性分析中的应用

介绍了摄动随机有限元法的基本原理 ,并给出了土坡可靠性的 PSFEM计算公式 .数值算例结果表明 ,PSFEM在解决土坡可靠性问题时 ,理论框架严格且计算结果准确 ,因而是一种可靠且有效的数值方法 .

Effects of Different Absorbing Medium on Microwave Remediation of Chlordane Contaminated Soil

Objective] This study almed to compare the effects of three absorbing medium on microwave degradation of chIordane in contaminated soiI under alkaline condition. [Method] SoiI sampIes were coI ected from the original site of a reIocated pesticide production enterprise as experimental materials, to investigate the effects of Cu2O, MnO2 and activated carbon powder as absorbing medium on soiI warming and removal rate of chIordane under alkaline condition with 20% moisture content. In addition, the effects of activated carbon as the optimal absorbing media on the removal rate of chIordane in contaminated soiI were analyzed, and the effects on the removal rate of chIordane in different weights of soiI sampIes were investigated. [Result] The effects of three different absorbing medium on the removal rates of chIordane demonstrated a descending order of activated carbon ＆gt; MnO2 ＆gt; CuO2. Under the same microwave condition, the removal rate of chIordane decreased with the increase of soiI weights, but the utiIization efficiency of microwave was improved continuousIy and tended to be stabiIized with the increase of soiI weights. [Conclu-sion] This study provided a theoretical basis for further Iarge-scale appIication in soiI remediation.

CENTRIFUGAL TEST STUDY ON THE BEHAVIOR OF SOFT CLAY AT SEA BOTTOM UNDER THE ACTION OF WAVE FORCE

The importance of studying the behavior of the soil at the sea bottom under the action of wave force has arisen with the development of offshore engineering.In this paper,the behavior of the soft clay under the action of wave forces is studied by performing centrifugal tests.The soil profile and the wave characters were simulated in the centrifugal model cell according to the typical environmental conditions of the oil fields in the Bohai gulf.Test results show that the soft clay layer will be seriously softened near the upper surface under the maximum wave height and slightly affected in the deeper layer,and that no liquefaction was recorded in the silty sand sublayer during the test.It is proven that the centrifugal test is a valid technique for simulating the interaction between soil and wave.

The runoff characteristics and harmonic analysis of the soil moisture dynamics in Robinia pseudoacacia stand

Robinia pseudoacacia stands act as a typical ecological protection forest in hilly semi-arid area of China. Two fields of surface runoff were separately set up in R. pseudoacacia stand and its clearcut area in the western Liaoning Province (1850-12225 E, 4024-4234 N) for measuring the characteristics of runoff and sediment as well as soil moisture dynamics. Contractive analysis of the two land types showed that there existed a significant difference in volumes of runoff and sediment between the sites of R. pseudoacacia stand and its clearcut area. The runoff volume and sediment volume in clearcut area were much bigger than those in R. pseudoacacia stand, with an increase amount of 40%-177% for runoff and 180%-400% for sediment. Hydrograph of surface runoff of typical rainfall showed that the peak value of runoff in R. pseudoacacia stand was decreased by 1.0-2.5?0-3m3s-1 compared with that in its clearcut area, and the occurring time of peak value of runoff in R. pseudoacacia stand was 10-20 min later than that in its clearcut area. Harmonic analysis of soil moisture dynamics indicated that the soil moisture in R. pseudoacacia stand was 2.3 % higher than that in clearcut area, and the soil moisture both in R. pseudoacacia stand and its clearcut area could be divided into dry season and humid season and varied periodically with annual rainfall precipitation. It was concluded that R. pseudoacacia stand plays a very important role in storing water, increasing soil moisture, and reducing surface runoff and soil erosion.

Comparison of microwave and conventional heating routes for kaolin thermal activation

The effect of activation properties of the precursors of zeolite directly prepared from kaolin influenced by microwave field and conventional heating was investigated.XRD,TG-DSC,FT-IR,SEM,particle size analysis,specific surface area(BET),pore size distribution(BJH)and N2 adsorption-desorption were discussed to determine the optimal activation temperature.It is concluded that the conversion of kaolin to metakaolin in the microwave field is at 500°C holding for 30 min,which is 100°C lower than that in conventional calcination and 90 min shorter,and the phase transition process of kaolin under the effect of microwave field is the same as that of conventional heating method.SEM analysis indicates that the particle size is more uniform and agglomeration appears slightly in the microwave field.The N2 adsorption-desorption isotherm,BET and BJH of kaolin indicate that the pore properties are almost invariable regardless of calcination route during the process of calcining kaolin into metakaolin.It indicates that microwave calcination is superior to conventional calcination in the activation pathway of kaolin.It is attributed to microwave heating relying on objects to absorb microwave energy and convert it into thermal energy,which can simultaneously and uniformly heat the entire substance.

Experimental study on the wave pressure of liquefied silty soil

A number of studies focus on the pore-water pressure in seabed under thewaves and seabed instability induced by liquefaction, but rarely on the wave pressureof liquefied soil. In this paper, flume tests were performed at varying wave heightsunder both conditions of liquefied and stable seabed. The total pressures equal to soilpressures and pore water pressures were measured and analyzed at each depth. Theresults showed that the liquefied seabed had little difference from the stable seabed onthe peak pressures. However, the pressure amplitude of the liquefied soil increased byseveral to 10 times and decreased faster with increasing soil depths, compared with thestable soil. According to the experiments and further analysis, an empirical equationbetween pressure amplitude of the liquefied soil and wave parameters was put forwardunder the flume test. The results provide a valuable reference for engineeringapplications.

Advances in Research on Soil Moisture by Microwave Remote Sensing in China

Soil moisture is an important factor in global hydrologic circulation and plays a significant role in the research of hydrology, climatology, and agriculture. Microwave remote sensing is less limited by climate and time, and can measure in large scale. With these characteristics, this technique becomes an effective tool to measure soil moisture. Since the 1980s, Chinese researchers have investigated the soil moisture using microwave instruments. The active re- mote sensors are characteristic of high spatial resolution, thus with launch of a series of satellites, active microwave remote sensing of soil moisture will be emphasized. The passive microwave remote sensing of soil moisture has a long research history, and its retrieval algorithms were developed well, so it is an important tool to retrieve large scale moisture information from satellite data in the future.

Microwave pretreatment for enhanced selective nitric acid pressure leaching of limonitic laterite

As clean energy,the microwave is commonly used to pretreat various ores.In this work,the microwave dielectric properties of limonitic laterite ore were measured by resonant cavity perturbation technique and the effects from microwave were systematically investigated.Results indicated that limonitic laterite had high microwave absorbance.After microwave pretreatment,the microstructure of the laterite became less aggregated and more porous and the main phase transformed from goethite to hematite that improved leaching in nitric acid(1.2 kg HNO3/kg ore);Ni,Co,Fe,and Mg extraction ratios were 95.2%,98.1%,1.8%and 15%,respectively,after leaching for 60 min at 200°C and 500 r/min.Furthermore,in the process of goethite to hematite by microwave pretreatment,the nickel-containing mineral is activated,which makes nickel be leached easily.The leaching process has high Ni extraction ratio compared to that without microwave(82%)and conventional pretreatment(90.4%).Therefore,microwave pretreatment of limonitic laterite before nitric acid pressure leaching is an effective way to improve the selectivity and extraction of the leach.

A Preliminary Stndy on Identification of Clay Minerals in Soils with Reference to Reflectance Spectra

The characteristics of the reflectance spectra of clay minerals and their influences on the reflectancespectra of soils are dealt with in the paper. The results showed that dominant clay minerals in soils couldbe distinguished in light of the spectral-form parameters of the reflectance spectra of soils, thus making itpossible to develop a quick method to determine clay minerals by means of reflectance spectra of soils in thelab. and providing a theoretic basis for retnote sensing of clay minerals in soils with a high resolution imagingspectrometer.

Dynamic response law about gravity retaining wall to seismic characteristics and earth fill properties

In order to find the dynamic response laws of retaining walls affected by certain earthquake loads,the influence of the seismic wave characteristics and sub-grade fill parameters(including the foundation surface slope) were focused on,and a series of tests were performed.The results show that the maximum stress of the retaining wall decreases as internal friction angle,foundation slope,filled soil cohesion and the biggest dynamic elastic modulus increase,while it increases with the seismic frequency and seismic input peak dropping.The addition value of dynamics earth pressure increases when seismic frequency and seismic input peak are reduced,while it decreases when the filled soil cohesion and internal friction angle rise.Meanwhile,dynamic elastic modulus and foundation slope have no obvious influences on addition value of dynamics earth pressure.The slope will be instable if the seismic input peak exceeds 0.5g and be disruptive if seismic frequency is larger than 2.5 Hz.The mid-lower parts of retaining walls are in most heavy and obvious response to these factors,which reveals the mechanism of "belly burst" in retaining wall that appears commonly in practical projects.

Seismic response analysis of GRPS embankment under oblique incident P wave

In order to investigate the seismic performance of geosynthetic reinforced and pile supported(GRPS) embankment under seismic loads, an input method for three-dimensional oblique incidence of P wave was proposed. This method is based on the explicit finite element method while considering the viscous-spring artificial boundary(VSAB) condition. Using the proposed method, a numerical study was conducted, and the influence of oblique incidence on the seismic response of GRPS embankment under the oblique incident P waves was analyzed. The results indicate that in comparison with vertical incidence, the oblique incidence can significantly increase the displacement, velocity and acceleration of key locations in the GRPS embankment. The existence of geosynthetics can alleviate the impact of seismic load on the response of the embankment to a certain degree. Moreover, the number of reinforcement layers and modulus of geogrid also greatly influence the seismic performance of GRPS embankment.

Multi-time scale analysis of precipitation variation in Guyuan, China:1957-2005

Morlet wavelet transformation is used in this paper to analyze the multi time scale characteristics of pre cipitation data series from 1957 to 2005 in Guyuan region.The results showed that(1) the annual precipitation evo lution process had obvious multi time scale variation characteristics of 15 25 years,7 12 years and 3 6 years,and different time scales had different oscillation energy densities;(2) the periods at smaller time scales changed more frequently,which often nested in a biggish quasi periodic oscillations,so the concrete time domain should be ana lyzed if necessary;(3) the precipitation had three main periods(22 year,9 year and 4 year) and the 22 year period was especially outstanding,and the analysis of this main period reveals that the precipitation would be in a relative high water period until about 2012.

Evaluation of dynamic characteristics of silt in Yellow River Flood Field after freeze-thaw cycles

Frothing is a main disease of highways in Yellow River Flood Field, due to the loss of dynamic strength of roadbed soils under the couple effects of temperature, salt, and vehicle traffic load. This is strongly linked to the dynamic characteristics of silt in this region. To analyze these couple effects on the dynamic characteristics of silt, a series of tests(i.e., freeze-thaw cycling tests, vibration triaxial tests and ultrasonic wave velocity tests) were conducted and two kinds of silt(i.e., salt-free and 3%-salt silt) were designed. The results indicate that the dynamic shear strength and dynamic modulus decrease with increasing freeze-thaw cycles, while the damping ratio simultaneously increases. Furthermore, compared to salt-free silt, the decrement of dynamic shear strength and dynamic modulus of silt with 3% salt is more significant, but the damping ratio of 3%-salt silt is larger. In ultrasonic wave velocity tests, ultrasonic wave velocity of frozen soil specimens decreases as the number of freeze-thaw cycles increases. Based on the results of ultrasonic wave velocity tests, a preliminary model is proposed to evaluate damage of silt through field measurement ultrasonic data. The study could provide a theoretical basis for the treatment of silty soil highway.

Numerical Analysis of Effect of Water on Explosive Wave Propagation in Tunnels and Surrounding Rock

Based on the application of practical engineering,propagation processes of explosive waves in rock with water well and tunnel are simulated by ANSYS/LS-DYNA software. The evolution of damage in rock is presented. The effect of water on the damage of the concrete slab in a tunnel is compared with damage inflicted without water. The numerical simulation illustrates that water plays an important role in the evolution of damage of the concrete slab in a mine tunnel. In the presence of water in the rock the concrete slab is damaged more severely than without water in rock. The effect of water location in the rock is also considered. It is found that the concrete slab in the tunnel shows various degrees of damage as a function of the different locations of water. Attenuation laws of stress waves over time-space in rock with water are also obtained. Numerical results indicate that,under blast loading,there are three zones in the rock: a crushed zone nearby the explosive charge,a damaged zone and an elastic zone. The conclusions of numerical analysis may provide references for blasting designs and structure protection.

Influence of water saturation on propagation of elastic waves in transversely isotropic nearly saturated soil

Biot' s two-phase theory for fluid-saturated porous media was applied in a study carried out to investigate the influence of water saturation on propagation of elastic wave in transversely isotropic nearly saturated soil. The characteristic equations for wave propagation were derived and solved analytically. The results showed that there are four waves: the first and second quasi-longitudinal waves (QP1 and QP2), the quasitransverse wave (QSV) and the anti-plane transverse wave (SH) . Numerical results are given to illustrate theinfluence of saturation on the velocity, dispersion and attenuation of the four body waves. Some typical numerical results are discussed and plotted. The results can be meaningful for soil dynamics and earthquake engineering.

Soil Moisture Content Monitoring Based on ERS Wind Scatterometer Data

The ERS-1/2 wind scatterometer （WSC） has a low resolution cell of about 50 km but provides a high repetition rate （〈4 d） and can make measurements at multiple incidence angles. In order to estimate effective surface reflectivity （related to soil moisture content） over bare soil Using WSC data, an original methodology based on the advance integral equation model （AIEM） is presented, which takes advantage of its multiple view angular characteristics. This method includes two steps. First, a simplified two-parameter surface scattering model is calibrated by AIEM simulated-database over a wide parameter space. Second, regression analyses are carded out using the simulated database to build the relation between those parameters of our model at different incident angles from two observations of Mid and Fore beams. From the model simulated database, our technique works quite well in estimating Г^0. The possibility of applying the model to retrieve soil moisture is investigated using a set of data collected from the Intensive Observation Period field campaign in 1998 of the Asian Monsoon Experiment Tibet （GAME-Tibet）. The retrieved values obtained for the bare land surface are consistent with ground measurements collected in these areas and the correlation coefficient between retrieved soil moisture and the measured one reaches 0.65.

Transient response of a spherical cavity with a partially sealed shell embedded in viscoelastic saturated soil

Based on Biot’s wave equation, this paper discusses the transient response of a spherical cavity with a partially sealed shell embedded in viscoelastic saturated soil. The analytical solution is derived for the transient response to an axisymmetric surface load and fluid pressure in Laplace transform domain. Numerical results are obtained by inverting the Laplace transform presented by Durbin, and are used to analyze the influences of the partial permeable property of boundary and relative rigidity of shell and soil on the transient response of the spherical cavity. It is shown that the influence of these two parameters is remarkable. The available solutions of permeable and impermeable boundary without shell are only two extreme cases of this paper.

Pore pressure fluctuations of overlying aquifer during residual coal mining and water-soil stress coupling analysis

Three test models and a simulation model were constructed based on the prevailing conditions of the Taiping coalmine in order to analyze pore pressure fluctuations of an overlying aquifer during residual coal mining. As well, the relation between pore pressure and soil stress was evaluated. The model tests show the vibrations of pore pressure and soil stress as a result of mining activities. The simulation model tells of the response characteristics of pore pressure after mining and its distribution in the sand aquifer. The comparative analysis reveals that pore pressure and soil stress vibration are activated by unexpected events occurring in mines, such as collapsing roofs. An increased pore pressure zone always lies above the wall in front or behind the working face of a mine. Both pore pressure and vertical stress result in increasing and decreasing processes during movements of the working face of a mine. The vibration of pore pressure always precedes soil stress in the same area and ends with a sharp decline. Changes in pore pressure of sand aquifer are limited to the area of stress changes. Obvious changes are largely located in a very small frame over the mining face.

EXPERIMENTAL STUDY ON SOIL MOISTURE USING DUAL-FREQUENCY MICROWAVE RADIOMETER

An experiment of measuring soil moisture was carried out by using dual-frequency microwave radiometer designed by the authors. The measured data were analyzed by using statistical regression method and the empirical regression model of retrieving soil moisture in L-band and C-band was developed. The soil moisture in a rainfall event was retrieved using the experiential regression model, which is consistent well with the field sampling value. The results show that when soil moisture is lower than 75%, the brightness temperature is linear with soil moisture. However, when soil moisture is higher than 75%, the brightness temperature is not linear with soil moisture, so it is difficult for microwave radiometer to measure the changes of soil moisture. The experiment verifies the effectiveness and feasibility of microwave remote sensing soil moisture. Although this method for linear regression based on the data measured with the radiometer is simple, and has strong adaptability, generally it has only local application value, and lacks universal applicability for different areas and different conditions.

Evaluation of the Community Microwave Emission Model Coupled with the Community Land Model over East Asia

The Community Microwave Emission Model (CMEM) developed by the European Centre for Me-dium-Range Weather Forecasts (ECMWF) can provide a link between surface states and satellite observations and simulate the passive microwave brightness temperature of the surface at low frequencies (from 1 GHz to 20 GHz).This study evaluated the performance of the CMEM cou-pled with the Community Land Model (CLM) (CMEM-CLM) using C-band (6.9 GHz) microwave brightness temperatures from the Advanced Microwave Scanning Radiometer on Earth Observing System (AMSR-E) over East Asia.Preliminary results support the argument that the simulated brightness temperatures of CMEM-CLM from July 2005 to June 2010 are comparable to AMSR-E observational data.CMEM-CLM performed better for vertical polarization,for which the root mean square error was approximately 15 K,compared to over 30 K for horizontal polarization.An evaluation performed over seven sub-regions in China indicated that CMEM-CLM was able to capture the temporal evolution of C-band brightness temperatures well,and the best correlation with AMSR-E appeared over western Northwest China (over 0.9 for vertical polarization).However,larger biases were found over southern North China and the middle and lower reaches of the Yangtze River.