裂隙型硬粘土的力学模型及其在边坡工程中的应用

硬粘土是介于软岩和硬土之间的一种介质, 其中含有规律分布的裂隙, 具有明显的方向性和各向异性特征; 本文从实际应用的角度出发, 提出一种适用于裂隙性硬粘土的损伤力学模型, 并应用于南水北调中线渠道边坡工程的数值模拟分析。     

粘土矿物钝化改性及岩土的力学性质

本文以自行研制的粘土矿物钝化剂对广东省和武汉市等六地区的土壤进行了钝化改性实验研究，并对钝化效果的影响因素做了初步的分析探讨。实验表明，虽然6个地区11个样品中的粘土矿物种类和含量不同，但钝化剂对所有样品都有稳定的作用。其稳定效果，不仅与样品的物相组成和粒度分布有关；而且还与粘土矿物的种类及其含量密切相关。就三种主要粘土矿物来说，钝化效果的顺序是高岭土＞伊利石＞蒙脱石。     

Local site effects and dynamic soil behavior

Amplitudes of seismic waves increase significantly as they pass through soft soil layers near the earth's surface. This phenomenon, commonly known as site amplification, is a major factor influencing the extent of damage on structures. It is crucial that site amplification is accounted for when designing structures on soft soils. The characteristics of site amplification at a given site can be estimated by analytical models, as well as field tests. Analytical models require as inputs the geometry of all soil layers from surface to bedrock, their dynamic properties (e.g. density, wave velocity, damping), and the incident bedrock motions. Field tests involve recording and analyzing the dynamic response of sites to artificial excitations, ambient forces, and actual earthquakes. The most reliable estimates of site amplification are obtained by analyzing the recorded motions of the site during strong earthquakes. This paper presents a review of the types and the generating mechanisms of site amplification, and the models and methods that are used to characterize them from earthquake records.     

Stiff soil amplification effects in the 7 September 1999 Athens (Greece) earthquake

The Athens, Greece, earthquake of 7 September 1999 provided a number of reliable strong motion recordings and well-defined patterns of damage at sites with known geological and geotechnical conditions. Joint evaluation of this evidence shows that the very stiff soils of the Athens basin, compared to the nearby outcropping soft rocks, have amplified the peak horizontal acceleration by an average of 40% or more and have shifted elastic response spectra to higher periods. US and the European seismic code provisions (NEHRP-97 and EC-8), place stiff soils and soft rocks at the same site category and consequently fail to predict these adverse effects. A larger number of site categories and new site coefficients that depend on the seismic excitation frequency appear necessary in order to overcome this deficit of the codes.     

Identification of soil–structure interaction effect in base-isolated bridges from earthquake records

Identification of system parameters with the help of records made on base-isolated bridge during earthquakes provides an excellent opportunity to study the performance of the various components of such bridge systems. Using a two-stage system identification methodology for non-classically damped systems, modal and structural parameters of four base-isolated bridges are reliably identified using acceleration data recorded during 18 earthquakes. Physical stiffness of reinforced concrete columns, dynamic properties of soil and foundation impedance are found by available theoretical models in conjunction with pertinent information from the recorded accelerographs. Soil–structure interaction (SSI) effect in these bridges is examined by comparing the identified and physical stiffness of the sub-structure components. It is found that SSI is relatively pronounced in bridges founded in weaker soils and is more strongly related to the ratio of pier flexural stiffness and horizontal foundation stiffness than soil shear modulus, G_s, alone. However, substantial reduction in G_s is observed for moderate seismic excitation and this effect should be taken into account while computing foundation impedance.     

Cyclic hysteretic flow in porous medium column: model, experiment, and simulations

A periodic vertical movement of the groundwater table results in a subsequent cyclic response of the water content and pressure profiles in the vadose zone. The sequence of periodic wetting and drying processes can be affected by hysteresis effects in this zone. A one-dimensional saturated/unsaturated flow model based on Richards’ equation and the Mualem (Soil Sci. 137 (1984) 283) hysteresis model is formulated which can take into account multi-cycle hysteresis effects in the relation between capillary pressure and water content. The numerical integration of the unsaturated flow equation is based on a Galerkin-type finite element method. The flow domain is discretised by finite elements with linear shape functions. Simulations start with static water content and pressure profiles, which correspond to either a boundary drying or wetting retention curve. To facilitate the numerical solution of the hysteretic case an implicit non-iterative procedure was chosen for the solution of the nonlinear differential equation. Laboratory experiments were performed with a vertical sand column by imposing a high frequency periodic pressure head at the lower end of the column. The total water volume in the column, and the periodic water content profile averaged over time were measured. The boundary drying and wetting curves of the relation between water content and capillary pressure were determined by independent experiments. The simulations of the experimental conditions show a clear effect of the hysteresis phenomenon on the water content profile. The simulations with hysteresis agree well with the measurements. Computed dimensionless water content profiles are presented for different oscillation frequencies with and without consideration of hysteresis.     

Seasonal and event-scale variations in solute chemistry for four Sierra Nevada catchments

Hydrobiogeochemical processes controlling stream water chemistry were examined in four small (<5 km²) catchments having contrasting bedrock lithologies in the western Sierra Nevada foothills of California. The Mediterranean climate with its cool/wet and hot/dry cycle produces strong seasonal patterns in hydrological, biological and geochemical processes. Stream water solutes fall into three general groups according to seasonal fluctuation in concentration: strong, rainy season minimum–dry season maximum (Cl⁻, SO₄²⁻, base cations); weak, rainy season minimum–dry season maximum (Si); and rainy season maximum–dry season minimum (NO₃⁻ and K⁺). Solute dynamics in soil solutions and stream water suggest that mixing of drainage waters from bedrock and soil sources regulate stream water solute concentrations. Patterns are further altered by the leaching of solutes accumulated in the soil over the summer period of desiccation and the temporal discoupling of nutrient cycles that occurs due to differences in the timing between vegetation growth (late spring) and leaching (early winter). Solute concentrations are remarkably similar between watersheds with varying bedrock types, with the exception of nitrate, sulfate and bicarbonate. Three watersheds have nitrogen-bearing metasedimentary bedrock that contributes to elevated nitrate concentrations in stream waters. Watersheds whose bedrock includes mineralized veins of sulfide and carbonate minerals similarly have greater sulfate and bicarbonate concentrations in stream water. Hydrobiogeochemical processes are highly dynamic at the seasonal and storm-event temporal scales and spatially complex at the watershed scale making management of stream water chemical composition, such as nitrate concentrations, very challenging.     

我国江淮流域近40年异常初终霜冻的分析

该文用地面最低温度资料，以≤0℃作为霜冻指标，定量地确定出现异常霜冻的判别标准，研究了近40年初终霜冻异常的气候特征。结果表明:初终霜冻的异常明显存在地区差异。其变化周期以2～3年和准12年最普遍。其偏离均值大致有两种波型:反向变化和同向变化。前者在淮河流域较突出，后者在长江流域较普遍。当其出现反向变化趋势，且二者偏离均值达最大时，该时期为初霜冻异常偏早(偏晚)，终霜冻异常偏晚(偏早)的活跃期。同样，当初、终霜冻出现同向变化时，初、终霜冻异常活路期亦呈现同向变化。     

渍害遥感识别的基本原理与方法

本文论述了渍害遥感识别的主要标志，通过土壤热惯量、土壤含水量及土壤温度等渍害相关因子的讨论，阐明了渍害遥感识别的基本原理及几种主委方法。由于渍害涉及诸多因素，本文给出了以地学相关分析为基础的渍害判别模型。本研究表明，用遥感方法研究渍害是切实可行的。     

Thermal convection of soil air on hillsides

Although diffusion is usually considered to be the main transport process for volatile constituents in the unsaturated zone of soils and other surficial materials, an alternative process of thermally driven convection may be significant, especially on hillsides and over irregular bedrock. Convection in this mode is driven by buoyancy forces arising from differences in soil-air density in a temperature gradient. For bodies with sloping boundaries, the conventional Rayleigh criterion is not directly applicable, so that flow of air is possible in a wide variety of situations. Numerical simulations for several simple cases show that air convection is expected within relatively permeable materials such as sandy soils, gravel deposits, and talus on slopes.