Topographic zonation of infiltration in the hilly loess region,north china

Field infiltration tests using portable rainfall infiltrometers were conducted in the Wangjiagou experimental basin in the hilly loess region of north China. Based on data collected at 27 sites, a topographic zonation of infiltration characteristics was observed. The average steady infiltration rate and the average ponding time decreased from the hilltop to the hillslope and further decreased to the gully wall. Such a zonation is closely related to the variations of topography, soil and land use conditions in the study area. A general infiltration model is proposed. Collected field data are used to establish the applicability of the proposed model in the study area.     

Formation of asymmetrical loess gullies in the northeastern loess plateau of China

Loess gullies are the most active and changeable landform unit on the Loess Plateau of China. Under the influence of inhomogeneous internal and external forces, various gully morphologies have been identified as specific forms of asymmetrical loess gullies in the northeastern Loess Plateau. Thus, the formation mechanisms of asymmetrical gullies should be examined to better understand the gully evolution processes in this area. In this study, a typical asymmetrical gully area and its geological background in the northeastern Loess Plateau are investigated. Then, the asymmetrical gullies are extracted and ordered under different watershed hierarchies using 5 m horizontal resolution digital elevation models. The asymmetrical gullies are characterized using the gully deviation index and gully asymmetrical coefficient to quantitatively and qualitatively describe the gully formation from the perspective of gully morphology. Subsequently, environmental factors, such as the bedrock, climate, vegetation and interactions with neighbouring watersheds, are combined to achieve an in-depth understanding of the mechanisms of asymmetrical gully formation. The results show that most watersheds shift to the right side of the watershed geometric centre line, thereby forming a specific asymmetrical gully morphology. The phenomenon in which the asymmetrical degree characteristics decrease with the increase in drainage area suggests evident morphological differences on both sides of the main channel on a small scale, and relatively weak morphological differences on both sides of the main channel on a large scale. The degree of loess gully asymmetry appears higher in the area where only the windward slope is covered by loess than in areas where all slopes are covered by loess. The interaction between adjacent watersheds also influences the formation of asymmetrical gullies. These results support the understanding of asymmetrical gully formation in relation to the underlying bedrock structure and gully reorganization, thereby contributing to the development of process-based gully evolution models.     

The loess record in southern Tajikistan and correlation with Chinese loess

In the present study, the Chashmanigar loess–soil sequence in southern Tajikistan is studied; this loess section has a paleomagnetic basal age of about 1.77 Myr. Magnetic susceptibility, color reflectance and grain size were systematically measured for closely spaced samples from the section. Paleosols consistently have a finer grain size distribution, higher magnetic susceptibility, redder color reflectance and lower dust sedimentation rate than loess horizons, suggesting a colder, drier and dustier environment during glacial periods than in interglacial periods. The grain size record was tuned to variations in obliquity and precession of the Earth’s orbit. The resulting magnetic susceptibility, grain size and color reflectance time series all show well-expressed astronomical periodicities during the Pleistocene. The mid-Pleistocene climate transition, characterized by a shift of dominant climatic periods from 41 kyr to 100 kyr at about 1.0–0.8 Myr, is clearly documented in these proxy records. Comparison of the Chashmanigar loess record with the Lingtai loess section in China and the ODP site 677 δ¹⁸O record shows that during the entire Pleistocene, the climate cycles recorded by the Central Asian loess can be well correlated to the Chinese loess and deep-sea oxygen isotope records. It is suggested that alternations of loess and soil horizons both in Central Asia and China could be basically forced by global ice volume variations, although different wind systems have controlled the Pleistocene loess transport and sedimentation in the two areas.     

最大峰值加速度与有效峰值加速度的大小比例关系及影响因素探讨

分别以最大峰值加速度(以下简称PGA)和有效峰值加速度(以下简称EPA)为参数,对金沙江流域上12个工程场点进行了地震危险性分析,得到了各个场点在不同的年超越概率下的基岩PGA和EPA值。通过对PGA、EPA值比较分析认为:PGA与EPA值的大小比例关系主要受年超越概率大小的影响,当年超越概率较大时,表现为PGA>EPA;当年超越概率较小时,PGA与EPA的比例关系还与场点周围的潜源分布形式及潜源的震级上限的大小有关,不同的年超越概率、不同的潜源分布形式和震级上限,可使PGA>EPA,也可使PGA相似文献   

黄土塬覆盖区的层析反演静校正方法研究

我国北方地区黄土塬覆盖区的静校正问题是地震数据处理中的难点问题之一.黄土塬表层覆盖巨厚黄土,高差起伏较大,地震静校正问题严重;而且黄土塬覆盖区的潜水面普遍较深,常规折射静校正方法无法取得令人满意的处理效果.本文针对黄土塬覆盖区的静校正难题,研究层析反演静校正方法在黄土塬地区的适用性和可靠性.层析反演静校正利用地震波初至走时数据、通过迭代反演的方法构建速度模型,进而依据所得的近地表速度模型对地震数据进行静校正处理.本文的迭代反演采用同步迭代重构算法（SIRT）,并且对同步迭代重构算法进行了改进,使得层析反演的迭代过程趋于稳定.但是,因为黄土塬覆盖区地表高程的横向变化剧烈,相邻检波点的高差及其静校正量有时差异很大,在运用层析静校正求取长波长静校正量的同时,还需采用初至波剩余静校正方法求取短波长静校正量.实例证明,综合应用依据初至波走时数据的层析静校正和剩余静校正方法,同时计算长波长和短波长的静校正量,能够有效地解决黄土塬覆盖区实际地震资料的静校正问题.

     

Comparison of infiltration models with regard to design of rectangular infiltration trenches

ABSTRACT

Guidelines for the design of infiltration trenches of rectangular cross-section are compared. Four concepts of infiltration into a native soil from linear soakaways of rectangular cross-section are discussed. The results of calculations using analytical equations are compared with numerical two-dimensional (2D) simulations using HYDRUS computer code and field measurements. Satisfactory agreement is achieved for Kozeny’s concept of infiltration and the free-surface approach, applied to a trench in a highly saturated sandy loam. Theoretical solutions, neglecting matric potential, suggest that the mean infiltration rate along the wetted perimeter of a rectangular trench varies in the range 1.0 to 1.5 of the value of saturated hydraulic conductivity.     

Comparison of infiltration models

Fourteen popular, representative infiltration models, some physically based, some semi‐empirical and some empirical, were selected for a comparative evaluation. Using the Nash and Sutcliffe efficiency criterion, the models were evaluated and compared for 243 sets of infiltration data collected from field and laboratory tests conducted in India and the USA on soils ranging from coarse sand to fine clay. Based on a relative grading scale, the semi‐empirical Singh–Yu general model, Holtan model and Horton model were graded respectively as 6·52, 5·57 and 5·48 out of 10. The empirical Huggins and Monke model, modified Kostiakov and Kostiakov model were graded as 5·57, 5·30 and 5·22, respectively. The physically based non‐linear and linear models of Smith–Parlange were graded as 5·48 and 5·22, respectively. Other models were ranked lower than these models. All the models generally performed poorly in field tests on Georgia's sandy soils, except the Robertsdale loamy sand. Copyright © 2003 John Wiley & Sons, Ltd.     

Time derivative of earthquake acceleration

Unlike acceleration, velocity, and displacement, the time derivative of acceleration (TDoA) of ground motion has not been extensively studied. In this paper, the basic characteristics of TDoA are evaluated based on records from the 1999 Chi-Chi, earthquake (Mw 7.6) and one of its aftershocks (Mw 6.2). It is found that the maximum TDoA at a free-field station was over 31,200 cm/s3 (31.8 g/s); and the duration of "strong" TDoA, between the first and the last time points exceeding 2,000 cm/s3 (2 g/s), was almost one minute near the epicenter area. Since ground TDoA sensors are not commonly available, the time series are calculated by direct numerical differentiation of acceleration time series. Relative error analysis shows that the error is non-transitive and total error is within 4%. The density function of TDoA amplitude, frequency content and spatial distribution of peak ground jerk (PGJ) are evaluated. The study also includes examination of some TDoA responses from a seven-story building and comparison of ground TDoA with the limit TDoA used in the transportation industry for ride comfort. Some potential impacts of TDoA on humans have also been reviewed.     

黄土的湿陷和震陷

黄土的湿陷性和震陷性分别是黄土在遇水和地震作用下产生的岩土灾害。黄土湿陷性评价及防治已经相对成熟。有些专家试图联系二者,以便解决黄土震陷性的工程评价和处理。本研究中,作者分析了黄土湿陷性与震陷性之间的联系与差异。研究认为,二者的产生都基于黄土的亚稳态结构,都是黄土架空结构破坏所引起,但其触发机制却是不同的。湿陷性产生的主要原因是吸力丧失,而震陷性主要由黄土在动荷载作用下的土体剪切破坏所导致。因此,关于二者之间的联系还不存在坚实的物理基础。     

Experimental study of loess disintegration characteristics

Loess structures with large joints and fissures often undergo natural disintegration when subjected to contact with water. The slaking of loess results in the formation of loess gullies, caves, and landslides. To study the disintegration properties and the factors influencing them, we carried out field and laboratory tests. First, we carried out an in situ disintegration test using different sample shapes obtained from Heifangtai and analysed the effect of soil sample shape on loess disintegration. We then developed an improved disintegrator and tested the effect of different factors on the disintegration of loess. The effects of water content, salinity, and composition on disintegration are discussed. The results show that the loess disintegration process can be divided into three broad stages – wetting, softening, and subsidence – the disintegration is mainly concentrated in the third stage, while the first two stages are short and show very weak disintegration. The main factors influencing the disintegration of loess samples are shape, size, and clay mineral content. During the in situ disintegration test, the edge angles of soil samples are disintegrated, to soften all their edges. Disintegration duration increases with increasing sample size, but the extent of disintegration was found to decrease. Disintegration duration is inversely proportional to the loess disintegration rate. The loess disintegration rate is positively correlated with water temperature within a certain range; however, the reverse is observed with soil sample size and initial water content, and salinity was found to have little effect on the disintegration rate. Higher clay content of cohesive soil and weaker permeability leads to a slower disintegration rate. Additionally, lower cementation may easily cause loess disintegration. © 2019 John Wiley & Sons, Ltd.     

粘粒含量对甘肃黄土抗液化性能的影响

甘肃黄土是介于砂土与粘土之间的一种过渡性土壤,它具有砂土的某些特性,又具有粘土的某些特性,存在一定的粘塑性。通过对含粘粒黄土所做的实验研究,包括：粘粒含量不同的原状土样所做室内的动三轴试验、激光粒度分析试验、化学分析和电镜扫描,试验结果分析对比后,得出了含粘粒黄土抗液化性能的特性。并得出以下结论：（1）粘粒颗粒级配不同,也引起黄土动力稳定性的变化;（2）液化强度与粘粒含量并非呈单调增加关系,无论固结压力如何,粘粒含量Pc=15％左右时抗液化性能最低;（3）粘粒含量为一定值时,液化孔压比偏大,偏离这一值时,液化孔压比偏小。     

First high-resolution luminescence dating of loess in Western Siberia

The south of Western Siberia is an important part of the Eurasian loess belt, containing an extensive record of Quaternary landscape and climate evolution in up to 100 m thick loess deposits with as many as 10 pedocomplexes. However, this important Quaternary archive lacks a reliable absolute chronology, and this has prevented the linking of the widely accepted regional chronostratigraphic correlations with those of other parts of the Eurasian loess belt. Here we present the first results of detailed luminescence dating of the Late Pleistocene loess-palaeosol sequence at the Western Siberian stratotype section of Lozhok. According to the classical regional chronostratigraphic scheme, this sequence records the main stages of the environmental evolution of the region, including three palaeosols correlated with the warming stages of MIS 5e, MIS 5c and MIS 3. Our absolute chronology is based on 38 new luminescence ages (OSL, IR₅₀, pIRIR₂₉₀). Good agreement between the OSL and pIRIR₂₉₀ ages suggests sufficient bleaching before deposition. The resulting chronology reveals that, rather than being only Upper Pleistocene in age, the loess-palaeosol sequence at Lozhok actually formed in the Middle and Upper Pleistocene. The ages of individual horizons do not correspond to the previously accepted stratigraphic units and morphological features of pedocomplexes. Our Bayesian chronological model reveals remarkable variation in dust accumulation and preservation at the site. The new results unambiguously identify the presence of an erosional boundary with a hiatus lasting ∼90 ka. The upper pedocomplex, immediately below this discontinuity, formed in sediment deposited between 131 ± 9 ka and 122 ± 11 ka and clearly corresponds to MIS 5. The lower pedocomplex is found in sediment deposited between 240 ± 12 and 199 ± 9 ka, and correlates closely with MIS 7. These new findings demonstrate the urgent need for a wider programme to date the main stratotypes of loess-palaeosol sections in Western Siberia. Only then can the global implications of the regional climate record in this important continental-scale archive be correctly interpreted.     

A probabilistic investigation of infiltration in the vadose zone: proposal for a new formula of infiltration rate

The infiltration rate in the unsaturated zone is analysed from a probabilistic point of view. It is shown that the empirical formulas of Horton and Kostiakov, without apparent physical basis, are explained in a probabilistic approach. Horton's formula reflects a Markovian process contrary to Kostiakov's formula. This approach made it possible to explain why Kostiakov's formula is more powerful than that of Horton. A new equation of infiltration is proposed. The three formulas were compared, for four types of soil, with the model of van Genuchten based on the Richards equation. Copyright © 2006 John Wiley & Sons, Ltd.     

Two-stage acceleration of solar cosmic rays

On the basis of data from the Radio Solar Telescope Network (RSTN), as well as the Geostationary Operational Environmental Satellite (GOES) and the WIND spacecraft, for the period from 1989 to 2006 covering 107 flare events, we investigated the relationship between the intensity of solar cosmic rays and parameters of continuum radio bursts (25?C15400 MHz), as well as type II radio bursts in the meter and decahectometer wavelength ranges. Proton fluxes with energies E _p > 1?100 MeV were calculated with regard to a reduced heliolongitude. The maximum correlation between solar cosmic rays and solar parameters of microwave bursts was 0.80. Its value was no more than 0.40 for the drift rate of type II bursts and 0.70 for the compression rate of coronal shock waves. Based on linear regression equations, we estimated the contribution of coronal shock waves to the acceleration of protons. We found that major acceleration processes occur in the area of burst energy release and complimentary processes occur at the fronts of coronal shock waves. The contribution of the latter to the acceleration process increases significantly with proton energy.     

黄土的钻孔剪切试验特性研究

为研究钻孔剪切试验在黄土中的应用效果,在西安东郊典型的Q₃黄土中进行不同首级法向应力和不同法向应力增量条件下钻孔剪切试验。试验结果表明,抗剪强度随法向应力增大呈曲线形式增大,存在某一临界法向应力值,超过该值后抗剪强度与法向应力之间呈良好的线性关系,能较好地符合摩尔-库仑强度准则,所测得的抗剪强度参数相差较小;在分级加载试验中,法向应力增量越小,达到同一法向应力时的抗剪强度越大;分别加载试验与分级加载剪切试验相比,在相同法向应力下测得的抗剪强度值偏小,随法向应力增大,偏离程度增大;当法向应力较小时,剪切齿难以压入硬土中,导致所测得的黏聚力偏小、内摩擦角偏大,为此建议开发适合不同软硬土质的剪切板,并增加法向位移观测系统,用于判断法向应力施加过程的齿尖压入孔壁情况。     

The historical acceleration of the earth

In this paper, we review the current state of knowledge about the acceleration of the Earth's spin, and about the closely related acceleration of the Moon. It is now established at a high confidence level that the acceleration of the Moon, when taken respect to Universal time, has changed by a large amount, and that it has even changed sign, within historic times. This almost certainly means that the acceleration of the Earth's spin has also changed by a large amount. At present we do not have enough information to say whether the changes have been in the contributions from tidal friction, in the contributions that do not arise from tidal friction, or both. Further, we do not know yet whether or not the variations in the Earth's rotation can account for the observed fluctuations in the longitudes of the Sun, the Moon, and the planets.