Vertisols with Gilgai Microtopography: Classification and Parameters of Microtopography and Morphological Types of Soils (a Review)

Data on clayey swelling soils with gilgai microtopography are systematized. Classifications of gilgai microtopography representing regularly alternating microhighs and microlows are discussed, and its geometric parameters under different landscape conditions are considered. Gilgai microtopography is developed within flat or slightly inclined elements of the mesorelief composed of swelling clays of different geneses. These materials are characterized by the high swelling–shrinking capacity upon wetting–drying cycles owing to the predominance of clay minerals of smectitic group. These processes are especially pronounced under conditions of the impeded surface drainage and contrasting of the wet seasons with strong soil moistening by atmospheric precipitation or surface water and the seasons with deep soil drying under the impact of physical evaporation and transpiration. The areas with gilgai microtopography have complex soil cover patterns composed of Vertisols and vertic soils. Their formation is related to lateral movements of solid material in the soil profiles and along the curved soil surface. The morphological types of soil complexes in such area are systematized.     

Origin and terminology for gilgai in Australia

The names given to soil micro-relief forms are reviewed and a rational classification is proposed. The term gilgai should be confined to surface features, and a new term, mukkara, is proposed for the associated sub-soil features. By analogy with geological structures, it is suggested that gilgai/mukkara are piercement structures resulting from differential surface loading.     

Micromorphology, submicroscopy and microprobe study of carbonate pedofeatures in a Vertisol gilgai soil complex, South Russia

Carbonate nodules and soft masses were studied in a gilgai soil complex in the North Caucasus, South Russia. Microrelief with an amplitude about 30 cm resulted in a wetter environment with stronger leaching in the microlow and a drier pedoenvironment with carbonate accumulation in the microhigh. Various macroforms of carbonate nodules and soft masses were identified in soil pits and sampled for micromorphology, scanning electron microscopy (SEM), and microprobe analyses to better characterize them and elucidate their pedogenesis. Common and unique attributes were described for carbonate pedofeatures depending on loci in gilgai soil complex. The most probable hypothesis for their formation is as follows. Nodules represent early pedogenic products that were initiated before gilgai formation. Modern hydrology resulted in variability of dissolution/recrystallization of the nodules along the gilgai microtopography. The variability in degree of impregnation, aggregation into pellets, and presence of hard nodular cores reflects several generations of soft masses.     

The genesis of vertisols with gilgai microtopography: A review

Different hypotheses about the genesis of gilgai microtopography and corresponding soil complexes with clayey swelling soils are considered in this review. Their diversity is stipulated by specificities of the objects themselves and by the history of studies of the composition, properties, regimes, and landscape conditions of the areas with Vertisols in different countries. Most of the hypotheses about the genesis of Vertisols with the gilgai microtopography suggest that strong swelling–shrinking processes take place in these soils in the course of moistening–drying cycles; the origin of shear stress in the soils, its spatial patterns, and the particular ways of translocation of the soil material are discussed. At the early stage of Vertisol studies, a hypothesis about the leading role of the process of “self-swallowing” of the soils as a result of filling of open cracks with the material from the upper soil horizons was popular. However, numerous facts suggest that the intensity of this process is relatively low, so that it cannot play the major role in the gilgai formation and cyclic changes in the thickness and properties of the soil horizons in Vertisols. Another important mechanism is the uneven moistening and drying of the whole soil volume resulting in the irregular distribution of inner tensions in the soil with the development of shear stress and plastic deformation of the soil mass. The hypotheses suggested in the recent decades are based on the models of soil mechanics. A number of hypotheses consider possible alternation and duration of evolutionary stages of the development of Vertisols with the gilgai microtopography.     

Structural analysis and mechanical origins of gilgai at Boorook,Victoria, Australia

Gilgai microrelief at an undisturbed site is described. Surface and subsurface structural patterns in a duplex soil (solodic planosol) are analysed using principles and techniques adapted from structural geology. The microrelief is situated on a gently dipping regional slope and some mounds show evidence of surface erosion. Large cracks on the ground surface have an orientational relationship with the strike and dip of the regional slope. Some of the surface cracks may post-date the original time of gilgai formation. Beneath the microrelief surface a lenticular gravel layer of sedimentary origin is folded into a series of anticlines and synclines. Compositional layers also have fold-like geometries. Two-dimensional crack pattern analysis on a vertical section through several mounds, revealed upwards fan-like and concentric-convex patterns, where upwards movement had occurred. Three-dimensional measurements were made on monoliths and on an undisturbed block sample. The mean slickensided shear plane dip below a mound is 43° (standard deviation 9°). There is a statistical decrease in shear plane dip with depth, which is in partial agreement with soil mechanics theory. Shear planes are distributed from 0.3 m below ground surface down to a projected limit of 1.3 m to 1.8 m which is shallower than the limits reported for slickensided cracks in non-gilgai soils of Israel. The mechanism proposed to explain the surface and subsurface structures involves moisture concentrations that focus near, and below pre-gilgai surface cracks and a gravel lens. The moisture interacts with a swelling component and a triaxial state of stress is achieved. Differences between lateral and vertical stresses due to swelling pressures and overburden loads are sufficient to cause small, inclined shear displacements in definable depth zones. Accumulations of vertical movement components arising from the shear displacements, and vertical sliding of blocky non-sheared units nearer the ground surface, cause the gilgai microrelief and fold-like deformations in the soil profile. Zones of possible downward movement are located at the margins of mounds. Mechanical models proposed in the past are assessed in the light of the Boorook findings. Some proposals appear to be mechanically unlikely for the Boorook gilgai.     

Properties and regimes of vertisols with gilgai microtopography (a review)

Data on the morphology and spatial distribution of slickensides and cracks, particle-size distribution, the organic carbon content, the content and forms of carbonate concentrations, and physical and physicochemical properties of Vertisols with the gilgai microtopography are systematized. Relatively scarce information on the functioning regimes of gilgai soil complexes (their temperature and moisture conditions, redox potential, vertical and horizontal deformations, and soil density changes) is discussed. Common properties of gilgai soils are the clayey texture of their profiles and the high portion of smectitic minerals specifying the high shrink–swell capacity of the soil material. The most important specificity of soils with the gilgai microtopography is a significant horizontal differentiation of the soil profiles with alternation of bowl-shaped morphostructures with a thick dark layer without carbonates in microlows and diapiric morphostructures composed of the rising material of the lower layers with diverse carbonate concentrations on microhighs. Data on the spatial distribution of soil properties within the gilgai microcatenas can be applied in the studies of the genesis and evolution stages of the gilgai soil complexes.     

Modelling soil salinity across a gilgai landscape by inversion of EM38 and EM31 data

The soil in arid and semi‐arid areas is often markedly saline, which can severely limit agricultural productivity. Increasingly, geophysical methods are being implemented to map the levels and areal extent of soil salinity. One of the most effective methods is electromagnetic (EM) induction with instruments designed to measure apparent soil electrical conductivity (EC_a). This study describes the generation of electromagnetic conductivity images (EMCIs) by inverting EC_a data obtained with the EM38 and EM31 devices along two closely‐spaced transects by the EM inversion approach in the EM4Soil package. The EM38 EC_a data are shown to be a more effective predictor of soil EC_e. Calibration equations based on calculated true electrical conductivity (σ) and measured electrical conductivity of a saturated soil‐paste extract (EC_e) provide reliable estimates of EC_a. The patterns of σ in a test of the method in soil developed over thick alluvium on a clay plain in central New South Wales, Australia, compare favourably with existing pedological mapping; the mounds and depressions of gilgai were strongly differentiated from the more sandy alluvial sediments that characterize prior stream channels. The overall approach is potentially useful for generating a single calibration equation that can be used to predict EC_e at various depths in the soil. Improvements in EMCI modelling can also be sought by joint inversion of EM with other geophysical datasets.     

基于TCR传热原理的混凝土复合保温衬砌渠道防冻胀效果研究

中国北方寒冷地区广泛采用保温措施进行渠道防冻胀,在苯板保温防冻胀设计中铺设厚度一般根据半理论半经验确定,并没有考虑衬砌板与保温板接触热阻及交错布置对保温性能与削减冻胀的影响。该文依据固体材料接触热阻(thermal contact resistance,TCR)原理与压力相关的传热本构模型,提出了混凝土复合保温衬砌新型式。通过ABAQUS有限元软件采用热力耦合模拟将其与普通型式的苯板保温渠道进行比较。结果表明:与普通保温衬砌渠道相比,外界负温时,复合保温衬砌的保温及消减冻胀力效果显著。理论上复合保温衬砌冻胀量消减40%以上,法向冻胀力减少66%,切向冻结力减小58%。对寒区衬砌渠道保温防冻胀设计提供了相应的理论参考。     

山西省盐渍土的类型及其改良途径

山西省位于黄土高原东部;与黄土高原西部有很大的差异,主要表现为境内多山,而又多山间盆地。吕梁、太行两山系,约作南北向贯穿全省。山边均有不同高度的黄土丘陵及黄土阶地,组成高原特征;在两山系间由于陷落关系,形成一系列大、小不同的地塹式盆地,亦约作南北向罗列,仅南端偏西,北端略偏东而已。这些盆地再被东西向山地分割,因而形成互不相联的分割盆地,如大同盆地与忻定盆地为雁门关(鳗头山)山地分割。     

Morphology,Radiocarbon Age,and Genesis of Vertisols of the Eisk Peninsula (the Kuban–Azov Lowland)

Data on the morphology and radiocarbon ages of humus of dark vertic quasigley nonsaline clayey soils with alternating bowl-shaped (Pellic Vertisols (Humic, Stagnic)) and diapiric (Haplic Vertisols (Stagnic, Protocalcic)) structures are discussed, and the genetic concept for these soils is suggested. The studied soils develop on loesslike medium clay in the bottom of a large closed depression on the Eisk Peninsula in the lowest western part of the Kuban–Azov Lowland. The lateral and vertical distribution of humus in the studied gilgai catena displays a lateral transition of a relatively short humus profile of the accumulative type with a maximum near the surface and with a sharp increase in ¹⁴C dates of humus in the deeper layers within the diapiric structure to the extremely deep humus profile with a maximum at the depth of 40–80 cm, with similar mean residence time of carbon within this maximum, and with a three times slower increase in ¹⁴C dates of humus down the profile within the bowl-shaped structure. The development of the gilgai soil combination is specified by the joint action of the lateral–upward squeezing of the material of the lower horizons from the nodes with an increased horizontal stress toward the zones a decreased horizontal stress, local erosional loss of soil material from the microhighs and its accumulation in the adjacent microlows, leaching of carbonates from the humus horizons in the microlows, and the vertical and lateral ascending capillary migration of the soil solutions with precipitation of calcium carbonates in the soils of microhighs.     

混凝土防渗渠道冬季输水运行中冻胀与抗冻胀力验算

为了明确渠道冬季输水时防渗衬砌层结构的抵抗渠床基土冻胀破坏作用的能力,该文理论分析了大气负温下,介入刚性防渗面层对渠基土冻胀的约束,得到作用于坡板上冻胀力的作用形式为法向冻胀力和指向坡顶的切向冻胀力,对被视为底端简支、板内无接缝、受冻胀作用的构件受力进行理论分析,得到冬季输水渠道边坡板的冻胀问题属于非垂直非全周的冻拔问题的结果,并进一步根据力学基本原理研究了刚性面层(衬砌层)承受荷载力的求解方法。依据桩的抗冻拔验算和拉弯构件的强度验算可实现冬季输水渠道抗冻胀力的计算,建立了适用于防渗渠道刚性衬砌结构设计的方法,为冬季输水梯形混凝土防渗抗冻胀渠道衬砌层厚度的准确确定提供了计算方法。     

Mountain-meadow soils of the highlands in the Western Caucasus

The published and author’s data on soil-forming conditions, morphology, substance composition and physicochemical properties, total chemical and mineralogical composition, and micromorphology of mountain-meadow soils of the Western Caucasus Range are analyzed. On the basis of the analytical data obtained, the transformation of minerals and features of chemical element profile patterns developed in the course of soil formation are characterized. The main processes accompanying the transformation of mineral and organic parts of the soil mass and migration of soil-formation products are described. Soil formation is shown to be accompanied by two major elementary soil processes developing with participation of soil biota: humus accumulation and clay formation. Ways to improve the classification of mountain-meadow soils are proposed.     

Mechanics of mole drainage channel deterioration

The nature of the soil disturbance caused by standard mole ploughs is described and the major types of failure mechanism causing channel deterioration are identified. Direct links have been established between the kinds of mole plough disturbance and many of the channel failure mechanisms, opening up possibilities for the future for modifying the implement to improve channel stability.
Following mole channel observations on six different clay soil sites, the influence of soil conditions at channel installation and subsequent weather patterns on long-term channel stability were determined. The extent of the ageing period between channel formation and its first significant wetting and weather extremes later, were identified as being particularly important influences on the subsequent life of the channel.     

基于昼夜温度变化的混凝土衬砌渠道冻胀有限元分析

为了掌握衬砌渠道冻胀量及冻胀力随昼夜气温变化的发展规律及冻胀破坏极限状态,根据冻土力学及冻土物理学理论,利用有限元软件ANSYS按瞬态温变模式加载温度,对衬砌渠道冻胀过程进行数值模拟,研究了其温度场和冻胀变形及法向冻胀力与切向冻胀力随时间的变化规律。结果表明：渠道冻融破坏除因渠基土冻胀外,阴阳两坡的温度、冻胀变形、冻胀力既不均匀不对称变化又不同步,也是渠道冻胀破坏的重要原因;阳坡滞后阴坡约15 d冻结,最大冻胀量及最大冻胀力滞后日平均最低气温约4 d,日内最大冻胀量及最大冻胀力滞后日最低气温约1 h;模拟结果与野外观测资料基本吻合,但比稳态数值模拟结果偏大,表明了运用瞬态数值模拟进行渠道抗冻胀设计的正确性和合理性。     

开放系统预制混凝土梯形渠道冻胀破坏力学模型及验证

预制混凝土衬砌渠道在中国北方寒冷地区得到普遍应用,而其在高地下水位条件下的冻胀力学分析尚无简捷、可靠的方法。该文假定渠道基土服从Winkler假设,从而在特定地区相似的土质、气候条件下衬砌板各点的基土冻胀强度仅与相应点的水分补给强度有关,结合冻胀力、基土冻胀率和地下水埋深三者相互间的函数关系,提出了一种计算渠道衬砌冻胀受力分布的方法。将其应用到一类预制板尺寸适中的预制混凝土衬砌梯形渠道中,建立了冻胀破坏力学模型。结合力学分析和工程实践,对预制混凝土衬砌结构可能发生的冻胀破坏形式和原因进行了分类,并确定了相应的冻胀破坏验算控制截面,提出了相应的冻胀破坏判断准则。采用单位荷载法提出了一种对板间接缝处法向冻胀位移进行直接验算的方法。最后,结合工程实例进行了计算,结果表明,模型合理可靠,可为工程设计提供一定的参考和理论依据。     

基于部分保温法的渠道保温板厚度计算与数值模拟

保温板是北方渠道常用的保温材料,其铺设厚度一般通过经验或全部保温法的热工计算确定,工程造价较高。该文以聚苯乙烯泡沫板为例提出了部分保温法,分析了其合理性和适用条件之后,基于热阻等效原理给出了其计算方法,同时选取新疆车排子西干渠进行部分保温法保温板厚度设计,并与全保温法计算量进行比较。结果表明：部分保温法比全保温法降低了19%的工程造价。最后利用ANSYS有限元程序对原渠道和部分保温渠道进行热力耦合数值模拟。数值分析表明：部分保温渠道的最大冻胀量为1.35 cm小于设计允许值2 cm,满足抗冻胀要求,部分保温法是可行的;其冻胀量、冻胀力不但分布更加均匀,且被大幅削减,其中阴坡被削减达80%以上。     

刚性衬砌渠道不同纵缝削减冻胀效果的数值模拟

为了探明刚性衬砌渠道设置不同纵缝削减冻胀的机理及量化影响规律,提出削减冻胀的有效工程措施,该文利用有限元软件ADINA对坡脚处、1/3坡高处、宽底板的中心处分别设纵缝和不设纵缝的刚性衬砌渠道冻胀过程进行数值模拟,分析了温度场、变形场及应力场,特别研究了衬砌板的冻胀变形及其法向和切向冻胀力分布规律。通过对比分析表明：合理设置纵缝不仅能降低最大冻胀量61%,最大法向冻胀力45%,最大切向冻胀力32%,而且可使冻胀分布更加均匀,显著削减刚性衬砌渠道的冻胀破坏;削减冻胀的显著性依次是1/3坡高处设纵缝、坡脚处设纵缝、不设纵缝;但针对坡板较短、底板较宽情况在坡脚及底板中心处都设纵缝效果最好,降低最大冻胀量67%,最大法向冻胀力59%,最大切向冻胀力45%;数值模拟结果与工程实践基本一致。研究结果表明渠道冻胀的有限元数值模拟能够为季节冻土区渠道工程设计及力学计算提供参考和科学依据。     

Simulation modelling of variable patterns of water movement through a cracking clay soil

Abstract. This paper describes the development and application of a simple empirical model describing differences in water movement through a cracking clay soil at Brimstone Farm, Wiltshire, UK. An extended data set comprising readings of soil water tension has been collected from an area of 9 m² instrumented with 4 nests each of 3 tensiometers. The cracks are responsible for considerable differences both in water pathway and flow magnitude. Variations in water flow suggested by changes in soil-water tension are described by a model developed using 'ModelMaker' and applied separately to each profile nest. The model envisages water flow to occur through three soil layers, and to be partitioned into matrix and macropore flow components. Water is lost via drainage to clay tile drains at 60 cm depth. Water flow between layers is described as a function of the hydraulic gradient using Darcy's Law, with additional drainage from structural voids within the soil. Differences in the effective hydraulic conductivity describing slow and rapid flow components equate to macro and matrix flow for each tensiometer profile. The results illustrate heterogeneous patterns of flow through a soil block and demonstrate that a comparatively simple model is able to represent satisfactorily water flow dynamics through a cracking clay soil.     

Within-storm soil surface dynamics and erosive effects of rainstorms

This study deals with the characteristics which make a rainstorm an event that can produce intense erosion and even trigger the formation of a badlands site. In order to keep the presentation closely linked to a real situation, a rainstorm which took place on an experimental farm equipped for soil erosion studies was selected. The effects of the erosive rainstorm, which fell on dry antecedent moisture conditions, are given in terms of total rill erosion and rill cross-section along the slope. Unfortunately, the data collected did not answer the basic question, i.e., what combination of factors makes a rainstorm critical? A set of rainfall simulation experiments was therefore carried out, in the field and in the laboratory, in order to evaluate the soil surface variations caused by the rainstorm. All the experiments were performed on dry antecedent soil moisture conditions. It was confirmed that the characteristics of the infiltration curve are modified considerably during such rain events. The saturated conductivity of the first thin top-layer is also modified and it can easily decrease by a factor of 10 due to drop impact forces. The runoff coefficient is also influenced by the raindrop impacting energy and it increases sharply with cumulate energy until a maximum value is reached. The surface micro-relief dynamics was also studied. It was very clearly shown that impacting drop kinetic energy is the rainfall characteristic which is linked to random roughness decay. Cumulative rainfall was not able to align all the data in a single trend. The effect of surface micro-relief decay on the rainstorm erosive power was examined using two equations, thus linking Manning's hydraulic roughness to random roughness. Using a simulated runoff over the field plots that were particularly eroded by the rainstorm, it was possible to observe that the runoff drag forces reached values of between 3 and 100 times the ones which would have been calculated if the random roughness had been constant during the same event. Many of the soil surface characteristics that are modified interact with one another and with erosion. Examining each of them in isolation cannot explain the drastic increase in erosivity of a rainstorm, as the latter is the result of the combined effects of all the surface modifications.     

Chemisch-mineralogische und mikromorphologische untersuchung einer eutrophen (Ramann-) braunerde des Budapester Hügellandes

In spite of the fact that Ramann's concept of Braunerde was extensively used throughout the world, some pedogenic processes and soil properties which are important for the formation and existence of Brown Forest Soils (eutrophic brown earths) are still not well known. Hence, a soil was investigated which was classified as a “Braunerde” by Ramann in 1909. The main question was, whether there might be soil constituents such as inorganic amorphous substances (allophanes) which are able to stabilize the brown-earth fabric, or to inhibit clay migration. From chemical data as well as from the magnitude of the pH-dependent CEC, it was deduced that there are no appreciable amounts of allophanes within the soil. The fabric, however, seems to be stabilized by colloid-chemical flocculation of the clay particles caused by large amounts of carbonates and silicates deposited with the parent material (loess). The decalcified solum is still rich in silicates, especially sand and coarse-silt-sized micas and feldspars (60–200 and 20–60 μm fractions, respectively). Since - in comparison - loesses and loess-derived soils of the Central German mountain region contain less silicates, mainly in fine and medium silt fractions (2–6 and 6–20 μm diameter, respectively), the coarser-grained silicates were assumed to be important for maintaining the Ca²⁺ and Mg²⁺ saturation of the soil by continuous weathering and thus stabilizing the brown-earth fabric.Although the soil is saturated predominantly with Ca²⁺ and Mg²⁺ ions, clay migration proceeds within the upper horizons. This was shown by calculation of the amounts of clay formed by breakdown of micas originally present in the parent material (“clay formation balance”), as well as by micromorphological studies. Furthermore, micromorphological studies and x-ray diffraction data gave some evidence for the migration of preferably finest grained montmorillonitic clays (smectites) penetrated by organic substances (humus). This kind of “selective clay migration” was assumed to be caused by high Ca²⁺ (or Mg²⁺) concentrations in soil solution required for flocculation of humus-penetrated (humus-coated) smectites. From the occurrence of these “humus-smectites” the possibility was assumed that the soil studied has been developed from a former Chernozem type.Quantitatively, clay migration does not reach the amounts of clay formation (breakdown of micas) accompanied by precipitation of iron oxides on mineral surfaces (“Verbraunung”). Thus, the soil profile visually and macromorphologically clearly exhibits the features of brown earths. On the other hand, however, some clay migration was observed. Hence, the soil was classified as a “brown earth with some clay migration” (“schwach durchschlämmte Braunerde”).Judging from the results of the “clay formation balance” an appreciable pedogenic (autigenic) clay formation from weathering products of feldspars was excluded for the soil studied.