Increase In Soil Density Research Articles

INFLUÊNCIA DA COMPACTAÇÃO DO SOLO NO CRESCIMENTO DE MILHO (ZEA MAYSL.) EM LATOSSOLO VERMELHO-AMARELO

Soil compaction is a limiting factor to growth and vegetative development, reducing agricultural productivity. In this context, the aim of the present study was to evaluate the effects of the depth of the compacted layer and the level of compaction of a Dystrophic Red-Yellow Oxisolon the growth of maize seedlings. The experimental design was completely randomized in split plots in time, arranged in a factorial 2 ×2 + 1, being two soil densities (1.5 and 1.7 g cm-3), two layers of compacted layer (0 -3 cm and 8 -11 cm) and a control with natural soil density (1.3 g cm-3), with three replications. Hybrid maize AG 1051 were cultivated in columns, over the period of 31 days. During the trial period, were evaluated: the leaf area (LA), the number of leaves (NL), stem diameter (SD), stem length (SL), root volume (RV), leaves dry matter (LDM), stem (SDM) and root (RDM), the absolute growth rate (AGR) and relative (RGR). According to the results, the increase in soil density promoted morphological changes in stem diameter, and the volume of the root, and consequently, the root dry mass and total dry matter. The compression in the surface layer is more harmful to crop growth than in the subsurface layer.

Soil Class, Mechanical Impedance and Irrigation: Impact on Physiological Performance in Green Dwarf Coconut

The objective of this study was to assess the physiological aspects of young green dwarf coconut cultivated in greenhouse as a function of soil class and different compaction levels and moisture conditions. The experiment was carried out in a greenhouse, using a randomized complete block design with nine replications and with 32 treatments in a 2 × 4 × 4 factorial scheme, with two soil classes—Typic Kandiudult and Umbric Dystrochrept, four compaction levels and four soil moisture conditions. Leaf predawn water potential (Ψw), net photosynthetic (A), stomatal conductance (gs), transpiration rates (E) and growth traits were higher in coconut grown in Umbric Dystrochrept soil. Moreover, these plants showed the highest values of maximum quantum yield of photosystem II (Fv/Fm) and leaf ‘greenness' (SPAD reading) was higher, but only in the lowest soil moisture condition, when compared with Typic Kandiudult. Higher soil moisture led to a higher Ψw for both soil classes. Close relationship between SPAD reading and the increase in soil moisture as well as between Fv/Fm and the increase in soil moisture for coconuts grown in Typic Kandiudult soil was observed. Furthermore, good correlations were observed between Ψw and the increase in soil moisture in coconuts grown in both soil classes as well as between Fv/Fm and the increase in soil density in coconuts grown in Typic Kandiudult soil. Effects of soil compaction were not observed on other physiological variables. Overall, green dwarf coconut trees grown in Umbric Dystrochrept soil allowed the higher water storage, which may contribute to increases in circumference, plant height, leaf area and dry weight (leaves, stem and root) linked to high photosynthetic rates.

Arbuscular mycorrhizal fungi on the biomass and nutrition of Urochloa decumbens at different soil densities

Abstract: The objective of this work was to evaluate the influence of arbuscular mycorrhizal fungi (AMF) on the accumulation of shoot and root biomass and on the nutrient contents of Urochloa decumbens grown in soils with different densities. The experiment was carried out in a randomized complete block design, in a 4x2 factorial arrangement: four soil densities (1.0, 1.2, 1.4, and 1.6 kg dm-3) with and without inoculation of AMF, with four replicates. The biomass accumulation (dry matter weight of shoot and roots) and macro- and micronutrient contents of U. decumbens were determined at different soil densities. The mycorrhizal colonization of the plants was evaluated, and the number of mycorrhizal spores present in the soil was determined. The biomass accumulation of shoot and roots and macro- and micronutrient contents, as well as the number of mycorrhizal spores in the soil, were negatively affected by the increase in soil density. Only root biomass increased with AMF inoculation. There was no interaction between soil density and inoculation for shoot and root biomass accumulation. Arbuscular mycorrhizal fungi influence the accumulation of biomass in the roots and of N and Ca contents in the shoots of Urochloa decumbens even at the highest soil densities.

Centrifuge model testing on reliquefaction characteristics of sand

Soil can liquefy more than once (reliquefaction) when earthquakes occur in succession. A distinctive characteristic of soil reliquefaction behavior is that reliquefaction resistance may be lower than the first liquefaction occurrence, despite an increase in soil density caused by the drainage of groundwater; this characteristic has been proven in some previous laboratory and 1g shaking table tests. The study presented in this paper addresses an attempt to verify whether this decreasing tendency of reliquefaction resistance still exists in centrifuge model tests, which can simulate the gravitational stress of the actual ground under ng conditions. Moreover, the effects of two essential factors including grain size characteristics and the magnitude of the earthquake motion on the reliquefaction behaviors were investigated. The testing results demonstrated that the reliquefaction resistance tends to decrease in terms of the development speed of excess pore water pressure (EPWP), which is because the ground can reliquefy more quickly in the 2nd and subsequent shaking events than in the 1st shaking event. However, the ground settlement caused by the first liquefaction is still larger than that caused by subsequent reliquefaction, which indicates that the ground density still plays a significant role in determining the ground settlement. For the same input motion, the tendency of the EPWP development speed to increase during reliquefaction is more remarkable in medium-coarse sand than that in find sand. For the same sand, different input motions can cause a similar decreasing tendency in reliquefaction resistance for the 2nd shaking event. However, from the 3rd shaking event on, the enhanced effect of reliquefaction resistance due to the increase in ground density is more significant for a smaller input motion.

Top-meter soil organic carbon stocks and sources in restored mangrove forests of different ages

Knowledge of the changes in the soil organic carbon (OC) stock and its sources with forest age is crucial to understanding the carbon processes and carbon sequestration benefits associated with mangrove restoration. The present study compared the soil OC contents and stocks among three restored Kandelia obovata mangrove forests with different ages (12, 24 and 48 years) in South China. The contributions of mangrove and allochthonous suspended particulate organic matter (SPOM) in tidal water to soil OC were also estimated. The results showed increases in soil OC content and density with forest age, and the OC stocks in the top meter of soil were 13.0 ± 0.5 kg C m−2, 15.1 ± 0.7 kg C m−2 and 17.0 ± 0.9 kg C m−2 at the 12-year site, 24-year site and 48-year site, respectively. We also found a higher soil labile OC content at the 48-year site. The higher soil OC content was accompanied by more 13C-depleted OC in the older forests, and the significantly negative relationship between soil OC contents and δ13C values indicated that the increase in soil OC content relied on the input of 13C-depleted mangrove organic matter. Isotope mixing calculations showed that the soil OC was dominated by SPOM at the 12-year site but was dominated by both mangrove-derived OC and SPOM at the 48-year site. Moreover, the findings also suggested that the effect of mangrove restoration on the soil OC content and stock was more substantial in the upper soil layers.

INFLUENCE OF SOIL PROCESSING ON CHERNOZEM AGROPHYSICAL STATE AND SPRING WHEAT PRODUCTIVITY

Results are given from evaluation study (2013–2015) of basic processing methods influence on soil agrophysical state and spring wheat productivity. Shallow medium-loamy chernozem of Krasnoyarsk forest-steppe was under study. The soil under basic processing was characterized with normal composition (0.96–1.02 g/ сm3) and perfect structure of 0–20 сm layer on agronomical valuable aggregates content (70–71 %). Experiment scheme included three variants of tillage: dump plowing of black steam with PLN- 4–35 to 20–22 cm depth (control); autumn disc harrowing of black steam with Rubin 9600KU cultivator to 10–12 сm depth (minimal processing); chemical steam and direct sowing with John Deer seed drill (zero processing). There is established that basic processing type defined the character of seasonal soil density dynamics (Сv=1–25 %) and structural composition (Cv = 28 %). Optimal wheat productivity was obtained under dump plowing cultivation and minimal processing (24–25 c/ha). Direct wheat sowing contributed to soil density increase by 0.06–0.04 g/ сm3 with optimal parameters maintenance and reduced spring wheat productivity by 0.6–0.7 t/ha in comparison with the dump plowing and minimal processing

Response of circular footing on dry dense sand to impact load with different embedment depths

Machine foundations with impact loads are common powerful sources of industrial vibrations. These foundations are generally transferring vertical dynamic loads to the soil and generate ground vibrations which may harmfully affect the surrounding structures or buildings. Dynamic effects range from severe trouble of working conditions for some sensitive instruments or devices to visible structural damage. This work includes an experimental study on the behavior of dry dense sand under the action of a single impulsive load. The objective of this research is to predict the dry sand response under impact loads. Emphasis will be made on attenuation of waves induced by impact loads through the soil. The research also includes studying the effect of footing embedment, and footing area on the soil behavior and its dynamic response. Different falling masses from different heights were conducted using the falling weight deflectometer (FWD) to provide the single pulse energy. The responses of different soils were evaluated at different locations (vertically below the impact plate and horizontally away from it). These responses include; displacements, velocities, and accelerations that are developed due to the impact acting at top and different depths within the soil using the falling weight deflectometer (FWD) and accelerometers (ARH-500A Waterproof, and Low capacity Acceleration Transducer) that are embedded in the soil in addition to soil pressure gauges. It was concluded that increasing the footing embedment depth results in increase in the amplitude of the force-time history by about 10-30% due to increase in the degree of confinement. This is accompanied by a decrease in the displacement response of the soil by about 40- 50% due to increase in the overburden pressure when the embedment depth increased which leads to increasing the stiffness of sandy soil. There is also increase in the natural frequency of the soil-foundation system by about 20-45%. For surface foundation, the foundation is free to oscillate in vertical, horizontal and rocking modes. But, when embedding a footing, the surrounding soil restricts oscillation due to confinement which leads to increasing the natural frequency. Moreover, the soil density increases with depth because of compaction, which makes the soil behave as a solid medium. Increasing the footing embedment depth results in an increase in the damping ratio by about 50-150% due to the increase of soil density as D/B increases, hence the soil tends to behave as a solid medium which activates both viscous and strain damping.

The effects of chemical admixtures and physical factors on the treatment of dispersive soils

Dispersive soils are very abundant around the world; upon contact with water, the clay minerals in dispersive soils become strongly repulsed by each other and remain suspended apart from each other, a dangerous trend which has led to a number of irreparable damages. The soil used in this test was completely virgin and could be classified as a dispersive soil. In the first section of this study, the pinhole test was conducted on more than 20 selected additives; the results of these tests demonstrated that the best amending agents were calcium oxide and calcium hydroxide salts, in addition to polymer and cement compounds. A closer examination of the results obtained from the pinhole test for the six ideal additives, used at different percentages, revealed that even low percentages of lime, cement, and calcium hydroxide would dramatically reduce soil dispersivity. The combined effect of lime compounds with any of the (high pH) additives, including aluminum sulfate, pozzolan, and sulfur, at identical ratios represents their cumulative effect on the amendment intensity. The second section simultaneously explores the effects of several physical parameters of the amended soil including density, moisture, and time, through the test design method. The results obtained from this phase suggested that both increasing soil density and time would effectively amend the soil if used within their respective ranges, the former directly and the latter to a certain extent.

Expansion reduction of clayey soils through Surcharge application and Lime Treatment

Expansive clayey soils produce heaving and cracking of floor slabs and walls. Expansive soils owe their characteristics to the presence of swelling clay minerals. This soil expands and contracts due to changes in the moisture content of the soil. In this study the surcharge required to counteract soil expansion was measured in natural expansive soils (untreated soils) and lime treated soils starting at 19.61kPa (2Ton/m2) and continuing with increments of 19.61kPa. Additionaly in lime treated soils the amount of lime was determined under different surcharges in order to reduce the expansion. The test results indicated that the surcharges applied to untreated soils were not proportional to the decrease of expansion which is probably due to the increase of soil density. In fact, only the initial surcharge of 19.61kPa significantly decreased the expansion. According to the results, the soil expansion was considerably reduced (1.54%) with the surcharge of 78.45kPa, therefore this surcharge can be considered as the Swelling pressure. On the other hand the soil tested (high compressibility clay) was stabilized with 6% of lime (without surcharges) which was determined with the lowest value of liquid limit and plastic index as well as expansion test. After the application of surcharges and lime treatment to expansive soil, the surcharges of 39.22kPa and 58.84kPa decreased expansion and increased their resistance. This was concluded by similar low values of expansion (without settlements) under both surcharges of each treated soil tested (2, 4 and 6% of lime). It can be concluded that the surcharge contributed to the decrease of soil expansion due to the decrease of the amount of lime required (6%) without surcharge. So, 4% of lime was enough for the surcharge of 19.61kPa and 2% of lime required the surcharge minimum of 39.22kPa. This shows that the surcharge of a house on expansive soil reduces soil expansion and therefore reduces costs of any method of soil improvement and special foundation.

English

This study aimed to evaluate the effects of seed-furrow openers and soil compaction on parameters such as sowing quality and root growth of soybean. The experiment was conducted using a randomized blocks experimental design with split plots, with the plots arranged by compaction level (1.16, 1.20, 1.22 and 1.26 Mg m-3) and the subplots by type of furrow opener (double disk and shank type). Root growth was assessed at three depths (0.00-0.10; 0.10-0.20 and 0.20-0.30 m) in the sowing line and interrow. The sowing quality data means were compared using the Tukey test (p≤0.05), while the root growth data means were compared using the LSD test (p≤0.05). Penetration resistance increased with increasing soil compaction to a depth of 0.20 m. The sowing depth and mobilized soil area were not affected by soil compaction levels. The type of furrow opening mechanism only influenced the sowing depth, with greater depth achieved using the double disc. Neither the seed-furrow openers nor the level of soil compaction significantly influenced soybean root growth when evaluated in the sowing line. The type of furrow opening mechanism did not influence any of the evaluated parameters. Soil compaction altered soybean root growth in the interrow, but did not impede rooting. Regardless of the assessment depth in the interrow, there was a reduction in root volume, length, surface area and diameter with increased soil density.   Key words: No-tillage, seeder, soil density, sowing depth, penetrometer resistance.

Сезонна динаміка щільності складення чорнозему опідзоленого західного Лісостепу України за різного використання в агроценозах

Soil as multicomponent organized and complex ecosystem has a number of important ecosystem functions. Fertility is the most integrated of it, which is directly connected with all the functions and properties of the soil and is the result of effective cooperation. Thus, essential for optimal functioning of soil fertility is implementing its agrophysical properties that are the basis of the formation of high and stable crops yields. A special place to optimize the agrophysical properties takes soil structure density, which is the most objective and comprehensive summary measure. This statement came through the work of Y. B. Revuta, and his followers. These works had significant impact on the soil science development; thru bulk density peoples began to assess soil physical condition and its changes due to human impact. Soil compaction is the main reason of it productivity reducing. Plants feel strong anoxia when soil density index falls below 15%. Over compaction reduces soil biological activity, including nitrification, total number of cellulose destructors and actinomycetes. Soil density increase in 0.1 g/cm3 compared to an optimum – course crops yield reduction by 15-20%, and 0.2 g / cm3 - 50%. Soil structural condition, bulk density, water-physical properties, crop productivity are largely dependent on its tillage type, nutrient management in crop rotation. Tillage (especially deep plowing) and fertilization significantly change the natural structure of black soil. Thus, the result of years of plowing at the same depth a dense plow sole is formed. It affects many soil processes, especially in water, temperature and soil gas regime. V. D. Mukhas’ found that one of the main signs of land degradation indicators are bad soil structure and density structure of the soil during the growing season. Vladimir Medvedev says’ that mechanical tillage and soil structural changes caused by it are the main reason of water-physical properties degradation in arable land. Fedorovskyi D.V. notes’ that high soil density make soil water and nutrients unavailable for plants. Wheat roots do not penetrate into the layers of soil with a density of 1.65, roots of vegetables - 1.45 g / cm3. Apple trees are not durable if there is compaction layer under 1.55 in 2 meter layer of medium loamy soil, and more than 1.30 g/cm3 on clay soils. Kopytko P.G. indicates that density of soil with loamy texture (20-80 cm layer) in root zone under highly productive apple orchards is around 1.2-1.3 g/cm3. Therefore, these figures can be considered as an optimal for the functioning of the root system and fruit crops nutrition. In particular, it is known that manure as an organic improves soil physical, chemical, agrophysical properties and humus regime. Nowadays manure becomes irrelevant from economic point of view. Therefore against the backdrop of rising rates agrotehnogenesys in the literature there are more and more reports of adverse changes in the properties of soils under the influence of mineral fertilizers. Thus, G.V. Dobrovolsky indicates that fertilizer even in small doses lead to dispersion structure, reduced agrigates strength, reducing the visible poroznosti and increase bryluvatosti (Dobrovolski, 1983). That is why additional study of the effect of different soil tillage and nutrition plans on podzolic chernozem bulk density in different soil-climatic and farm specific conditions is needed.

Shoot and root development of brachiaria grass (Urochloa ruziziensis) under different levels of soil density

For mitigation of negative effects of human activities on the soil density, the use of cover crops in no-tillage system (NTS) has been strongly recommended. This study aims to evaluate the shoot and root development of Urochloa ruziziensis subjected to soil density levels in dystrophic Oxisol. The experiment was conducted in a greenhouse with a completely randomized design, with five treatments and four replications. The treatments consisted of U. ruziziensis submitted to five levels of soil density (1.0, 1.2, 1.4, 1.6 and 1.8 Mg m -3 ), twenty experimental units in total. The Urochloa ruziziensis showed reduced plant height, leaf area and number of leaves with increasing soil density, resulting in morphological and physiological changes from densities higher than 1.6 Mg m -3 . However, these results demonstrate the ability of this species to break the compacted ground and form biopores. The Oxisols value of 1.4 Mg m -3 is restrictive for the plant growth and development.

Load-Carrying Mechanism of Vertical Plate Anchors in Sand

AbstractAn experimental study on the load-carrying mechanism of vertical plate anchors is presented and discussed. It was found that, with a shallow anchor, the rupture surface reached the ground surface, leading to a general shear failure, whereas with deeper embedment, the rupture surface was localized around the anchor. Anchors placed close to the ground surface failed in linear rupture but, when embedded within the failure mechanism, were very close to the polar curve of a logarithmic spiral, which, however, tends to be nearly circular for deeper depths of embedment. The size of rupture surface increases with an increase in density of fill soil that mobilizes higher resistance, leading to enhanced anchor capacity. The critical embedment depth beyond which the anchor breakout factor does not change much is found to be approximately 7 times the anchor height for dense soil, whereas it is approximately 5 times the anchor height for loose soil. The anchor when placed below the critical depth, settlement, ...

Hubungan Teoritis Antara Berat Isi Kering Dan Kadar Air Untuk Menentukan Kepadatan Relatif

Soil stabilization can be done with a few way, by increasing soil density or compaction. Compactable soil can increase soil strength and bearing capacity to working payload. Laterite soils as embankment soil that stabilized with compacting method, influenced by water content, dry unit weight and compacting dissociation energy. To know theoretical connection between water contents, dry unit weight, degree of saturation and energy of compaction is done in laboratory with method Standard Proctor and Modified Proctor to know optimum water content zone at some Sr and determines minimum energy that needed to gets relative density of 90% ( RC 90%) so that economic compacting can be reached. From result of this research, it is gotten that optimum water content resided at Sr 75% and there is no compacting curve cuts Sr 100% ( ZAV). By using theoretical connection between dry unit weight , water content, Sr and compacting energy, it can determine the water content zone and minimum energy that needed to reachs relative density of 90% ( RC 90%).

English

Monitoring the physical quality of soils under intensive sugarcane production requires sustainable forms of use and soil management. Thus, the objective of this research was to evaluate the influence of soil tillage systems on soil porosity and density in ratoon-cane cultivation, in addition to possible changes which may occur during the season. The experiment was carried out in the state of Goiás, Brazil. The Experimental design was randomized blocks with four replications. The following tillage systems were evaluated: 1. Moldboard plow + Harrow; 2. Subsoiler + Harrow; 3. Direct planting; 4. Subsoiler + Direct planting; 5. Stubble thrasher + Subsoiler; 6. Stubble thrasher + Harrow + Moldboard plow + Harrow, in soil layers 0-0.2; 0.2-0.4 and 0.4-0.6 m. Regardless of the tillage system used during sugarcane cultivation, the ratoon crop showed reduced total soil pore volume and macroporosity, as well as increased soil density in the 0.4-0.6 m layer. However, the use of direct planting resulted in +higher ​​soil macroporosity values in the 0-0.2 m layer and yields similar to conventional systems which use the moldboard plow. Therefore, it is recommended for producers to adopt conservation soil tillage systems, combining productivity and soil quality.   Key words: Soil management, ratoon-cane, soil compaction, conservation system.

Effect of surface roughness on the shaft resistance of non-displacement piles embedded in sand

This paper presents the results of axial load tests performed on instrumented model piles pre-installed in a large-scale, half-circular chamber with a viewing window in its flat-side wall. Uniform silica sand samples were prepared with different densities using dry pluviation. The effects of pile surface roughness and soil density on the response of the soil during loading of the model piles were studied by analysing sequences of digital images using the digital image correlation technique. Test results show that the extent of the zone next to the pile that is affected by loading of the pile increases as the pile surface roughness and soil density increase. The development of a shear band next to the pile shaft was also studied by carefully analysing images taken with a digital microscope during loading of the model piles. The average thickness of the shear band is in the 3·2D50–4·2D50range for rough model piles, whereas no shear band was observed for smooth model piles. Understanding of shear band formation along the pile–soil interface provides insights into the calculation of the shaft resistance of the pile as a function of initial soil density and stress as well as pile surface roughness.

Hydromechanical constraints on piping failure of landslide dams: an experimental investigation

Understanding the internal structure and material properties of landslide dams is essential for evaluating their potential failure mechanisms, especially by seepage and piping. Recent research has shown that the behaviour of landslide dams depends on the internal composition of the impoundment. We here present an experimental investigation of the hydromechanical constraints of landslide dam failure by piping. Experiments were conducted in a 2 m × 0.45 × 0.45 m flume, with a flume bed slope of 5°. Uniform dams of height 0.25 m were built with either mixed or homogeneous silica sands. Uniform-sized pebbles encased in a plastic mesh were used to initiate internal erosion. Two laser displacement sensors were used to monitor the behaviour of the dams during the internal erosion process while a linear displacement transducer and a water-level probe were deployed to monitor the onset of internal erosion and the hydrological trend of the upstream lake. Five major phases of the breach evolution process were observed: pipe evolution, pipe enlargement, crest settlement, hydraulic fracturing and progressive sloughing. Two major failure modes were observed: seepage and piping-induced collapse. Majority of the dams composed of homogeneous material failed by seepage and downstream slope saturation, whereas dams built with mixed material failed by piping. We found that an increase in soil density and homogeneity of the dam materials reduced the potential to form a continuous piping hole through the dams. Furthermore, the potential for piping and progression of the piping hole through the dams increased with an increase in the percentage of fines and a decrease in hydraulic conductivity. The rate of pipe enlargement is related to the erodibility of the soil, which itself is inversely proportional to the soil density. This study provides new insights into the governing conditions and breach evolution mechanisms of landslide dams, as triggered by seepage and piping.

Cyclic and Post-cyclic Shear Behaviour of a Granite Residual Soil – Geogrid Interface

The dynamic frictional properties of the soil-geosynthetic interface play an important role in the design and stability analysis of geosynthetic-reinforced soil structures under repeated loadings, such as those induced by compaction, traffic and earthquakes. This paper describes a laboratory study carried out using a large-scale direct shear test device, aiming to investigate the cyclic and post-cyclic behaviour of an interface between a granite residual soil and a biaxial woven geogrid. In the cyclic direct shear tests, the interface was subjected to 40 cycles of sinusoidal displacement, with semi-amplitude and frequency ranging from 1-10 mm and 0.05-0.5 Hz, respectively. To evaluate the effect of the cyclic loading on the interface shear strength, monotonic direct shear tests were performed immediately following the cyclic tests. The results indicated that the loading frequency has little impact on the interface shear stiffness during the loading cycles. In contrast, the influence of the displacement semi-amplitude on the interface stiffness was found to be significant. The cyclic loading did not lead to the degradation of the post-cyclic interface shear strength. The post-cyclic peak shear strength tended to increase with the semi-amplitude of the shear displacement, which may be associated with an increase in soil density.

The Influence of Physical Properties of Sod-Podzol Soil on its Ammonifying and Nitrifying Capacity

The research was conducted by the Chair of Agricultural Chemistry and Crop Farming of the Mari State University. The model experiment helped to study the influence of temperature, moisture, and density on nitrifying and ammonifying capacity of sod-podzol midclay low-humic soil. It was found out that change of physical properties factors of sod-podzol soil influenced nitrifying and ammonifying capacity and mineral nitrogen content. Maximum content of nitrate and mineral nitrogen and the biggest nitrifying capacity were at a soil temperature of +15°C and had the following corresponding values: 74.4, 81.3, and 31.9 mg/kg. Moistening conditions optimal for developing nitrifying and ammonifying bacteria were formed at a soil moisture of 20-25% (60-75% WFC). At this moisture there were the biggest figures of nitrifying capacity (31.5-35.0 mg/kg) and maximum values of content of nitrate nitrogen (74.0-77.5 mg/kg) and mineral nitrogen (78.7-82.3 mg/kg). Soil firming had a negative effect on the microflora of soil. With soil density increase from 1.1 to 2.0 g/cm3 nitrifying capacity decreased from 21.0 mg/kg down to 10.4 mg/kg, while nitrate nitrogen content in soil decreased from 63.5 to 32.1 mg/kg. The best conditions for nitrification and ammonification in sod-podzol soil were as follows: soil temperature of +15°C, soil moisture of 20-25%, and soil density of 1.1 g/cm3. Dependence of mineral nitrogen content in soil on its temperature and moisture was curvilinear and was described by a second-order regression equation, while dependence on its density was linear and was described by a first-order regression equation.

Multiple-Liquefaction Behavior of Sand in Cyclic Simple Stacked-Ring Shear Tests

AbstractFollowing major earthquakes that occurred in New Zealand (2010–2011) and Japan (2011), soil multiple liquefaction, or reliquefaction, regained major attention in the field of geotechnical earthquake engineering. Not only can liquefaction occur multiple times at the same site, but the devastation caused by reliquefaction is often more severe than that triggered by the first liquefaction. In this study, to address this issue and provide new insights into reliquefaction mechanisms, a series of cyclic simple shear tests was conducted with the use of a newly developed stacked-ring shear apparatus. In the multiliquefaction tests, subsequent liquefaction stages were applied to a single Toyoura sand specimen sheared at different levels of maximum shear strain double amplitude (γDAmax), from 2% to 10%. Tests results showed that: (1) the increase in soil density during the postliquefaction reconsolidation stages had only a minor effect on sand resistance against multiple liquefaction; (2) the extent of γDAm...