Soil Box Research Articles

Coupled Nonlinear Finite-Element Analysis of Soil–Steel Pipe Structure Interaction

Numerical simulation of staged-construction modeling of large-diameter steel pressure pipes is accompanied by several complexities. Finite-element (FE) analysis was performed to simulate the behavior of buried steel pipes during staged-construction installation. The model deflections during the staged-construction process were verified with four different experimental soil box test results. The FE model and its associated analysis algorithm considered large deformation using total Lagrangian formulation. The material and contact nonlinear algorithms were also included in the analysis for both soil and steel pipe materials. The contact between each soil layer and soil-to-pipe was carefully implemented. Uniform thermal loading was applied to simulate the stresses induced by compaction forces on the pipe and trench walls. Finally, the vertical and lateral load-deformation plots obtained from the FE analysis results were compared with the full-scale experimental test results during the staged construction process and after the application of surcharge load. The results of FE analysis are shown to accurately model and simulate the test results.

High Frequency Impedance Dispersion of Corroding Galvanized Steel in Soils

Electrochemical Impedance Spectroscopy at the open circuit potential of galvanized steel buried in soil showed a marked region of near constant imaginary component element (CIE) behavior [1], illustrated in Figures 1 and 2, representative of results from multiple samples. The near-CIE region spans frequencies ranging from the practical high frequency end (~10 kHz) to ~ 1 Hz. Figure 1 corresponds to a medium size 1.2 cm diameter rod specimen 20 cm long (surface area 60 cm2) inside a soil-containing cylindrical cell 10 cm in diameter. Figure 2 corresponds to a much larger (4060 cm2) rod mesh specimen of the same material, placed inside a large soil box 2.5 m x 1.2 m x 0.9 m. The soil in both cases was typical backfill used in mechanically stabilized earth walls, with 40% of the pore space filled with fresh water and contaminated with ~100 ppm of chloride ions, resulting in a medium of ~ 7000 ohm cm resistivity. In both cases the counter electrode was large enough to result in even excitation current distribution on the working electrode. The reference electrode was a solid metal/metal oxide activated Ti rod placed near the working electrode surface. The observation of near-CIE behavior in both large and small cells of different geometries, and preliminary calculations of possible effects, suggest that macroscopic current distribution in a resistive medium due to counter electrode configuration and placement is not the primary cause of this phenomenon. The low frequency end of the spectrum (1mHz to 0.1Hz) can be well fitted in both cases to a simple constant phase element (CPE) - resistance (R) parallel combination, as shown in both figures. Treating R as a polarization resistance and using a Stearn-Geary constant value B=22 mV [2] yielded in both cases apparent galvanized layer corrosion current density in the order of iCORR ~0.8 μA/cm2 for day 90 of exposure and ~0.4 μA/cm2 for day 220, consistent with typical behavior of buried galvanized steel in similar conditions and ages [3]. That analysis implicitly assumes that the high frequency part of the spectrum represents the series combination of two elements. The first is a solution resistance, responsible for the impedance up to about 10 kHz and found to be approximately consistent with the cell dimensions, reference electrode placement, and soil resistivity value. The second is an unknown impedance component ZUNK responsible for the near-CIE behavior. The overall analog equivalent circuit is then as shown in Figure 3a. Figure 3b shows an alternative combination where an element Z*UNK is placed in parallel with a polarization resistance R*p. This alternative is likely to fit the data successfully as well but results in a sometimes appreciably lower value of iCORR, with consequent uncertainty in the interpretation of the results for nondestructive corrosion rate evaluation. It is therefore of interest to elucidate the cause the near CIE behavior. Work in progress to explain that behavior is presented including characterization of the Zn oxide film on the surface of the specimens, to assess its electronic properties especially in regard to the effect of localized states on the frequency response of the film, as done in other systems where significant frequency dispersions resulted [4]. In addition, while as indicated above macroscopic current distribution effects do not appear to be a primary cause of the behavior, calculations are in progress to assess the possible effect of microscopic current distribution in the corrosion product/sand particle aggregate immediately next to the galvanized surface.

The dynamic effects of pastures and crop on runoff and sediments reduction at loess slopes under simulated rainfall conditions

Ryegrass (Lolium perenne L.) and alfalfa (Medicago sativa L.) are widely-planted pastures, and spring wheat (Triticum aestivum L.) is one of the common crops on the Loess Plateau of China where serious erosion exists. However, their roles in regulating runoff and sediments have not been fully understood. This study investigated the effects of these vegetation types at various growth stages on reducing runoff and sediments in soil boxes under simulated rainfall conditions. Growth stages were set as: early stage (late May), middle stage (late June), and late stage (late July). Four indices were used to assess the capacity of reducing runoff and sediments in terms of runoff reduction benefit (RRB), sediment reduction benefit (SRB), ratio between runoff and sediment reduction (RRSR), and soil average/stable infiltration rate. The results showed that at the early and middle stages, RRB, SRB, RRSR, and soil average/stable infiltration rate were the largest for ryegrass followed by spring wheat and alfalfa. At the late stage, however, alfalfa following ryegrass performed better than spring wheat in reducing runoff and sediments. With the growth of vegetation, the capacity of ryegrass and alfalfa in reducing runoff and sediments increased. The RRB and SRB for the late-stage ryegrass were 69.5% and 98.6%, respectively, while they were 61.6% and 95.4% for the late-stage alfalfa, respectively. Spring wheat at middle stage performed best in reducing runoff and sediments over the whole growing period, with the RRB and SRB of 65.31% and 97.63%, respectively. In particular, the SRB for different vegetation types at all stages were over 90%, and were apparently higher than the RRB. In addition, the RRSR increased greatly from the early to middle growth stage for all vegetative treatments, indicating that the reduction in runoff was more effective than the reduction in sediment when vegetation grew mature. Since the majority of heavy rainstorms fall in the late growth stage (July–September) on the Loess Plateau, the functioning of artificial grass in reducing slope runoff and sediments should be stressed and investigated in further details.

Uplift Resistance of Wooden Pile using Soil box According to Soil type

Uplift Resistance of Wooden Pile using Soil box According to Soil type

Effects of Soil Type and Cover Condition on Cryptosporidium parvum Transport in Overland Flow

Overland transport kinetics of pathogens is controlled, in large part, by soil and vegetation. With an increasing number of concentrated animal operations, there is becoming a greater need to dispose of a vast amount of manure in a single, localized area. Animal manure contains a substantial amount of microbial pathogens, including Cryptosporidium parvum that may pose a threat of contamination of water resources. This study examines the kinetics of C. parvum in overland transport and critical factors involved in the design of best management practices, especially vegetative filter strips, to prevent the transport of harmful pathogens to water bodies. Three soil types were tested (Catlin silt-loam, Alvin fine sandy-loam, Darwin silty-clay), spanning the entire spectrum of typical Illinois soils. A 20-min rainfall event was produced using a small-scale (1.07 m × 0.66 m) laboratory rainfall simulator over a soil box measuring 0.67 m × 0.33 m. Each soil type was tested for pathogen transport kinetics with bare surface conditions as well as with smooth brome and fescue vegetative covers. Surface runoff, soil cores, and near-surface runoff were each analyzed for infective C. parvum oocysts using cell culture infectivity assays. Results showed that vegetation greatly reduced the recovery of infective oocysts, in addition to delaying the time to the peak recovery. However, there was no clear evidence of any one vegetation type being advantageous over another. The bare soil experiments resulted in a higher recovery of C. parvum oocysts from the Darwin soil compared to other two soils. Analyses of soil cores show a slightly higher recovery of oocysts in the Catlin soil compared to Alvin or Darwin soils.

黄土坡面细沟侵蚀形态试验

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土坡面细沟侵蚀形态试验 DOI: 10.5846/stxb201309172298 作者: 作者单位: 西北农林科技大学 资源环境学院 黄土高原土壤侵蚀与旱地农业国家重点实验室,西北农林科技大学 资源环境学院;中国科学院 水利部 水土保持研究所,西北农林科技大学 资源环境学院 黄土高原土壤侵蚀与旱地农业国家重点实验室,西北农林科技大学 水土保持研究所,中国科学院 水利部 水土保持研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（41271299）；水利部公益性行业科研专项资助项目（201201083） An experimental study on rill morphology at loess hillslope Author: Affiliation: College of Resources and Environment,Northwest A F University,College of Resources and Environment,Northwest A F University,College of Resources and Environment,Northwest A F University,College of Resources and Environment,Northwest A F University,Graduate University Chinese Academy of Science Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于同一降雨强度下的室内连续模拟降雨试验，研究了典型坡度条件下黄土坡面细沟侵蚀形态，分析了细沟的空间分布特征、发育状况及距细沟沟头长度、细沟宽度和深度关系。结果表明：第1次降雨坡面以断续细沟为主，侵蚀方式主要为溯源侵蚀，细沟累积长度为39.3 m，坡面细沟总面积占试验土槽面积的14.2%；第2次降雨坡面以连续细沟为主，细沟沟壁崩塌增强，坡面的破碎程度增加，细沟累积长度增加32.1%，坡面细沟总面积增加115.6%。与第1次降雨相比，第2次降雨后细沟平均宽度、深度和坡面细沟侵蚀平均深度均增加，且在4-7 m坡段内增加幅度最大。单位斜坡长上细沟平均宽度和深度随斜坡长度的增加呈现先增加后减小的趋势，表明径流能量的消长对坡面细沟侵蚀发育过程及形态特征有明显影响。第1次降雨单条细沟长度均小于3 m，细沟宽度随距细沟沟头长度的增大而增大，第2次降雨则呈现先增大后减小的趋势，细沟深度随距细沟沟头长度的增加一直呈现先增大后减小的趋势，细沟宽度与深度的拟合关系最好，细沟深度随宽度的增加而增大，后趋于稳定。 Abstract:Rill erosion is known as the most important form of water erosion on agricultural land. Rill morphology plays a significant role in determining the runoff and soil loss from sloping farmland. However, few attempts have been done on the accurate description of rill throughout the study area for that eroding rill evolves morphologically in time and space. The objective of this study was to quantify the natural rill morphology under controlled laboratory conditions, aimed to provide more insight and detail information for later experiments. The soil used in this study was the loess soil with 28.3% sand, 58.1% silt, and 13.6% clay content from Ansai, Shaanxi province, China. It was collected from the top 20 cm in the A horizon of a well-drained site. The loess soil was packed in a soil box which is 10 m long, 3 m wide and 0.5 m deep, and performed to two sequent simulated rainfalls at an interval of 24 h. The slope was set as 15°. Each simulated rainfall lasted 65 minutes and the rainfall intensity was 60 mm/h. Rainfall intensity, rainfall uniformity and raindrop diameter were calibrated and reached the experimental requirements. In this study, the spatial distribution of rill erosion, rill development situation and relationships between the length away from rill head, rill width and depth were analyzed systematically. Results showed that discontinuous rills were widely distributed on the slope and headward erosion was the pre-dominant erosion manners in the first simulated rainfall. The accumulated length of all rills was 39.3 m and the total surface area reached up to 14.2% of the total soil box. However, the second simulated rainfall was mainly dominated by continuous rills, and the side-wall collapse of rills and fragmentation degrees of the slope strengthened. Meanwhile, the accumulated length increased by 32.1% and total surface area rose by 115.6%.Compared with the first simulated rainfall, average rill width, depth and rill erosion average depth all increased during the second run. And the increases occurred principally in the 4-7 m slope. The average rill width and depth of unit slope length increased firstly and decreased afterwards along with the increase of slope length. This indicated the growth and decline of runoff energy could affect the development processes and morphological characteristics of rill erosion. The length of each rill was less than 3 m and rill width increased with the length away from rill head for the first simulated rainfall. But the trend increased first and then decreased for the second simulated rainfall. Moreover, similar trends of rill depth developments were found for the two simulated rainfalls. The best regression relationship was found between rill width and depth. Rill depth increased with rill width at first, and then kept stable. 参考文献 相似文献 引证文献

Laboratory soil piping and internal erosion experiments: evaluation of a soil piping model for low‐compacted soils

ABSTRACTMechanistic models have been proposed for soil piping and internal erosion on well‐compacted levees and dams, but limited research has evaluated these models in less compacted (more erodible) soils typical of hillslopes and streambanks. This study utilized a soil box (50 cm long, 50 cm wide and 20 cm tall) to conduct constant‐head, soil pipe and internal erosion experiments for two soils (clay loam from Dry Creek and sandy loam from Cow Creek streambanks) packed at uniform bulk densities. Initial gravimetric moisture contents prior to packing were 10, 12 and 14% for Dry Creek soil and 8, 12, and 14% for Cow Creek soil. A 1‐cm diameter rod was placed horizontally along the length of the soil bed during packing and carefully removed after packing to create a continuous soil pipe. A constant head was maintained at the inflow end. Flow rates and sediment concentrations were measured from the pipe outlet. Replicate submerged jet erosion tests (JETs) were conducted to derive erodibility parameters for repacked samples at the same moisture contents. Flow rates from the box experiments were used to calibrate the mechanistic model. The influence of the initial moisture content was apparent, with some pipes (8% moisture content) expanding so fast that limited data was collected. The mechanistic model was able to estimate equivalent flow rates to those observed in the experiments, but had difficulty matching observed sediment concentrations when the pipes rapidly expanded. The JETs predicted similar erodibility coefficients compared to the mechanistic model for the more erodible cases but not for the less erodible cases (14% moisture content). Improved models are needed that better define the changing soil pipe cross‐section during supply‐ and transport‐limited internal erosion, especially for piping through lower compacted (more erodible) soils as opposed to more well‐compacted soils resulting from constructing levees and dams. Copyright © 2013 John Wiley & Sons, Ltd.

Bank undercutting and tension failure by groundwater seepage: predicting failure mechanisms

ABSTRACTGroundwater seepage can lead to the erosion and failure of streambanks and hillslopes. Two groundwater instability mechanisms include (i) tension failure due to the seepage force exceeding the soil shear strength or (ii) undercutting by seepage erosion and eventual mass failure. Previous research on these mechanisms has been limited to non‐cohesive and low cohesion soils. This study utilized a constant‐head, seepage soil box packed with more cohesive (6% and 15% clay) sandy loam soils at prescribed bulk densities (1.30 to 1.70 Mg m−3) and with a bank angle of 90° to investigate the controls on failure mechanisms due to seepage forces. A dimensionless seepage mechanism (SM) number was derived and evaluated based on the ratio of resistive cohesion forces to the driving forces leading to instability including seepage gradients with an assumed steady‐state seepage angle. Tension failures and undercutting were both observed dependent primarily on the saturated hydraulic conductivity, effective cohesion, and seepage gradient. Also, shapes of seepage undercuts for these more cohesive soils were wider and less deep compared to undercuts in sand and loamy sand soils. Direct shear tests were used to quantify the geotechnical properties of the soils packed at the various bulk densities. The SM number reasonably predicted the seepage failure mechanism (tension failure versus undercutting) based on the geotechnical properties and assumed steady‐state seepage gradients of the physical‐scale laboratory experiments, with some uncertainty due to measurement of geotechnical parameters, assumed seepage gradient direction, and the expected width of the failure block. It is hypothesized that the SM number can be used to evaluate seepage failure mechanisms when a streambank or hillslope experiences steady‐state seepage forces. When prevalent, seepage gradient forces should be considered when analyzing bank stability, and therefore should be incorporated into commonly used stability models. Copyright © 2013 John Wiley & Sons, Ltd.

Effect of Rainfall Kinetic Energy on Crust Formation and Interrill Erosion of an Ultisol in Subtropical China

Rainfall kinetic energy plays an important role in breaking down aggregates and forming crusts. A laboratory rainfall simulation study was conducted on an Ultisol from subtropical China to investigate the effect of rainfall kinetic energy on crusting, infiltration, runoff, and erosion. Two treatments, that is, high kinetic energy (HKE) and low kinetic energy (LKE), were applied during this study. Air‐dried soil was packed in a soil box (50 by 50 cm), and the soil box was subjected to 38 mm h−1 rainfall with three replicates. The runoff, splash, erosion, and percolation were measured during the simulation. For each treatment, an additional soil box was dedicated to sampling the undisturbed soil samples at different time intervals to make thin sections. The entire soil surface was covered by structural or sedimentary crust at the end of the experiment. When compared with the HKE rainfall, the LKE rainfall reduced the direct physical impact of raindrops that disintegrated the soil aggregates and compacted the soil surface; therefore, the LKE preserved the soil infiltration capability and subsequently postulated the formation of crust. This resulted in a higher infiltration rate and greater cumulative infiltration and percolation but lower splash, runoff, and soil erosion in the LKE treatment compared with the HKE treatment. The results show that Ultisols are prone to crusting and that rainfall kinetic energy is a major driver of crust formation. This finding indicates that mulching the soil surface is an effective way to alleviate crusting, to conserve more water, and to reduce erosion.

3D finite element simulation of a single-tip horizontal penetrometer–soil interaction. Part I: Development of the model and evaluation of the model parameters

A fundamental step to employing a horizontal penetrometer for on-the-go measurement of soil compaction is to characterize the horizontal penetrometer resistance (PR) as affected by soil mechanical/physical properties and design/operational parameters of the penetrometer. Such complicated soil–tool interactions are preferably investigated using numerical analyses, e.g. finite element (FE) method. A symmetric 3D FE model for a single-tip horizontal penetrometer–soil interaction was developed and evaluated in ABAQUS/Explicit. In the first paper of this study, we focus on the development of the model and the evaluation of some affecting parameters, namely (i) boundary effects, (ii) element size (mesh density) around the conical tip of the penetrometer, (iii) sensitivity of the predicted PR with respect to (a) soil mechanical properties (b) tip extension (i.e. the distance between cone base and shin of the carrying tine), (c) working depth, and (iv) soil layering and the effect of working depth in relation to the tine critical depth. The elastic–plastic parameters of the soil constitutive model (Drucker–Prager) were determined from samples taken within the working depth of the penetrometer in a soil bin. The results showed that for the tested penetrometer dimensions and the given soil specifications (i) the simulated soil box should be at least 0.8m long and 0.4m wide to avoid interference from the boundaries on predicted PR; (ii) the element size around the cone should be fine enough (9mm) for a stable steady-state simulated PR; and (iii) the tip extension must be >4cm to avoid the effect of tine on PR. PR was found to be most sensitive to soil internal angle of friction and compressive yield stress, whilst Poisson's ratio had no significant effect, and Young's modulus of elasticity and soil-metal coefficient of friction showed only minor impacts on PR. Due to soil surcharge, PR increased by 30% when increasing the working depth of the penetrometer from 5 to 40cm in a homogenous soil profile. An effective radius of 6cm was found for the soil failure around the cone. The simulations showed that when the cone was located above the tine critical depth (i.e. inside the crescent failure zone), the PR was lower and the PR signal was unstable compared with when the cone worked out of crescent failure zone at the same depth. The model developed here can be used to characterize PR with respect to the state of soil strength/compaction across soil types.

Soil Resistivity Measurements to Predict Moisture Content and Density in Loose and Dense Soil

In the past, most of the soil electrical resistivity charts were developed based on stand-alone geomaterial classification with minimal contribution to its relationship to some of geotechnical parameters. Furthermore, the values cited a very wide range of resistivity with sometimes overlapping values and having little significance to specific soil condition. As a result, it created some ambiguities during the interpretation of observations which were traditionally based on qualitative anomaly judgments of experts and experienced people. Hence, this study presents soil resistivity values based on laboratory experiment with a view to predict the soil moisture content and density in loose and dense soils. This study used a soil box and a resistivity meter to test a clayey silt soil, increasing its water usage from 1-3% based on 1500 gram of dry soil. All the moisture contents and density data were observed concurrently with 25 electrical soil resistance observations being made on the soil. All testing and formula used were in accordance with that specified in BS1377 (1990). It was apparent that the soil resistivity value was different under loose (L) and compact (C) condition with moisture content (w) and density (ρbulk) correlations being established as follows; ρbulk(C) = 2.5991ρ-0.037, ρbulk (L) = -0.111 ln (ρ) + 1.7605, w(L) = 109.98ρ-0.268, and w(C) = 121.88ρ-0.363 with determination coefficients, R2 that ranged between 0.69 0.89. This research therefore contributes a means of predicting these geotechnical parameters by related persons such as geophysicist, engineers and geologist who use these resistivity techniques in ground exploration.

Sorption, Leaching, and Surface Runoff of Beef Cattle Veterinary Pharmaceuticals under Simulated Irrigated Pasture Conditions

The use of veterinary pharmaceuticals in beef cattle has led to concerns associated with the development of antibiotic resistance in bacteria and endocrine disruption in aquatic organisms. Despite the potential negative consequences, data on the transport and mitigation of pharmaceuticals in grazed watersheds with irrigated pasture are scarce. The objective of this study was to assess the transport of common beef cattle pharmaceuticals (oxytetracycline, chlortetracycline, and ivermectin) via surface runoff and leachate from manure amended to grass-vegetated soil boxes under irrigated pasture conditions. The transport of pharmaceuticals from animal manure in surface runoff and soil leachate was relatively low and appears to be limited by desorption and transport of pharmaceuticals entrained in the manure. In surface runoff, less than 4.2% of applied pharmaceuticals in manure (initial concentration: 0.2 mg kg of manure) was detected after 3 wk of irrigation. Concentrations of pharmaceuticals in surface runoff and leachate never exceeded 0.5 μg L. The major portion of pharmaceuticals (up to 99%) was retained in the manure or in the soil directly beneath the manure application site. Based on the minimal transport of oxytetracycline, chlortetracycline, and ivermectin, the risk of significant transport for these targeted beef cattle pharmaceuticals to surface water and groundwater from manure on irrigated pasture appears to be relatively low.

Experimental investigation of plastic demands in piles embedded in multi-layered liquefiable soils

Multi-layered soil profiles, where one or more layers consist of loose liquefiable material, most commonly require pile foundations extending beyond the liquefiable layer to competent material. Under seismic loads, if the loose layer liquefies, then large localized plastic demands may be generated in the piles. To study this behavior and provide detailed data to validate numerical models, a 1-g shaking table experiment was conducted considering a single reinforced concrete pile embedded in a three-layer soil system. The model pile of 25cm diameter was tested under increasing amplitude earthquake excitation in a sloped laminar soil box. The test specimen was designed at the lower bound of typical design to promote yielding, per ATC-32 (Applied Technology Council, 1996) [1]. The pile penetrated 7D (D=pile diameter) into a multi-layered soil configuration composed of a stiff uppermost crust overlying a saturated loose sand layer and a lower dense layer of sand. Plastic demands in the pile were characterized using curvature profiles coupled with back-calculation of the plastic hinge length and post-test physical observations. Results from this test quantify the post-yield behavior of the pile and serve as a complement to previously conducted centrifuge tests.

Tracking the dynamic characteristics of a nonlinear soil-pile system in multi-layered liquefiable soils

Saturated soils, particularly cohesionless soils, may liquefy when subjected to earthquake excitation, resulting in reductions in strength and stiffness of the soil. A change in stiffness equates to a change in period, and hence, in response to future seismic loading. Furthermore, for pile foundations, a reduction of vertical or lateral soil resistance may cause failure of the structure. To study this, a unique one-g soil-pile model was constructed in a gently sloped laminar soil box which was subsequently placed on a uniaxial shake table. A 3-layer soil configuration of a stiff crust, liquefiable sand, and dense sand layer was constructed with an embedded pile and subjected to sequentially increasing amplitude earthquake motions. Lateral spreading of the liquefiable sand layer and stiffness degradation of the crust during shaking events were observed. The percent change in period may be translated to a change in effective shear modulus to articulate the softening effect of the system. To investigate this degradation, spectral and fourier ratios are computed and analyzed to study the nonlinear dynamic state of the pile-multi-layered soil system.

Soil Moisture Content and Density Prediction Using Laboratory Resistivity Experiment

Natural soils are an intimate mixture of solid, liquid and gas phases. This study establishes a correlation for moisture content and density of a soil with its electrical resistivity. In the past, most of the conventional geotechnical site investigation required bulky and heavy equipment to determine the geotechnical parameters necessary for design and construction purposes. Consequentially, time and cost of the project is increased especially when dealing with some difficult site such as on mountainous terrain. This study is based on laboratory soil box resistivity meter observations made on soils mixed with additions of consistent increments of 1-5 % of water to 1500 gram of remolded soils in loose condition. At least 24 repetitive resistivity test observations were made and the moisture content and soil density was determined concurrently for each of the tests. The observations showed that the electrical resistivity variation decreased in a curvilinear manner with increasing percentage of moisture content. A regression equation and coefficient of determination, R2 for moisture content against soil electrical resistivity value was established by moisture content, w = 152.87ρ-0.312 (ρ = soil electrical resistivity) and R2 = 0.7718 respectively. While a regression equation and R2 value for bulk density versus soil electrical resistivity value was observed to be ρbulk = -0.107 ln (ρ) + 1.7249 and 0.7016 respectively. Hence, a viable method is demonstrated where the electrical resistivity value was applicable and has a great potential for geotechnical data prediction of parameters such as moisture content and soil density.

Deriving Parameters of a Fundamental Detachment Model for Cohesive Soils from Flume and Jet Erosion Tests

Abstract. The erosion rate of cohesive soils is commonly quantified using the excess shear stress model, which is dependent on two major soil parameters: the critical shear stress (I„ c ) and the erodibility coefficient (k d ). A submerged jet test (jet erosion test, or JET) is one method that has been developed for measuring these parameters. The disadvantage of using the excess shear stress model is that parameters I„ c and k d change according to erosion conditions, such as soil structure, soil orientation, type of clay, presence of roots, and seepage forces. A more mechanistically based detachment model, called the Wilson model, is proposed in this article for modeling the erosion rate of soils using hydraulic analysis of a JET. The general framework of the Wilson model is based on two soil parameters (b 0 and b 1 ). The objectives of this study were to: (1) develop methods of analysis of the JET to determine parameters b 0 and b 1 for the Wilson model in a similar fashion to the previous methodology developed for open-channel flow, and (2) compare the excess stress model parameter (k d ) and the Wilson model parameters (b 0 and b 1 ) determined from the flume tests and JETs for two cohesive soils. Flume tests, treated as the standard test method, and original and “mini” JETs were conducted on two soils to independently measure the excess shear stress model parameter (k d ) and the Wilson model parameters (b 0 and b 1 ). Soil samples of two cohesive soils (silty sand and clayey sand soils) were packed in a soil box for the flume tests and the JETs at water contents ranging from 8.7% to 18.1%. No statistically significant differences were observed for the excess shear stress model parameter (k d ) and for the Wilson model parameters (b 0 and b 1 ) when determined from the flume tests and JET devices, except for b 1 with the original JET. The Wilson model is advantageous in being a more mechanistic, fundamentally based erosion equation as compared to the excess shear stress model. The Wilson model can be used in place of the excess shear stress model with parameters that can be estimated using existing JET techniques.

지반굴착에 소요되는 전기에너지와 표준관입시험 N값과의 상관관계 연구 I : 기초연구(실내토조실험)

지반굴착은 지반조사, 연약지반 개량, 선굴착 말뚝 시공 등 지반공학 분야에서 널리 사용되고 있다. 지반을 굴착하기 위해서는 오거의 상부에 설치된 구동모터를 회전시키는 전기에너지가 필요하게 된다. 본 논문에서는 지반굴착시 구동모터에 소요되는 전기에너지와 지반의 표준관입시험 N값의 상관관계를 분석하고자 하였다. 이를 위하여 지반굴착시 변화하는 전류값과 굴착깊이를 계측하기 위한 측정센서, 데이터 저장시스템, 굴착시스템 등의 실내실험 장치를 개발하였으며, 모형토조 실험을 수행하였다. 계측된 전류값과 굴착깊이는 표준관입시험 N값 추정에 이용되었으며 추정된 표준관입시험 N값은 실내실험으로부터 실측된 N값과 비교하였다. 비교결과 지반굴착에 소요되는 전기에너지를 이용하여 표준관입시험 N값을 추정할 수 있음을 확인하였다. Ground drilling is a common method to conduct site investigation, soil improvement, and pile installation. In the point of construction ground drilling requires electrical energy to drill a hole in ground in which the energy exerts into the motor located on the head of auger and generates rotational power. In this paper it is verified that the exerted electrical energy is closely related to the strength characteristics of ground. Measurement sensors, recording system, and drilling system were developed to obtain exerted motor current and drilling depth and laboratory soil box tests were carried out. The measured motor current and boring depth were applied to predict SPT N-value and the prediction results were compared to SPT N-value of laboratory tests. The test results show that the exerted electrical energy to bore ground be a good index to estimate SPT N-value.

Thermal enhancement of natural magnetism as a tool for tracing eroded soil

ABSTRACTDetermining sources, quantities and travel distances of eroding soil is of increasing importance given its impact on‐ and off‐site, the sediment‐associated transport of nutrients, metals and micro‐organisms and the ongoing need to provide data for soil erosion model development and validation. Many soil tracers have been developed; however, most comprise foreign materials, such as fluorescent beads and rare earth oxides, which cast doubts on the validity of tracing results given their different physical characteristics. To avoid these problems, we have investigated the potential of soil, which has been heated under reducing conditions to enhance its ferrimagnetic content, as a soil erosion tracer; while the technique has been used successfully to trace river sediment it has not been successfully applied to soil erosion studies. For a suite of 16 magnetic concentration‐dependent properties, values were found to be significantly greater, by at least one order of magnitude, after heating, both for the bulk soil and nine individual particle size fractions. Individual size fractions could be differentiated using two different magnetic properties, thus illustrating the technique's potential to provide information on particle size‐specific erosion. Soil box experiments demonstrated the potential for both in situ measurement of magnetic susceptibility and laboratory measurement of the magnetic properties of eroded sediment, to trace and quantify soil erosion. Thus, heated soil, with artificially‐enhanced ferrimagnetic properties, is successfully demonstrated to have great potential as a size‐specific, cost‐effective and representative soil erosion tracer. Copyright © 2012 John Wiley & Sons, Ltd.

An efficient strategy of managing irrigation water based on formulating highly absorbent polymer–inorganic clay composites

Summary The management of irrigation water presents a great challenge for the agriculture field. In view of increasing soil water-holding capacity and increasing water-use efficiency, an efficient strategy of managing irrigation water based on formulating highly absorbent polymer–inorganic clay composite (polyacrylic acid–layered double hydroxide; PAA–LDH) was offered. The PAA–LDH composite was synthesized by an incorporation/in situ polymerization technique. Scanning electron microscopy, X-ray analysis and infrared spectroscopy were used to confirm the composite structure. The thermal gravimetric analysis was applied to investigate the polymer thermal stability after the composite formation. The irrigation experiments were conducted in a wooden soil box with a transparent plexiglas side by using a subsurface drip irrigation system. The X-ray patterns and infrared spectra confirmed the incorporation of acrylic acid monomer (AA) into the gallery of LDH. The SEM images emphasized the composite structure of PAA–LDH and indicated its ability to absorb and keep water. The stability of PAA was promoted against the thermal decomposition after the composite formation. The composite structure of PAA–LDH worked as water barrier and secondary water source during the irrigation process. The soil moisture distribution patterns were enhanced after the application of PAA–LDH composites as a soil conditioner.

Electro-dynamic soil-plate-oscillator transducer for monitoring the buried vibration response to airborne sound excitation

A plastic drum-like anti-personal mine simulant (2 inch diam, by 1 inch tall, by ¼ inch thick aluminum tube, capped by a ¼ Al bottom circular plate and an elastic acrylic 1/16 inch thick circular top plate) was constructed. It was then modified to generate an electrical response to top-plate vibration. The mine simulant was converted to a transducer by fastened a sewing machine size bobbin wound with fine enamel copper wire onto the inside face on the bottom plate of the simulant. Next, a rare earth magnet was fastened to the inside surface of the elastic top plate (using a tacky wax). Leads were connected using insulated feed through connectors to complete the transducer design. In testing out the electro-dynamic transducer landmine simulant, results showed that the design was adequate to detect the vibration resonant response using a 2 inch burial depth in a concrete soil box filled with dry masonry sand. Two 12 inch diameter subwoofers were located a meter above the soil box and radiated sound levels on the order of 80-90 dB re 20 micro Pa, were measured near the soil surface. The swept sinusoidal transducer/microphone response exhibited a fundamental resonance near 190 Hz.