Microscopic Analysis of Cementitious Sand and Gravel Damming Materia

The mechanical properties of cementitious sand and gravel damming material have been experimentally determined by means of microscopic SEM(Scanning Electron Microscopy)image analysis.The results show that the combination of fly ash and water can fill the voids in cemented sand and gravel test blocks because of the presence of hydrated calcium silicate and other substances;thereby,the compactness and mechanical properties of these materials can be greatly improved.For every 10 kg/m^(3) increase in the amount of cementitious material,the density increases by about 2%,and the water content decreases by 0.2%.The amount of cementitious material used in the sand and gravel in these tests was 80-110 kg/m^(3),the water-binder ratio was 1-1.50.Moreover,the splitting tensile strength was 1/10 of the compressive strength,and the maximum strength was 7.42 MPa at 90 d.The optimal mix ratio has been found to be 50 kg of cement,60 kg of fly ash and 120 kg of water(C50F60W120).The related dry density was 2.6 g/cm^(3),the water content was 6%,and the water-binder ratio was 1.09.

Long-term effects of gravel―sand mulch on soil organic carbon and nitrogen in the Loess Plateau of northwestern China

Gravel-sand mulch has been used for centuries to conserve water in the Loess Plateau of north- western China. In this study, we assessed the influence of long-term （1996-2012） gravel-sand mulching of cultiv- ated soils on total organic carbon （TOC）, light fraction organic carbon （LFOC）, microbial biomass carbon （MBC）, total organic nitrogen （TON）, particulate organic carbon （POC）, mineral-associated organic carbon （MOC）, perma- nganate-oxidizable carbon （KMnO4-C）, and non-KMnO4-C at 0-60 cm depths. Mulching durations were 7, 11 and 16 years, with a non-mulched control. Compared to the control, there was no significant and consistently positive effect of the mulch on TOC, POC, MOC, KMnO4-C and non-KMnO4-C before 11 years of mulching, and these organic C fractions generally decreased significantly by 16 years. LFOC, TON and MBC to at a 0-20 cm depth in- creased with increasing mulching duration until 11 years, and then these fractions decreased significantly between 11 and 16 years, reaching values comparable to or lower than those in the control. KMnO4-C was most strongly correlated with the labile soil C fractions. Our findings suggest that although gravel-sand mulch may conserve soil moisture, it may also lead to long-term decreases in labile soil organic C fractions and total organic N in the study area. The addition of manure or composted manure would be a good choice to reverse the soil deterioration that occurs after 11 years by increasing the inputs of organic matter.

Effects of gravel mulch on aeolian transport:a field wind tunnel simulation

The shape,size and coverage of gravels have significant impacts on aeolian sand transport.This study provided an understanding of aeolian transport over the gravel mulching surfaces at different wind velocities by means of a mobile wind tunnel simulation.The tested gravel coverage increased from 5% to 80%,with a progressive increment of 5%.The gravels used in the experiments have three sizes in diameter.Wind velocities were measured using 10 sand-proof pitot-static probes,and mean velocity fields were obtained and discussed.The results showed that mean velocity fields obtained over different gravel mulches were similar.The analysis of wind speed patterns revealed an inherent link between gravel mulches and mean airflow characteristics on the gravel surfaces.The optimal gravel coverage is considered to be the critical level above or below which aeolian transport characteristics differ strongly.According to the present study,the optimal gravel coverage was found to be around 30% or 40%.Threshold velocity linearly increased with gravel coverage.Sand transport rate first increased with height above the wind tunnel floor（Hf）,reaching a peak at some midpoint,and then decreased.

Effects of Different Gravel Mulched Years on Soil Microbial Flora and Physical and Chemical Properties in Gravelsand Mulched Fields

Soil microbial flora and influencing factors of soil microbes in soil and gravel-sand mixed layer（ SGSML）,roots denseness layer（ RDL）,eluviate layer（ EL） and calcium accumulation layer（ CAL） in gravel-sand mulched fields（ GSMFs） with different gravel mulched years（ 1,6,12,19 and 25 years） were studied. The results showed that in the composition of soil microbes in the GSMFs,the quantity of bacteria was the largest,followed by actinomycetes,while the number of fungi was the smallest. The total quantity of soil microorganisms in the GSMFs dropped rapidly with the increase of soil depth,which was related to the sudden decrease in the quantity of bacteria. The number of microbes in the RDL was larger than that in the SGSML with few roots due to the effects of root distribution. The number of bacteria and actinomycete in the growing season was larger than that in the non-growing season,while the quantity of fungi in the growing season was smaller than that in the non-growing season. The quantity of bacteria and fungi was the largest in the GSMFs which had been mulched with gravel for 6-12 years. With the increase of mulching time,the GSMFs aged gradually,so their quantity reduced gradually. The quantity of actinomycetes was the smallest in the GSMFs which had been mulched with gravel for 6-12 years and increased with the increase of mulching time. The number of soil microbes in the GSMFs had a good correlation with soil moisture content,p H and mulching time. Soil total carbon content was an important factor restricting the quantity of soil microbes in the GSMFs.

Response of Watermelon to Gravel-Mulch and Supplementary Irrigation: Yield, Water Use Efficiency and Root Distribution

A field experiment was conducted to investigate the effect of supplementary irrigation on watermelon (Citullus lanatus) yield, water-use efficiency (WUE) and root distribution in gravel-mulched field in northwest Loess Plateau, China, during 2001 and 2002 growing seasons. The results showed that gravel mulch significantly improved seedling emergence, increased yield and WUE, and alleviated the influence of drought on plant growth. Regardless of gravel mulch application, supplementary irrigation increased watermelon yields, average fruit weight and number of fruit, especially yield increased as the amount of irrigation increased (P<0.05). Generally, WUE of irrigated treatments were higher than that of non-irrigation treatment in gravel-mulched field. The effect of water supply on root distribution was different in two years. In 2001, average root length density (RLD) and root weight density (RWD) whole the soil profile increased. In 2002, however, RLD and RWD decreased as water supply increased. The average RLD and RWD in 2001 were significantly higher than those in 2002. Maybe we can interpret the phenomenon with the theory that there is a need to optimize root distribution (in terms of water relations) and aboveground biomass for a given water supply.The yield may not depend as much on root growth as on the amount of water required at critical stages. A significant effect of soil depth on RLD and RWD were observed in both years, but did not rapidly decrease with depth.

Long-term effects of gravel-sand mulch thickness on soil microbes and enzyme activities in semi-arid Loess Plateau,Northwest China

In semi-arid areas of China,gravel and sand mulch is a farming technique with a long history.In this study,a sample survey was conducted on long term gravel sand mulch observational fields in the Northwest Loess Plateau to determine the effects of long term mulch on soil microbial and soil enzyme activities.We found that after long term gravel-sand mulch,compared with bare ground,soil organic matter,alkali nitrogen,conductivity decreased,while pH and soil moisture increased.Urease,saccharase and catalase decreased with increased mulch thickness,while alkaline phosphatase was reversed.The results of Illumina MiSeq sequencing shows that after gravel-sand mulch,the bacterial and fungal community structure was different from bare land,and the diversity was reduced.Compared with bare land,the bacteria Proteobacteria and Acidobacteria abundance increased with increased thickness,and Actinobacteria was opposite.Also,at the fungal genus level,Fusarium abundance was significantly reduced,and Remersonia was significantly increased,compared with bare land.Redundancy analysis(RDA)revealed that soil environmental factors were important drivers of bacterial community changes.Overall,this study revealed some of the reasons for soil degradation after long term gravel-sand mulch.Therefore,it is recommended that the addition of exogenous soil nutrients after long term gravel-sand can help improve soil quality.

Effects of Different Gravel Mulching on Soil Moisture Status and Regression Model Prediction in Arid Regions

Drought is one of the main factors limiting the agricultural planting and production;gravel mulching is an effective inhibiting evaporation and water-saving planting pattern in the arid regions. In this study, experiments were conducted to study soil moisture effect and regression model with different gravel mulching, the soil moisture content and evaporation were compared that gravel mulched with different particle sizes, different thickness layer and different mulched years. The results showed that: 1) The cumulative soil evaporation of gravel mulched was only 29.3% of that bare fields. Mulching gravel could significantly reduce soil moisture evaporation. 2) The effects of inhibiting soil moisture evaporation are the best when mulch gravel thickness is 10 - 15 cm. 3) The particle size of gravel mulched is smaller, the evaporation inhibition effect will be better. Considering the water holding capacity and material economy, it is the most suitable to mulch gravel with the particle size of 3 - 5 cm. 4) Mulching gravel on the soil surface for 1 - 3 years can improve the soil moisture content. However, the gravel was mulched for more than five years, the soil moisture content decreased significantly. 5) The quadratic polynomial regression fitting model can better simulate and predict the cumulative evaporation on different gravel mulched, and the regression fitting degree R2 is more than 0.98.

Information Technology Research on Productivity Evaluation of Gravel-mulched Field in Ningxia

The evaluation process of traditional land productivity is relatively complex,and the evaluation indices and results cannot display visually.With the development of geographic information system science,there are more and more studies on the GIS-based land productivity evaluation.GIS system can combine the evaluation model with information system software,realizing the visual display of all the evaluation factors.In this paper,with the development process of GIS-based management information system as references,the management information system for GIS-based gravel-mulched field productivity evaluation was designed and developed by combining with the SI model for gravel-mulched field productivity evaluation.The system was developed under VB environment,integrated with MapInfo,and the evaluation results could be shown visually in the system windows.

Experimental and Numerical Analysis of Particle Migration and Patterning Behavior in a Gravel Pack

Due to its long lifespan and high sand-removal efficiency,gravel packing is one of the most applied sand control methods during the recovery of reservoirs with sanding problems.The blockage and retention of injected sand in a gravel pack is a complex process affected by multiple mechanisms.The majority of existing studies based on the phenomenological deep bed filtration(DBF)theory focused on the gravel pack’s overall permeability damage and failed to obtain the inner-pore particle distribution pattern.In this work,experiments and simulations were carried out to reveal the particle distribution in a gravel pack during flooding.In particular,through real-time monitoring of particle migration,the penetration depth and distribution pattern of invaded particles with different gravel-sand particle ratios,fluid viscosities and injection rates could be determined.By simplifying each unit bed element(UBE)into a pore-throat structure with four tunnels(two horizontals for discharge and two verticals for sedimentation),a new network simulation method,which combines deep bed filtration with a particle trajectory model,was implemented.Cross comparison of experimental and numerical results demonstrates the validity and accuracy of the model.

砾石覆盖下的农田土壤环境效应:研究进展与展望

砾石覆盖是旱区特有的一种保护性耕作模式。长期的农业生产实践已经证明,地表覆砂能够很好地适应旱区严酷、恶劣的自然环境,并为当地农业发展和效益提升带来极大助力。然而,砾石覆盖农田退化所带来的一系列负面效应愈加凸显,成为当地农业发展的障碍因子。文章以砾石覆盖的土壤环境效应为脉络,归纳总结了砾石覆盖对土壤水热环境、土壤盐分、土壤有机质、土壤微生物和酶活性,以及水土保持等方面的影响效应和相关机制。同时,进一步指明旱区砂田当前所面临的问题与挑战,并提出该领域未来可持续深化和拓展的方向,主要包括:(1)砾石覆盖农田退化过程中土壤环境的综合演变机制;(2)“砾石-土壤-作物”系统间的协同作用机制;(3)应对砂田退化的农业修复模式及可持续发展路径;(4)砾石覆盖对局部区域气候的影响机制。

砂卵石地层矿山法隧道长管棚支护机理及应用

研究目的:砂卵石地层由于卵石强度高且颗粒分布无序,因此长管棚施工地层扰动大且支护效果难以保证,已成为制约隧道实际应用的一大瓶颈。本文以某轨道交通暗挖法车站为依托工程,采用理论分析、现场测试与数值模拟相结合的方法,对不同直径、不同环向间距条件下长管棚的支护效果进行了深入研究,以期揭示砂卵石地层矿山法隧道长管棚支护机理,提出最佳支护参数。研究结论:(1)砂卵石地层,暗挖隧道管棚超前支护条件下,地层沉降变形在向地表传递过程中,沿高度方向的折减率约为0.91 mm/m;(2)管棚超前支护效果对矿山法隧道工程安全具有决定性作用,须采取措施减小管棚施工扰动及相应地层变形;(3)根据单因素敏感性分析结果,地表沉降随管棚支护长度的增加而增大,随管棚环向间距的增大而增加,且基本呈正相关;(4)为有效控制地表沉降并提高工程经济效益,建议直径127 mm管棚环向间距宜为35 cm,支护长度宜为40 m;直径159 mm管棚建议环向间距宜为40 cm,支护长度宜为40 m;直径209 mm管棚建议环向间距宜为45 cm,支护长度宜为50 m;管棚直径与其最佳打设长度正相关;(5)本研究结论可为砂卵石地层矿山法隧道支护措施提供借鉴与参考。

TRD工法在赣江尾闾围堰防渗工程中的应用

赣江下游尾闾综合整治工程4支枢纽采用TRD工法对防渗墙进行施工,并针对重难点区段调整了施工工艺,该做法克服了地质条件复杂、砂卵砾石地层厚度大、防渗墙深度大等不利因素的影响,施工效率高且安全环保,取得了良好的防渗效果。

基于BP神经网络的胶结砂砾石应力-应变关系预测

在前期宏观试验基础之上,采用离散元模拟和BP神经网络相结合的方法获取不同胶凝材料掺量和围压下胶结砂砾石的应力-应变关系。根据前期胶凝材料掺量分别为20、40、60、80、100 kg/m3的胶结砂砾石三轴排水剪切试验结果,开展离散元数值模拟。以试验数据为学习样本,开展BP神经网络模型训练,预测胶凝材料掺量分别为30、50、70、90 kg/m3的胶结砂砾石应力-应变关系,并将预测结果和离散元模拟结果进行对比。研究结果表明,BP神经网络能够实现胶结砂砾石应力-应变关系的预测,并在较低围压下具有较好的精度。

旱区连作砂田土壤质量和土地生产力演变与调控研究进展

砾石覆盖在改变旱区水文循环和物质转化方面有着至关重要的作用。然而,长期连作给砂田土壤质量及土地生产力带来危机和不确定性。以连作砂田为研究对象,归纳总结了连作年限对砂层质地结构、土壤物理结构、土壤水盐热效应、土壤养分状况、土壤酶活性、土壤微生物特性、作物生长发育以及产量品质的影响效应和可能机制,发现砂田土壤生态环境和土地生产力在人类活动及自然侵蚀的扰动和破坏下整体呈现退化态势,但对不同覆盖条件、施肥水平和种植结构等农田管理措施的响应过程表现出差异性。继而,基于土壤质量和土地生产力的协同和互作效应深入揭示了砂田性能逐年退化机理,并简述了生物、农业及工程调控措施在砂田退化阻控和修复方面的应用进展。在此基础上,提出了砂田退化进程中急需解决的关键科学问题和未来发展方向,主要包括土壤质量演变的基本过程及其发生机制、“砾石-土壤-微生物-植物”系统的叠加和互作效应及其分子机理、土壤改良与生物防治措施的定量化及其调控机制三个方面。在气候变化、植被演替和土地退化背景下,废弃风化砾石的劣化增肥机制及其环境效应将是今后研究的重点。

基于沙漠治理智能小车的创新实验教学系统设计

针对教育部提出的提高高校学生的创新和实践能力,该实践教学系统依托学科竞赛,设计了沙漠治理自动化装置,将智能小车和砾石铺设装置组合在一起,通过控制系统控制智能小车的行驶轨迹,同时控制砾石铺设装置,将砾石按田字形规律铺设,达到减轻人工铺设的劳动量,提高铺设效率。该实践教学系统激发了学生的兴趣和潜能,培养了学生的科研能力和创新精神。

面板堆石坝含特细砂砂砾石填筑料碾压特性研究

阿尔塔什水利枢纽工程大坝主堆石区填筑料以砂砾石料为主,该地区河滩砂砾石料颗粒级配中的砂为特细砂,其在砂的级配中缺少中粗砂、级配不连续、保水性较差等特殊性级配料的特点导致其在施工过程中势必会影响到碾压的压实效果,给施工过程的质量控制带来很大难度。阐述了施工中通过对含特细砂砂砾石填筑料进行的不同加水量、不同厚度、不同碾压遍数及碾压机械等不同的碾压工艺参数进行试验检测、综合统计分析研究,探索出适合该工程的相关碾压施工参数标准,优化了施工碾压参数,提升了施工现场试验检测控制的时效性,为大坝填筑建设提供了稳定、可靠的施工参数,增强了坝体整体填筑的可靠性,为减小坝体沉降变形、提高大坝抗震安全储备和控制大坝施工质量等提供了有利条件。

小山口水电站砂砾石面板坝三维静、动力有限元计算分析

鉴于小山口水电站为软岩基础,坝体较长,且混合坝接头部位非常复杂。为了解决该坝体面临的变形控制难、坝体抗震等级高等设计难题,结合砂砾石面板坝结构、坝壳料设计,通过构建三维有限元模型,该模型包括坝体、泥岩和沙质泥岩基础组成。在静力本构分析中,采用了非线性邓肯E-B模型,而在动力本构分析中,则使用了等效线性粘弹性模型。通过这个模型,对坝体的应力和变形进行了全面系统的研究和分析,同时对坝体的抗震性能和抗震稳定性进行了验证。结果表明,在各种工况下坝体所表现出的变形规律合理。同时在混凝土面板最大拉应力和压应力都符合所采用混凝土材料的允许应力要求,坝体的抗震性能和抗震稳定性满足规范要求。

南海岛礁珊瑚砂砾混合料动力特性试验研究

在南海岛礁实际建造工程中,上部吹填地基材料以大小砂砾共存、混杂无序的状态分布。地层中砂砾混合分布状态使地基在地震等动荷载下呈现出复杂的力学响应。通过开展一系列不同含砾量、密实度、围压和初始剪应力条件下的不排水循环三轴剪切试验,研究珊瑚砂砾混合料在不同工况下的动力特性。试验结果表明,无论是在松散还是密实状态,含有珊瑚砾的混合料试样在循环荷载下表现出更缓的轴向应变增长和孔隙水压上升的变化趋势。与单一珊瑚砂所构成的试样相比,珊瑚砂砾料试样具有更高的抗液化能力。珊瑚砂砾混合料抗液化强度随着含砾量、密实度和初始剪应力的增大而显著提高。密实珊瑚砂砾料的抗液化强度随围压的增大而减小,而针对松散试样没有发现明显规律,这可能是围压和密实度耦合影响引起的。试验结果表明含砾量对试样抗液化强度的影响主要受混合料骨架结构所控制,混合料骨架大致可分为粗颗粒(珊瑚砾)和细颗粒(珊瑚砂)结构主导两种状态。二元介质属性是开展砂砾混合料力学特性研究所必须考虑的影响因素。

根-土复合体抗剪强度影响因素研究

为比较根-土复合体组分及法向应力对其抗剪强度的影响程度,选取四川省喜德县冕山镇坡面(安宁河流域砾砂区)云南松根-土复合体和素土作为研究对象,通过室内直剪试验获得其抗剪强度,烘干试验获得各组分质量,利用根-土复合体的干土质量、水质量和干根质量进行Pearson相关分析,构建回归分析模型计算根-土复合体各组分质量与抗剪强度的标准化回归系数。结果表明:根-土复合体的干土质量与干根质量间存在显著负相关关系(P=0.002<0.01,r=-0.792),根-土复合体中水质量与干土质量和干根质量之间均无显著相关关系(P>0.05);云南松根-土复合体中干土质量、干根质量和水的质量与抗剪强度的标准化回归系数分别为0.06、0.03和0.03,表明干土质量对根-土复合体抗剪强度的影响程度较水的质量和干根质量的影响程度大;与素土的内摩擦角和黏聚力相比,云南松根-土复合体的内摩擦角增加了1.31%~1.97%,黏聚力增加了16.71%~34.74%。

复合过水围堰高效填筑技术

针对非洲的朱利叶斯·尼雷尔(Julius Nyerere)水电站大坝成功截流后,上游过水围堰建造期短、工程量大、施工要求高等难题,提出了一种复合过水围堰新型高效填筑技术,重点介绍了底部赶水混凝土浇筑、左岸堆石混凝土浇筑、下游预制挡块模板施工、上游黏土防渗层平起施工、主体胶凝砂砾石变态碾压施工5种高效填筑施工流程及关键技术。工程实践表明,该新型高效填筑技术大幅优化了施工组织与效率,最终在汛期来临之前安全、高效、优质地完成了过水围堰的修筑工作。