Effects of mixed-based biochar on water infiltration and evaporation in aeolian sand soil

Aeolian sandy soil in mining areas exhibits intense evaporation and poor water retention capacity.This study was designed to find a suitable biochar application method to improve soil water infiltration and minimize soil water evaporation for aeolian sand soil.Using the indoor soil column method,we studied the effects of three application patterns(A(0-20 cm was a mixed sample of mixed-based biochar and soil),B(0-10 cm was a mixed sample of mixed-based biochar and soil and 10-20 cm was soil),and C(0-10 cm was soil and 10-20 cm was a mixed sample of mixed-based biochar and soil)),four application amounts(0%(control,CK),1%,2%,and 4%of mixed-based biochar in dry soil),and two particle sizes(0.05-0.25 mm(S1)and<0.05 mm(S2))of mixed-based biochar on water infiltration and evaporation of aeolian sandy soil.We separately used five infiltration models(the Philip,Kostiakov,Horton,USDA-NRCS(United States Department of Agriculture-Natural Resources Conservation Service),and Kostiakov-Lewis models)to fit cumulative infiltration and time.Compared with CK,the application of mixed-based biochar significantly reduced cumulative soil water infiltration.Under application patterns A,B,and C,the higher the application amount and the finer the particle size were,the lower the migration speed of the wetting front.With the same application amount,cumulative soil water infiltration under application pattern A was the lowest.Taking infiltration for 10 min as an example,the reductions of cumulative soil water infiltration under the treatments of A2%(S2),A4%(S1),A4%(S2),A1%(S1),C2%(S1),and B1%(S1)were higher than 30%,which met the requirements of loess soil hydraulic parameters suitable for plant growth.The five infiltration models well fitted the effects of the treatments of application pattern C and S1 particle size(R2>0.980),but the R2 values of the Horton model exceeded 0.990 for all treatments(except for the treatment B2%(S2)).Compared with CK,all other treatments reduced cumulative soil water infiltration,except for B4%(S2).With the same application amount,cumulative soil water evaporation difference between application patterns A and B was small.Treatments of application pattern C and S1 particle size caused a larger reduction in cumulative soil water evaporation.The reductions in cumulative soil water evaporation under the treatments of C4%(S1),C4%(S2),C2%(S1),and C2%(S2)were over 15.00%.Therefore,applying 2%of mixed-based biochar with S1 particle size to the underlying layer(10-20 cm)could improve soil water infiltration while minimizing soil water evaporation.Moreover,application pattern was the main factor affecting soil water infiltration and evaporation.Further,there were interactions among the three influencing factors in the infiltration process(application amount×particle size with the most important interaction),while there were no interactions among them in the evaporation process.The results of this study could contribute to the rational application of mixed-based biochar in aeolian sandy soil and the resource utilization of urban and agricultural wastes in mining areas.

Effects of forest cover types and environmental factors on soil respiration dynamics in a coastal sand dune of subtropical China

Trees on sand dunes are more sensitive to environmental changes because sandy soils have extremely low water holding capacity and nutrient availability. We investigated the dynamics of soil respiration(Rs) for secondary natural Litsea forest and plantations of casuarina,pine, acacia and eucalyptus. Results show that significant diurnal variations of Rsoccurred in autumn for the eucalyptus species and in summer for the pine species, with higher mean soil respiration at night. However, significant seasonal variations of Rswere found in all five forest stands. Rschanged exponentially with soil temperatures at the 10-cm depth; the models explain 43.3–77.0% of Rs variations. Positive relationships between seasonal Rsand soil moisture varied with stands. The correlations were significant only in the secondary forest, and the eucalyptus and pine plantations. The temperature sensitivity parameter(Q10 value) of Rsranged from 1.64 in casuarina plantation to 2.32 the in secondary forest; annual Rswas highest in the secondary forest and lowest in the pine plantation. The results indicate that soil temperatures and moisture are the primary environmental controls of soil respiration and mainly act through a direct influence on roots and microbial activity. Differences in root biomass, quality of litter,and soil properties(pH, total N, available P, and exchangeable Mg) were also significant factors.

The Effects of Different Ratios of Feldspathic Sandstone and Sand Compound Soil on Water-stable Aggregates in 4 Years Crop Planting

To study the formation process of feldspathic sandstone and sand compound soil in the Mu Us Desert,1∶ 1,1∶ 2 and 1∶ 5 ratios of feldspathic sandstone and sand were mixed to obtain compound soil to plant crops,and analyze the rules of changes in water-stable aggregates of the compound soil among the 4 years crops growing process. The results showed,before crop planting,the order of mass percent of> 0. 25 mm and 0. 25-2. 00 mm water-stable aggregates in three kinds of compound soil was 1∶ 1 > 1∶ 2 > 1∶ 5,showing that the overall content was low; the mass percent of > 0. 25 mm water-stable aggregates remained at 18. 38%-28. 22%; the mass percent of 0. 25-0. 50 mm,0. 50-2. 00 mm,2. 00-5. 00 mm,and > 5. 00 mm water-stable aggregates was close with each other in each kind of compound soil. After4 years of planting,the mass percent of > 0. 25 mm water-stable aggregates in 1∶ 2 compound soil increased significantly and exceeded other2 kinds of compound soil,reached 32. 34%; the main components of > 0. 25 mm water stable aggregates in 1∶ 1,1∶ 2,and 1∶ 5 compound soil were 0. 25-0. 50 mm( 53. 54%),0. 25-0. 50 mm( 59. 43%),0. 05-2. 00 mm( 52. 16%),aggregates; 0. 25-2. 00 mm aggregates increased significantly in all three kinds of compound soil,with the highest increase in 1∶ 2 compound soil; the organic matters of 1∶ 2 compound soil were significantly correlated with 0. 25-0. 50 mm and 0. 25-2. 00 mm water-stable aggregates. The results showed that the ratio of 0. 25-2. 00 mm aggregates in the three kinds of compound soil was increased after 4 years of crop planting and 1∶ 2 compound soil was most favorable for the formation of aggregates.

Impact of sand burial on maize(Zea mays L.)productivity and soil quality in Horqin sandy cropland,Inner Mongolia,China

Croplands are often suffering from sand burial in dry regions of northern China. For studying this phenomenon, we carried out a case study of field experiment including four sand burial levels, i.e. shallow （1-3 cm）, moderate （8-12 cm） and deep （15-20 cm） sand burials, and no sand burial （control, CK）, in a typical agro-pastoral transitional zone in Naiman Banner of eastern Inner Mongolia. The aim of this study was to assess the impacts of sand burial on maize （Zea rnays L.） productivity and the soil quality along a gradient of burial depths. Results showed that there was a strong negative effect of sand burial on maize productivity and soil quality, which significantly declined （P〈0.05） under moderate and deep sand burial treatments. In comparison with the CK, the maize yield and above-ground biomass reduced by 47.41% and 39.47%, respectively. The soil silt and clay, soil water, soil organic carbon and total nitrogen contents under deep sand burial decreased by 67.85%, 40.32%, 86.52% and 82.11%, respectively, while microbial biomass carbon, microbial abundance and enzyme activity decreased by 89.78%, 42.28%-79.66% and 69.51%-97.71%, respectively. There was no significant effect on crop productivity and soil quality with shallow sand burial treatment. The correlations analysis showed that there was significant positive correlations of both maize yield and above-ground biomass with soil silt and clay, soil organic carbon and total nitrogen contents, pH, electrical conductivity, soil water content, microbial abundance and biomass and all tested soil enzyme activities. Stepwise regression analysis indicated that soil water and total nitrogen contents, urease, cellobiohydrolase and peroxidase activities were key determining factors for maize productivity. This combination of factors explains reason of the decreased maize productivity with deep sand burial. We found that degradation of cropland as a result of sand burial changed soil physical-chemical properties and soil enzyme activities in the plow layer, and decreased overall maize productivity. Furthermore, decreased soil enzyme activity was a better indicator to predict sandy cropland degradation.

Soil restoration research advances of artificial sand-binding vegetation ecosystem in the Tengger Desert, Northern China

Soil plays an important role in desert ecosystem, and is vital in constructing a steady desert ecosystem. The management and restoration of desertified land have been the focus of much discussion. The soil in Shapotou desert region has developed remarkably since artificial sand-binding vegetation established in 1946. The longer the period of dune stabilization, the greater the thickness of microbiotic crusts and subsoil. Meanwhile, proportion of silt and clay increased significantly, and soil bulk density declinced. The content of soil organic matter, N, P, and K similarly increased. Therefore, soil has developed from aeolian sand soil to Calcic-Orthic aridisols. This paper discusses the effects brought about by dust, microbiotic soil crust and soil microbes on soil-forming process. Then, we analyzed the relation between soil formation and sand-binding vegetation evolution, in order to provide a baseline for both research on desert ecosystem recovery and ecological environment governance in arid and semi-arid areas.

Factors Influencing the Soil-Water Characteristics of Unsaturated Tropical Silty Sand

Fine grain soils have a complex engineering behaviour which depends but not limited to moisture content, changes in external pressure and characteristics of the pore medium. Sand often contains a considerable percent of silt which is expected to alter its natural behaviour. This composite matrix is referred to as silty-sand. To understand the behaviour of this matrix under varying moisture conditions, some of the factors influencing the soil-water characteristics of unsaturated silty sands were investigated. Representative samples were collected from a river bank after its index properties were predetermined in the laboratory. The samples were compacted at different moisture conditions and compactive efforts. With the pressure plate extractor device, the Soil-Water Characteristic (SWC) was obtained and SWC Curves plotted. Compaction at greater compactive effort (modified proctor) and optimum moisture content produced the largest air entry value and reduced air voids. The air entry values of the soils obtained ranged from 21 kPa to 57 kPa. Also changes in the shape of the SWCC were consistent with changes in pore size which occur by varying compaction conditions. Result shows that soil structure, compaction water content, compactive effort and percentage of fine particles are factors affecting the Soil-Water Characteristics.

Discussion on wind factor influencing the distribution of biological soil crusts on surface of sand dunes

Biological soil crusts are widely distributed in arid and semi-arid regions, whose formation and development have an important impact on the restoration process of the desert ecosystem. In order to explore the relationship between surface airflow and development characteristics of biological soil crusts, we studied surface airflow pattern and development characteristics of biological soil crusts on the fixed dune profile through field observation. Results indicate that the speed of near-surface airflow is the lowest at the foot of windward slope and the highest at the crest, showing an increasing trend from the foot to the crest. At the leeward side, although near-surface airflow increases slightly at the lower part of the slope after an initial sudden decrease at upper part of the slope, its overall trend decreases from the crest. Wind velocity variation coefficient varied at different heights over each observation site. The thickness, shear strength of biological soil crusts and percentage of fine particles at crusts layer decreased from the slope foot to the upper part, showing that biological soil crusts are less developed in high wind speed areas and well developed in low wind speed areas. It can be seen that there is a close relationship between the distribution of biological soil crusts in different parts of the dunes and changes in airflow due to geomorphologic variation.

SAND: An Additive for Stabilzation of Swelling Clay Soils

An experimental program carried out in this study seeks to understand the physical mechanisms of stabilization of an expansive soil by adding an inert material (sand) at various forms;mixing and intercalation layers of sand. The first aim of the study is to analyze the effect of stabilization on the variation of soil consistency. The results show a marked improvement in soil consistency. Then a study of the effect of the additives on the variation of the swelling in order to solve the lifting structures caused by this phenomenon is carried out. It can be seen that the addition of sand is capable of reducing the swelling action. We complete the study using an ultrasonic device, measuring the propagation velocities of ultrasonic pulse through the tested clay samples. This shows a change occurring in the porosity of the clay when sand is added to it. As a result some interesting conclusions concerning the expansive soil-material amendment are drawn.

Effects of dune stabilization on vegetation characteristics and soil properties at multiple scales in Horqin Sandy Land,Northern China

Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however information on how dune stabilization influences vegetation and soil at different spatial scales is still lacking. In this study, we measured vegetation characteristics and soil properties across three spatial scales （10, 100 and 1,000 m^2） along gradient dune stabilization stages （mobile dune, semi-fixed dune and fixed dune） in Horqin Sandy Land, Northern China. Vegetation cover over all scales significantly increased with degree of dune stabilization, as well as species richness and C/N ratio at 10 m^2 scale. Species richness significantly increased with the increase in measured scales at each stage of dune stabilization and was higher in fixed dune than that in mobile dune and semi-fixed dune at 100 and 1,000 m^2 scales. Over all scales, aboveground biomass was lower in mobile dune than that in semi-fixed dune and fixed dune, and soil organic C, total N, EC, very fine sand and silt ＋ clay contents were higher in fixed dune than those in mobile dune and semi-fixed dune. These results suggest that along the gradient dune stabilization, species richness has strong spatial scale-dependence, but vegetation cover, aboveground biomass and soil properties is generally scale independent （i.e., the pattern of response is consistent across all scales）. Effect of dune stabilization on vegetation and soil over all spatial scales results in the positive correlation among vegetation cover, species richness, biomass, soil organic C, total N, C/N, EC, very fine sand and silt ＋ clay along the gradient dune stabilization. In addition, species response to dune stabilization. Thus, the monitoring strategies diversity in semiarid dune ecosystems. richness at the smallest scale （10 m^2） has more sensitive at small scales are essential to detect changes of species

Experimental research on the mixed sand ratio and initial dry density of weathered sand improved expansive soil free load swelling rate

In this paper, through the indoor free load swelling rate test, expansive soil in a section of a first- class highway reconstruction project in Yichang City was studied. It emphatically analyzed the interrelations among free load swelling rate, non-load time, the proportion of mixed sand and initial dry density. Experimen- tal studies have shown that： Free load swelling deformation is mainly divided into three stages of rapid expan- sion, slow expansion and final stability; when the initial dry density is constant, free load swelling rate of the weathered sand modified soil will reduce rapidly before they slow down with the increase of sand proportion, and weathered sand modified soil free load swelling rate is not sensitive to the large amount of sand mixed; in the same mixed sand ratio, weathered sand modified soil free load swelling rate increases rapidly with the in- crease of initial dry density, there is a good linear correlation between them. To take appropriate control of the initial dry density during the expansive soil subgrade construction helps to reduce its swelling deformation and ensures the stability of the embankment.

泡沫轻质土回填管道沟槽路面表层动力响应研究

市政道路下伏管道沟槽常采用土、砂子、碎石等传统散体材料回填,由于沟槽空间受限,压实度难以满足设计要求,管道破损渗漏或交通荷载作用下,容易造成路面开裂,甚至塌陷。泡沫轻质土具有轻质、高强、自密实、抗渗漏等特性,可以将其应用于管道沟槽回填工程。为了研究泡沫轻质土回填管道沟槽的路面动力响应特性,以振动加速度和动位移为动力响应指标,开展泡沫轻质土回填段和中砂回填段的路面动力响应现场试验。试验车速分别为20,40和60 km/h,车重分别为空载、半载、满载,共9种试验工况。研究结果表明,泡沫轻质土回填区段测点振动加速度最大值、动位移最大值分别为31.93 mm/s^(2)、6.23μm,而中砂回填区段分别为35.79 mm/s^(2)、6.90μm。振动加速度峰值、动位移峰值均随车重、车速的增加而增大。车重由空载变为满载时,泡沫轻质土回填区段测点动位移峰值变化幅度仅为中砂回填区段测点的15.2%~51.0%;车速由20 km/h增加至60 km/h时,动位移峰值变化幅度为中砂回填区段测点的16.8%~66.8%。泡沫轻质土回填区段振动加速度峰值衰减率、动位移峰值衰减率分别为中砂回填区段的1.16~1.38倍及1.15~1.33倍,削减了沟槽回填区段路面测点振动的高频和低频成分,泡沫轻质土回填区段整体刚度较好,减振效果良好。研究成果可为泡沫轻质土回填管道沟槽的设计施工提供参考。

基于含冰量的冻结砂土-混凝土接触面蠕变特性

保证高含冰量冻土区桩基础的长期稳定性是多年冻土区桥梁桩基础安全服役中的关键问题,为研究含冰量对冻土-混凝土接触面蠕变特性的影响,采用自行研制的大型蠕变剪切仪,在−2℃条件下开展含冰量为6%、12%、16%、23%、36%、60%、80%的冻结砂土与混凝土接触面蠕变试验.试验结果表明:在恒定的剪应力作用下,除含冰量为6%试样出现加速蠕变外,其他试样仅出现衰减蠕变及稳定蠕变2个阶段;随含冰量的增大,试样黏性变形占比增大,含冰量为80%试样的黏性变形超过总变形量的80%;稳定蠕变速率受到干密度及含冰量的综合影响,含冰量为16%时稳定蠕变速率最小;Burgers黏弹性模型能较好地模拟高含冰量冻结砂土-混凝土接触面蠕变曲线;随着含冰量的增大,初始剪切模量和稳定蠕变阶段黏滞系数先增大后减小,初始蠕变阶段的渐进剪切模量呈幂函数减小,初始蠕变阶段黏滞系数呈幂函数增大.

A 3D Numerical Simulation of Sand Drain Element in the Soft Soil of Guangzhou-Zhujiang Highway,China

The behavior of sand drain was estimated so that the size of very large load-pressure could be eliminated by changing the configuration of the sand drain elements into sand wall.A 3D mathematical model was formulated to transform the configuration of a sand drain into a sand wall to minimize or eliminate the excessive stress and primary settlement on the road base.This was barely considered in the past. According to soil mechanics theory and seepage characteristics of sand drain in road base foundations, a 3D sand drain element in FEM format was generated,and a matrix expression was formulated which was introduced into 3D Biot Consolidation

由石蜡基相变材料和煤渣改良的粉砂土的冻融性能

【目的】针对季节冻土区渠道的衬砌结构因冻融作用而受损的现状,同时为了解决石蜡基相变材料(phase change materials, PCM)的泄露,并满足煤渣的再利用需求,研究石蜡基PCM和煤渣对土体冻融性能的影响。【方法】以粉砂土为研究对象,选取石蜡基PCM和煤渣作为改良剂,制备石蜡基PCM改良土和石蜡基PCM-煤渣改良土;通过冻融循环作用下的体积变化率试验、无侧限抗压强度试验,微观结构及潜热研究土体的体积和无侧限抗压强度的变化。【结果】石蜡基PCM能抑制粉砂土的冻融变形,质量分数为8%时2种改良土的体积变化率最小;随着冻融循环次数的增加,土体的无侧限抗压强度均降低,降低速率先大后小;循环次数相同时,加入煤渣的改良土的无侧限抗压强度均大于未加入煤渣的;冻融循环9次后,石蜡基PCM质量分数为10%的石蜡基PCM改良土的无侧限抗压强度最低;2种改良土的结构比粉砂土更密实、稳定;潜热的吸收或释放延缓了土体冻融过程。【结论】将石蜡基PCM和煤渣共同掺入粉砂土,能控制土体的冻融变形且效果稳定,改善土体的冻融性能,减轻季节冻土区输水渠道衬砌结构的冻害,提高煤渣的利用率。

Characteristics of soil seed banks at different geomorphic positions within the longitudinal sand dunes of the Gurbantunggut Desert, China

Understanding the characteristics of soil seed banks in sand dunes is crucial to stabilize the dune systems and maintain the plant populations in deserts. In this study, we conducted a survey investigation in the field and a seed germination experiment in the laboratory to explore the characteristics of soil seed banks at various geomorphic positions of longitudinal sand dunes in the Gurbantunggut Desert, China. Totally, 17 plant species belonging to 17 genera and 9 families were identified in soil seed banks, and 35 plant species belonging to 34 genera and 17 families were identified in aboveground vegetation. Plant species richness in soil seed banks decreased with increasing soil depth. The highest species richness was presented in the upper slope of the windward slope and the lowest species richness was presented in the base of the windward slope. There was no significant difference in seed density of soil seed banks among the examined seven geomorphic positions. The highest seed density occurred in the lower slope of the leeward slope while the lowest occurred in the crest. Moreover, seed density decreased with increasing soil depth, being the highest in the upper soil layer （0-2 cm）. For both soil seed banks and aboveground vegetation, there was no significant difference in Simpson＇s diversity index among the seven geomorphic positions; however, Shannon-Wiener diversity index and Pielou＇s evenness index showed significant differences among the seven geomorphic positions. Those results showed that although there was no significant difference in seed density of soil seed banks among the seven geomorphic positions, the geomorphic positions significantly affected the species richness, diversity and distribution of soil seed banks. Therefore, understanding the characteristics of soil seed banks at different geomorphic positions of sand dunes is essential to vegetation restoration or reestablishment. Furthermore, the Jaccard＇s similarity coefficients of plant species between soil seed banks and aboveground vegetation at the seven geomorphic positions were low, suggesting that vegetation restoration or reestablishment processes should be promoted through adding seeds to surface layers.

Vertical distribution of soil moisture and surface sandy soil wind erosion for different types of sand dune on the southeastern margin of the Mu Us Sandy Land,China

Soil moisture is a critical state affecting a variety of land surface and subsurface processes. We report investigation results of the factors controlling vertical variation of soil moisture and sand transport rate of three types of dunes on the south- eastern margin of the Mu Us Sandy Land. Samples were taken from holes drilled to a depth of 4 m at different topographic sites on the dunes, and were analyzed for soil moisture, grain-size distribution and surface sediment discharge. The results show that： （1） The average soil moisture varies in different types of dunes, with the following sequences ordered from highest to lowest： in the shrubs-covered dunes and the trees-covered dunes the sequence is from inter-dunes lowland to windward slope to leeward slope. The average moisture in the bare-migratory sand dunes is sequenced from inter-dunes lowland to leeward slope to windward slope. （2） Vegetation form and surface coverage affect the range of soil moisture of different types of dunes in the same topographic position. The coefficient of variation of soil moisture for shrubs-covered dunes is higher than that of other types of dune. （3） The effect of shrubs on dune soil moisture is explained in terms of the greater ability of shrubs to trap fine-grained atmospheric dust and hold moisture. （4） The estimated sand transport rates over sand dunes with sparse shrubs are less than those over bare-migratory dunes or sand dunes with sparse trees, indicating that shrubs are more effective in inhibiting wind erosion in the sandy land area.

含泥量对砂类硫酸盐渍土工程特性的影响分析

为了明确含泥量对砂类硫酸盐渍土的盐胀和力学特性的影响,人工配制了不同细粒土含量的砂类硫酸盐渍土,在1%和3%(质量分数,下同)含盐量单向冻结盐胀试验的基础上,选取了细粒土含量为5%、15%、30%和40%的砂样进行常温、低温三轴剪切试验。研究结果表明:此试验条件下,不同级配砂类硫酸盐渍土的冻结温度为-0.7~-0.1℃,当砂样孔隙溶液浓度在冻结温度之上达到饱和时,降温过程中会首先生成盐结晶;1%含盐量条件下,高细粒土含量(≥30%)砂样的起胀温度在4~9℃之内,而低细粒土含量砂样的起胀温度在0℃附近,3%含盐量砂样的起胀温度为20~23℃;试验含水率和细粒土含量通过影响土体中自由水的含量对盐冻胀产生显著影响。在力学特性方面,随着细粒土掺量的增加,砂类硫酸盐渍土的抗剪强度表现出先增大后减小的趋势,细粒土由增强摩擦转变为颗粒间的“润滑”作用;此外,冻结后砂土转变为承载能力更强的“土-盐-冰骨架结构”,抗剪强度大幅提高,并呈现出明显的脆性破坏特征,由于冻结砂土受相对温度的影响,随着含盐量的增加,破坏应力呈先减小后增大的趋势。

泡沫轻质土和砂土回填管道沟槽动力响应数值模拟对比分析

市政道路下覆管道回填区采用砂土等散体材料回填时,控制压实度是施工的关键技术难题之一。引入泡沫轻质土作为管道沟槽回填区材料能较好地解决回填压实度低的问题。为了研究回填管道沟槽泡沫轻质土的动力特性,结合某市政道路回填段行车激励现场试验,沿行车线路横向路面布设8个监测点,建立管道-回填区-路基路面三维动力模型,并施加不同工况下的三轴货车行车荷载激励,数值模拟结果与现场监测点实测数据对比验证了模型的可行性。运用此模型对泡沫轻质土、砂土回填区段的路基路面、管道外壁动力响应及路基工作区深度展开对比分析。结果表明:1)泡沫轻质土回填区沿深度方向动应力峰值衰减率、振动加速度衰减率分别为砂土回填区段的1.63~1.93倍及2.13~3.7倍。2)车重由空载变为满载时,泡沫轻质土回填区和砂土回填区管顶动应力峰值分别增加18.03 kPa和17.86 kPa,说明在回填区上行驶重型车辆时会导致埋地管道振动显著增加。3)泡沫轻质土、砂土回填区管顶和靠近行车一侧动位移峰值比例分别为1.31、1.96,泡沫轻质土回填区管道外壁动位移峰值分布较砂土回填区更加均匀。4)采用泡沫轻质土回填时路基动敏感区和动影响区深度分别为砂土回填的0.68~0.78倍、0.77~0.79倍,对路基稳定性有利。研究结果可为泡沫轻质土在市政道路管道沟槽回填中的相关应用提供参考。

风沙土混拌刀具的改良设计与试验

为解决风沙土改良设备研制中存在的核心问题,探讨混拌刀具与风沙土-改土材料间相互作用机理,以国标旋耕刀IT245为基础,分析其作用原理,在此基础上设计了专用于风沙土改良的混拌刀具,通过离散元仿真模拟及室内沙槽试验,以改土材料体积比为评价指标对国标刀及专用刀具5层深度下的混拌效果进行分析。结果显示,风沙土混拌刀具偏转角度越大,改土材料体积比越大,当深度150—120 mm、偏转角为60°时达到最大值(35.67%);风沙土混拌刀具弯折角越大,改土材料体积比越大,当深度150—120 mm、弯折角为130°时达到最大值(36.02%)。风沙土混拌刀具与国标旋耕刀IT245混拌效果相比,深度越浅,改土材料体积比越大,混合效果越好,在深度90—60、60—30 mm时,偏转角60°的风沙土混拌刀具作业后改土材料体积比分别比IT245增加了3.19%、5.11%。研究结果为风沙土混拌刀具及风沙土治理机械的设计与优化提供依据。

上砂下黏地层中桩-筒复合基础V-H承载特性

海上风机基础不仅受自重等竖向力V作用,也因水流、波浪和风等影响而承受水平荷载H。为探讨上砂下黏地层中一种由单桩和吸力筒组成的新型海上风机桩-筒复合基础受V-H组合作用时的承载特性,自主设计完成了一系列室内桩-筒复合基础V-H组合加载模型试验,获得不同组合参数下桩-筒复合基础的荷载-位移曲线和桩身弯矩分布曲线,并绘制出V-H承载力包络线。在此基础上,采用ABAQUS建立了上砂下黏地层中桩-筒复合基础三维数值分析模型,经模型验证与参数分析,进一步讨论了砂土厚度、筒径、筒高以及加载高度等参数对桩-筒复合基础承载特性的影响曲线,并拟合出桩-筒复合基础承载力简化计算公式,分析结果表明:桩-筒复合基础能显著提高桩身水平承载力,增幅达30%~90%,且增加筒径比增加筒高更有利于提高基础水平承载力;上部砂土层较厚时,桩-筒复合基础存在一个使复合基础水平承载力达到最大的预加竖向荷载最佳值,其值随不同载荷工况在(0.4~0.7)Vult范围内变化。