Do cover crops change the lability of phosphorus in a clayey subtropical soil under different phosphate fertilizers?

Plants have developed different mechanisms to absorb and solubilize phosphorus (P) in the soil, especially in environments with low P availability. This study evaluated the effects of different winter cover crops on soil P availability in a clayey subtropical (Hapludox) soil receiving soluble P fertilizer and a rock phosphate applied to the summer crop, under no‐tillage. The experiment was carried out over 3 yrs (2009–2011) with five different cover crop species: common vetch, fodder radish, ryegrass, black oat, white clover and fallow as control. The soil was sampled after the third year of cover crop cultivation and analysed for inorganic and organic P forms according to the well‐established Hedley fractionation procedure. Phosphate fertilizers promoted accumulation of both labile and nonlabile P pools in soil in the near surface layer, especially under rock phosphate. Fertilizer applications were not able to change P fractions in deeper layers, emphasizing that the Brazilian clayey soils are a sink of P from fertilizer and its mobility is almost nil. Although the cover crops recycled a great amount of P in tissue, in a short‐term evaluation (3 yrs) they only changed the content of moderately labile P in soil, indicating that long‐term studies are needed for more conclusive results.     

单轴压缩条件下岩石破损过程的CT试验分析

采用工业计算机层析(ICT)设备与全数字液压实验系统EHF-EG200KN试验机,对大台煤矿冲击倾向性煤层底板岩石试样进行了单轴压缩荷载作用下的CT试验,得到了单轴压缩荷载作用下不同应力阶段岩石试样微裂纹发展的CT图像。通过对CT图像灰度值的分析,得到单轴压缩荷载作用下岩石的损伤破裂过程。为进一步研究煤层底板岩石的破坏及冲击地压的发生机理提供依据。     

西南喀斯特区砾石对石灰土土壤孔隙及水分入渗的影响

[目的] 砾石是影响土壤孔隙和水分入渗的重要因素,明确砾石通过改变哪些土壤孔隙特征进而影响水分入渗具有重要意义。[方法] 以西南喀斯特地区砾石含量高的石灰土为研究对象,采用CT扫描和室内一维土柱入渗试验,对比分析2种砾石粒径(2.0~5.0,5.0~12.5 mm)和5种砾石含量(0,10％,20％,30％,40％)条件下的土壤孔隙特征及水分入渗特性,并使用结构方程模型探究土壤孔隙特征与入渗特性之间的耦合关系。[结果] (1)含砾石土壤的大孔隙度、孔隙连通率、孔隙形状因子、孔隙表面积和孔隙体积均高于无砾石土壤;且当砾石含量为20%和30%时,孔隙连通率与孔隙形状因子和无砾石土壤之间存在显著性差异(p<0.05);(2)砾石改善土壤入渗性能,粒径为2.0~5.0 mm时,砾石含量从10%到40%的稳定入渗率分别是无砾石土壤的4.02,5.00,2.88,5.14倍,累积入渗量分别是1.67,1.76,2.49,2.39倍;粒径为5.0~12.5 mm时,土壤稳定入渗率分别是无砾石的2.20,2.67,4.78,2.78倍,累积入渗量分别是1.42,1.75,2.46,2.02倍。(3)在结构方程模型中砾石含量与孔隙连通率、孔隙等效直径呈正相关关系,孔隙连通率对稳定入渗率的影响最大,孔隙等效直径对累积入渗量的影响最大。[结论] 砾石含量主要通过增加土壤孔隙连通率和孔隙等效直径促进水分入渗,研究结果可为深入认识西南喀斯特地区含砾石土壤的水文过程提供科学依据与理论参考。     

保水剂对用于高陡岩石边坡人工基质的性状影响

 客土基质配方对基质在陡峭岩石边坡上的抗侵蚀能力以及构成客土基质的各个组分及其相互作用对植物生长的影响的研究势在必行。本研究以解决上述工程技术使用过程中的人工基质水分问题为目的,对保水剂加入土壤后的保水、吸水特性及保水剂对土壤物理性质的影响进行系统研究。结果显示：所用保水剂的最大吸水倍率达到500倍以上,将其加入土壤后,土壤水分状况得到显著改善（p<0.05）,同时,土壤对保水剂的吸水和保水特性均有显著影响。在30℃及50℃的温度胁迫下,可分别持续保水12h和8h。另外,土壤容重,比重随着保水剂添加浓度的增加而下降,而孔隙度随保水剂的增加而上升,但3个物理变量值在各处理浓度间的差异均不显著（p>0.05）。     

金安桥水电站初次蓄水对导流洞稳定性影响的计算分析

金安桥水电站下闸蓄水后，陡升的库水位将对导流洞结构稳定造成不利影响。为保障堵头封堵前的导流洞结构稳定性，运用三维弹塑性损伤有限元，在模拟进水口边坡及导流洞开挖支护的基础上，计算汛前下闸水位时的岩体渗流场，对导流洞围岩和衬砌在岩体渗流作用下的结构稳定性进行复核分析。分析结果表明，导流洞的围岩稳定性在蓄水后仍有保障，衬砌结构受力较小，现有环向配筋满足结构内力要求，但在进水口变截面和导流洞变截面部位沿水流方向的拉应力较大，使得衬砌出现开裂。进一步分析表明，上述区域的开裂范围有限，对整体衬砌结构影响较小。     

The Influences of Surrounding Rock Deformation in Deep Roadway under Different Supporting Structures

随着煤矿开采深度的不断增加，围岩变形特征更加复杂。基于ANSYS数值模拟软件，研究4种不同支护条件下深部巷道围岩的变形情况，研究结果表明：30MPa原岩应力作用下，联合支护产生的水平位移和垂直位移都要比其他支护小，变形影响区域也最小，最为适合围岩地质条件较差的巷道。     

The Application of Pre-splitting Blasting to Excavation on High Slope in Soft Rock Section

Based on analyzing about blasting mode of slope in the construction of road, the paper shows that pre splitting blasting is mostly suitable in the section of severely weathering soft rock with developed joints and fractures, introduced the laying out about the hole of pre splitting blasting that can apply in the high slope of the expressway in the section, and designed the parameter. The practice shows that it gained favourable effect by this method.     

直墙拱形巷道围岩应力场分析

为得出直墙拱形巷道围岩应力分布规律,应用复变函数弹性理论推导了直墙拱形巷道围岩应力分布的解析表达式。对直墙拱形巷道边界的围岩应力和巷道水平线方向的围岩应力分布规律进行分析,并考虑直墙拱形巷道断面高宽比和侧压系数对其影响规律。研究表明：在不同巷道断面高宽比、侧压系数下,直墙拱形巷道围岩应力集中区域主要集中在直墙底部底角处、拱形顶板中点附近和底板中部3个位置。不同巷道断面高宽比下,直墙拱形巷道沿水平线的应力分布规律基本相同。侧压系数大于1时,采用巷道断面高宽比小于1较有利于巷道稳定;侧压系数小于等于1时,采用巷道断面高宽比大于1较有利于巷道稳定。