Lagged Surface Collapse Mechanism of Shield Construction in Sandy Pebble Stratum

As for many lagged surface collapse cases that shield crosses the sandy cobble stratum in Chengdu metro No.1 and 2 lines, lagged surface collapse mechanism in sandy pebble stratum was studied. Conditions of engineering geology about sandy cobble stratum were analyzed. Mechanical behavior of sandy pebble was obtained via large-scale tri-axial test. Discrete element method was adopted for numerical computation on lagged surface collapse mechanism. According to the tri-axial numerical test method, the relation between the micro parameters and macro parameters of the sandy pebble stratum layer in Chengdu was calibrated. The face failure of shield tunneling and upward movement of cavity was simulated by numerical calculation. When supporting pressure is small, the particles with the displacement of over 0.1 m have low contact force. The porosity of earth in the region becomes larger and its mechanical behavior becomes worse. Therefore the region can be identified as instability region. Cavity in the ground will be caused after shield tunneling. Soil arching effect is obvious under shield construction. Even though there is cavity in the ground, surface collapse will not bring about immediately. This is important reason for lagged surface collapse phenomena of shield construction in sandy pebble stratum.     

A Three Dimensional Simplified Method for Analysis of Soil Arching Effect in the Pile-supported Embankments

To improve the understanding of the soil aching effect in the embankment fill, a series of model tests and finite element analysis were carried out. It is found that for low fill height relative to the net pile spacing, H/s－a≤1, the failure surface is vertical or slightly inclined which starts from the pile edge and goes through the whole fill height. For H/s－a≥1.5, the developed bulb shaped rupture surface is located near the pile head and can be approximated as a logarithmic spiral surface. By using the failure surface shape determined from the model test and FEM analyses, a three dimensional simplified method to evaluate the soil arching effect was proposed. The computed results were compared with FEM results and the experimental data collected from literatures, it is found that the present simplified method can predict reliable results.     

宁夏白芨滩地区风沙土理化性质初步研究

为了研究宁夏河东沙区白芨滩地区风沙土的理化性质,通过野外调查、采样及室内实验分析,对研究区流动沙丘、半流动沙丘及草方格固定沙丘风沙土理化性质进行了测定分析。结果表明:土壤含水量均较低,土壤含水量的平均值表现为草方格固定沙丘半流动沙丘流动沙丘。风沙土土壤粒度组成表现为各层均以细沙颗粒为主,中沙颗粒含量次之,极细沙含量较小。流动沙丘的表层含有非常少量的粗沙颗粒,半流动沙丘和草方格固定沙丘各层几乎没有粗沙颗粒。而草方格固定沙丘的表层含有少量的粉沙颗粒,其余各层均无粉沙颗粒。土壤容重从表层向下逐渐减小,流动沙丘和半流动沙丘容重较为接近,而草方格表层沙土容重明显较小。土壤养分流动沙丘、半流动沙丘和草方格固定沙丘的养分含量较接近,差异不显著,而且各类型沙丘养分的垂直变化无明显规律,变化不稳定。     

秸秆改良材料对沙质土壤饱和含水量的影响

为提高沙质土壤饱和含水量,以作物秸秆为主材,以膨润土和聚丙烯酰胺(PAM)为添加剂配制沙质土壤改良材料,采用模拟试验研究秸秆改良材料不同配比、施用量与时间等因素对沙质土壤饱和含水量的影响。结果表明：施加秸秆改良材料可以增加沙质土壤饱和含水量,不同秸秆改良材料改良效果不同,且随着改良材料施用量、配方中PAM含量（<2%）的增加、土培时间（< 60天）的延长,沙质土壤饱和含水量呈现增加趋势;添加剂量为10 g/kg,配方中PAM含量为2%的麦秆改良材料的土样,在土培60天后,饱和含水量为52.6%,是对照的2.32倍,对沙质土壤团粒结构改良效果最为明显。可见,添加秸秆改良材料可以增加沙质土壤饱和含水量。     

秸秆改良材料对冷沙黄泥土壤钾素吸附解吸的影响

为了研究秸秆改良材料对沙质土壤钾素的调控作用,采用土培试验,研究作物秸秆、膨润土和聚丙烯酰胺(PAM)配制的秸秆改良材料,对冷沙黄泥土壤钾素吸附、解吸的影响。结果表明,秸秆改良材料能够显著提高沙质土壤对钾的吸附性能,增强固钾能力,随秸秆改良材料中PAM用量的增大,钾吸附量增加,不同土培时期,相比F0(900:100:0),F3(900:100:30)处理土壤钾素总平均吸附量达最大,10天、30天、60天、90天的F3(900:100:30)处理土壤钾素总平均吸附量分别增加6.1%、9.2%、10.9%、13.9%。施用秸秆改良材料促使土壤钾素解吸量提高,但低于吸附量,随秸秆改良材料中PAM所占比例提高,土壤中钾解吸率显著提高,与F0相比,10天、30天、60天、90天的F3处理使土壤中钾解吸率分别提高6.1%、18.2%、17.2%、15.4%。秸秆改良材料能提高沙质土壤固钾能力,是适合修复沙质土壤的改良材料。     

毛乌素沙地南缘不同植被恢复类型的土壤养分效应

为了探讨植被恢复对土壤养分的影响,研究了毛乌素沙地南缘天然草地、人工封育草地、撂荒地、退耕还林地、固定沙地5种不同植被恢复类型区的土壤养分特征。结果表明：不同植被恢复类型对土壤有机质、全氮、有效氮、速效磷的影响存在明显差异;灌草结合的人工封育草地、退耕还林地、固定沙地土壤有机质、全氮、有效氮的含量高于以草本为主的天然草地和撂荒地,但土壤速效磷的含量刚好相反;植被对表层0~20 cm土壤养分的影响大于下层20~60 cm土壤,植被作用下土壤养分向表层富集;采用柠条进行退耕还林,能够充分发挥其根系特性,有利于改良深层土壤养分。     

BGA土壤调理剂在风沙土上的施用效果研究

为了解决宁夏土地沙化问题,提高风沙土土壤质量和土地生产力,通过田间试验研究了BGA土壤调理剂对风沙土土壤理化性质和作物生长发育的影响,评价了BGA土壤调理剂的施用效果。研究结果表明,与不施肥相比,施用BGA土壤调理剂改善了风沙土土壤理化性质,促进了酿酒葡萄、樱桃番茄和甘草的生长发育,显著提高了酿酒葡萄和樱桃番茄的产量,改善了酿酒葡萄和甘草品质;与配方施肥相比,施用BGA土壤调理剂改善了风沙土土壤理化性质,促进了酿酒葡萄和樱桃番茄的生长发育,显著降低了甘草产量,改善了酿酒葡萄品质。施用BGA土壤调理剂大幅度增加了生产投入成本,建议进一步降低BGA土壤调理剂的生产成本或与化肥配合施用。     

黄泛平原粗砂潮土农田土壤水分动态研究

根据土壤物理性质测定和水分定位观测结果,结合当地气候、作物生育特点,将黄泛平原粗砂潮土土壤水分垂直性分布划分为：速变层（０～４０ｃｍ）,活跃层（４０～１００ｃｍ）和稳定层（１００ｃｍ以下）;将土壤水分季节性动态划分成：强烈腾发期、补充下淋期、缓慢消耗期和相对稳定期。     

Stability of Particle size Improved Roadbed in Permafrost

Roadbed stability, including thermal and strength stability, is the ability of roadbed to adapt to pavement settlement, slurry effusion, shear slide and haunching up of the roadbed resulting from moving vehicles and many natural influences. Thermal stability is the sensitivity of the thermal state of the roadbed to the external environmental condition. It is the key point of the roadbed stability in permafrost. Research concerning roadbed thermal stability in permafrost is analyzed, and the judgment principle of thermal stability is discussed. The regular change of the ground temperature and deformation of particle size improved roadbeds are analyzed by studying field observation data of the particle size improved roadbed after two freezing and thawing cycles. We conclude that the particle size improved roadbed can raise the upper limit of frozen soil. Based on the judgment principle, the particle size improved roadbed is regarded as a new type of stable structure.     

砂薄地夏玉米施钾效应研究

研究了砂薄地玉米施钾效应,田间试验结果表明：砂薄地玉米产量随施钾量的增加而增加,且以施钾量225kg/hm2为最佳,此时钾肥产投比最高,达5.2,能取得较高的产量和获得较高的钾肥利用率;施钾能够提高砂薄地玉米籽粒蛋白质含量,但与施钾的产量效应变化趋势不同,在施钾225kg/hm2时蛋白质含量最高,继续提高施钾量则蛋白质含量呈现下降趋势。土壤速效钾含量随施钾量的增加而增加,欲保持玉米生长周期结束后土壤钾素肥力平衡,施钾量应达到150kg/hm2。玉米籽粒产量与生育期内玉米体内钾素含量呈显著正相关,其中拔节期、喇叭口期、抽雄期和成熟期的植株钾含量与产量之间相关系数分别达0.87、0.95、0.94、0.99。     

Numerical Analysis on Stability of Rock in Sijiaotian Tunnel

The Sijiaotian Tunnel in Yunnan Dabao Highway lies in the narrow defile landscape,and the engineering geology condition is complex,with plenty of cienega.According to the actual situation of the Sijiaotian Tunnel Project in Yunnan Dabao Highway,the stability of the surrounding rock mass is studied by using a 3-D non-linear FEM.The Drucker-Prager criterion is chosen as the failure criterion of the rock.The relatively dangerous zone and the monitoring points in the tunnel are determined.The numerical results show that the Sijiaotian Tunnel is relatively stable.The conclusion has some significance for guiding the construction of similar projects.     

3D Dynamic Coupled Mechanical and Hydraulic Analysis of Geogrid-reinforced Pile-supported Embankments

In order to investigate the dynamic behaviors of geogrid-reinforced pile-supported embankments under traffic loading, three-dimensional coupled mechanical and hydraulic numerical simulations are conducted using FLAC 3D. Four cases are studied including unreinforced and no-pile embankments, reinforced embankments, pile-supported embankments, and geogrid-reinforced pile-supported embankments. The behaviors of vertical displacement, horizontal displacement, pile-soil stress ratio, excess pore water pressure and acceleration under four cases are analyzed. It is found that the vertical displacement, nonuniform settlement and horizontal displacement of geogrid-reinforced pile-supported embankments are smaller than those of other cases due to soil arching effect and reinforcement effect. Pile-soil stress ratio decreases with the increase of loading number. The crest value of acceleration and the time for acceleration to be steady are also smaller than those of other cases. The dissipation velocity of excess pore is quicker than that of unreinforced embankments.     

科尔沁沙地最典型地区50年气候变化分析

为了研究干旱少雨、生态环境脆弱、土地荒漠化严重的科尔沁沙地的沙漠化发展变化特征,为其治理提供理论依据,根据其最典型地区奈曼旗1961-2010年的气象资料,分析了近50年气温、降水、蒸发及风沙天气的变化。结果表明：近50年间,科尔沁沙地的气温呈上升趋势,冬、春季增温尤为显著;降水量年际间波动较大,总体呈下降趋势;年平均风速自20世纪90年代至今较平稳地在3.2~3.3 m/s之间波动;风沙天气从1995年开始基本得到遏制。温度升高、蒸发量增加及降水量减少对科尔沁沙地的沙漠化起到一定的推动作用,平均风速和风沙天气对其生态环境的影响正逐渐减小。     

不同杉木种源在贵州省适生栽培区高生长及稳定性分析

杉木在我国有广泛的分市区。以北纬21°41′至北纬34°03′,东经101°45′至东经121°53′之间的广阔亚热带区域都有杉木的自然分布。由于长期的自然条件和漫长的自然选择影响,必然产生了对各种生态因子要求各异的群体,这些不同群体如在分布区内不同生态区进行交流,很有可能会产生各种各样的适应程度表现。 我国目前杉木引种已很普遍。选择生长量高且具有稳定增产效益的引种对象,已是人们日益关心的问题。本文对贵州省已有栽培的来自全国各地共64个种源在贵州省不同栽培地点稳定性进行分析,结合差异分析,为贵州省不同地区的杉木种子调拨区划提供数量化依据。     

胡萝卜汁中色素稳定性分析

通过测定胡萝卜汁中色素吸光度的变化并计算其吸光度残存率,探讨不同光照条件、温度、pH、蔗糖浓度、防腐剂及金属离子对胡萝卜汁中色素稳定性的影响。结果表明:胡萝卜汁中的色素具有极佳的热稳定性与耐糖性;具有一定的光稳定性,但对日光直射较敏感;在偏酸性条件下较为稳定,在对胡萝卜汁进行酸化护色时,最佳pH值为6.0~6.5;苯甲酸钠对胡萝卜汁中的色素有一定的增色作用,山梨酸钾对胡萝卜汁中的色素有一定的破坏作用;Na~+、Al~(3+)、Ca~(2+)对胡萝卜汁中的色素有护色作用,K~+对胡萝卜汁中的色素有增色作用,Fe~(3+)、Fe~(2+)、Cu~(2+)会使胡萝卜汁产生明显变色现象,在胡萝卜汁生产与储藏过程中应尽量避免与Fe~(3+)、Fe~(2+)、Cu~(2+)接触。     

豫东砂壤土区强筋小麦施钾增产保优效应研究

为了在强筋小麦次适宜种植区实现高产优质目标,采用田间试验及统计分析方法,对易缺钾的砂壤土类型区栽培强筋小麦进行施用钾肥增产保优效应研究。结果表明,在豫东砂壤土区耕层土壤速效钾(K₂O)含量为90 kg/hm²左右的条件下,在施用氮磷肥的基础上,增施钾肥(K₂O) 60~300 kg/hm²,强筋小麦增产18.7%~41.4%,平均增产30.6%。砂壤土强筋小麦产量与施钾量之间呈二次曲线函数关系,即y= 5296.35+22.20x-0.059x2,F=55.76**。增施钾肥小麦籽粒蛋白质含量平均为15.32%,平均提高1.72个百分点,相对提高12.6%。钾肥增进了小麦面粉的加工品质,湿面筋含量达到35.2%~38.0%,平均37.1%,超过一等强筋小麦≥35%的国家标准。施钾小麦面粉沉降值为45.1~47.3 mL,较对照增大3.2~5.4 mL,同时较全面地改善了面团流变学性能,如形成时间增加0.6~1.8 min,平均增加1.3 min;稳定时间延长1.9~ 4.4 min,平均延长约3.4 min;弱化度(FU)则下降2.8~9.3,平均下降6.3。钾肥提高产量、改善品质的主要生理生化基础是促进了开花至灌浆期旗叶光合速率,提高了挑旗至灌浆期旗叶磷酸蔗糖合成酶(SPS)活性。在本试验条件下,豫东砂壤土强筋小麦增产保优最佳的施钾(K₂O)量为180 kg/hm²。适宜的氮磷钾肥施肥配比(N:P₂O₅:K₂O)为1:0.78:1.30。     

砂薄地冬小麦-夏玉米轮作施钾效应

在大田条件下研究了砂质潮土冬小麦-夏玉米轮作施钾效应,田间试验结果表明：砂质潮土地冬小麦产量随施钾量的增加而增加,以施钾量150kg/hm2（基肥：追肥=5：5）的经济效益最佳,增产822.7 kg/hm2,每公顷增收724.1元,产投比为2.42;玉米生产也以施钾量150kg/hm2分次施用为最佳,增产1368.4kg/hm2,每公顷增收1281.7元,产投比为2.52。冬小麦-夏玉米轮作体系中,施钾量为150 kg/hm2时,两季连续分次施用钾肥经济效益最佳,施钾量为300 kg/hm2时,小麦分次施用钾肥而玉米不施钾肥的经济效益最好。     

乌兰布和沙区不同供水量下杨树林地土壤水分和温度效应研究

为了提高干旱区水资源利用率,确定沙区杨树人工速生林的合理供水量,实现杨树人工林的科学化管控目标,通过4年定位观测试验,研究了乌兰布和沙区‘小美旱杨’林地不同年供水量(1500、3000、4500、6000、7500 m3/hm2)下的土壤水分和温度效应。结果表明,不同供水量对土壤的增湿效应存在差异。各土层、各月土壤含水量均随供水量的增加而增加;最大年供水量的土壤含水量峰值出现在7月,而其他的出现在6月;‘小美旱杨’速生丰产的年供水量阈值为7500 m3/hm2,它能使剖面土壤水分补给层达70 cm以上,且补给层以及6-9月高温时期的土壤含水量均保持在20%以上;供水量越大,土壤含水量随树龄增加而降幅越大。年供水量每增加1500 m3/hm2可提高土壤贮水量4.69%~7.43%,增加土壤有效含水量1.42%~15.5%;供水量对田间持水量影响不明显;随供水量的增加,土壤水分亏缺明显趋于平缓,土壤温度递减,在同一土层内下降1.66~3.26℃,沿剖面向下降低8.64~9.66℃。最小和最大供水量应分别在4月低温期和7月高温期进行,以满足林木生长的水分和温度之需。     

北疆地区阿克达拉灌区土壤成因和特性特征分析

针对新疆“沙漠绿洲灌溉农业”这一典型特点,灌区建设在北疆地区农牧业发展中具有重要作用,而灌区土壤条件作为灌区立足的根本具有举足轻重的地位,因而正确地对灌区土壤成因及土壤肥力做出评价,才能保证灌区土壤水土资源的合理开发利用和实现农牧业可持续发展。以新疆阿勒泰地区阿克达拉灌区作为研究对象,通过对灌区土壤现状的调查、资料收集、样品采集及室内化验分析,分析研究了灌区内土壤形成因素、分布以及不同类型土壤的特征特性。研究表明,灌区内土壤形成条件主要是自然因素中的冰冻作用、风力作用和温差变化作用,灌区主要分布有荒漠淡棕钙土和风沙土。风砂土质地为含土粉砂砾层-粉细质沙土,成土母质为运距离搬运的风沙为主;荒漠淡棕钙土质地为中细砂,且中细砂含量从坡上部至下部具有规律性,成土母质系为三系砂质、泥岩风化后被洪水携带或原地残留,且近代以来该区域沙化趋严重。研究成果为阿克达拉灌区和北疆类似灌区进一步开发区域内水土资源理论基础和技术依据。