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1.
《浙江大学学报(A卷英文版)》2019,(11)
目的:研究边坡段基桩的水平承载特性,以期指导工程实践。创新点:提出一种新的p-y曲线,以考虑边坡坡角和桩在边坡中位置的影响。方法:1.针对平地桩基和坡地桩基两种工况开展两组室内模型对比试验;2.采用ABAQUS建立数值模型,并研究桩径、桩长和土体的弹性模量对桩基水平受荷性能的影响;3.对室内模型试验结果和数值模拟结果进行对比分析,并得出坡地桩基的p-y曲线。结论:1.边坡中侧向受力桩的侧向挠度和弯矩沿桩长的分布与水平埋置桩的分布相似;然而,边坡倾角对单桩的侧向荷载特性有着重要的影响;在相同的荷载条件下,较高的倾斜角度会引起较大的桩身变形和弯矩。2.对于埋置长度不变的桩,桩的极限侧向承载力与坡趾距桩截面中心的距离近似呈双线性关系。3.对于埋置长度不同的桩,其极限承载力随坡脚至桩截面中心距离的增加呈线性增加。 相似文献
2.
《浙江大学学报(A卷英文版)》2017,(11)
目的:静钻根植竹节桩是一种由预制桩和水泥土组成的组合桩基,其桩身具有预制桩-水泥土和水泥土-桩周土体两个接触面。本文以桩土接触面剪切试验、模型试验和现场试验数据为基础,提出一种静钻根植竹节桩简化沉降计算方法,为静钻根植竹节桩的沉降计算提供依据;并通过所提出的简化计算方法对静钻根植竹节桩桩端水泥土扩大头以及桩周水泥土直径对静钻根植竹节桩承载性能的影响进行研究。创新点:1.通过剪切试验对预制桩-水泥土接触面的剪切性能进行研究,得到接触面侧摩阻力与相对位移的关系;2.建立同时考虑预制桩-水泥土接触面和水泥土-桩周土体接触面作用的静钻根植竹节桩简化沉降计算方法。方法:1.通过桩土接触面剪切试验,得到预制桩-水泥土接触面摩擦模型;2.通过对模型试验结果的分析,得到水泥土-桩周土体接触面摩擦模型;3.根据试验结果编写静钻根植竹节桩沉降计算程序,通过与试验结果的比较验证所提计算方法的可靠性;4.通过提出的静钻根植竹节桩简化计算方法对静钻根植竹节桩承载力影响因素进行分析与研究。结论:1.预制桩-水泥土接触面摩擦性能远优于水泥土-桩周土体接触面摩擦性能;2.由于水泥浆的渗透作用,水泥土-桩周土体接触面的初始剪切刚度有所提高;3.所提出的计算方法能够有效地计算出静钻根植竹节桩单桩在成层土体中的荷载位移关系曲线;4.桩端水泥土扩大头能够有效地提高静钻根植竹节桩桩端承载性能,并且增加桩周水泥土直径能够提高静钻根植竹节桩承载性能。 相似文献
3.
钻孔灌注桩作为一种基础形式,目前在我国基础工程建设中得到了广泛的应用.但因为钻孔灌注桩在成孔时要穿越各种土质或软硬变化较大的土层(如各类黏性土、砂土、碎砾石土、风化岩及多夹层的岩层),且施工环节较多,技术要求高,工艺较复杂,稍有疏忽,很容易出现一些质量事故,甚至造成病桩、断桩等重大质量事故,危及桩基工程的安全.以下内容从勘察、设计、施工诸因素方面成因入手,找出质量事故发生的原因,研究相应对策,尽可能防止质量事故发生. 相似文献
4.
超长钻孔灌注群桩承载特性的实验研究和数值分析 总被引：1，自引：0，他引：1
采用离心机模型试验和三维有限元模型对天兴洲大桥的超长嵌岩钻孔灌注群桩进行了分析.离心机试验中,根据相似理论,不同的原型材料用不同的指标进行模拟,细砂、桩身、承台分别以天然密度、抗压刚度、抗弯刚度作为指标进行模拟.对土体未开挖阶段、钻孔阶段、混凝土灌注阶段和养护阶段的应力场进行了详细的讨论,并应用ANSYS进行了分析.根据2种方法得到的结果,从荷载沉降曲线、桩身轴力分布和侧向摩阻分布等方面,对比分析了加载和卸载条件下超长钻孔群桩的承载特性.结果表明,有限元计算模型与离心机试验模型沉降观测的结果吻合得很好;桩顶反力的分布规律复杂,与承台的自身刚度、相应的假定和分析方法有关;轴力随着深度先稍微增加,后逐渐减少,并且在岩层中减少的速度远比砂土中快. 相似文献
5.
目的:探讨中密和密实砂液化场地混凝土低承台群桩和地基动力响应存在的差异性,并揭示引起这种差异性的原因,以期获得加密后砂土液化场地混凝土低承台群桩和地基动力反应的基本特征与规律。创新点:1.利用振动台试验,成功实施中密和密实砂液化场地低承台群桩基振动台试验;2.基于试验结果,对比中密和密实砂层液化场地群桩和地基的动力响应规律,考察两种液化场地条件下群桩效应基本特征。方法:1.通过对比白噪声扫频,获得中密砂和密实砂层液化场地下体系模态参数的差异性(图2和表1);2.通过对比砂层孔压、加速度和位移(图3–8),获得中密砂和密实砂液化场地动力反应显著的差异性;3.基于上部结构和承台的位移与加速度,讨论中密砂和密实砂液化场地上部结构动力反应与回复力特性(图9和10);4.基于桩上记录的应变时程,考虑桩的非线性,反算混凝土桩的弯矩时程,对比两类场地群桩弯矩存在的差异性,获得两类场地对群桩效应的影响效应(图12–14)。结论:1.密实砂液化场地加速度在砂层液化后未出现弱化现象,表现出明显的循环流动性,密实砂液化场地比中密砂液化场地刚度更大;2.上部结构动力响应与砂土密实状态密切相关;3.中密砂液化场地桩的最大弯矩发生在土层分界处,而密实砂液化场地中桩的最大弯矩发生在桩头处;4.群桩效应在密砂层中更显著,而在中密砂层并不显著。 相似文献
6.
《浙江大学学报(A卷英文版)》2021,(4)
目的:地下水位下降会增大土体的有效应力,使其发生固结沉降,桩基础受到的负摩阻力也随之增加,进而引发桩基显著附加沉降,严重时可能超过高速铁路墩台基础工后沉降控制要求。目前,相关研究多集中于短桩且主要以数值模拟为主,试验研究较少,对长桩的研究更不充分。本文旨在通过联合离心模型试验和数值模拟开展深入分析,揭示地下水位下降对长桩基础的影响。创新点:1.通过离心模型试验和数值模拟,重现地下水位下降过程中不同长度桩基的力学响应;2.获得了桩-土相互作用及桩轴力计算参数β随水位下降的发展规律;3.通过实际工程案例分析,提出了考虑地下水位下降的桩基设计方法。方法:1.通过离心模型试验和自主研发的水位控制系统研究地下水位下降对不同长度桩基的影响;2.结合数值模拟,分析桩基沉降、轴力、摩阻力、群桩效应、参数β等随水位下降的发展规律;3.通过实际工程案例,分析地下水位下降对高速铁路桩基沉降发展的影响,并提出考虑地下水位下降的桩基设计方法。结论:1.地下水位下降会增大桩-土差异沉降,引起摩阻力增长,从而造成桩基下沉。2.桩中性点位置对水位下降不敏感;当水位下降幅值相同时,桩长越长,桩身轴力越大,但轴力增长比呈下降趋势。3.在列车荷载下水位下降不仅会因固结效应增加桩基沉降,还通过增加桩摩阻力改变桩基沉降发展模式。4.在列车循环荷载下,为使桩基沉降发展收敛,桩基承载力须增大60.9%以抵抗地下水位下降2 m的影响。 相似文献
7.
新建铁路线交叉穿越既有公路线和铁路线的施工是隧道建设中的技术难点之一,因施工不当引起的路面变形甚至坍塌,将会导致巨大的经济损失和不良的社会影响.以新建赣深铁路林寨隧道为背景,结合隧道下穿S229省道的工程特点,采用有限元软件对该标段的开挖进行数值模拟,对隧道开挖下穿既有省道的相互影响进行分析研究,提出了林寨隧道下穿既有... 相似文献
8.
通过室内缩尺模型试验,比较和分析了嵌岩桩(RSP)和砂土桩在水平荷载下的承载能力.试验使用磷石膏来模拟底部岩石,采用夯实法制作上层砂土.试验前进行了颗粒分析试验以确认土壤的均匀程度.采用圆锥负荷试验(CPT)评估土壤,确认所有试验分组的土壤条件相似,即土体性质引起的误差可以忽略不计.通过有限元模拟对嵌岩桩的承载能力进行了验证,数值模拟结果与试验结果吻合良好.研究表明：嵌岩桩和砂土桩的弯矩分布一致,桩身最大弯矩的位置在2～3倍桩径深度处,但嵌岩桩的最大弯矩位置比砂土桩深约1倍桩径(5 cm);当上层覆土较浅时,嵌岩桩的承载效果更显著,承载力相对于砂土桩增加约41%;由于岩石的挤压效应,嵌岩桩的横截面变形明显小于砂土桩. 相似文献
9.
姜元懂 《商情·科学教育家》2013,(25)
在我国沿海及内陆地区广泛分布着软弱粘性土层及夹砂层.由这些土形成的地基在构筑物及外部荷载作用(列车、地震等)下会产生较大的沉降,而且沉降持续时间较长,这对工后沉降要求高的地基(如建筑物、台后过渡段等)很难满足.另外,对于松散的砂层,在地震等外部荷载作用下可能会发生震动液化,造成地基下沉量聚增,这对构筑物的使用来说是不安全的.秦沈客运专线设计要求台后过渡段工后沉降不大于8Cm.因此,在特大桥、大桥、中桥等台后过渡段均设置半刚性桩进行地基加固.碎石桩就是其中一种. 相似文献
10.
桩土相互作用及单桩承载力确定模拟研究 总被引：4，自引：0，他引：4
谈传华 《石家庄铁路职业技术学院学报》2011,10(1)
以灌注桩桩土相互作用的原位试验为基础,结合苏嘉杭高速公路具体土层结构、性质特点,采用有限单元法对软土地区的砼灌注桩桩土相互作用进行仿真模拟,研究桩土相互作用、荷载的传递规律、桩土相对位移与桩侧摩阻力的关系,通过桩载试验资料对比,得出三维有限元法的模拟结果与实测值相近.在此基础上,根据侧摩阻力最大值发挥不同步这一特点和桩土相互作用的实质及荷载传递规律,提出一种新的单桩极限承载力计算公式. 相似文献
11.
12.
We investigated the effect of emphasising the realistic modelling complexity in text or in the accompanying picture on the solution of P-items, in relation to pupils’ grade. 290 pupils from the 5th and 6th grade of various elementary schools in Flanders (Belgium) made a paper-and-pencil task with 7 word problems that are problematic from a realistic modelling perspective (so-called P-items). Pupils were divided in four conditions, involving the four combinations of the two above-mentioned task variables. Their reactions to the P-items were coded as realistic or non-realistic. We found a relatively small but significant effect of emphasising the realistic modelling complexity in the text of the P-items on the number of realistic reactions, whereas no effect was observed for the accentuation of that complexity in the picture nor for the interaction of the two manipulated task variables. Theoretical and educational implications of these results are discussed. 相似文献
13.
This paper presents the explosion cratering effects and their propagation laws of blast waves in dry standard sands using
a 450 g-t geotechnical centrifuge apparatus. Ten centrifuge model tests were completed with various ranges of explosive mass, burial
depth and centrifuge accelerations. Eleven accelerometers were installed to record the acceleration response in sand. The
dimensions of the explosion craters were measured after the tests. The results demonstrated that the relationship between
the dimensionless parameters of cratering efficiency and gravity scaled yield is a power regression function. Three specific
function equations were obtained. The results are in general agreement with those obtained by other studies. A scaling law
based on the combination of the π terms was used to fit the results of the ten model tests with a correlation coefficient of 0.931. The relationship can be
conveniently used to predict the cratering effects in sand. The results also showed that the peak acceleration is a power
increasing function of the acceleration level. An empirical exponent relation between the proportional peak acceleration and
distance is proposed. The propagation velocity of blast waves is found to be ranged between 200 and 714 m/s. 相似文献
14.
Stanislaw Schukajlow Dominik Leiss Reinhard Pekrun Werner Blum Marcel Müller Rudolf Messner 《Educational Studies in Mathematics》2012,79(2):215-237
In this study which was part of the DISUM-project, 224 ninth graders from 14 German classes from middle track schools (Realschule)
were asked about their enjoyment, interest, value and self-efficacy expectations concerning three types of mathematical problems:
intra-mathematical problems, word problems and modelling problems. Enjoyment, interest, value and self-efficacy were assessed
before and after a ten-lesson teaching unit promoting modelling competency related to the topics “Pythagoras’ theorem” and
“linear functions”. The study aimed to answer the following research questions: (1) Do students’ enjoyment, value, interest
and self-efficacy expectations differ depending on the type of task? (2) Does the treatment of modelling problems in classroom
instruction influence these variables? (3) Are there any differential effects for different ways of teaching modelling problems,
including a “directive”, teacher-centred instruction and an “operative-strategic”, more student-centred instruction emphasising
group work and strategic scaffolding by the teacher? The findings show that there were no differences in students’ enjoyment,
interest, value and self-efficacy between the three types of tasks. However, teaching oriented towards modelling problems
had positive effects on some of the student variables, with the student-centred teaching method producing the most beneficial
effects. 相似文献
15.
Patrick H. M. Sins Elwin R. Savelsbergh Wouter R. van Joolingen 《International Journal of Science Education》2013,35(14):1695-1721
Although computer modelling is widely advocated as a way to offer students a deeper understanding of complex phenomena, the process of modelling is rather complex itself and needs scaffolding. In order to offer adequate support, we need a thorough understanding of the reasoning processes students employ and of difficulties they encounter during a modelling task. Therefore, in this study 26 students, working in dyads, were observed while working on a modelling task in the domain of physics. A coding scheme was developed in order to capture the types of reasoning processes used by students. Results indicate that most students had a strong focus on adjusting model parameters to fit the empirical data with little reference to prior knowledge. The successful students differed from the less successful students in using more prior knowledge and in showing more inductive reasoning. These observations lead to suggestions for the design of appropriate scaffolds. 相似文献
16.
Patrick H. M. Sins Elwin R. Savelsbergh Wouter R. van Joolingen Bernadette H. A. M. van Hout‐Wolters 《International Journal of Science Education》2013,35(9):1205-1229
While many researchers in science education have argued that students’ epistemological understanding of models and of modelling processes would influence their cognitive processing on a modelling task, there has been little direct evidence for such an effect. Therefore, this study aimed to investigate the relation between students’ epistemological understanding of models and modelling and their cognitive processing (i.e., deep versus surface processing) on a modelling task. Twenty‐six students, working in dyads, were observed while working on a computer‐based modelling task in the domain of physics. Students’ epistemological understanding was assessed on four dimensions (i.e., nature of models, purposes of models, process of modelling, and evaluation of models). Students’ cognitive processes were assessed based on their verbal protocols, using a coding scheme to classify their types of reasoning. The outcomes confirmed the expected positive correlation between students’ level of epistemological understanding and their deep processing (r = 0.40, p = .04), and the negative correlation between level of epistemological understanding and surface processing (r = ?0.51, p = .008). From these results, we emphasise the necessity of considering epistemological understanding in research as well as in educational practice. 相似文献
17.
准备活动是体育教学的重要组成部分,正确地认识准备活动的作用,设计和编排一个合理的、全面的、有针对性的准备活动,将影响体育教学的质量和效果。针对目前体育课准备活动中存在的问题,从编排准备活动应遵循的全面性原则、科学性原则、针对性原则和创新性原则四个方面进行系统的阐述,望能对体育教师创编准备活动,提高教学质量,更好地完成教学任务起到一定的参考价值。 相似文献
18.
Problem solving is an essential skill for nuclear engineering graduates entering the workforce. Training in qualitative and quantitative aspects of problem solving allows students to conceptualise and execute solutions to complex problems. Solutions to problems in high consequence fields of study such as nuclear engineering require rapid and accurate analysis of the problems, design of solutions (focusing on public safety, environmental stewardship and ethics), solution execution and monitoring results. A three-month course in problem solving, modelling and simulation was designed and a collaborative approach was undertaken with instructors from both industry and academia. Training was optimised for the laptop-based pedagogy, which provided unique advantages for a course that includes modelling and simulation components. The concepts and tools learned as part of the training were observed to be utilised throughout the duration of student university studies and interviews with students who have entered the workforce indicate that the approaches learned and practised are retained long term. 相似文献
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INTRODUCTIONTheTianzilingwastelandfillbuiltin 1991toproperlydisposeofmunicipalsolidwaste(MSW)hasadesignedservicelifeof13years.Itwasfilledstagebystageatthebeginningoftheelevationof 50 .5m .Bynow ,thelandfillhasreachedthelevelof 10 2 .5m ,whichex ceedst… 相似文献
20.
本研究以大连开发区老年人参加体育活动为切入点进行实地调查,研究现阶段我区老年人参加体育活动的现状及存在的问题。采用文献资料法、问卷调查法、现场调查法,着重调查老年人参加体育活动的动机、运动项目、场地设施、运动强度等方面内容,并对影响老年人体育活动的因素进行综合分析,并提出适合老年人锻炼的健身模式,为培养老年人健康的生活方式,引导老年人科学锻炼,促进老年体育健康科学和我市健康老龄化的发展提供决策依据。 相似文献