论建筑工程中深基坑支护设计优化及施工要点

近年来随着建筑业的不断发展,在深基坑开挖的施工过程中,基坑内外的土体将由原来的静止士压力状态向主动土压力状态转变,应力状态的改变引起土体的变形,即使采取了支护措施,一定数量的变形总是难以避免的“这些变形包括：深基坑支护结构以及周围土体的沉降和侧向位移。无论哪种位移的量值超出了某种容许的范围,都将对基坑支护结构造成危害”深基坑开挖工程往往在繁华的市中心进行,施工场地四周有建筑物和地下管线,本文针对建筑工程深基坑支护设计优化及施工要点进行一定的探讨。     

FLAC3D在某工程深基坑开挖数值模拟中的应用

运用FLAC3D软件对某工程深基坑进行了开挖模拟。计算中采用摩尔-库仑弹塑性模型,基坑围护结构与上体之间的接触面运用接触单元。通过计算得出不同开挖阶段的地表沉降和墙体侧向位移,为工程设计与施工提供参考。     

基坑开挖数值模拟中土体本构模型的选取

基坑开挖数值分析中的一个关键问题是选取一个合适的土体本构模型。该文通过对基坑开挖过程中土体的主要应力变化路径进行分析, 指出开挖条件下的土体本构模型应能合理考虑土体变形特性的应力路径相关性和压硬性。在介绍与分析几种常用土体本构模型特点的基础之上, 通过模拟应力路径三轴试验、基坑工程算例与工程实例的对比分析, 探讨了常见土体本构模型的适用性。分析表明, Hardening Soil Model采用了不同的加荷与卸荷模量, 能够反映土体应力路径的影响, 且考虑了土体模量的应力水平相关性, 能预测得到较合理的坑壁侧移、地表沉降以及支护结构的内力, 因而建议采用Hardening Soil Model进行基坑开挖数值模拟分析。     

高层建筑深基坑支护施工技术探讨

近年来,随着建筑工程施工项目的不断增加,深基坑工程支护在建筑工程施工中应用非常广泛。特别是目前城市建筑施工往往位于建筑物、公路桥梁、地铁隧道及人防工程附近,而且地下管线错综复杂,这也给深基础支护施工带来了较大的难度。在对深基坑工程设计时,往往需要以开挖施工时的各种技术参数作为依据,但由于在具体施工过程中,支护结构内力和位移、基坑内外土体情况等极易出现变形及各种变化,因此需要进一步提高深基坑支护施工技术,确保施工的安全性。     

逆筑法施工技术探析

某高层建筑地下室工程对深基坑的图护变形和土体的位移、地表和管线沉降等各项指标都有严格要求。经方案比选后，采用“逆筑法”施工技术，该法能有效地保护周边环境，且具有施工工期快，节省基坑支护费等优点，取得了满意的效果。     

深基坑开挖边坡稳定探讨

深基坑工程施工主要包括基坑支护体系设计与施工和土方开挖,是一项综合性很强的系统工程。深基坑工程的支护体系设计与施工和土方开挖不仅与工程地质水文地质条件有关,还与基坑相邻建（构）筑物和地下管线的位置、抵御变形的能力、重要性,以及周围场地条件有关。有时保护相邻建（构）筑物和市政设施的安全是纂坑工程设计与施工的关键。因而深基坑施工前,要认真调查场地周围建（构）筑物和地下管线的情况,从而制定出基坑支护设计、基础降水、土方开挖以及基坑监测等方案。确保深基坑边坡稳定或周边建（构）筑物的安全。     

钻孔灌注桩、水泥搅拌桩在基坑支护工程的应用

深基坑的支护，不仅要求保证基坑内安全、高效地工作，而且要防止基坑周边土体滑移，保证基坑周边的建筑物、道路、地下管线等工程不受破坏、正常运作。通过某大型商场基坑支护的工程管理。介绍了工程中使用的钻孔灌注桩结合水泥搅拌桩的施工工艺、质量控制措施及检测方法。为日后类似的工程积累了经验。     

城市地铁深基坑穿越临江断裂带涌水治理关键技术

城市地铁工程通常具有环境复杂的特点,工程自身的安全风险会直接导致周边建(构)筑物、地下管线等环境风险。地铁车站深基坑工程施工中重大施工风险主要有:支护及体系变形失稳、基底管涌、基底土体隆起等,如不采取有效的加固处置措施势必造成基坑坍塌、周边环境破坏等严重安全事故。本文以某城市地铁深基坑施工为例,简要阐述了深基坑穿越临江断裂带过程中涌水治理、基坑支护体系加固等关键技术,以期为类似工程提供参考。     

地铁车站深基坑支护技术措施

地铁深基坑支护施工方案的可靠性和施工质量不仅直接影响土方开挖、车站主体结构施工阶段的人员、财产安全,还会影响周边构筑物和各种地下管线的安全。随着近年来我国地铁工程的大规模建设,车站深基坑施工技术的重要性日益凸显。分析当前车站深基坑支护存在的安全问题,提出深基坑支护设计、施工中的应注意的事项和预防措施。     

深基坑开挖的计算机模拟及稳定性分析

本文采用三维非线性有限元程序，对深基坑开挖过程进行逐步计算机模拟，通过选择合理的分析模型和屈服准则，分析了开挖过程中基坑周围的应力分布，位移分布以及塑性破坏区的产生与发展趋势，从而为进一步进行深基坑支护设计提供了依据。     

穿越非均匀土体埋地管道地震离心实验研究

穿越非均匀土体经历不同地震作用的埋地管线的变形和残余强度严重影响着管道的安全。该文采用离心振动台分别平行于埋地管道长度方向输入0.6 g和0.3 g峰值地面加速度地震波,研究了埋地管道在一系列地震作用和不均匀土体变形共同作用下的响应,得到了PVC和铝合金两种埋地管道穿越软土/硬土土体的地震响应规律。地震引起不均匀土体的瞬时变形,导致埋地管道最大应变发生在土体分界面和软土中,管道拉伸应变幅值软土要大于硬土,而压缩应变幅值正好相反,硬土中管道拉伸应变幅值小于压缩应变幅值,硬土中管道压缩应变幅值受地震烈度影响比软土大。地震引起的土体永久变形对埋地管道残余变形影响很大,硬土中的管道残余应变为压应变,软土中管道的残余应变为拉压应变交替分布。     

Model test study on influence of freezing and thawing on the crude oil pipeline in cold regions

Buried pipelines are one of most economical and convenient methods for the transportation of large volumes of oil and gas. When a pipeline is buried in cold regions, it may suffer frost damage. Previous studies of pipelines and the surrounding soils in cold regions have tended to concentrate on the theory and practical engineering problems. This paper reports the results of a model test to investigate the stresses and strains on the buried pipeline and surrounding soils in the permafrost and seasonal frost areas based on the Mo'he–Daqing section of the China–Russia Crude Oil Pipeline (CRCOP). The temperature of the soils surrounding the pipeline, displacement and axial strain as well as stress in the pipeline induced by frost heave and thaw settlement are monitored and analyzed. The test results will have some significance in guiding the construction of the CRCOP in cold regions.     

Model test study on influence of freezing and thawing on the crude oil pipeline in cold regions

Buried pipelines are one of most economical and convenient methods for the transportation of large volumes of oil and gas. When a pipeline is buried in cold regions, it may suffer frost damage. Previous studies of pipelines and the surrounding soils in cold regions have tended to concentrate on the theory and practical engineering problems. This paper reports the results of a model test to investigate the stresses and strains on the buried pipeline and surrounding soils in the permafrost and seasonal frost areas based on the Mo'he-Daqing section of the China-Russia Crude Oil Pipeline (CRCOP). The temperature of the soils surrounding the pipeline, displacement and axial strain as well as stress in the pipeline induced by frost heave and thaw settlement are monitored and analyzed. The test results will have some significance in guiding the construction of the CRCOP in cold regions.     

Application of the novel composite earth retaining structure method to urban excavations: a constructability analysis

ABSTRACT

The objective of this study is to propose and evaluate a novel composite earth retaining structure method to be applied in urban excavations in terms of construction safety, cost, and duration. The novel composite structure is a multipurpose structure, which may counteract uplift pressure acting on the foundation base, provide lateral support at ground level, and function as king posts during excavation. To evaluate the feasibility and advantages of utilizing the composite earth retaining structure in deep excavations, the case of a commercial building development in Taipei has been studied. In this project, the original excavation design employed top-down construction for the foundation and basement. Two alternative designs employing the composite earth retaining structure method were later proposed to the owner for evaluation and selection. The analyses of the two alternatives include a three-dimensional geotechnical finite element analysis using PLAXIS3D and an analysis of time using PROJECT 2013 as well as a study of cost impacts. The results from the analyses show that the novel method can be superior to the original design in terms of construction safety, project cost, and construction duration.     

考虑近断层脉冲型地震动影响的埋地管道地震易损性分析

近断层脉冲型地震动具有短时高能量的脉冲特性,会对埋地管道等长周期结构造成较为严重的破坏。为研究近断层脉冲型地震动影响的埋地管道抗震性能,该文基于简化速度脉冲模型,结合脉冲周期、脉冲峰值的经验统计公式,模拟了不同地震动的方向性脉冲分量和滑冲脉冲分量,通过与ATC-63报告推荐的远场地震动中的高频成份进行叠加,合成了具有多种频率成分的近断层脉冲型地震动;在此基础上,进一步考虑空间变异性,生成了的空间相关多点非平稳地震动。利用ANSYS软件进行有限元建模,输入人工合成的地震动进行增量动力时程分析,建立了PGV与埋地管道最大应变之间关系的概率地震需求模型,结合管道极限破坏状态的划分,进而建立了考虑不确定性的不同管材、管径、壁厚及填覆土的埋地管道地震易损性模型。该模型为跨断层埋地管道地震风险评估中的地震易损性分析提供了理论基础。     

Stresses and deformations in a buried oil pipeline subject to differential frost heave in permafrost regions

Differential frost heave of the buried oil pipelines in permafrost regions can have an adverse effect on the mechanical status of the pipeline, and seriously endanger the pipeline security. In order to reduce the damage to the pipeline during its designed lifetime, it is necessary to analyze the mechanical behavior of oil pipelines taking into consideration the differential frost heave in the design of the pipelines in permafrost regions. In this paper, an elastico-plastic finite element model for the mechanical behaviors of the pipeline-soil system was established. In order to simplify computations, the effects of the temperature and moisture fields on the problem were considered by applying the computed temperature zones of soils surrounding the pipeline from the thermal analysis, and actual frost heaving ratio of the soils was applied to the mechanical model to calculate the stresses and deformations of the pipeline in permafrost regions. These analyses may provide some useful insights into the possible mechanical states of the pipeline-soil system for the design, construction and operation of the buried oil pipelines in permafrost regions.     

基于延缓固结法的地基工后沉降控制的数值分析

延缓固结法(地基延缓固结处理法)是一种通过限制工程运营期间地基的孔隙压力消散来消除后期的地基固结沉降,从而达到控制地基工后沉降目的的新型地基处理方法。通过设置深层水平防渗层完善了延缓固结法,并以此为基础完成该文的研究工作。有限元模拟计算表明,延缓固结法处理的地基工后沉降随帷幕的深度增加而减小,但是当帷幕达到一定深度以后,再增加帷幕的深度,工后沉降不再减小,而竖向防渗帷幕的深度非常小时,延缓固结法反而会使地基工后沉降加大。采用有限元方法比较了分别采用延缓固结法和刚性桩处理地基的超孔压分布、竖向位移场的分布、沉降时程曲线和控制地基工后沉降的效果,且粗略地比较了二者的经济性能。在竖向防渗帷幕的深度适宜的情况下,延缓固结法控制地基工后沉降的作用确实存在。当处理深度在一定范围之内时,延缓固结法和刚性桩相比具有经济和技术双重优势。     

Stresses and deformations in a buried oil pipeline subject to differential frost heave in permafrost regions

Differential frost heave of the buried oil pipelines in permafrost regions can have an adverse effect on the mechanical status of the pipeline, and seriously endanger the pipeline security. In order to reduce the damage to the pipeline during its designed lifetime, it is necessary to analyze the mechanical behavior of oil pipelines taking into consideration the differential frost heave in the design of the pipelines in permafrost regions. In this paper, an elastico-plastic finite element model for the mechanical behaviors of the pipeline–soil system was established. In order to simplify computations, the effects of the temperature and moisture fields on the problem were considered by applying the computed temperature zones of soils surrounding the pipeline from the thermal analysis, and actual frost heaving ratio of the soils was applied to the mechanical model to calculate the stresses and deformations of the pipeline in permafrost regions. These analyses may provide some useful insights into the possible mechanical states of the pipeline–soil system for the design, construction and operation of the buried oil pipelines in permafrost regions.     

埋地管道的非平稳随机振动

将实际地震地面运动看作为非平稳随机过程，研究了埋地管道的非平稳随机响应，考虑地面运动的相关性，导出了轴向和横向振动响应(应力和位移)的相关函数的解析表达式，实例计算了一条埋地管道非平稳随机振动的应力和位移的时间历程。     

Mechanical behaviour analysis of a buried steel pipeline under ground overload

Ground overload is one of the most important factors that threaten the safe operations of oil and gas pipelines. The mechanical behaviour of a buried pipeline under ground overload was investigated using the finite element method in this paper. The effects of the overload parameters, pipeline parameters and surrounding soil parameters on the stress–strain response of the buried pipeline were discussed. The results show that the maximum von Mises stress appears on the top of the buried pipeline under the loading area when the ground load is small, and the stress distribution is oval. As the ground load increases, the maximum stress increases, and the high stress area extends. The von Mises stress, plastic strain, plastic area size, settlement and ovality of the buried pipeline increase as the ground load and loading area increase. The buckling phenomenon of the no-pressure buried pipeline is more serious than the pressure pipeline. As the internal pressure increases, the high stress area and the maximum plastic strain of the buried pipeline first decrease and then increase, the settlement of the buried pipeline increases, and the ovality decreases. The von Mises stress, maximum plastic strain, settlement and ovality of the buried pipeline decrease with increasing buried depth, the surrounding soil's elasticity modulus, Poisson's ratio and cohesion. The maximum von Mises stress, high stress area, the maximum plastic strain, plastic area and ovality increase as the diameter–thickness ratio increases. The critical diameter–thickness ratio is 60, and the settlement of the buried pipeline first increases and then decreases as the diameter–thickness ratio increases. Finally, a protective device of the buried pipeline is designed for preventing ground overload. It can be repaired in a timely manner without stopping the transmission of oil and gas and widely used in different locations because of its simple structure and convenient installation.