High-strain dynamic model of large-diameter pipe piles with soil plug for vertical vibration analysis

A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.

A theoretical analysis of vertical dynamic response of large-diameter pipe piles in layered soil

Considering the viscous damping of the soil and soil-pile vertical coupled vibration,a computational model of large-diameter pipe pile in layered soil was established.The analytical solution in frequency domain was derived by Laplace transformation method.The responses in time domain were obtained by inverse Fourier transformation.The results of the analytical solution proposed agree well with the solutions in homogenous soil.The effects of the shear modulus and damping coefficients of the soil at both outer and inner sides of the pipe pile were researched.The results indicate that the shear modulus of the outer soil has more influence on velocity admittance than the inner soil.The smaller the shear modulus,the larger the amplitude of velocity admittance.The velocity admittance weakened by the damping of the outer soil is more obvious than that weakened by the damping of the inner soil.The displacements of the piles with the same damping coefficients of the outer soil have less difference.Moreover,the effects of the distribution of soil layers are analyzed.The results indicate that the effect of the upper soil layer on dynamic response of the pipe pile is more obvious than that of the bottom soil layer.A larger damping coefficient of the upper layer results in a smaller velocity admittance.The dynamic response of the pipe pile in layered soil is close to that of the pipe pile in homogenous soil when the properties of the upper soil layer are the same.

A Theoretical Analysis of the Bearing Performance of Vertically Loaded Large-Diameter Pipe Pile Groups

This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups.The interactions between group piles result in different bearing performance of both a single pile and pile groups.Considering the pile group effect and the skin friction from both outer and inner soils,an analytical solution is developed to calculate the settlement and axial force in large-diameter pipe pile groups.The analytical solution was verified by centrifuge and field testing results.An extensive parametric analysis was performed to study the bearing performance of the pipe pile groups.The results reveal that the axial forces in group piles are not the same.The larger the distance from central pile,the larger the axial force.The axial force in the central pile is the smallest,while that in corner piles is the largest.The axial force on the top of the corner piles decreases while that in the central pile increases with increasing of pile spacing and decreasing of pile length.The axial force in side piles varies little with the variations of pile spacing,pile length,and shear modulus of the soil and is approximately equal to the average load shared by one pile.For a pile group,the larger the pile length is,the larger the influence radius is.As a result,the pile group effect is more apparent for a larger pile length.The settlement of pile groups decreases with increasing of the pile number in the group and the shear modulus of the underlying soil.

Analytical approach and field monitoring for mechanical behaviors of pipe roof reinforcement

Considering the delay effect of initial lining and revising the Winkler elastic foundation model,an analytical approach based on Pasternak elastic foundation beam theory for pipe roof reinforcement was put forward. With the example of a certain tunnel excavation,the comparison of the values of longitudinal strain of reinforcing pipe between field monitoring and analytical approach was made. The results indicate that Pasternak model,which considers a more realistic hypothesis in the elastic soil than Winkler model,gives more accurate calculation and agrees better with the result of field monitoring. The difference of calculation results between these two models is about 7%,and Pasternak model is proved to be a better way to study the reinforcement mechanism and improve design practice. The calculation results also reveal that the reinforcing pipes act as levers,which increases longitudinal load transfer to an unexcavated area,and consequently decreases deformation and increases face stability.

Effect of Application of Pipe Roof Method by Using Pipe Jacking on Behavior of Surrounding Soil

Tunnels in an urban area, in many cases, are constructed in soft ground which contains underground water, near existing facilities and structures. Structural stability for the tunnel and also the nearby structures and facilities is vital in this kind of work. Slurry pipe jacking was firmly established as a special method for the non-disruptive construction of underground pipelines of sewage systems. This method utilizes mud slurry that is formed around the pipes in order to stabilize the surrounding soil. In the pipe roof method the tubing elements that are constructed by slurry pipe jacking are near each other longitudinally, and create a rigid and stable lining before the excavation of the main tunnel. This paper discusses ＇the application of a slurry pipe jacking system on ＇the pipe roof method by means of numerical analysis. Because of the rigid behavior of the lining, the results show little subsidence, making this method a reliable method of constructing large tunnels with small cover in an urban area.

A Frost Heaving Prediction Approach for Ground Uplift Simulation Due to Freeze-Sealing Pipe Roof Method

Freeze-sealing pipe roof method is applied in the Gongbei tunnel,which causes the ground surface uplift induced by frost heave.A frost heaving prediction approach based on the coefficient of cold expansion is proposed to simulate the ground deformation of the Gongbei tunnel.The coefficient of cold expansion in the model and the frost heaving rate from the frost heave test under the hydration condition can achieve a good correspondence making the calculation result closer to the actual engineering.The ground surface uplift along the lateral and longitudinal direction are respectively analyzed and compared with the field measured data to validate the model.The results show that a good agreement between the frost heaving prediction model and the field measured data verifies the rationality and applicability of the proposed model.The maximum uplift of the Gongbei tunnel appears at the center of the model,gradually decreasing along with the lateral and longitudinal directions.The curve in the lateral direction presents a normal distribution due to the influence of the constraint of two sides,while the one along the lateral direction shapes like a parabola with the opening downward due to the temperature field distribution.The model provides a reference for frost heaving engineering calculation.

Analysis of mechanical behaviors of big pipe roof for shallow buried large-span tunnel

A series of researches on mechanical behaviors of big pipe roof for shallow large-span loess tunnel were carried out based on the Wenxiang tunnel in Zhengzhou—Xi'an Special Passenger Railway. The longitudinal deformations of the pipe roofs were monitored and the mechanical behaviors of the pipe roofs were analyzed at the test section. A new double-parameter elastic foundation beam model for pipe roof in shallow tunnels was put forward in Wenxiang tunnel. The measured values and the calculation results agreed well with each other,revealing the force-deformation law of big pipe roof in loess tunnel:At about 15 m in front of the excavating face,the pipe roof starts to bear the load;at about 15 m behind the excavating face,the force of the pipe roof tends to be stabilized;the longitudinal deformation of the whole pipe roofs is groove-shaped distribution,and the largest force of pipe roofs is at the excavating face. Simultaneously,the results also indicate that mechanical behaviors of pipe roof closely relate to the location of the excavation face,the footage of the tunnelling cycle and the mechanics parameters of pipe roof and rock. The conclusions can be reference for the design parameter optimization and the construction scheme selection of pipe roofs,and have been verified by the result of numerical analysis software FLAC3Dand deformation monitoring.

双层管棚穿越市政道路引起地表竖向位移研究

本文以长春某隧道暗挖段穿越市政道路项目为依托,利用MIDAS GTS NX有限元软件,建立了双层管棚支护下不同管棚直径、管间间距、层间间距参数下的三维有限元模型,分析各参数对围岩竖向位移的控制效果,结果表明:三种参数对竖向位移的变化影响分别为正相关、负相关、正相关,且均表现为对拱顶的沉降控制效果最好;当直径与层间间距增大或环向间距减小到某个数值后,其对沉降的控制效果会减弱,故管棚直径、环向间距、层间间距三种参数的选择需要从工艺、技术、进度、成本等方面综合考虑。

管幕法隧道下穿既有公路路基沉降的研究

管幕法隧道下穿既有高速公路引起路基路面沉降,威胁既有公路交通安全。文章以某国道新建隧道工程为背景,采用有限元软件MIDAS/GTS-NX建立地层结构法计算模型,分析计算隧道下穿全过程各工序对既有公路路基沉降规律。计算结果表明,隧道采用管幕法及CRD法穿越粉土层时,隧道整体稳定性及变形可控,公路路面沉降受步序影响较大,公路路面最大沉降出现隧道穿越处路面中央位置,路面沉降满足《公路路基设计规范》要求。研究结果可为穿越粉土地层类似工程提供一定理论参考。

隧道管棚支护承载特性及支护参数试验研究

为探究隧道管棚注浆钢管不同支护参数对管棚支护承载能力的影响,引入Pasternak双参数模型构建出更符合实际情况的管棚支护力学模型,通过多组室内试验,对管棚在不同注浆钢管管径、壁厚、注浆饱满度及加设钢筋笼条件下的承载能力进行定量研究。研究表明:1)管棚注浆钢管支护参数中,对管棚承载能力的影响排序为:管径>注浆饱满度>壁厚>钢筋笼。2)增大管棚注浆钢管管径可大幅提高管棚的承载能力,相比管径为108 mm的管棚,管径为159、219、299 mm时管棚承载能力分别增大183.58%、398.62%、874.86%。3)管棚钢管注浆不饱满会较大程度削弱管棚的承载能力,钢管注浆饱满度由100%降至75%、50%时,管棚承载能力分别降低29.8%、34.5%,注浆饱满度为50%时管棚的承载能力与未注浆时相差不大。4)管棚钢管壁厚和钢筋笼加设与否对管棚的承载能力影响较小。因此,在实际工程中,可通过增大管棚钢管管径提升管棚的承载能力,通过减小管棚钢管壁厚及不加设钢筋笼节约用钢量。

托顶煤巷道易片冒顶板变形机理与超前导管预注浆控制技术研究

目的 为探究厚煤层易片冒区域托顶煤巷道顶板变形破坏机理,并对易片冒区托顶煤巷道顶板进行有效控制,方法 以常村煤矿2701工作面皮带运输巷为例,通过等截面梁理论分析托顶煤巷道顶板破断成因,研究托顶煤巷道顶板的稳定性与巷道宽度和顶煤强度的关系。通过极限平衡准则得到巷帮位移的计算公式,证明托顶煤巷道具有帮顶协同变形机制。建立托顶煤巷道数值模型,研究巷道埋深、侧压系数、顶煤厚度和顶煤强度与托顶煤巷道围岩稳定性的关系。结果 结果表明:巷道埋深越大,其对托顶煤巷道两帮稳定性的影响越大;侧压系数的增加对巷道两帮和底鼓量的影响更大,对顶板影响较小;顶板下沉量与顶煤厚度呈正相关,底鼓量则与顶煤厚度呈负相关;顶煤强度的增加使巷道顶板下沉量与两帮移近量均近似呈线性减小趋势,底鼓量基本保持不变。结论 通过幂律型流体柱形渗透注浆扩散理论得到超前导管注浆半径,由此提出托顶煤巷道超前导管预注浆帮顶联合控制技术,成功控制易片冒托顶煤巷道顶板冒落问题,可为类似地质条件的托顶煤巷道顶板控制提供借鉴。

污水处理厂生化反应池加设混凝土顶盖工艺设计

地上式污水处理厂生化反应池加设混凝土顶盖设计是一项系统性工作,合理的顶盖设计是后期安全、便捷运行及景观效果良好的基础。以西安市鱼化污水处理厂生化反应池混凝土顶盖设计为例,探讨顶盖巡检通道设置、主要设备及管路布置、覆土绿化等方面设计时需考虑的关键内容。实际运行效果表明,通过合理利用顶盖空间设置主次巡检通道、布置设备、管路及增加覆土绿化,创造了便利的巡检、维护条件,可取得良好的工程绿化及密封除臭效果,可为供类似污水处理项目参考借鉴。

异形加强冻结管外壁保温对管幕冻结效果影响试验研究

新型管幕冻结法冻结系统由充填混凝土的实顶管内布置圆形主力冻结管和限位管、未充填混凝土的空顶管内布置异形加强冻结管组成。为分析该新型管幕冻结系统中空顶管周围的冻结效果,通过拱北隧道管幕冻结现场原型试验,对空顶管中异形加强冻结管是否采取外表面保温措施展开研究,利用冻土帷幕厚度的变化对异形加强冻结管保温措施与不保温状态进行冻结效果对比分析。结果表明:异形加强冻结管保温不利于冻土帷幕的形成,随着冻结时间推移,冻土帷幕的发展会越来越慢;协同冻结模式下60 d后保温与不保温的冻土厚度之差约为冻结20 d的2倍。可以把空顶管作为“大冻结管”来考虑,利用异形加强冻结管对空顶管内部整体降温,更有利于顶管周围冻土帷幕的发展。

管幕和横梁作用下大断面开挖变形响应研究

基于管幕与横梁作用下大断面开挖相似模型试验,研究开挖引起的管幕变形和地表沉降变化规律.为充分研究参数变化对管幕变形和地表沉降的影响,运用有限元软件建立三维数值模型,以此模型为依据,分析管幕抗弯刚度和横梁抗弯刚度对管幕变形和地表沉降的影响,并根据模糊数学理论对最优刚度匹配进行研究.研究结果表明:管幕结构整体变形类似于“板”,且关于中间管幕对称,管幕跨中断面地表沉降呈“凹槽”型,符合Peck曲线分布;管幕变形和地表沉降均与横梁刚度和管幕刚度呈指数函数关系,且对横梁刚度变化更为敏感;管幕刚度与横梁刚度分别为0.5D和2K时,可以兼顾安全性与经济性.

预应力倒三角管桁架钢屋盖滑移施工技术

广交会展馆四期展馆扩建工程地处城市核心区,环境复杂,铁、隧、馆多重结构交互。工程体量大,结构复杂,施工难度大,总工期仅644d,在同类工程中工期最短,工期履约压力大。其中展厅屋盖钢结构为预应力倒三角管桁架结构,钢构体量大。针对此屋盖钢结构特点、难点,从缩短工期、高效建造方面开展研究,创新提出超长大跨度钢桁架分段等节奏滑移施工技术,即展馆两侧附属混凝土结构先行施工,提供滑移支撑体系,屋盖钢结构滑移与展厅下部2层主体混凝土结构同步施工,实现了展厅屋盖钢结构提前插入安装,各专业平面、立面穿插施工,缩短了关键线路工期;研发了基于装配式、自稳定高空平台的大跨度钢桁架拼装技术,实现超长大跨度重型钢桁架分单元快速拼装;针对主体结构作为滑移支撑体系两侧异标高的特点,设计双向滑移轨道,并研制滚针式滑靴及动力系统,确保滑移安全稳定;应用倒三角预应力钢绞线快速穿束和张拉技术,解决了超长预应力筋穿束张拉与高空滑移技术难题;液压同步控制系统与智能施工监测确保了大跨超重钢桁架屋盖滑移的应力、应变可控,按方案模拟过程平稳进行。

High-frequency interference in low strain integrity testing of large-diameter pipe piles

The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transientpoint load is applied. An analytical solution of vertical vibratory response of large-diameter pipe piles in low strain testing isdeduced in this paper. The analytical solution is verified by both numerical simulation and model test results. The time-domainvelocity responses on pile top are analyzed. The calculation results indicate that the time-domain responses at various pointssuffer different high-frequency interferences, thus the peak values and phases of different points are different. The influence ofvibratory modes on high-frequency interference is analyzed. It is found that the high-frequency interference at 90° point main-ly derives from the second flexural mode, but for other points it mainly originates from the first flexural mode. The factors af-fecting the frequency and peak value of interference waves have been investigated in this study. The results indicate that thelarger radius angle between the receiving and 90° points leads to greater peak value of high frequency wave crest. The leasthigh-frequency interference is detected at the angle of 90°. The frequency of interference waves is decreased with the increaseof pile radius, while the peak value is almost constant. The frequency is also related to pile modulus, i.e. the larger pile modu-lus results in greater frequency. The peak value varies with impulse width and soil resistance, i.e., the wider impulse width andlarger soil resistance cause smaller peak value. In conclusion, the frequency of interference waves is dependent on the geomet-rical and mechanics characteristics of the piles such as pile radius and modulus, but independent of the external conditionssuch as impulse width and soil resistance. On the other hand, the peak value of interference waves is mainly dependent on theexternal conditions but independent of the geometrical and mechanics characteristics of the piles. In practice, some externalmeasures should be adopted to weaken high-frequency interference such as using soft hammer, hammer cushion and adoptingsuitable receiving point.

大跨度屋盖振动舒适度分析及管桁架结构施工技术研究

某中学风雨操场屋盖为大跨度倒三角空间管桁架结构,同时兼具运动功能,承受重型荷载。因此,需在深化设计阶段对风雨操场屋盖进行共振技术分析,保证操场运动人员舒适性及屋盖下空间不受干扰。研究大跨度倒三角空间管桁架测量及监测技术、侧拼与吊装施工技术,以达到设计效果。研究结果表明,通过共振分析得出的结构竖向自振频率与最大加速度满足要求;采用临时支撑、起拱、汽车式起重机单榀整体吊装等方式解决吊装问题,达到了设计精度;通过精准测量及监测确保了加工、安装过程质量和安全。

地下工程咬合型管幕构件抗弯承载力研究

基于咬合型管幕试件的抗弯性能试验,研究了咬合型管幕试件的力学性能及破坏形态。为进一步研究关键结构参数对咬合型管幕试件抗弯性能的影响,运用ABAQUS建立了咬合型管幕试件的有限元模型,并通过室内试验验证了模型的正确性;进而分析了钢管咬合程度、钢管壁厚及钢筋直径对咬合型管幕试件抗弯性能的影响。结果表明:咬合型管幕试件抗弯性能良好,试件最终发生延性破坏;钢管咬合程度、钢管壁厚对试件的抗弯承载力影响显著,钢筋直径对试件的抗弯承载力影响不明显。最后,给出了钢管咬合程度、钢管壁厚及钢筋直径与抗弯承载力的关系式;并通过多元线性回归得到了咬合型管幕试件抗弯承载力简化计算公式。

管幕法连拱隧道下穿高速公路路基段沉降变形规律分析

依托某下穿高速公路匝道路基段隧道工程,简要介绍了管幕法连拱隧道设计施工方案,建立数值模型对管幕法连拱隧道下穿高速公路路基段沉降变形进行动态模拟,得到了路基段沉降变形规律曲线,并与现场监控量测数据对比,分析了下穿高速公路路基段沉降变形规律。结果表明:1)各监测点连成的路基沉降变形规律曲线为“U”型曲线,沉降大值分布在隧道与匝道相交区域内;2)路基沉降变形值随着隧道开挖进尺的增大而增大,位于隧道与匝道相交区域内的匝道沉降变形速率最大,距离隧道越远,匝道沉降变形速率越小;3)隧道与匝道夹角越小,路基沉降相应的影响范围越大;4)根据数值模拟计算结果和实测匝道沉降实测值分析得知,管幕法连拱隧道下穿匝道路基引起沉降数值不超过10 mm,沉降得到有效控制,对高速公路影响较小。

“三软地层”超前探放水综合控制技术

“三软地层”探放水钻孔孔口管固管安装困难、顶板遇水塌陷渗水、疏放水钻孔坍塌堵孔以及钻孔缩颈的施工技术一直难以解决。通过理论计算与工程实践,摸索了一套探放水创新施工工艺,进行了优化钻孔参数设计,11701工作面大部分顶板疏放水钻孔垂高取200 m,终孔孔距不大于60 m,富水区域进行加密。技术上攻克了套管加长后固结难的技术难题,研发出一套“分级注浆固管法”,将整个套管牢固安装在设计位置,实现了在软岩区域快速固结安装超长孔口套管的新工法。针对“三软地层”的钻孔探放水,为了解决“三软地层”的探放水钻孔在成孔后坍塌堵塞的技术难题,创造性的研发出三级注浆以及“全孔花管护壁新工艺”;工程实践证明该套技术方案很好地解决了“三软地层”探放水钻孔施工难题。