Fiber optic monitoring of an anti-slide pile in a retrogressive landslide

Anti-slide piles are one of the most important reinforcement structures against landslides,and evalu-ating the working conditions is of great significance for landslide mitigation.The widely adopted analytical methods of pile internal forces include cantilever beam method and elastic foundation beam method.However,due to many assumptions involved in calculation,the analytical models cannot be fully applicable to complex site situations,e.g.landslides with multi-sliding surfaces and pile-soil interface separation as discussed herein.In view of this,the combination of distributed fiber optic sensing(DFOS)and strain-internal force conversion methods was proposed to evaluate the working conditions of an anti-sliding pile in a typical retrogressive landslide in the Three Gorges reservoir area,China.Brillouin optical time domain reflectometry(BOTDR)was utilized to monitor the strain distri-bution along the pile.Next,by analyzing the relative deformation between the pile and its adjacent inclinometer,the pile-soil interface separation was profiled.Finally,the internal forces of the anti-slide pile were derived based on the strain-internal force conversion method.According to the ratio of calculated internal forces to the design values,the working conditions of the anti-slide pile could be evaluated.The results demonstrated that the proposed method could reveal the deformation pattern of the anti-slide pile system,and can quantitatively evaluate its working conditions.

Shaking table test for reinforcement of soil slope with multiple sliding surfaces by reinforced double-row anti-slide piles

Despite the continuous advancements of engineering construction in high-intensity areas,many engineering landslides are still manufactured with huge thrust force,and double-row piles are effective to control such large landslides.In this study,large shaking table test were performed to test and obtain multi-attribute seismic data such as feature image,acceleration,and dynamic soil pressure.Through the feature image processing analysis,the deformation characteristics for the slope reinforced by double-row piles were revealed.By analyzing the acceleration and the dynamic soil pressure time domain,the spatial dynamic response characteristics were revealed.Using Fast Fourier Transform and half-power bandwidth,the damping ratio of acceleration and dynamic soil pressure was obtained.Following that,the Seism Signal was used to calculate the spectral displacement of the accelerations to obtain the regional differences of spectral displacement.The results showed that the overall deformation mechanism of the slope originates from tension failure in the soil mass.The platform at the back of the slope was caused by seismic subsidence,and the peak acceleration ratio was positively correlated with the relative pile heights.The dynamic soil pressure of the front row piles showed an inverted"K"-shaped distribution,but that of the back row piles showed an"S"-shaped distribution.The predominant frequency of acceleration was 2.16 Hz,and the main frequency band was 0.7-6.87 Hz;for dynamic soil pressure,the two parameters became 1.15 Hz and 0.5-6.59 Hz,respectively.In conclusion,dynamic soil pressure was more sensitive to dampening effects than acceleration.Besides,compared to acceleration,dynamic soil pressure exhibited larger loss factors and lower resonance peaks.Finally,back row pile heads were highly sensitive to spectral displacement compared to front row pile heads.These findings may be of reference value for future seismic designs of double-row piles.

Centrifuge and numerical modeling of h-type anti-slide pile reinforced soil-rock mixture slope

Due to the loose structure,high porosity and high permeability of soil-rock mixture slope,the slope is unstable and may cause huge economic losses and casualties.The h-type anti-slide pile is regarded as an effective means to prevent the instability of soilrock mixture slope.In this paper,a centrifuge model test was conducted to investigate the stress distribution of the h-type anti-slide pile and the evolution process of soil arching during the loading.A numerical simulation model was built based on the similar relationship between the centrifuge model and the prototype to investigate the influence factors of the pile spacing,anchored depth,and crossbeam stiffness,and some recommendations were proposed for its application.The results show that the bending moment distribution of the rear pile exhibits Wshaped,while for the front pile,its distribution resembles V-shaped.The soil arching evolution process during loading is gradually dissipated from bottom to top and from far to near.During the loading,the change of bending moment can be divided into three stages,namely,the stabilization stage,the slow growth stage,and the rapid growth stage.In engineering projects,the recommended values of the pile spacing,anchored depth,and crossbeam stiffness are 4.0d,2.0d,and 2.0EI,where d and EI are the diameter and bending stiffness of the h-type anti-slide pile respectively.

Anchoring Depth Research of Anti-Slide Piles of Anchor Bar in Soil

The model test result of earth force in the side of anti-slide pile of anchor bars was introduced.There are three groups of the tests.The loads were on the back side of the slope in two groups.The other one was loaded just behind the pile by the jack.In order to get the force of the soil,some earth-pressure boxes were used to get the earth pressure on the side of the piles.The part of the max pressure and the earth pressure was mainly focused under the slip line

Dynamic response of a slope reinforced by double-row antisliding piles and pre-stressed anchor cables

Large-scale shaking table tests were conducted to study the dynamic response of a slope reinforced by double-row anti-sliding piles and prestressed anchor cables. The test results show that the reinforcement suppressed the acceleration amplification effectively. The axial force time histories are decomposed into a baseline part and a vibration part in this study. The baseline part of axial force well revealed the seismic slope stability, the peak vibration values of axial force of the anchor cables changed significantly in different area of the slope under seismic excitations. The peak lateral earth pressure acting on the back of the anti-sliding pile located at the slope toe was much larger than that acting on the back of the anti-sliding pile located at the slope waist. The test results indicate an obvious load sharing ratio difference between these two anti-slide piles, the load sharing ratio between the two anti-sliding piles located at the slope toe and the slope waist varied mainly in a range of 2-5. The anti-slide pile at the slope waist suppressed the horizontal displacement of the slope surface.

Approximate Calculation of Oblique Wave Transmission from A Single-Row of Rectangular Piles

Transmissions of oblique incident wave from a row of rectangular piles are analyzed theoretically. The incident angle of plane wave is taken as g = 90° , there then is the transmission coefficient ｜T｜ = 1 （This is a paradox）. In this paper, by means of the approximate relation between the transmitted and incident wave angle found from the shape of a slit, the paradoxical phenomenon is removed. On the basis of the continuality of the pressure and flux and the analysis of flow resistance at the row of rectangular piles, formulas of reflection and transmission coefficients are obtained. The transmission and reflection coefficients predicted by the present model quite agree with those of laboratory experiments in previous references

Co-Evolution Optimization of Anchored Row Piles for Deep Foundation Pit

The thinking of co evolution is applied to the optimization of retaining and protecting structure for deep foundation excavation, and the system of optimization of anchored row piles for deep foundation pit has been already developed successfully. For the co evolution algorithm providing an evolutionary mechanism to simulate ever changing problem space, it is an optimization algorithm that has high performance, especially applying to the optimization of complicated system of retaining and protecting for deep foundation pit. It is shown by many engineering practices that the co evolution algorithm has obvious optimization effect, so it can be an important method of optimization of retaining and protecting for deep foundation pit. Here the authors discuss the co evolution model, object function, all kinds of constraint conditions and their disposal methods, and several key techniques of system realization.

Pre-Stressed Rope Reinforced Anti-Sliding Pile

Pre-stressed rope reinforced anti-sliding pile is a composite anti-sliding structure. It is made up of pre-stressed rope and general anti-sliding pile. It can bring traditional anti-sliding pile＇s retaining performance into full play, and to treat with landslide fast and economically. The difference between them is that the pre-stressed rope will transfix the whole anti- sliding pile through a prearranged pipe in this structure. The working mechanics, the design method and economic benefit are studied. The results show that the pre-stressed rope reinforced anti-sliding pile can treat with the small and middle landslides or high slopes well and possess the notable advantage of technology and economic.

Shaking Table Tests on Bridge Foundation Reinforced by Antislide Piles on Slope

Based on the requirement of seismic reinforcement of bridge foundation on slope in the Chengdu-Lanzhou railway project,a shaking table model test of anti-slide pile protecting bridge foundation in landslide section is designed and completed. By applying Wenchuan seismic waves with different acceleration peaks,the stress and deformation characteristics of bridge pile foundation and anti-slide pile are analyzed,and the failure mode is discussed. Results show that the dynamic response of bridge pile and anti-slide pile are affected by the peak value of seismic acceleration of earthquake,with which the stress and deformation of the structure increase. The maximum dynamic earth pressure and the moment of anti-slide piles are located near the sliding surface,while that of bridge piles are located at the top of the pile. Based on the dynamic response of structure,local reinforcement needs to be carried out to meet the requirement of the seismic design. The PGA amplification factor of the surface is greater than the inside,and it decreases with the increase of the input seismic acceleration peak. When the slope failure occurs,the tension cracks are mainly produced in the shallow sliding zone and the coarse particles at the foot of the slope are accumulated.

3-D Simulation Study on Seismic Response of Bridge Piles in Landslide

The anti-slide support structure is widely used in the anti-seismic reinforcement of bridge foundations,but related experimental research was processing slowly. Based on the prototype of the Jiuzhaigou bridge at the Chengdu-Lanzhou Railway,a 3-D simulation model was established on the basis of the shaking table model test,and the rationality of the dynamic analysis model was verified by indicators such as the bending moment of the bridge piles,peak soil pressure,and PGA amplification factors. The results show that the inertia force of the bridge pier has an important influence on the deformation of the pile foundation. The bending moment and shearing force are larger in lateral bridge piles,and the maximum value is near the pile top. The PGA amplification factor is stronger in the back of the rear anti-slide piles and so is it in front of the bridge pier,and the soil is prone to slip and damage. The bedrock is rigid and the dynamic response is maintained at a low level. The anti-slide piles in the rear row play a major role in the anti-seismic reinforcement design,and the anti-slide piles in the front row can be used as an auxiliary support structure.

软土地区基坑前排倾斜双排桩支护现场试验及工作机理

基坑倾斜桩支护大幅提高了无支撑支护结构的适用深度,具有造价低、施工便捷、绿色低碳、变形控制好等特点,然而目前研究多集中在单排倾斜桩,对前排倾斜双排桩支护的试验、理论与应用的研究均较少。针对前排倾斜双排桩支护基坑开展了现场试验,同时采用有限元方法分别从前排斜桩、桩顶连梁及桩间土体作用3个方面深入探究了前排倾斜双排桩支护的工作机理,进一步分析了直斜桩长度和排距对前排倾斜双排桩支护结构受力变形性能的影响。结果表明,相比传统竖直双排桩,前排倾斜双排桩支护结构的支护性能显著提升,前排斜桩主要发挥“斜撑”作用,连梁主要起到将直斜桩及冠梁连接成一个空间刚架的作用,桩间土体能够提高桩土摩阻力,进而有效减小前排倾斜双排桩变形。研究成果有助于前排倾斜双排桩的推广和应用。

深基坑三排桩支护结构被动区力学特性研究

文中以某船坞工程采用的新型三排桩支护结构作为依托工程,结合地质勘察报告,运用有限元分析法和弹性支点法对其典型断面的桩前被动土压力计算公式参数进行了反演分析.通过改变土体参数、开挖深度,以及前排桩桩径等影响因素,对比分析计算得到桩前土压力有限元计算值与弹性支点法计算值的比值变化规律.结果表明:被动土压力合力的模型计算结果E_(p模型)与理论公式计算结果E_(p理论)的比值约为0.4~0.7.在此基础上,对三排桩支护结构桩前土压力的弹性支点法公式进行了改进,为修正系数提出了合理建议,改进后公式为:p_(s)=(0.4~0.7)(k_(s)v+p_(s0)),并研究了各系数的分布规律.

地基中混凝土排桩主动隔振研究

为了探究地基中设置混凝土排桩后,排桩的各参数变化对近场主动隔振的影响规律,在有限元软件中建立与试验场地一致的三维有限元模型,通过计算与分析验证了有限元计算结果的有效性;参考TB 10621—2014《高速铁路设计规范》建立了足尺寸的有限元模型,分析在列车荷载作用下排桩的各参数变化对隔振效果的具体影响规律。研究结果表明:桩长参数对隔振效果影响较为明显,随着参数增大,隔振效果越理想,当桩长参数为10.5以后,继续增加比值,隔振效果提升不显著;随着桩间距参数越大,隔振效果越不理想,较小的桩间距可获得理想的隔振效果;埋深参数对隔振效果影响显著,参数越大,隔振效果越不理想,当参数为3.5时,隔振效果已很不理想,较浅埋深能获得较理想的隔振效果。

排桩倾斜对双排桩支护结构性状影响分析

依托某双排桩基坑工程实践建立有限元模型,分析前、后排桩倾斜对基坑支护效果的影响,并与现场监测数据进行对比验证。研究结果表明:前排桩倾斜一定的角度,桩身弯矩和轴力增大,前排桩发挥斜撑作用,桩身水平位移及桩顶沉降减小,支护效果提高;随着前排桩倾斜角度的增大,支护效果提升幅度减弱;后排桩倾斜可提高支护效果,不同倾斜角度下,桩身弯矩、轴力、水平位移和桩顶沉降变化幅度不同,但倾斜角度过大导致支护效果减弱;相同排桩倾斜角度下,前排桩倾斜对双排桩支护效果的提升显著优于后排桩倾斜,前排桩倾斜15°时支护效果最优。

单、双排桩支护路堑边坡动力响应特性的振动台试验研究

结合西部艰险山区铁路实际工程背景,开展了El-Centro波作用下单、双排桩支护路堑边坡大型振动台模型试验,基于位移、加速度等参数深入研究了两种模型边坡动力响应特性的差异,并结合快速傅里叶变化(fast Fourier transform,简称FFT)谱探讨了两种边坡出现差异的原因。结果表明:抗滑桩的支护效果和差异均随输入波幅值的增大而逐渐体现;当输入波幅值为0.1g~0.3g时,单、双排桩边坡均处于稳定状态,总体动力响应特性差异较小;当输入波幅值为0.4g时,两边坡动力响应开始出现较大差异,单排桩边坡宏观破坏更明显,坡表位移增大较多,土体损伤累积,非线性特征显现;当输入波幅值为0.5g~0.6g时,两种模型边坡的地震波峰值加速度(peak ground acceleration,简称PGA)放大系数高程效应明显,且均在路堑面和桩后坡面处出现塑性区,抗滑桩的存在有效地抑制了PGA放大系数沿坡面向上的增大趋势和坡表双塑性区的贯通,而单排桩边坡PGA放大效应更明显,塑性区范围更广,深度更大,局部失稳更严重,抗震支护作用相对较弱;引入FFT谱比可知,单、双排桩边坡在5~10 Hz频段振幅放大效应的不同是造成单、双排桩边坡动力响应差异的主要原因;在地震作用下,单排桩边坡破坏历经边坡自稳定→坡表土体塑性变形→边坡局部塌陷溃散3个阶段,双排桩边坡破坏历经前两阶段。

某深厚软土层基坑双排桩位移影响因素分析

基坑支护结构变形过大会严重影响基坑和周边建筑物安全。探明影响基坑支护变形因素对基坑设计和施工安全具有重要指导意义。以某深厚软土船闸基坑工程为例,采用有限元软件建立三维模型模拟基坑开挖过程,研究土体参数、临边荷载、桩间土加固强度以及桩体刚度因素对支护结构变形的影响规律,运用灰色关联度理论分析各影响因素敏感程度。结果表明:当土体内摩擦角下降或临边荷载增加,桩顶水平位移增加明显;桩顶水平位移对各因素敏感程度依次为土体参数、临边荷载、桩间土加固强度和桩身刚度。在深厚软土基坑设计与施工中,应重视软土触变、流变问题,提高土体强度并减少支护桩外临边荷载,以保障基坑工程和周围建筑物安全。

基坑双排管桩与盖板接头开裂原因分析及优化研究

珠江三角洲某双排管桩基坑支护结构,在基坑开挖过程中发现盖板出现沿基坑边线方向开展的裂缝。为深入研究基坑开挖后双排管桩与盖板相互影响的受力特性、开裂原因及裂缝控制措施,本文采用ABAQUS有限元软件对该工程进行数值模拟计算,并根据不同荷载工况,分析管桩与盖板连接处的应力分布和变化的规律,探讨盖板开裂的原因,提出合理控制盖板开裂的改良措施。研究结果表明:盖板中严重受拉区域主要分布在前排桩前表面与盖板连接处和前排桩上方的盖板上表面,受拉应力最大值始终位于前排桩前表面与盖板连接处,内部钢筋较大应力值主要分布在后排桩;盖板开裂的直接原因在于前排管桩发生较大变形,由节点连接处传递变形挤压盖板;通过调整管桩桩顶锚入盖板深度与采用暗梁钢筋布置两项改良措施,可起到有效降低应力、控制裂缝的作用。

湖中基坑-双排钢管桩围堰受力变形分析

为便于施工,位于水域中的基坑工程通常需要施作围堰来保证施工场地干燥,但目前对围堰变形的研究尚不完善。以南昌艾溪湖隧道工程为研究背景,利用Midas GTS NX有限元软件,研究围堰宽度、拉杆位置对双排钢管桩围堰变形规律的影响,并通过将模拟计算结果与实测数据进行对比,验证了模型的合理性。研究结果表明:围堰宽度有一个合适的范围,过小过大均会造成围堰变形过大。在本工程中,围堰合理宽度范围为3.5~4.5 m,围堰宽度的改变对围堰内基坑开挖变形影响较小;综合两侧钢管桩变形来看,拉杆设置在围堰顶部0.8 m处时两侧钢管桩变形较小。

基于动态神经网络NARX时间序列的双排桩基坑变形预测

针对目前基于含基本假设或经验公式的传统土力学计算方法,不能有效地反映具有多因素交叉性以及时空性的基坑变形规律,而监测数据时间序列能够真实地表现基坑土体变形的演变,以南宁市亭洪路72号河南水厂住宅小区危旧房改造项目双排桩基坑工程为依托,考虑开挖深度和土体暴露时间这2个因素对监测时间序列的影响,提出一种带有外部输入的非线性自回归(NARX)动态神经网络时间序列模型,多方位预测关键断面重要测点的竖向位移和水平位移。结果表明:预测值和实际监测数据的变化趋势具有较好的一致性,且竖向位移预测值与实际监测值的预测残差小于1.0 mm,水平位移预测残差小于0.3 mm。该模型预测效果良好,同时验证了此模型应用于双排桩基坑变形动态分析的可行性。

膨胀土基坑双排桩支护结构数值模拟研究现状

总结了国内外学者对膨胀土在物理性质和力学特性方面的研究,并整理了关于膨胀土基坑事故产生的原因。重点阐述了膨胀土基坑双排桩支护结构在数值模拟和理论分析方面的研究现状。针对目前双排桩支护结构应用在基坑支护工程方面存在的问题,对以后的研究工作提出探讨和展望,为双排桩支护结构在膨胀土基坑中的应用研究提供了思路。