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.

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

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.

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

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.

矩形桩水平承载力特性分析

桩基础因其良好的水平受力特性,在基坑开挖支护体系中被广泛应用。相较于等截面面积的圆桩,矩形桩具有更强的水平荷载抵抗能力。本研究采用数值分析方法,比较了具有等截面面积的矩形桩和圆桩的水平承载力,并定量分析了矩形桩的水平承载力特性,探究了不同长宽比和泥皮厚度等因素对矩形桩承载能力的影响。结果显示,在相同条件下,矩形桩的水平承载力提高了12%以上。随着长宽比的增加,平均提升比率稳定在17%左右。然而,在存在泥皮的情况下,矩形桩的水平承载力低于没有泥皮的圆桩。因此,针对矩形桩的现场施工,需要采取相应的处理措施,为未来矩形桩的施工提供了有益参考。

复杂环境中矩形顶管始发端地层加固方案优化研究与应用

矩形顶管的始发阶段是矩形顶管施工中风险最高的施工阶段,在施工过程中,必须在始发前对始发端地层进行预加固处理。城市核心区域由于受到地面和地下建筑物、管线的影响,经常遇到加固盲区、加固不到位的问题。基于此,本研究总结提出了一种旋喷桩加固结合钢板桩防护的施工方法,在始发基坑洞门处围护结构外侧,密贴围护结构打设钢板桩,结合旋喷加固、洞门凿除等工艺改进措施,有效降低始发端地层施工风险,保证工程自身和周边环境安全。

Experimental study on seismic reinforcement of bridge foundation on silty clay landslide with inclined interlayer

A shaking table test for a bridge foundation reinforced by anti-slide piles on a silty clay landslide model with an inclined interlayer was performed.The deformation characteristics of the bridge foundation piles and anti-slide piles were analyzed in different loading conditions.The dynamic response law of a silty clay landslide with an inclined interlayer was summarized.The spacing between the rear anti-slide piles and bridge foundation should be reasonably controlled according to the seismic fortification requirements,to avoid the two peaks in the forced deformation of the bridge foundation piles.The“blocking effect”of the bridge foundation piles reduced the deformation of the forward anti-slide piles.The stress-strain response of silty clay was intensified as the vibration wave field appeared on the slope.Since the vibration intensified,the thrust distribution of the landslide underwent a process of shifting from triangle to inverted trapezoid,the difference in the acceleration response between the bearing platform and silty clay landslide tended to decrease,and the spectrum amplitude near the natural vibration frequency increased.The rear anti-slide piles were able to slow down the shear deformation of the soil in front of the piles and avoid excessive acceleration response of the bridge foundation piles.

矩形桩施工技术及应用研究

现阶段矩形桩在应用上得到了一定的发展。基于泰国拉玛三至曼谷西外环高速公路项目矩形桩工程实践,对矩形桩施工关键技术及应用进行分析探讨,给出了矩形桩施工过程中各关键施工环节的控制措施,并介绍了两种特殊的新型矩形桩施工工艺。

考虑泥皮影响的矩形桩水平承载能力分析——基于泰国拉玛三至曼谷西外环高速公路项目

文章基于泰国拉玛三至曼谷西外环高速公路项目,首先介绍了该项目的施工特点及自然地理情况,之后针对项目中矩形桩的应用情况,通过ABAQUS有限元软件,分析了矩形桩在成桩过程中产生的泥皮对桩体水平承载性能的影响。结果表明,矩形桩相对圆桩具有水平承载性能好和施工成本低等特点,泥皮的存在显著降低了矩形桩的承载能力,建议在成桩后增加后注浆,以提高泥皮强度,防止泥皮强度不足导致承载力不足。

某矩形深基坑软土地层开挖监测研究

为研究矩形基坑几何效应及基坑缺角对于基坑变形特性的影响,文中以汕头某扩建项目矩形深基坑工程为例,通过现场实测数据,研究了矩形基坑几何效应对于基坑周边地表沉降和围护桩水平位移影响,分析了基坑在时间上和空间上的变形规律和影响因素。结果表明地表沉降随基坑开挖工况的进行不断增大,以向下沉降变形为主;围护桩水平位移随时间不断增大,且沿围护桩埋置深度方向呈现出先增大后减小的抛物线型变形规律,存在一段明显鼓起处;矩形基坑缺角处更为薄弱,由于矩形基坑缺角产生几何效应影响,造成围护桩侧向位移和地表沉降在缺角处更为显著。研究结果可为同类型基坑开挖和设计提供参考。

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.

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.

基于控制点排序的透视变换原木截面测量方法

木材被盗案件中,需要先找到被盗的可疑树木,然后和留在地面的基部伐桩进行比对,确认可疑树木为被盗树木。为了辅助公安机关判断可疑木材是否为被盗木材,需要精确测量被盗木材的基部伐桩和可疑木材的截面大小等特征。首先对留在地面的基部伐桩进行拍照,并对找到的可疑木材截面进行拍照,然后比对2个截面的相似性,从而判断可疑木材是否属于被盗木材。由于被盗木材一般数量庞大,摄像机拍照存在畸变,拍照的姿态、角度和焦距以及环境光照都对成像有具体影响,因此,提出采用矩形棋盘格和最小二乘透视变换的方法,将所有的棋盘格角点作为控制点,并根据透视变换的直线特征不变性,构建了一种基于Hough变换的控制点排序方法。该方法能够将不同角度、不同姿态拍摄的图像变换到鸟瞰图像,并缩放到原始尺寸,从而进行测量。对于不同角度、不同姿态、不同焦距、不同光照条件下的图像,本研究提出的透视变换方法均可以把特征棋盘格及棋盘格后面的伐桩图像校正到图像的中间位置,得到伐桩的鸟瞰图,精确地复原伐桩的原貌。对校正后的图像采用MATLAB的imtool工具进行测量,测量结果表明,该方法测量误差最大为2.45%,能满足公安机关对可疑木材是否为被盗木材的辅助判断需求。

考虑管-土/泥浆接触状态的浅埋大断面矩形顶管隧道摩阻力计算方法研究

研究分析顶管-土体/泥浆的接触状态,进而结合全土柱地层压力理论和摩擦学理论,建立考虑管-土/泥浆接触状态的浅埋大断面矩形顶管隧道摩阻力计算方法,并开展工程实例验证与应用。研究结果表明:本文所建立的考虑管-土/泥浆接触状态的矩形顶管隧道摩擦力计算方法的理论计算结果与实测结果较吻合,该方法具有可靠性,可用于指导实际工程的设计与施工;受顶管姿态、泥浆套质量影响,顶管管壁接触存在完全管-泥浆、完全管-土和管-土/泥浆共存3种接触状态,在实际施工中,以管-土/泥浆共存接触状态为主;顶管顶进初期,受端头井地层加固及泥浆套形成质量等因素影响,界面接触模式应按管-土接触考虑,管壁摩阻力大;在富水地层中,泥浆套质量受地下水渗流作用影响显著,泥浆易稀释、流失,减阻效应减弱。

碎石土地基中矩形桩水平承载特性及m值分析

为探究碎石土地基中桩身抗弯刚度对桩基水平承载特性及地基水平抗力系数的比例系数m值的影响,以桩身等截面积为基准,展开不同抗弯刚度矩形桩水平荷载作用下承载特性研究,并采用m法对其进行计算分析.试验结果表明:桩身位移衰减特征表现为刚性桩时,荷载传递深度是受载边长的8.3倍,表现为柔性桩时,荷载传递深度是受载边长的1.5倍;碎石土地基的m值可在32.9~58.7 MN/m^(4)范围内取值.桩身位移及弯矩的衰减规律表明,桩身抗弯刚度影响桩土荷载传递机理,刚性桩的荷载传递深度较柔性桩大,空间受力更为显著;通过m法计算得到的位移与实测位移吻合,表明m法可作为矩形桩位移计算的预测方法.

圆形截面抗滑桩配筋方式优选

圆形截面抗滑桩作为抗滑桩的一种形式,采用机械成孔,不仅能够缩短工期,而且能够有效避免人工挖孔所存在的风险。基于ABAQUS有限元软件对3种配筋形式(沿桩周均匀配筋、沿桩周非均匀配筋和配置矩形钢筋笼)的抗滑桩支护滑坡在静力荷载作用下的位移、钢筋受力特点等进行定量分析研究。研究结果表明:①相同荷载作用下,圆形非均匀配筋抗滑桩与矩形钢筋笼抗滑桩支护效果相对较好;②选用圆形非均匀配筋形式和矩形钢筋笼形式能够较大程度发挥钢筋作用。③当配筋量不大时,在可以准确定位情况下选用圆形非均匀配筋形式,可在满足承载力要求的同时节约钢筋量,但在滑坡推力较大,配筋量较大时,用矩形钢筋笼形式更有利于钢筋的布置。

Limit analysis on seismic stability of anisotropic and nonhomogeneous slopes with anti-slide piles

This study employs the limit analysis method to evaluate the seismic stability of anisotropic and nonhomogeneous slopes stabilized with anti-slide piles. The pseudo-static approach is used to simplify the earthquake load. The yield seismic acceleration factor is obtained from the optimization procedure and the results are verified with the published data. Then, the seismically-unstable slope is reinforced with anti-slide piles, and the seismic stability of the reinforced slope is explored. The results show that the anisotropy and nonhomogeneity of soils have significant effects on the stabilizing force required from the anti-slide piles and the optimal location of the pile is near the toe of the slope.