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.

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.

New method of designing anti-slide piles——the strength reduction FEM

At present,the thrust of an anti-slide pile can be worked out with some calculation methods. However,the resistance in front of the pile,the distributions of resistance and thrust,and appropriate pile length cannot be easily obtained. In this paper,the authors applied the strength-reduction finite element method (FEM) to several design cases of anti-slide piles. Using this method,it is possible to take the pile-soil interactions into consideration,obtain reasonable resistance in front of pile and the distributions of thrust and resistance,and reasonable lengths of anti-slide piles. In particular,the thrust and resistance imposed on embedded anti-slide piles can be calculated and composite anti-slide pile structures such as anchored piles and braced piles can be optimized. It is proved through the calculation examples that this method is more reliable and economical in the design of anti-slide pile.

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.

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.

Study on distribution rule of sliding pushing force and remnant resistant sliding force acting on anti-sliding pile

Anti-slide pile is one of the important methods to administer landslide geological disaster because of its advantages.It plays important role in administering landslide.It is a premise of reasonable economy and technological advance to know the distribution rule and feature of the force between anti-sliding pile and surrounding rock.To determine the sliding force and remnant resistant sliding force,according to need of study,this paper sets up the geological model and mechanics model in term of a typical landslide,and analyzes the effect rule of sliding body distortion,strength and gravity to the pushing force and remnant resistant sliding force by use of the numerical model.The distribution rule of pushing force and remnant resistant sliding force of the type of landslide is given.

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.

Axisymmetrical analytical solution for vertical vibration of end-bearing pile in saturated viscoelastic soil layer

Based on elasticity and the theory of saturated porous media, and regarding the pile and the soil as a single phase elastic and a saturated viscoelastic media, respectively, the dynamical behavior of vertical vibration of an end-bearing pile in a saturated viscoelastic soil layer is investigated in the frequency domain using the Helmholtz decomposition and variable separation method. The axisymmetrical analytical solutions for vertical vibrations of the pile in a saturated viscoelastic soil layer are obtained, and the analytical expression of the dynamical complex stiffness of the pile top is presented. Responses of dynamic stiffness factor and equivalent damping of pile top with respect to the frequency are shown in figures using a numerical method. Effects of the saturated soil parameters, modulus ratio of the pile to soil, slenderness ratio of pile and pile＇s Poisson ratio, etc. on the stiffness factor and damping are examined. It is shown that, due to the effect of the transversal deformation of the pile and the radial force of the saturated viscoelastic soil acting on the pile, the dynamic stiffness factor and the damping derived from the axisymmetrical solution are greatly different from those derived from the classical Euler-Bernoulli rod model, especially at some specific excitation frequencies. Therefore, there are limitations on applicability of the Euler-Bernoulli rod model in analyzing verticai vibration of the pile. More accurate analysis should be based on a three-dimensional model.

Evaluation of Unsaturated Layer Effect on Seismic Analysis of Unbraced Sheet Pile Wall

This paper is built upon the previous developments on lateral earth pressure by providing a series of analytical expressions that may be used to evaluate vertical profiles of the effective stress and the corresponding suction stress under steady-state flow conditions. Suction stress profile is modeled for one layer sand near the ground above the water level under hydrostatic conditions. By definition, the absolute magnitude of suction stress depends on both the magnitude of the effective stress parameter and matric suction itself. Thus, by developing the Rankine’s relations in seismic state, the composing method of active and passive surfaces in sides of unbraced sheet pile is examinated and the effects of soil parameter on those surfaces are evaluated by a similar process. The relations described the quantitative evaluation of lateral earth pressure on sheet pile and the effects of unsaturated layer on bending moment and embedded depth of sheet pile in soil.

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.

NONLINEAR DYNAMICAL CHARACTERISTICS OF PILES UNDER HORIZONTAL VIBRATION

The pile-soil system is regarded as a visco-elastic half-space embedded pile. Based on the method of continuum mechanics, a nonlinear mathematical model of pile-soil interaction was established-a coupling nonlinear boundary value problem. Under the case of horizontal vibration, the nonlinearly dynamical characteristics of pile applying the axis force were studied in horizontal direction in frequency domain. The effects of parameters, especially the axis force on the stiffness were studied in detail. The numerical results suggest that it is possible that the pile applying an axis force will lose its stability. So,the effect of the axis force on the pile is considered.

双参数地基横向受荷长桩参数反演方法研究

为了获取mz+C双参数地基模型下横向受荷长桩参数,基于m法原理,在地基系数等于零的位置建立坐标系,将地面以上桩身视为虚拟段。考虑剪力和弯矩共同作用时的情形,根据荷载效应等效原理,将地面处荷载简化到桩顶,建立了横向受荷长桩双参数计算模型。将桩土相对刚度和z0作为未知参数,提出了地基参数反演模型。该反演模型考虑了土抗力对荷载作用形式、地面处桩身位移和转角的影响。根据桩在地面处的位移和转角实测值反演地基参数,并结合算例通过桩身最大弯矩和地面处土抗力验证了反演方法的可行性。结果表明:本研究方法能够保证桩在地面处位移和转角理论值与实测值相符,最大弯矩及其位置误差很小;与m法相比,地面处土抗力变大对桩身弯矩影响程度沿深度先增大后减小,主要影响范围位于最大弯矩位置附近;桩身抗弯刚度与最大弯矩、地面处土体抗力均成线性关系,对二者影响较大且呈反向变化;根据最大弯矩和地面处土抗力实测值可以求得抗弯刚度的合理取值范围,考虑抗弯刚度随着桩顶荷载或位移的变化能够更好地模拟桩土的实际工作状况,可以提高mz+C双参数地基模型计算精度。

码头钢筋混凝土桩的细观损伤模型参数标定及模型验证

桩被用于码头中时,由于各种因素对桩身材料特性的劣化而降低桩身承载能力已成为高桩码头安全健康使用的重要影响因素。为更加准确地预测钢筋混凝土桩在内河码头复杂水工环境下(船舶荷载、波浪荷载等)的损伤情况和变形特性,设计出一种易于制作与操作的水平加载装置,对钢筋混凝土桩进行水平分级加载试验,得到桩底受拉荷载-应变曲线,通过PFC3D软件建立三维颗粒流离散元钢筋混凝土桩模型,对细观参数进行标定,并结合物理试验结果验证模型力学性能的合理性。

嵌岩桩承载性能对比分析及优化措施探讨

在实际工程中,岩土体参数取值及基础设计方案对工程造价存在较大影响。该文依托重庆秀山地区某工程嵌岩桩相关技术资料,通过有限元方法及经验参数法对基桩承载性能进行对比分析,分析表明:在相同工程条件下,经基桩有限元方法及经验参数法计算的侧摩阻及端阻占比差值有正有负,基桩承载力特征值计算结果差距大,有限元方法比经验参数法大20%以上,提出应从地质参数及桩型方面对其进行优化。通过对嵌岩桩承载性能对比分析及优化措施的探讨,以期为类似工程实践提供一定的参考及借鉴。

高桩结构Pushover抗震分析关键参数及规定

本文以某海外工程强震区的高桩结构为例,基于PIANC和ASCE/COPRI 61-14、POLB等现行国际抗震设计规范,总结了在实际Pushover抗震分析过程中如何应用国际规范确定动力放大系数、容许应变限值、材料期望性能、塑性铰长度等关键参数和如何考虑P-delta效应、地震荷载组合、地震质量等相关规定,可为类似项目的设计提供参考。

基于激光扫描的散货料堆实时三维重建与参数提取

文中针对港口散货料堆三维重建与参数获取问题,对自动化抓取中散货料堆的三维重建方式和料堆参数测算方法进行了研究。首先对港口散货料堆的作业方式和作业环境进行分析,设计并搭建了三维重建实验平台,然后对点云数据进行旋转变换,利用点云拼接技术实现从二维点云到三维点云的转换,最后通过求取极值并利用极值索引来获取最高点的坐标,通过AABB包围盒获取料堆的长宽高等数据,以此计算出散货料堆的占地面积。

小口径组合桩在滑坡抢险中的设计方法探讨

为适应滑坡抢险工程的时效性和安全性,在分析小口径组合桩加固机理的基础上,提出设计流程、计算方法及具体参数取值,并应用于某铁路大临道路工程修建期间诱发的一处滑坡整治工程中,通过监控量测和数值模拟分析,验证该设计方法在抢险工程中的可行性。工程效果证明,计算方法及具体参数取值较为合理。

高速公路边坡预应力锚索桩板墙结构参数优化与受力特征分析

桩板墙是高速公路滑坡治理中常用的一种支护措施,其结构参数的优化设计是工程施工的研究重点。以云南省红河州建水(个旧)至元阳高速公路工程AK0+560~AK0+660段桩板墙工程为背景,采用数值模拟与灰色关联分析、正交试验设计相结合的方法,研究桩体嵌固长度、桩间距、桩宽3种结构参数的影响与优化,最终验证优化后的结构参数在地震工况下的稳定性。结果表明:桩间距为主要影响因素,桩体嵌固长度和桩宽的关联度相近,为次要影响因素;桩板墙结构参数最优组合为桩体嵌固长度15.0 m、桩间距5.0 m、桩宽3.0 m;地震工况下,抗滑桩悬臂段土压力以及桩身偏移量和沉降差满足规范要求,边坡稳定性较好。