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.

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.

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.

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.

Evaluation of ultimate bearing capacity of Y-shaped vibro-pile

Based on Mindlin stress solution, a numerical computational method was proposed to calculate the stresses in the ground induced by side friction and the resistance of Y-shaped vibro-pile. The improved Terzaghi's and ЪерезанцевВГ's methods for ultimate bearing capacity evaluation were proposed by considering the stress strength induced by friction resistance at pile head level of Y-pile. A new method to calculate the ultimate bearing capacity of Y-pile was also proposed based on the assumptions of soil failure mode at the tip of Y-pile and the use of Mohr-Coulomb soil yield criterion and Vesic compressive correction coefficient with the induced stresses in the ground. Based on the comparisons with the field static load test results, it is found that the improved Terzaghi's method gives higher ultimate capacity, while the other two methods shows good agreement with the field results.

圆形抗滑桩-拱形挡土板支挡性能与参数分析

为规避当前施工方法的不足,发展安全、高效和可靠的施工方法。依托东北地区某高速铁路路堑边坡工程,采用适于机械钻孔的圆形抗滑桩代替现行矩形抗滑桩,预制拱形挡土板,本文提出一种新型拱形板-桩墙支挡体系;并构建有限元模型,分析桩长、桩径、桩间距以及拱形挡土板矢跨比对新型拱形板-桩墙支挡体系支护性能的影响;揭示不同参数下桩顶水平位移与桩身内力的变化规律。研究结果表明:桩长与桩身弯矩和剪力大小呈正相关关系,与桩顶水平位移呈负相关关系。桩长超过14 m时,其对桩顶水平位移、桩身弯矩和剪力的影响效应明显减弱;随着桩间距增大,桩顶水平位移增大但变化幅度逐渐减小。拱形挡土板矢跨比增大时,桩顶水平位移、桩身弯矩和剪力均减小。影响拱形板-桩墙体系支挡性能的因素依次为桩间距、桩长、桩径和矢跨比。研究结果为圆形抗滑桩-拱形挡土板支挡体系在实际工程中的应用提供新思路。

圆截面组合桩加固滑坡的作用机理与合理嵌固深度物理模型试验研究

目前在滑坡治理中,大截面人工挖孔桩因存在施工安全隐患大和效率低下等问题已在部分行业领域被限制使用,开展可机械化施工的圆截面组合桩研究已成为新的趋势,但当前对圆截面组合桩变形受力机理与合理嵌固深度的研究尚不够深入。基于自主研发的圆截面组合桩加固滑坡物理模型试验系统,开展了不同工况下圆截面组合桩加固滑坡的物理模型试验,分析了滑体的变形演化过程,研究了圆截面组合桩加固下滑体与抗滑桩的变形受力特征,并对比分析了不同嵌固深度和桩顶连系梁对圆截面组合桩变形特征的影响,揭示了圆截面组合桩加固滑坡的作用机理。结果表明:①滑体的变形演化过程可分为压密、匀速变形、加速变形和变形破坏4个阶段;②前后桩均存在反弯点,反弯点会随着试验进程向桩顶移动,且后桩的反弯点更接近于滑动面;③当一排桩的嵌固深度保持不变、另一排桩的嵌固深度改变时,可将36%的桩长作为合理的嵌固深度;④连系梁使后桩的最大桩顶位移减小了15.6%,而对前桩的影响不大;⑤连系梁的存在降低了滑动面处的最大桩身弯矩,从而使得桩身弯矩分布更加合理。该研究成果有望为圆截面组合桩的设计提供借鉴和参考。

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.

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.

地震作用下多锚点圆形抗滑桩动力响应特性研究

为探讨多锚点圆形抗滑桩(以下简称多锚点圆桩)加固滑坡的动力响应特性,本研究以概化地质模型为案例开展振动台试验,测试得到不同地震强度作用下多锚点圆桩的加速度及动态土压力等多属性数据信息。阐明了坡体的宏观灾变演化过程及加速度的区域性响应特性。基于桩体与锚索结构的受力响应数据对多锚点圆桩在高烈度地区的实际应用提出了建议。研究结果表明:在地震力、滑动面和桩体反力的耦合互馈效应影响下,坡体不同部位的灾变力学机制和加速度响应存在显著区别。超过0.2 g地震作用下,桩体加速度放大系数(M PGA)随地震强度增加而呈降低趋势,锚索结构极大地降低了抗滑桩发生倾倒或折断风险。实际工程中锚索结构应采用渐进式补偿设计原则,同时合理分配桩锚结构的抗力可充分发挥其加固性能。

Deformation Mechanism and Design Countermeasures of Tunnel Portal in Volcanic Deposit Clay Stratum

Shortly after tunneling,problems such as primary-support through cracks and clearance infringement are found in the shallow-buried section of tunnel No.4 of the Jakarta-Bandung High Speed Railway(Jakarta-Bandung HSR),and orthogonal cracks can be found on the earth surface in front of the working face,which brings great challenges to the tunnel construction.In view of the above engineering problems,the sliding surface is speculated according to the geological and field conditions,and the impact of landslides is applied in the model in the form of external load.The paper uses the numerical simulation method to analyze and compare the impact of landslides on the tunnel structure and deformation,and puts forward the reinforcement measures.The conclusions of the studies are:(1)under the influence of heavy rainfall,the strength index of volcanic deposit clay stratum drops sharply,and meanwhile the multiple factors including tunnel excavation are liable to cause sliding of the front slope;(2)parallel landslide in front of the tunnel has a great impact on the tunnel,so setting-up of pre-reinforcement measures to control landslide shall be the focus of similar projects during design;(3)the deformation and stress of the tunnel structure can be significantly controlled for safe construction by strengthening the shallow-buried tunnel with pile foundation and longitudinal and transverse beam frames during landslide.

浅埋超大直径双圆顶管侧穿高压铁塔桩基预加固方案

以深圳市铁岗-石岩水库水质保障工程2#顶管侧穿王洋Ⅰ线N14高压铁塔为背景,对浅埋超大直径双圆顶管侧穿高压铁塔桩基预加固方案进行系统研究。提出管幕支护、“管幕支护+钻孔灌注咬合桩+旋喷桩”、“管幕支护+微型桩+旋喷桩”3种预加固方案,通过MIDAS/GTS建立数值模型,分析3种方案加固效果。结果表明:方案一加固效果不理想;方案二加固效果明显提升,对桩基沉降最为显著,较方案一降低53%;采用方案三,塔基整体沉降、水平、纵向位移及相邻桩基沉降差较方案二分别减少42%、20%、16%及19%,更能有效控制桩基稳定;加固后,塔基最大沉降为5.49 mm,最大水平位移为3.99 mm,最大纵向位移为2.28 mm,相邻塔基最大差异沉降为0.95 mm,基础最大局部倾斜为0.03%,均满足施工控制标准。方案三加固技术能较好地控制铁塔桩基沉降,保证高压铁塔的安全和正常使用,可为类似工程提供借鉴。

竖向平行双隧道开挖对邻近群桩变形的影响

为了研究砂土地层中竖向平行盾构隧道施工引起邻近群桩的变形与各影响参数间的一般性规律,基于离心模型试验,采用PLAXIS 3D建立竖向平行双圆隧道邻近既有群桩开挖三维数值模型。通过与离心模型试验实测结果对比,对数值模型进行验证,并研究了土体参数、隧道和桩基尺寸对群桩沉降和倾斜的影响规律。研究结果表明:隧道开挖引起的群桩沉降和群桩倾斜度随土体模量、地层损失率、隧道直径的增大而增大,随桩基长度的增大而减小;且当下部隧道位于群桩正下方时群桩沉降受土体模量、地层损失率、隧道直径、桩基长度的影响较大;当下部隧道位于群桩桩趾水平处时群桩倾斜受土体模量、地层损失率和桩基长度的影响最大;土体模量大于35 MPa后,群桩沉降不再增加;土体模量大于20 MPa后,群桩倾斜度变化明显放缓;当双隧道均位于群桩一侧时,桩基长度大于35 m后群桩沉降基本不再变化;第二隧道位于群桩正下方时,当桩基长度大于45 m后群桩沉降和倾斜度变化量明显减少。

绿色低碳的循环基础调查分析

钢挡土墙是循环建筑(基础)的重要组成部分。本文介绍2023年4月至5月间对基础行业进行的调查,对结果做出分析和讨论,揭示了可循环钢挡土墙的优势、挑战和前景,并对循环基础的进一步推广实施提出了建议。钢挡土墙施工快速,与传统的混凝土挡土墙相比,在降噪、减碳、节能以及减少扰民方面有明显优势;从长远来看,钢挡土墙的社会和环境综合成本低于混凝土。现阶段因为设计师和开发商的认识不足以及成本的计算方法不一,阻碍了钢挡土墙的普及。调查发现,多数人对钢挡土墙的广泛应用持乐观态度,因为它符合国家循环经济导向,有利于双碳目标的实现。