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.

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.

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.

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.

硬岩地层微型钢管桩抑尘降噪绿色施工技术研究

硬岩地层微型钢管桩施工过程中,通常采用气动潜孔锤作为成孔设备,易产生较大的噪音及扬尘,尤其对于在闹市区施工的地铁作业,不利于安全文明施工,导致投诉、信访等相关负面影响产生。通过在钻机孔口位置加装大功率吸尘器进行钻渣、岩屑及粉尘收集,能有效降低空气中粉尘浓度,实现扬尘控制;采用声屏障材料制作隔音屏,使用新型带消音装置的空压机,从根源及传播途径上双重控制噪音传播,有效减小噪音对环境的污染。通过现场验证及周边调查走访,扬尘及噪音已不是制约现场钢管桩施工的因素,实现微型钢管桩成孔过程的抑尘降噪绿色施工。

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.

复杂山区微型钢管桩钻机的研制与应用

针对川藏铁路供电工程中复杂山区输电线路挖孔基础埋深较大、大部分依赖人工挖孔基础,施工作业人员工作安全隐患大且效率低下的问题,研制一种微型钢管桩钻机。基于川藏铁路供电工程山区的地理特性,对钻机运用模块化结构设计的理念,采用机液复合驱动系统和轻量化自行式底盘的设计方案,具有运输便捷、移动灵活、能耗低和钻进工作效率高等优点。分别在平原地区和高原山区对钻机展开试钻,以验证钻机的性能,测试获取发动机的外特性数据。试验结果表明:钻机的各项性能指标符合预期,成孔效率高,满足微型钢管桩基桩设计的要求;确定钻机的工作范围为2 700~3 200 r/min时,柴油机的输出特性和燃油经济性较好。钻机的成功研制,解决了复杂山区挖孔基础困难的问题,有效推进了山区输电线路机械化施工。

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.

基于“楔紧”作用的微型抗滑桩合理桩间距研究

微型桩桩位灵活,施工时对周围环境扰动小,常用于滑坡抢险工程中,以重庆市沙坪坝区G319石花水库段纯土质边坡微型抗滑桩抢险工程为例,从微型桩内部“楔紧”作用出发,分析微型桩群桩效率,结合桩间土拱效应和桩后土拱效应,探讨基于“楔紧”作用的微型抗滑桩合理桩间距的计算模型,推导了微型桩桩间距合理范围计算公式,并将其应用于工程实践,结合工程监测数据,验证了桩身承载力及基于“楔紧”作用的微型抗滑桩合理桩间距计算模型的合理性。

大直径人工挖孔桩加固设计及施工技术分析

文中以长沙金茂大厦桩基工程为例,提出一种大直径人工挖孔桩离析事故加固施工方案。结果表明,文中提出的离析事故加工施工方案具有较高的可行性和可靠性,有效保证了离析桩基加固效果,符合实际应用需求。

房建地基不均匀沉降超小型钢管桩基底加固技术应用

随着建筑范围不断扩大,有些坡地经回填、碾压等地基处理后也开始房屋建设。由于种种原因,地基出现不同程度的沉降,在业主入住后施工质量问题凸显,轻则出现墙体裂缝、门窗封闭不严等情况,重则出现危楼的情况,给人们的财产及人身安全造成重大隐患。由于此类问题涉及面广,修复困难,往往造成恶略的社会影响。论文依据山西省大同市平城区基础加固项目施工为例,对地基加固进行了研究,指出常用加固方式的施工困难,针对该困难,采用超小型钢管桩对建筑基础进行加固。实践证明采用该方法,确保施工质量,缩短施工工期,降低施工安全风险,成本大幅降低,对后续类似地基加固项目有指导意义。

回填红粘土地层微型CFG桩复合地基现场足尺试验

为了获得广西桂林红粘土地层微型CFG桩复合地基设计时的参数合理取值，进行了室外足尺试验，获取不同桩长微型CFG桩复合地基桩间土强度提高系数α、桩间土强度发挥系数β、单桩承载力发挥系数A以及桩土应力比n．结果表明：采用冲击振动挤密成桩，桩间土强度提高1．28～1．56倍；复合地基破坏时，桩间土强度能得到有效发挥，发挥系数为0．90～0．98；单桩承载力发挥系数比规范推荐值0．8～0．9大，可达1．12～1．56，且随着桩长的增加而减小；桩土应力比在试验荷载范围内随着荷载的增加而增加，但增加趋势逐渐减缓．桩长在2—5m时，α取1．2～1．5，β取0．9～1．0，λ取1．1～1．5．

边坡平台大孔径微型桩孔潜孔锤施工工艺研究

分析了潜孔锤钻进、排渣工艺的能量守恒通式,结合湖北通城至湖南平江高速公路边坡300mm大孔径微型抗滑桩施工,介绍了设备选型、施工工艺对地质环境条件的调控方法,提出了潜孔锤成孔的极限成孔结构.设计的潜孔锤施工最佳工况对平台微型抗滑桩机械成孔作业具有指导意义.