Large-scale model testing of high-pressure grouting reinforcement for bedding slope with rapid-setting polyurethane

Bedding slope is a typical heterogeneous slope consisting of different soil/rock layers and is likely to slide along the weakest interface.Conventional slope protection methods for bedding slopes,such as retaining walls,stabilizing piles,and anchors,are time-consuming and labor-and energy-intensive.This study proposes an innovative polymer grout method to improve the bearing capacity and reduce the displacement of bedding slopes.A series of large-scale model tests were carried out to verify the effectiveness of polymer grout in protecting bedding slopes.Specifically,load-displacement relationships and failure patterns were analyzed for different testing slopes with various dosages of polymer.Results show the great potential of polymer grout in improving bearing capacity,reducing settlement,and protecting slopes from being crushed under shearing.The polymer-treated slopes remained structurally intact,while the untreated slope exhibited considerable damage when subjected to loads surpassing the bearing capacity.It is also found that polymer-cemented soils concentrate around the injection pipe,forming a fan-shaped sheet-like structure.This study proves the improvement of polymer grouting for bedding slope treatment and will contribute to the development of a fast method to protect bedding slopes from landslides.

Assessing cutter-rock interaction during TBM tunnelling in granite:Large-scale standing rotary cutting tests and 3D DEM simulations

The widespread utilisation of tunnel boring machines(TBMs)in underground construction engineering requires a detailed investigation of the cutter-rock interaction.In this paper,we conduct a series of largescale standing rotary cutting tests on granite in conjunction with high-fidelity numerical simulations based on a particle-type discrete element method(DEM)to explore the effects of key cutting parameters on the TBM cutter performance and the distribution of cutter-rock contact stresses.The assessment results of cutter performance obtained from the cutting tests and numerical simulations reveal similar dependencies on the key cutting parameters.More specifically,the normal and rolling forces exhibit a positive correlation with penetration but are slightly influenced by the cutting radius.In contrast,the side force decreases as the cutting radius increases.Additionally,the side force shows a positive relationship with the penetration for smaller cutting radii but tends to become negative as the cutting radius increases.The cutter's relative effectiveness in rock breaking is significantly impacted by the penetration but shows little dependency on the cutting radius.Consequently,an optimal penetration is identified,leading to a low boreability index and specific energy.A combined Hertz-Weibull function is developed to fit the cutter-rock contact stress distribution obtained in DEM simulations,whereby an improved CSM(Colorado School of Mines)model is proposed by replacing the original monotonic cutting force distribution with this combined Hertz-Weibull model.The proposed model outperforms the original CSM model as demonstrated by a comparison of the estimated cutting forces with those from the tests/simulations.The findings from this work that advance our understanding of TBM cutter performance have important implications for improving the efficiency and reliability of TBM tunnelling in granite.

Large-scale model test study on the water pressure resistance of construction joints of karst tunnel linings

Model tests and numerical calculations were adopted based on the New Yuanliangshan tunnel project to investigate the water pressure resistance of lining construction joints in high-pressure and water-rich karst tunnels.A large-scale model test was designed and conducted,innovatively transforming the external water pressure of the lining construction joint into internal water pressure.The effects of the embedded position and waterstop type on the water pressure resistance of the construction joint were analyzed,and the reliability of the model test was verified via numerical calculations.The results show that using waterstops can significantly improve the water pressure resistance of lining construction joints.The water pressure resistance of the lining construction joint is positively correlated with the lining thickness and embedded depth of the waterstop.In addition,the type of waterstop significantly influences the water pressure resistance of lining construction joints.The test results show that the water pressure resistance of the embedded transverse reinforced waterstop is similar to that of the steel plate waterstop,and both have more advantages than the rubber waterstop.The water pressure resistance of the construction joint determined via numerical calculations is similar to the model test results,indicating that the model test results have high accuracy and reliability.This study provides a reference for similar projects and has wide applications.

A Simplified Nonlinear Model of Vertical Vortex-Induced Force on Box Decks for Predicting Stable Amplitudes of Vortex-Induced Vibrations

Wind-tunnel tests of a large-scale sectional model with synchronous measurements of force and vibration responses were carried out to investigate the nonlinear behaviors of vertical vortex-induced forces （VIFs） on three typical box decks （i.e., fully closed box, centrally slotted box, and semi-closed box）. The mechanisms of the onset, development, and self-limiting phenomenon of the vertical vortex-induced vibration （VlV） were also explored by analyzing the energy evolution of different vertical VIF components and their contributions to the vertical VIV responses. The results show that the nonlinear components of the vertical VIF often differ from deck to deck; the most important components of the vertical VIF, governing the stable amplitudes of the vertical VIV responses, are the linear and cubic components of velocity contained in the self-excited aerodynamic damping forces. The former provides a constant negative damping ratio to the vibration system and is thus the essential power driving the development of the VIV amplitude, while the latter provides a positive damping ratio proportional to the square of the vibration velocity and is actually the inherent factor making the VIV amplitude self-limiting. On these bases, a universal simplified nonlinear mathematical model of the vertical VIF on box decks of bridges is presented and verified in this paper; it can be used to predict the stable amplitudes of the vertical VIV of long-span bridges with satisfactory accuracy.

独柱曲线刚构匝道桥抗倾覆稳定试验研究

以2009年7月15日津晋高速公路港塘互通立交A匝道桥发生的桥梁倒塌事故为镜鉴,结合青银高速公路河北段自身的特点,确定出以永安立交两座独柱支承连续曲线混凝土单箱单室箱梁刚构桥作为主要的研究对象.并以有限元理论分析为基础,利用Ansys多工况仿真技术,辅以模型试验加以验证的方法,研究独柱曲线连续梁桥的力学性能.得出桥梁在各荷载工况作用下各个控制断面的应力及位移分布情况,并确定出车辆荷载最不利轮位及车辆吨位级数,获得了青银高速公路C匝道独柱混凝土曲线箱梁桥可能发生倾覆的极端荷载布置形式,提出现阶段避免此类桥型发生桥梁事故的建议,并为永久解决该桥的车辆荷载倾覆问题提出了加固方案.

土工膜/土工织物界面大型斜坡模型试验研究

复合衬垫系统广泛应用于垃圾卫生填埋场,是防止渗沥液污染物渗漏扩散的重要屏障。在垃圾重力及沉降作用下易造成斜坡上复合衬垫系统拉伸破坏或沿其界面产生滑移而失稳。目前,由于缺乏对复合衬垫系统内部剪力传递机理的认识,仍难完全解决以上两大岩土工程问题。因此,设计并采用复合衬垫系统大型斜坡模型试验装置开展了其内部剪力传递机理的研究。该装置通过砂袋加载模拟填埋过程,采用手拉葫芦为核心的滑移控制系统再现了土工膜/土工织物界面的渐进累积破坏过程。试验结果表明:当外部剪力小于峰值强度时,界面不会进入残余状态,上覆的土工合成材料锚固端的拉力也非常小;但当外部剪力超过界面峰值强度时,界面就会逐渐进入残余状态,并最终达到残余强度。同时,薄弱界面上覆的土工合成材料锚固端的拉力也显著增加,严重时甚至被完全拉断。

液压脉冲试验台建模与仿真研究

针对液压脉冲试验台要能可靠可控地产生脉冲波形这个关键技术问题,以管道-容腔物理模型为基础,利用Matlab对阶跃模型、斜坡模型和液电比拟方法对阶跃模型进行了数字仿真,仿真结果表明通过调整容腔体积、管道长度以及管道直径等系统参数,能产生符合标准的脉冲波形。对液压试验台建立了斜坡输入模型,推导出了斜坡响应输出表达式。计算结果表明斜坡输入模型的超调量最大为63.7%。根据阶跃输入和斜坡输入模型,从理论上分析得出了在斜坡输入时间不大于系统振荡周期1/10时,斜坡输入可以作为阶跃输入来处理。

高水头船闸阀后突扩体升坎形式优化

针对船闸输水阀门后突扩廊道的水力学问题,以银盘船闸为依托,建立比尺为1∶10的泄水阀门段物理模型,对突扩体升坎形式进行优化。通过非恒定流物理模型试验,对比研究了6种突扩廊道升坎形式的动水压力特性,探讨升坎形式对突扩廊道水动力荷载特性的影响,并提出了最优升坎形式。研究成果对高水头船闸阀门段廊道体形的优化设计具有一定的指导意义,可为其提供理论依据和技术支撑。

Decisive Parameters for Backwater Effects Caused by Floating Debris Jams

The dimensional analysis of the backwater effect caused by debris jams results in the Froude number of the approach flow in the initial situation prior to debris jam formation and the debris density as decisive parameters. For the more precise detection of the influence of both parameters the results of different hydraulic model test series at the Laboratory of Hydraulic and Water Resources Engineering of the Technical University of Munich concerning debris jams at spillways as well as at racks for the retention of wooden debris were uniformly evaluated. On the one hand a significant increase of the backwater effect with a rising Froude number of the approach flow could be shown. This is in good correlation to recent test results for debris jams at retention racks at the Laboratory of Hydraulics, Hydrology and Glaciology of the Swiss Federal Institute of Technology Zurich. On the other hand a significant increase of the backwater effect could also be shown for a rising debris density. However, the test results also show that significantly different backwater effects can occur in different test runs with identical test conditions. These differences are a result of the randomness of debris jam development, and therefore, a more exact quantification of the dependence of the backwater effect on the Froude number of the approach flow and on the debris density is not considered useful for the present results.

Model Testing for Ship Hydroelasticity: A Review and Future Trends

Conducting model experiments is an effective and reliable way in the investigation of ship hydrodynamic and hydroelastic behaviors. A survey of model testing techniques for ship hydroelasticity and its prospect are presented in this paper. The research highlights with respect to ship hydroelasticity and key points in model testing are summarized at first. Then testing techniques including laboratory tank test and full-scale sea trial are reviewed, and both their advantages and disadvantages are analyzed comprehensively. Based on the conventional testing approaches, a state-of-the-art testing approach which includes performing tests using large-scale model at sea is proposed. Furthermore, recommendations towards the further development of ship hydroelasticity tests are forecasted and discussed.

山区深覆盖层河道闸坝泄洪消能体型优化研究

采用模型试验方法,对某拟建于深厚覆盖层上的拦河闸坝的泄洪消能布置方式进行了优化研究,研究成果表明:采用"斜坡护坦+底流衔接+柔性消力池+局部防护"的泄洪消能模式可用于解决深厚覆盖层闸坝泄洪消能问题,在类似工程体型布置中需注意:出闸水流需在护坦内充分扩散、尽量减小护坦出口单宽流量与流速、入池水流角度宜为平射流或挑射流、以及柔性消力池需局部防护等。

Behavior of Pile Group with Elevated Cap Subjected to Cyclic Lateral Loads

The pile group with elevated cap is widely used as foundation of offshore structures such as turbines, power transmission towers and bridge piers, and understanding its behavior under cyclic lateral loads induced by waves, tide water and winds, is of great importance to designing. A large-scale model test on 3×3 pile group with elevated cap subjected to cyclic lateral loads was performed in saturated silts. The preparation and implementation of the test is presented. Steel pipes with the outer diameter of 114 mm, thickness of 4.5 mm, and length of 6 m were employed as model piles. The pile group was cyclic loaded in a multi-stage sequence with the lateral displacement controlled. In addition, a single pile test was also conducted at the same site for comparison. The displacement of the pile cap, the internal forces of individual piles, and the horizontal stiffness of the pile group are presented and discussed in detail. The results indicate that the lateral cyclic loads have a greater impact on pile group than that on a single pile, and give rise to the significant plastic strain in the soil around piles. The lateral loads carried by each row of piles within the group would be redistributed with loading cycles. The lateral stiffness of the pile group decreases gradually with cycles and broadly presents three different degradation patterns in the test. Significant axial forces were measured out in some piles within the group, owing to the strong restraint provided by the cap, and finally lead to a large settlement of the pile group. These findings can be referred for foundation designing of offshore structures.

An experimental study on stress-strain behavior and constitutive model of hardfill material

Hardfill is a new type of artificially cemented material for dam construction works,with a wide application prospect.Its mechanical behavior lies between concrete and rockfill materials.A series of large-scale triaxial tests are performed on hardfill specimens at different ages,and the stress-strain behavior of hardfill is further discussed.The strength and stress-strain relationship of hardfill materials show both frictional mechanism and cohesive mechanism.An age-related constitutive model of hardfill is developed,which is a parallel model consisting of two components,rockfill component and cementation component.Moreover,a comparison is made between the simulated and the experimental results,which shows that the parallel model can reflect the mechanical characteristics of both rockfill-like nonlinearity and concrete-like age relativity.In addition,a simplified method for the determination of parameters is proposed.

The role of polyurethane foam compressible layer in the mechanical behaviour of multi-layer yielding supports for deep soft rock tunnels

The polyurethane foam(PU)compressible layer is a viable solution to the problem of damage to the secondary lining in squeezing tunnels.Nevertheless,the mechanical behaviour of the multi-layer yielding supports has not been thoroughly investigated.To fill this gap,large-scale model tests were conducted in this study.The synergistic load-bearing mechanics were analyzed using the convergenceconfinement method.Two types of multi-layer yielding supports with different thicknesses(2.5 cm,3.75 cm and 5 cm)of PU compressible layers were investigated respectively.Digital image correlation(DIC)analysis and acoustic emission(AE)techniques were used for detecting the deformation fields and damage evolution of the multi-layer yielding supports in real-time.Results indicated that the loaddisplacement relationship of the multi-layer yielding supports could be divided into the crack initiation,crack propagation,strain-hardening,and failure stages.Compared with those of the stiff support,the toughness,deformability and ultimate load of the yielding supports were increased by an average of 225%,61%and 32%,respectively.Additionally,the PU compressible layer is positioned between two primary linings to allow the yielding support to have greater mechanical properties.The analysis of the synergistic bearing effect suggested that the thickness of PU compressible layer and its location significantly affect the mechanical properties of the yielding supports.The use of yielding supports with a compressible layer positioned between the primary and secondary linings is recommended to mitigate the effects of high geo-stress in squeezing tunnels.

带出口匝道城市隧道通风特性比尺模型试验

通风特性是影响城市隧道内外环境的关键,为深入研究带出口匝道城市隧道风量及风量分配的变化规律,获得隧道总风量及分流比的高效控制策略,基于相似理论,设计并搭建总长为38 m的1/20带匝道隧道通风比尺模型,研制可实现8台模型风机联动的变频控制系统、16个断面的速度及压力数据的实时测量与自动采集系统(该系统在风速u≥2.5 m·s^(-1)时,比尺模型同步满足阻力、惯性力和压力相似准则),进行各通风段射流升压力变化对隧道内风量及风量分配的影响试验。结果表明:隧道主线通风段与匝道通风段风量存在联动耦合效应,当调节某通风段射流升压力时,该通风段及与之串联的通风段风量均随着射流升压力的增大而增大,与之并联的通风段,风量随射流升压力的增大而减小;总风量和分流比分别是影响城市隧道内、外环境的关键因素,调节分流前主线段射流升压力不改变分流比,但对控制隧道总风量变化最为高效,单位射流升压力作用下的总风量变化幅度达1.43%·(N·m^(-2))^(-1);调节分流后主线段或匝道段射流升压力对隧道总风量的影响有限,但能有效控制分流比,单位射流升压力作用下的分流比增幅分别为(-4.43,4.16)%·(N·m^(-2))^(-1);利用分流前主线段的射流风机控制隧道内环境,利用分流后主线段或匝道段的射流风机控制隧道外环境,是最为高效的通风控制方法。

Geometry and Maximum Width of a Stable Slope Considering the Arching Effect

The stability of an arching slope in deformable materials above strong rocks strongly depends on the shape and width of the span.Equations for a free surface problem that incorporate these two parameters were derived using a simplified two-dimensional arching slope model,and were validated using physical model tests under 1 g and centrifugal conditions.The results are used to estimate the maximum excavation width for a weak claystone slope in a lignite mine,for which we calculate a safety factor of 1.31.

Experimental and numerical study on structural performance of reinforced concrete box sewer with localized extreme defect

An experimental and numerical investigation into the structural performance of reinforced concrete box sewers with typical corrosion-related extreme defects localized at the ceiling was conducted.Firstly,during the large-scale laboratory test,some key struc-tural responses were captured and evaluated,including the crack width development process(via digital image correlation measurement),ceiling deflection,and material strains of both complete and typical defective boxes.The failure modes and load-carrying mechanism throughout the specimen loading phases were analyzed.Furthermore,the specimen failure process was simulated using a damage-basedfinite element method,and a related parameter sensitivity analysis was performed.The results indicate that the defective ceiling cracked at mid-span under a low load value,but the bending capacity loss can be substituted by two shoulders and carry three tofive times more load before completely collapsing.The simulation matched the lab test qualitatively,and with the suggested set strategy of material parameters,the load-deflection feature curve could provide a practical prediction of the ultimate bearing capacity of the defec-tive sewers,with a 10–15%error on the safe side.