Durability of Lining Concrete of Subsea Tunnel under Combined Action of Freeze-thaw Cycle and Carbonation

Through the fast freeze-thaw cycle test,accelerated carbonation test,and natural carbonation test,the durability performance of lining concrete under combined action of freeze-thaw cycle and carbonation were studied.The experimental results indicate that freeze-thaw cycle apparently accelerates the process of concrete carbonation and carbonation deteriorates the freeze resistance of concrete.Under the combined action of freeze-thaw cycle and carbonation,the durability of lining concrete decreases.The carbonation depth of lining concrete at tunnel openings under freeze-thaw cycles and tunnel condition was predicted.For the high performance concrete with proposed mix ratio,the lining concrete tends to be unsafe because predicted carbonation depth exceeds the thickness of reinforced concrete protective coating.Adopting other measurements simultaneously to improve the durability of lining concrete at the tunnel openings is essential.

Service Life Prediction of Lining Concrete of Subsea Tunnel under Combined Compressive Load and Carbonation

Qingdao Jiaozhou Bay subsea tunnel is the second self-built tunnel in China with the designed service life over 100 years.The durability of lining concrete are one of an important factors to determinate the service life of tunnel.Considering the main environmental loads and mechanical loads of subsea tunnel,the durability properties of lining concrete under combined action of compressive load and carbonation has been studied through the critical compressive load test,accelerated carbonation test,natural carbonation test and capillary suction test.The tests results show that critical compressive load apparently accelerates the carbonation and deteriorates the anti-permeability of concrete.Under the combined action of critical compressive load and carbonation,the durability of lining concrete decreases.Based on the carbonization life criteria and research results,for the high-performance concrete with proposed mix ratio,the predicted service life of lining concrete for Jiaozhou bay subsea tunnel is about 80 years which fails to reach the required service life.It is necessary to adopt other measurements simultaneously to improve the durability of lining concrete.

Failure Patterns and Energy Analysis of Shaft Lining Concrete in Simulated Deep Underground Environments

The failure patterns and energy evolution of three types of shaft lining concrete subjected to static and dynamic loading were reported.The energy and damage characteristics of concrete were determined by means of a uniaxial hydraulic servo machine,acoustic emission (AE) equipment,a split Hopkinson pressure bar (SHPB) and an ultrasonic wave analyser.The experimental results indicate that the confluence of multiple cracks forms a penetrating cross section in normal high-strength concrete (NHSC) under the condition of static loading,while the elastic energy that surges out at failure can cause tremendous damage when subjected to dynamic loading.A single crack was split into multiple propagation directions due to the presence of fibres in steel fibre-reinforced concrete (SFRC);adding fibre to concrete should be an effective way to dissipate energy.The non-steam-cured reactive powder concrete (NSC-RPC) designed in this paper can store and dissipate more energy than normal concrete,as NSC-RPC exhibits a strong ability to resist impact.Applying NSC-RPC to the long-service material of a shaft lining structure in deep underground engineering is quite effective.

An expert system for diagnosing fire-caused damages to reinforced-concrete tunnel lining

During the last four decades, reinforced-concrete structure failures have been happening widely for many reasons, such as increased service loads, war accidents, fire, and durability problems. The economic losses due to those failures are very high. An expert system is an interactive computer-based decision tool that uses both facts and heuristics to solve difficult problems based on knowledge acquired from experts. To realize these requirements, a logic programming visual basic language is used together with visual diagnosis. The expert system, Diagnosis of Fire-Caused Damages to Reinforced-Concrete Tunnel Lining (DFCDRCTL) was developed in this work for diagnosing the annual damages caused by fire. The program is used as an alternative of a human expert to make annual technical decisions in diagnosing fire damages at the second reinforced-concrete tunnel lining segment. It is concluded that the proposed DFCDRCTL expert system is easy to use, and is fast and helpful for engineers.

Railway tunnel concrete lining damaged by formation of gypsum,thaumasite and sulfate crystallization products in southwest of China

The railway tunnel concrete lining exposed to sulfate-bearing groundwater beyond 40 years in southwest of China was investigated. Field investigation, sulfate ions content and corroded products analysis, macro/microscopic test were carried out. Results show that under the tunnel concrete lining structure and its served environmental conditions, sulfate solutions permeate concrete lining and accumulate on windward-side of concrete lining, resulting in the increase of sulfate ions content on windward-side and the diffusion of sulfate ions from windward-side to waterward-side, which cause the concrete lining of windward-side damaged seriously but the waterward-side of concrete lining is still in perfect condition. It is confirmed that structural characteristic of tunnel and environmental conditions lead to physical attack with the leaching of concrete and sodium sulfate crystallization as well as chemical corrosion with formation of gypsum in high sulfate concentration and formation of thaumasite in proper temperature rather than formation of ettringite. These achievements can provide academic and technical supports for understanding the deterioration mechanism of concrete lining as well as constructing railway tunnel under sulfate attack.

Research on Stress and Strength of High Strength Reinforced Concrete Drilling Shaft Lining in Thick Top Soils

High strength reinforced concrete drilling shaft linings have been adopted to solve the difficult problem of supporting coal drilling shafts penetrating through thick top soils. Through model experiments the stress and strength of such shaft linings are studied. The test results indicate that the load bearing capacity of the shaft lining is very high and that the main factors affecting the load bearing capacity are the concrete strength,the ratio of lining thickness to inner radius and the reinforcement ratio. Based on the limit equilibrium conditions and the strength theory of concrete under multi-axial compressive stressed state,a formula for calculating the load-bearing capacity of a high strength reinforced concrete shaft lining was obtained. Because the concrete in a shaft lining is in a multi-axial compressive stress state the compressive strength increases to a great extent compared to uni-axial loading. Based on experiment a formula for the gain factor in compressive strength was obtained: it can be used in the structural design of the shaft lining. These results have provided a basis for sound engineering practice when designing this kind of shaft lining structure.

Study on the propagation of interface crack of young concrete lining and rock under blasting load

In the construction of water conservancy and hydropower project,young concrete lining structure is often affected by blasting load. Young concrete has a lot of micro-fractures with random distribution,which are easier to propagate and connect under blasting load. This paper focuses on the calculation on dynamic stress intensity factors of bond interface crack of concrete-rock according to concrete age. Result shows that different incidence angles of stress wave lead to different crack propagation mechanisms. Under the normal incidence of impact load,the bonding interface crack propagation of the concrete lining is mainly caused by reflection tensile stress,which forms from the free surface. With horizontal incidence of stress wave,the bond interface crack propagation of concrete lining is affected by concrete age. With the increase of concrete age,the elasticity modulus margin between concrete and rock decreases gradually,and the crack propagation form changes from shear failure to tensile damage.

On the treatment of thermal cracks in lining concrete of water conveyance system of Three Gorges Project permanent ship locks

A comprehensive investigation was performed for repairing the different types of cracks appearing on the surface or inside the concrete lining at various depths.The mate- rial properties used in grouting and two methods for crack repair were discussed in details, and consequently reliable repair measures were proposed and implemented.It is a better choice to adopt the hole-drilling method for the relatively regular crack.The grouting pres- sure should not be too high and it is generally between 0.4～0.6 MPa.For the second time grouting,the pressure maybe increased to 0.8 MPa.Other method is the pasting nozzles method which is more suitable for irregular cracks such as cracks with intensive density and crossing cracks.Its grouting pressure is generally between 0.6～1.0 MPa.The in-situ tests in Three Gorges Project demonstrate favorably the feasibility and applicability of the proposed methods for crack repair within the lining concrete.

Ceramic Setting Phosphate Binders for Bonding Refractory Concretes

The ceramic setting binders obtained by means of the raw mix mechano-chemical processing(mechanical dispersion and chemical interaction processes combination), used for bonding refractory concretes, become more available with a subsequent increased interest in their properties because they develop initial strength during a heat up of the units within 8-10 h, in contrast to 24 h after placement for high Al_2O_3 cements(HAC). This strength development enables high temperature processing units to be relined with minimum turnaround time, thus providing a favored cost/performance ratio. The present paper identifies the predominant phosphate phases responsible for developing good mechanical-strength properties of zirconia and alumina concretes bonded with mechano-chemical binders. It sets out the colloid and crystalline phases resulted from interphase interaction that provide the basis for high concentrated bonding suspensions(HCBS) technology useful to the refractory industry.

Frost heaving force considering synchronous damage to tunnel lining and surrounding rocks under freeze—thaw cycles

In areas with seasonal freezing,when the tunnel lining concrete is saturated with water infiltrating the interior,the lining and the surrounding rocks will simultaneously freeze.However,the current calculation of the frost heaving force fails to consider the synchronous damage to the lining and surrounding rocks under freeze-thaw cycles.Therefore,as per the elastic calculation model of the frost heaving force and model of steady-state heat transfer of circular tunnels,this study introduces the frost heaving rate of lining and surrounding rocks.First,the analytical solution of frost heaving force is obtained for simultaneous frost heaving of lining and surrounding rocks under any steady-state temperature field.Then,based on the fracture theory and meso-damage mechanics,the damage variables of lining and surrounding rocks under freeze-thaw cycles are extracted,representing their elastic modulus and porosity.Finally,the formula of frost heaving force for synchronous damage to the lining and surrounding rocks at any steady-state temperature field is obtained.The calculation results demonstrate that the lower the temperature inside the lining,the greater the frost heaving force.With the increasing number of freeze-thaw cycles,frost heaving force tends to gradually increase initially,reaching a peak value at 85 freeze-thaw cycles,decreasing to 80%of the peak value at 140 cycles before reaching a constant value.The lining participates in frost heaving,increasing the frost heaving force.The initial increase rate of frost heaving force is 15.7%.Changing the fitting coefficients s1 and s2 of the lining and surrounding rocks can effectively control the magnitude of the frost heaving force in the tunnels.

Local Tensile Strength of Connection Between H-Steel Beam Flange and Concrete-Filled Circular Column Tube with Through Diaphragm

This paper focused on investigating local tensile strength of connection between steel beam flange and concrete-filled circular column tube with through diaphragm. Three specimens were designed and tested to failure, and the structure behavior was studied by experiment and FEM analysis. On the basis of the results obtained, an estimation for local plastic and ultimate strengths of the connections using yield line theory was attempted, which results in a good prediction.

钢筋锈蚀作用下隧道衬砌结构力学性能劣化研究

考虑锈蚀引起的钢筋力学性能劣化、混凝土有效截面减少、两者黏结性能退化等因素,建立围岩压力作用下钢筋锈蚀隧道衬砌模型,对不同锈蚀率下衬砌结构变形、损伤、内力重分布和裂缝宽度变化进行分析。研究结果表明,锈蚀对衬砌结构各部位损伤严重程度表现为拱顶>拱肩>拱脚>拱腰>仰拱;锈蚀引起结构内力重分布,当锈蚀率由0%发展到20%时,衬砌结构临空侧受拉处弯矩逐渐减小,围岩侧受拉处的弯矩逐渐增大,衬砌轴力整体变化不大,最大变化量仅为7.53%;拱顶裂缝宽度发展最快,拱肩和拱脚次之,当锈蚀率发展到2.7%时,拱顶最大裂缝宽度已不满足耐久性要求;开裂区钢筋锈蚀对衬砌力学性能劣化起主导作用,仅开裂区钢筋发生锈蚀时,衬砌结构力学性能劣化规律与钢筋全长锈蚀情况类似,但锈蚀导致的内力变化幅度和裂缝宽度减小。

Application of Fractal Theory in Brick-Concrete Structural Health Monitoring

In order to monitor and forecast the deformation of the brick-concrete building, by taking a brick-concrete building as research object, fiber grating sensors were used to collect the monitoring data and double logarithmic curve of limit value characteristic and monitoring data were obtained based on the fractal theory. Constant dimension fractal method cannot be used to analyze the data directly. With the method of variable dimension fractal, we accumulate data, and the double logarithmic curve is smooth. Piecewise fractal dimensions are close. The outer interpolation method is used to calculate the fractal dimension of the next point and then back calculate the vertical displacement. The relative errors are calculated by comparing the forecast values and monitoring values, and the maximum relative error is 5.76%. The result shows that the fractal theory is suitable to use in the forecast of the deformation and the accuracy is good.

超深埋隧洞防渗排水措施与衬砌外水压力分布规律

高外水压力是制约超深埋水工隧洞建设的关键性难题之一,以排水孔为中心的综合堵排措施是降低外水压力的主要举措。为克服传统排水孔实体单元法整体网格划分难度大和计算效率较低的问题,首先,基于ABAQUS平台开发了两节点排水孔线单元模型,并验证其在隧洞工程数值模拟分析中的正确性和有效性;其次,建立了考虑防渗排水措施的围岩-衬砌三维有限元模型,研究多种防渗排水措施下的隧洞渗流场及衬砌外水压力分布规律;最后,探讨了防渗灌浆圈与排水孔设计参数对外水压力分布的影响,提出了防渗灌浆圈与排水孔间隔布置的原则。研究结果表明:所开发的两节点排水孔线单元具有较高的精度,在排水孔数目繁多的模型中具有极高效率;排水孔数目越多、深度越大、排距越小,衬砌外水压力越低;排水孔能够有效降低衬砌的外水压力,而防渗灌浆圈降外压能力有限;在排水孔末端间隔一定厚度围岩后再施作防渗灌浆圈,可更有效发挥两者的降压作用。

地铁车站叠合墙内衬早龄期温度与应变演化规律

为探究叠合墙早龄期内衬温度与应变演化规律,依托地铁车站叠合墙工程开展早龄期内衬墙温度与应变现场监测,分析内衬墙的裂缝分布特征、温度与应变演化规律。结果表明:在早龄期,裂缝多从内衬墙的底部施工缝向上延伸,大部分裂缝为竖向裂缝,少量斜裂缝位于墙角;内衬墙的中部温度高于四周温度,而墙体中心的温度峰值与降温速率最大,表面温度峰值最小,并且墙体存在明显的里表温差;在早龄期,内衬墙存在明显的膨胀与收缩现象,并且不同方向上的应变演化规律存在明显的区别。

超大竖井整体提升式模筑衬砌施工技术

依托天山胜利隧道3号竖井,提出超大竖井整体提升式模筑衬砌施工技术,在井筒初期支护模筑混凝土内侧安装2块独立的半月牙形整体上行式液压金属模板,采用8台稳车同步提升,通过模板周身多个浇筑口连续、均匀、对称地浇筑混凝土,保证超大竖井衬砌快速和高质量施工。对单块模板吊装、模板整体起吊、混凝土浇筑工况下模板变形及强度特征进行分析,并对横肋、纵肋、限位杆等关键构件连接部位建立局部受力分析模型进行计算,保证模板设计的合理性与安全性。研究结果表明,单块模板吊装、模板整体起吊、混凝土浇筑工况下模板、横肋、纵肋、限位杆受力及变形均满足要求;超大竖井整体提升式模筑衬砌施工技术机械化程度高,实现平均200m/月的施工效率,保证浇筑混凝土在模板内有足够的水化反应时间,提高混凝土早期强度,确保施工质量。

基于陶粒纤维混凝土的衬砌渠道抗冻胀性能研究

为改善北方寒区预制混凝土衬砌渠道存在衬砌板件自重大、尺寸小、装配效率低等问题,探讨将陶粒纤维混凝土用于衬砌渠道。基于正交试验法开展9组陶粒纤维混凝土和1组C35普通混凝土冻融前后力学性能试验,并结合冻胀数值模拟分析衬砌渠道抗冻胀性能变化。结果表明:陶粒纤维混凝土抗压强度因素影响次序为页岩陶粒体积取代率>聚丙烯纤维(PP)掺量>陶粒预湿时间,抗拉强度因素影响次序为PP掺量>页岩陶粒体积取代率>陶粒预湿时间,冻融后陶粒纤维混凝土抗压、抗拉强度损失率低于普通混凝土;衬砌渠道数值模拟的抗冻胀性能变化与材料性能变化趋势一致,陶粒纤维混凝土衬砌渠道抗冻胀性能损失小于普通混凝土衬砌渠道,最优抗冻胀性能损失减小4.68%,同时衬砌板重量减小18.47%;陶粒纤维混凝土作为渠道衬砌材料具有明显质轻的装配化优势。

考虑预制混凝土“设缝”作用的梯形渠道冻胀机制影响研究

寒区衬砌渠道输水能力下降主要是由常年冻融作用下衬砌结构发生冻胀破坏所致,针对渠道衬砌结构冻胀破坏问题提出渠坡板纵向设缝的抗冻措施与数值分析方法。本文通过将渠道衬砌板与冻土视为整体处理的方法构建混凝土衬砌渠道热力耦合冻胀模型,以甘肃省景泰灌区某混凝土衬砌渠道为研究对象,考虑不同设缝措施与纵缝填充的接触本构对3种工况进行抗冻影响因素分析。结果表明:渠底深部基本不受渠道整体几何边界的影响,但渠道边界尺寸和基土热流分布均对基土上部温度场变化具有显著影响。渠道阴坡、渠底和阳坡最大冻深分别为86.3、67.5、58.2 cm。通过合理设缝措施可使渠道阴坡法向冻胀力降低40.7%、底板冻胀量减小63.5%、切向冻胀力降低43.8%,使渠道断面冻胀分布趋于均匀,且模型分析与实测结果相符,表明本文构建模型的合理性。研究结果可为长距离输水渠道数值计算提供理论依据。