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.

Influence of thermal insulation layer schemes on the frost heaving force in tunnels

In extreme cold regions,a thermal insulation layer(TIL)is commonly employed to mitigate the detrimental effects of frost heaving forces in tunnels.Optimizing the laying scheme of TIL,specifically minimizing frost heaving forces,holds considerable importance in the prevention of frost damage.This research developed a two-dimensional unsteady temperature field of circular tunnels by using the difference method(taking the off-wall laying method as an example)based on the law of conservation of energy.Then,the frozen circle and water migration coefficient were introduced to establish the relationship between the temperature field and frost heaving forces,and a reliable methodology for calculating these forces under the specific conditions of TIL installation was developed.Then(i)the influence of the air layer thickness of the off-wall laying method,(ii)different laying methods of TIL,(iii)the TIL thickness,(iv)the thermal conductivity of the TIL,and(v)the freeze-thaw cycles on the frost heaving force were investigated.The results showed that the frost heaving force served as a reliable and effective metric for evaluating the insulation effect in tunnels.In order to avoid frost damage in compliance with the design requirements,the insulation effects from various laying methods were established,in descending efficacy order as follows:off-wall laying,double layer laying,surface laying,and sandwich laying.Our findings revealed that the optimal thickness for the air layer in the offwall laying method was 0.10 m.The insulation effect of materials with a thermal conductivity below 0.047 W/(m·℃)was furthermore found to be good.Under freeze-thaw cycle conditions,it is concluded that to prevent frost damage,the TIL thickness should be the sum of the thickness r1 of the first freeze-thaw cycle without frost heaving forces and an additional reserve value 0.06r1 of the TIL thickness.

盾构始发与接收密闭钢套筒的改进与实践

采用土体防坍塌加固措施时,为了进一步降低风险,通常在盾构进出洞采用钢套筒进行盾构机始发和接收。针对传统钢套筒应用于焊接连接盾构机时,存在无法进行盾体组装焊接和拆解切割的难题,提出了一种改进的始发和接收钢套筒,具体改进措施包括:钢套筒两侧各设置两个切割密封门,密封门设置在钢套筒两侧的前盾与中盾、中盾与盾尾的焊缝位置;其次,在钢套筒顶部的前盾与盾尾上方密封门设置两个填砂和水的密封门;另外,切割密封门及填砂和水的密封门内侧设有一道可更换的遇水膨胀橡胶止水条,并采用螺栓与钢套筒进行连接。改进以后的密闭钢套筒经佛山南海地铁项目多次应用,具有显著的社会效益、经济效益和环境效益。

贝氏体等温淬火对H13热作模具钢组织及热疲劳性能的影响

采用光学显微镜、扫描电镜和热疲劳试验等研究了常规淬火和等温淬火两种不同工艺对H13钢显微组织和热疲劳性能的影响。结果表明:等温淬火处理后H13钢的显微组织为马氏体+下贝氏体(M/B下)。与常规淬火相比,具有M/B下复相组织的试验钢的硬度有所降低,冲击韧性有所提高。热疲劳裂纹分析表明,经等温淬火处理后试样的热疲劳裂纹在长度和密度上均小于常规淬火处理的试样,表明M/B下复相组织有益于提高H13钢的热疲劳性能。

基于导向滤波器的医学图像融合方法

针对医学图像融合过程中易产生人造纹理的问题,本文将引导滤波器应用到医学图像融合中,有效提高融合图像的空间连续性,减少人造纹理的产生。首先利用导向滤波器的细节增强特性获得图像的细节层信息,主要通过导向滤波器对原图像进行滤波处理得到其基础层图像信息,再与原图像作差运算即可得细节层图像信息;然后采用基于含可变参数p的邻域统计特性融合规则得到图像融合权值系数,该融合规则在原有的邻域统计特性中加入可变参数p,可以有效增强融合图像的细节信息;最后将原图像按照所得的图像融合权值系数进行融合,得到最终的融合图像。实验仿真结果对比分析表明,随着可变参数p的变化,融合效果也有明显的提高,当p>10后,融合效果基本趋于平稳。该融合方法可以有效地实现医学图像融合,与其他融合方法相比,具有一定的优越性。

H13型热作模具钢表面改性技术研究进展

在工业中,模具的变形、磨损和疲劳失效普遍存在,严重影响了生产效率和产线安全。为了更好地了解和分析模具失效的原因,改善模具的性能,提高其使用寿命,通过介绍国内外H13型热作模具钢的表面改性技术及研究现状,总结了激光加热处理、热喷涂处理、化学热处理3类表面改性技术的特点及在改善热作模具钢表面性能方面的研究成果。探讨了不同表面处理工艺对该热作模具钢表面性能的影响,对不同处理技术应用于该热作模具钢表面改性的优缺点进行了分析,并对该热作模具钢表面改性技术的发展方向进行了展望。

电炉半钢转杯离心粒化制备铁粉工艺

为了实现钛精矿电炉冶炼副产品半钢的高附加值利用,提出了以半钢为原料,采用转杯与冷却水幕相结合的转杯离心粒化工艺制备铁粉,并作为硫酸法钛白还原剂的新工艺。实验研究了转杯直径和转速对铁粉粒度的影响规律,结果表明铁粉粒度随着转杯直径和转速的增大而减小;转杯直径为150mm、转速为1800r/min时,颗粒粒径小于0.45mm的铁粉占比达到90.45%(质量分数);建立了适用于转杯离心粒化颗粒粒度的预测模型,平均相对误差为11.43%;利用扫描电镜观察了铁粉颗粒截面的显微结构,铁粉颗粒表面存在一层铁的氧化物;利用热重分析法研究了水幕对铁粉颗粒氧化程度的影响。论文最后提出了铁粉制备、余热回收与钛白制备相结合的新工艺。

深冷处理对H13钢组织结构和热稳定性的影响

为了研究深冷处理对H13热作模具钢热稳定性的影响及组织演化规律,利用洛氏硬度计、X射线衍射仪、扫描电子显微镜及透射电子显微镜等对经不同热处理工艺处理后H13热作模具钢的热稳定性及显微组织进行了表征。结果表明,深冷处理促使部分残余奥氏体转变为马氏体,导致深冷处理后试验钢的硬度高于淬火态试验钢的硬度。经深冷处理后试验钢在540℃回火20h过程中其硬度均比常规热处理的试验钢硬度高,深冷处理的试验钢具有更好的热稳定性。与常规热处理的试验钢相比,深冷处理促使钢中碳原子偏聚并在回火过程中以碳化物的形式析出,导致深冷处理的试验钢回火后马氏体基体中碳的质量分数降低。透射电镜结果显示,试验钢在回火过程中析出的大量弥散分布的纳米级M23C6型碳化物,经长时间回火后碳化物粗化致使试验钢硬度随着回火时间的增加而下降。

硅铁合金离心粒化工艺

提出采用多孔转杯作为粒化器的硅铁合金离心粒化工艺。为了研究该工艺的可行性,采用不同转杯开孔孔径和转速对硅铁合金进行粒化试验并对试验后所形成的颗粒进行分析。结果表明,通过该工艺可得到球形度好、粒度均匀可控的合金产品,同时避免小于1mm的细小颗粒产生;在本试验条件下采用开孔孔径为12mm的转杯,转速为100~200r/min得到颗粒平均粒径在10mm左右,结果最佳;粒化后硅铁合金颗粒粒径为10~13mm的硅铁合金吸氧率和氧化率分别为0.5%、0.14%,满足目前工业要求。