不同地质条件下浅埋偏压小净距隧道围岩稳定性研究

不同围岩条件下浅埋偏压小净距隧道的围岩稳定性相差很大,特别是半软半硬岩层隧道,由于软硬交界面的存在,其施工力学特性更加复杂。使用FLAC3D模拟不同净距下均质硬岩、均质软岩和竖向半软半硬岩隧道施工15种工况,对比分析中岩墙、拱顶上部围岩、仰拱处围岩和边坡的围岩稳定性。结果表明:隧道开挖引起均质围岩中岩墙上部水平位移最大,而半软半硬岩中部水平位移最大,中岩墙上部围岩稳定性最差;0.6B净距可以作为半软半硬岩偏压小净距隧道的临界值;半软半硬围岩隧道开挖引起拱顶沉降量和硬岩隧道比较接近,远小于软弱围岩隧道拱顶沉降;隧道开挖引起软岩侧洞室上覆盖层围岩稳定性变差;隧道开挖引起拱顶上部围岩破裂面整体呈"W"形,仰拱部围岩破裂面呈"M"形。     

冻融循环对青藏黏土抗剪强度影响试验研究北大核心CSCD

冻融作用会对土体结构和性质造成影响,在冻融作用下,不同类型土壤的抗剪强度变化呈现出不同规律。本文选取青藏高原具有代表性的黏土,开展不同初始含水率和不同冻融循环次数下的重塑土抗剪强度变化研究,结合压电陶瓷监测试验,探究冻融循环下青藏黏土抗剪强度指标的变化模式和规律。结果表明:在反复冻融作用下,青藏黏土抗剪强度、黏聚力和内摩擦角随含水率增大呈阶梯下降;同一含水率的抗剪强度和黏聚力劣化曲线可以分为快速劣化和稳定两个阶段,内摩擦角呈先减小后增大的变化趋势;冻融循环过程中第1次循环对青藏黏土抗剪强度影响最为明显;采用压电陶瓷监测的应力波信号通过小波包分析可以得到真实信号振幅和应力波能量,二者均能反映青藏黏土抗剪强度的劣化趋势。本文提出的强度劣化指标能很好地反映青藏黏土抗剪强度的劣化程度,这在未来工程实际中有着一定的应用前景。     

青藏铁路可调控通风管路基温度场的三维非线性分析

可调控通风管路基是一种理想的保护高温冻土的工程措施. 应用有限元法, 对青藏铁路普通通风管路基和可调控通风管路基在施工完10 a内的温度场变化进行了三维数值分析. 结果表明: 可调控通风管路基在夏季(8月份)0 ℃的等温线比普通通风管路基要高, 说明它的冻土上限抬升幅度较大, 使冻土得到更好地保护, 并且其路基下面从第二年开始也不会出现融化层; 可调控通风管路基下面的冻土平均温度降到 -1 ℃时的时间比普通通风管路基要早, 说明可调控通风管路基具有较好的降温速度和降温效果.     

青藏铁路可调式通风管路基的数值仿真分析

Finite Element Method has been used to operate the numerical analysis and comparison between the traditional ventilated embankment and the adjustable ventilated embankment adopted in Qinghai-Tibet Railway construction. The numerical results show that: 1) The adjustable ventilated embankments can prevent the thermal entry from air into ducts during summer from thawing the permafrost beneath the embankments; 2) The cooling effects of the adjustable ventilated embankments on permafrost is much better than the traditional ventilated embankments although two kinds of embankments can generate the thawing bulbs at the beginning of finishing construction; 3) The drop of the mean temperature of permafrost under the adjustable ventilated embankments keeps faster than that of the mean temperature of permafrost under the traditional ventilated embankments. It is clear that the adjustable ventilated embankments can keep the embankment more stable than the traditional ventilated embankments.     

青藏铁路通风路基边界条件研究

In permafrost regions, many methods about active cooling embankment are put forward, one of these representations is ventilated embankment, its cooling effect is the result of the air convection in the duct, and this leads to reducing the annual average ground temperature. The present work in this article is to determine the boundary conditions of the ventilated embankment and natural ground in numerical work. There are several effects which influence boundary conditions, they are: radiation, evaporation,phase change, convection and embankment material etc. Radiation and convection are the main effects in those. We mainly consider sun radiation in this article. The added-surface effect in ventilated embankment lowers its temperature, so the temperature on the wall of the ventilated embankment is different from the temperature in atmosphere. There are two methods in determining the surface temperature, experimental method and experiential method. Detailed research is discussed in the article.