公路隧道围岩的区间数组合分类法

公路隧道围岩的分类方法较多,每一种分类方法的结果都是对真实围岩状况的一种估计,通过一定的算法将这些分类结果进行合成,可以使各分类法取长补短,围岩信息得到充分利用。基于上述思路,并考虑到分类标准和被分类隧道围岩物理力学指标均为区间数的实际情况,提出了一种基于区间数的公路隧道围岩组合分类法。为充分利用区间数携带的信息,定义了一种新的区间数距离计算方法,选择能够兼顾各单一分类法之间功能性和协调性要求的加乘混合函数作为围岩分类函数,计算被分类围岩与分类标准各级别之间的分类函数值,最小值对应的类别即为被分类围岩的类别。针对某工程隧道2个典型段围岩的分类问题,在隧道围岩常用的岩芯质量指标ROD法、《公路隧道设计规范》(JTGD70-2004)BQ值法和弹性波速vp法进行分类的基础上,采用本文方法进行组合分类,结果表明:本文方法物理意义明确,计算过程简捷,分类指标稳定,分类结果与单一分类法相比能够更好地反映实际围岩状况,可供公路隧道勘察、设计、施工时参考。     

锚喷衬砌隧道结构稳定可靠度计算

根据地层特征曲线和围岩剪切滑移理论,分析围岩最小荷载计算方法。基于薄壁圆筒与锚杆端锚理论,分析喷射混凝土层(简称喷层)及锚杆的支护抗力确定方法。建立由锚杆支护抗力、喷层支护抗力和围岩荷载构成的圆形锚喷支护隧道结构功能函数。为了求解该非线性隐式功能函数的可靠度指标,首先,利用验算点与可靠度指标的关系,将极限状态方程由多自变量(结构基本变量)的隐式形式转变为单自变量(可靠度指标)的隐式形式;然后,通过泰勒公式将其展开成级数,截取其前若干项,导出可靠度指标的迭代逼近计算公式;再将复合函数求导法则与差分求导结合起来,推出逼近计算表达式中系数的导数求解格式。上述研究形成了基于泰勒级数与差分求导数结合的锚喷支护隧道结构稳定可靠度指标分析方法。采用该方法分析某公路隧道结构的稳定可靠度,并与蒙特卡罗方法的精确解进行对比,两者的绝对差异为0.018%,相对差异为4.47%。     

北京市公路绿化景观功能评价体系研究

在对北京市公路绿化调查研究的基础上,通过分析公路绿化景观功能,研究公路绿化景观评价的目标、原则、方法及指标体系,建立评价模型,最终建立了公路绿化景观功能评价体系.     

A stable CS-FEM for the static and seismic stability of a single square tunnel in the soil where the shear strength increases linearly with depth

A numerical procedure using a stable cell-based smoothed finite element method (CS-FEM) is presented for estimation of stability of a square tunnel in the soil where the shear strength increases linearly with depth. The kinematically admissible displacement fields are approximated by uniform quadrilateral elements in conjunction with the strain smoothing technique, eliminating volumetric locking issues and the singularity associated with the Mohr–Coulomb model. First, a rich set of simulations was performed to compute the static stability of a square tunnel with different geometries and soil conditions. The presented results are in excellent agreement with the upper and lower bound solutions using the standard finite element method (FEM). The stability charts and tables are given for practical use in the tunnel design, along with a newly proposed formulation for predicting the undrained stability of a single square tunnel. Second, the seismic stability number was computed using the present numerical approach. Numerical results reveal that the seismic stability number reduces with an increasing value of the horizontal seismic acceleration (α_h), for both cases of the weightless soil and the soil with unit weight. Third, the link between the static and seismic stability numbers is described using corrective factors that represent reductions in the tunnel stability due to seismic loadings. It is shown from the numerical results that the corrective factor becomes larger as the unit weight of soil mass increases; however, the degree of the reduction in seismic stability number tends to reduce for the case of the homogeneous soil. Furthermore, this advanced numerical procedure is straightforward to extend to three-dimensional (3D) limit analysis and is readily applicable for the calculation of the stability of tunnels in highly anisotropic and heterogeneous soils which are often encountered in practice.