考虑两种不同性质超固结的土体本构模型

结构对土体的变形特性有强烈影响,土体本构模型应该反映土体的结构性。通过调研分析将土体变形表现出的超固结划分为结构超固结与应力超固结这2种不同性质的超固结,从而使结构超固结与应力超固结统一起来。土体结构超固结采用结构超固结参数来表示。模型对修正剑桥模型进行扩展,模型的屈服面形状与修正剑桥模型一致,而屈服面的大小由结构超固结和应力超固结ps之和决定,而屈服面的变化由体积硬化与结构损伤共同来描述,模型采用相关联流动法则;从而提出了一个可考虑结构性的粘土本构模型。模型概念明确,参数简单并有物理意义。初步验证表明,模型可以较好的反映结构性土体的变形特性。     

Stabilizing blended calcium sulfate materials for roadway base construction

Blended calcium sulfate (BCS), a recycled fluorogypsum waste material, has been used in Louisiana as a pavement base layer for more than a decade. Without further chemical stabilization, the major concern of using raw BCS as a pavement structural layer is its moisture resistance. It could cause both short-term construction difficulties and long-term performance problems. In order to improve the moisture susceptibility of BCS, various cementitious agents were used in the laboratory for BCS stabilization. To further verify the efficiency of BCS stabilization schemes obtained from laboratory and assess the field performance for stabilized BCS materials as well as potential cost-benefits, three pavement test sections were constructed and tested using the accelerated loading facility (ALF) device. Both laboratory and field test results indicated that a grade 120 granulated ground blast furnace slag (GGBFS) of 10 vol.% stabilized BCS material possessed a superior performance over raw BCS in terms of water resistance, durability, and good long-term performance. Field test results further demonstrated that the GGBFS stabilized BCS base outperformed both a regular crushed stone base and a fly ash stabilized BCS base by a significantly large margin.A life-cycle cost analysis proved that, besides its outstanding laboratory and field performance, using the GGBFS stabilized BCS can provide a substantial long-term savings over regular crushed stone and fly ash stabilized BCS bases in a 30-year pavement design life period.     

Study of the function of the insulation layer for treating water leakage in permafrost tunnels

Qinghai–Tibet Railway is one of the national momentous construction projects in the West Development Plan of China. Kunlun mountain tunnel is the key control engineering of the railway. But, according to the observation in-situ data, on May 22, 2003, water irruption took place in the construction joints at DK977 + 620 section (the sign DK is an abbreviation of distance kilometer, the number 977 expresses the 977 km, and the number 620 expresses 620 m), and the maximum flux of the water reached to about 200 m³/d(1 m³/d means one cubic meter per day), and the water pressure increased violently. In this paper, the status of water leakage of Kunlun mountain tunnel on Qinghai–Tibet railway is introduced by the time step. Based on the status of water leakage, the reason for water leakage in the tunnel is opened out. According to the basal theories of heat transfer and seepage, considering the coupled effect of seepage field and temperature field, a three-dimensional calculational model of the coupled problem are given, and the finite element formulae are obtained by Galerkin’s method, and the computer program is written. Using this model and program, three-dimensional nonlinear analysis for the coupled problem of the flat buried part from DK977 + 578 to DK977 + 682 in Kunlun mountain tunnel on Qinghai–Tibet Railway are made either with or without the insulation layer. The result shows that it is necessary for treating water leakage to fit the insulation layer between the two linings in Kunlun mountain tunnel.     

Are the relative variation rates (RVRs) approximate in different cities when the same energy-efficiency reform is taken to the same building?

On the assumption that the same envelope reform is made on two buildings located in 19 cities of China, America and Europe, this paper simulates the annual heating and cooling energy consumption before and after the reform with tools of DOE-2, DeST-h and the authors' characteristic temperature method (CTM), and makes further analysis on the relative variation rates (RVRs) of energy consumption. It can be found that the absolute reductions of annual heating and cooling needs may differ up to tens of times in different cities for the same buildings with the same energy-efficient measures. On the other hand, there is no obvious difference in initial investment for the same energy-efficient reform in various cities of a country or an economic district, therefore, the energy efficiency potentiality and economic value of the same reform are completely different under various climatic conditions, which illustrates that it is very important to harmonize the local climates when selecting an energy-efficient project in different locations. However, when the same measures are taken to the same building, the annual heating RVRs are approximate and the annual cooling RVRs are also approximate in different cities, which is the common rule of building energy efficiency.     

Cavity reverse expansion considering elastoplastic unloading and application in cast-in-situ bored piles

The construction process of a cast-in-situ bored pile is too complicated to be described by the cavity expansion theory with a single process. An exact unified semi-analytical solution for both cylindrical and spherical cavities reverse expansion after unloading in drained soil is developed. The non-associated Mohr-Coulomb model and definition of logarithmic strain are adopted in the reverse plastic zone. This model can be used to solve the stress and displacement fields of the soil around a bored pile along both the horizontal and depth directions. Parametric analysis shows that the effect of the unloading phase does not change the ultimate pressure of cavity reverse expansion compared with in situ expansion. The cavity cannot re-expand to its initial radius even though the cavity pressure reloads to the initial value. The increase of internal friction angle, cohesion, and Young's modulus has a positive effect on radius recovery, while the dilatancy angle has a negative effect. A simulation of the construction process of cast-in-situ bored piles is presented, where the role of boring, mud wall protection, and concrete placement is defined. An example that describes the stress and displacement fields around a pile shows that the total radial displacement of soil around the pile is dominated by contraction displacement. And it is closely related to depth and horizontal distance. The results of both parameter analysis and example analysis demonstrate that a low reverse cavity pressure corresponds to a stress-reduction area surrounding the cavity.     

基于力密度法的树状结构找形及稳定承载力优化算法

力密度法通常用于张拉索网结构等不需要考虑稳定性的结构体系的找形分析,但对于树状结构,由于其在竖向荷载作用下所有构件仅受到轴向压力的作用,除了找形以外还需要考虑构件稳定承载能力的问题。利用力密度法对树状结构进行找形分析的基础上,引入欧拉稳定承载力计算理论以考虑构件几何长度对稳定承载力的影响,并提出了相应的迭代算法。推导了适用于树状结构的修正迭代力密度理论计算式,通过改变每一个分枝的力密度进而达到优化分枝长度的目标。通过与已有计算结果的对比验证所提对于平面树状结构算法的可靠性,对空间树状结构进行分析验证所提算法对于复杂树状结构的适用性。算例分析表明：采用所提算法迭代100次即可得到收敛的结果,耗时5min左右;与数值逆吊法找形相比,避免了双单元法抗弯刚度不恰当而导致的计算不收敛问题。     

深层排水孔堵塞对富水岩质高边坡稳定性的影响

高边坡施工或运营期间常因多种因素作用导致排水孔堵塞,从而抬升地下水位,影响边坡稳定性和支护结构的安全。基于渗流折射定律,采用空气单元法模拟排水孔,开展了岩质高边坡渗流应力耦合分析,重点研究了排水孔不同堵塞工况下的坡后地下水位变化及支护结构力学响应。计算结果表明:排水孔堵塞对坡后地下水位影响显著,坡内位移整体变化不大,坡趾位置岩体变形最大;坡体锚杆轴力明显增加,最大增长幅度达到45%。对于布设深层排水孔的岩质高边坡,排水孔堵塞后边坡支护结构的位移变化明显,对支护结构的影响不容忽视,尤其体现在坡趾剪出口位置。此外,排水孔接近完全堵塞时,边坡安全系数显著降低。提出了以框架式格构和锚杆共同作为支护体系的高边坡处理措施,即下部边坡加强格构支护强度,上部边坡增加锚杆锚固长度。     

桥梁工程教学中若干能力培养的探索

为适应土木工程专业培养方案的需要和桥梁工程自身特点,在桥梁工程教学中结合相应教学知识点的讲授,增强美学、力学分析、防灾减灾、极端事件、工程风险等能力的培养,提高学生学习兴趣,增强学生将理论知识和工程实践密切联系的能力,培养素质高和创新能力强的桥梁工程专业学生。     

基于“大工程”理念的工程实践教学改革探索

工程学科范围广阔,具有科学性、系统性、技术性和实践性等特征,而工程实践教学往往注重教学本身,强调工程学科的科学性和技术性,导致工程实践教育狭窄于技术或技术上的狭窄。在工程教育"回归工程"的发展趋势下,工程界对学生能力的多样化需求日益凸显,工程实践教学改革势在必行。文章在工程实践教学改革需求分析的基础上,对基于"大工程"理念的工程实践体系、教学内容以及教学模式改革进行了探讨。     

库水位升降作用下土质岸坡变形特征实验研究

库水位升降作用下三峡库区土质岸坡坡体吸水、应力集中及滑移变形,形成不同时段和不同空间部位的裂缝体系。通过模型试验的方法,分析了土质岸坡在一个蓄水降水循环周期内裂缝体系的时空演化分期配套规律。试验结果表明:蓄水初期,裂缝主要出现在岸坡前缘水位线附近,且出现频率高、规模逐渐增大,岸坡出现局部坍塌破坏;蓄水中期,岸坡前后缘均有裂缝出现,但出现频率低、规模减小;蓄水后期,前缘裂缝发育基本消失,后缘裂缝继续发育,岸坡以沿滑动面整体蠕滑为主;水位上升过程中暂停蓄水时裂缝发展缓慢。降水阶段,拉张裂缝主要出现在岸坡坡体后缘,初期降水裂缝出现频率较低,发展缓慢;后期降水裂缝出现频率、规模变大,产生下座变形及下错台坎;水位下降阶段岸坡沿滑动面发生整体缓慢蠕滑。