黄土高填方明洞土压力减载及力学特性研究

发布时间：2018-04-28 09:45

本文选题：高回填明洞 + 土压力　；参考：《兰州交通大学》2014年硕士论文

【摘要】：现行的设计规范中明洞各部位土压力尤其是垂直土压力计算仍采用土柱法计算，即P=γh。但是，已有研究表明这种计算方法具有一定的局限性。本文主要依托于某明洞高回填土项目，通过室内缩小比例模型试验、现场实际工程试验及数值模拟三方面，研究了明洞顶土压力的变化规律及土工格栅减载的减载效果，意在保证结构安全性、经济性的前提下，寻求能让目标明洞回填达到目标高度（64m）的最佳方式。本论文所完成的工作和研究成果如下：（1）根据实际明洞在试验室制作了（1∶30）缩小比例模型，对现场明洞进行模拟回填。通过：①不放拱；②放拱；两种方案分别探讨了，回填土压实不同（75%、80%、85%）时，对明洞顶土压力的影响规律。研究结果表明，随着填土高度的变化，当填土高度达到0.5m（模拟高度15m）后，明洞顶土压力呈曲线形式上涨，且曲线逐渐趋于平缓；随着填土压实度的增加明洞顶土压力逐渐减小，即填土压实度有利于明洞顶“土拱效应”的形成。（2）通过：①不布设格栅（即，不减载）；②布设多层格栅，不布设“减载孔”；③布设单层格栅+“减载孔”；④布设多层格栅+“减载孔”；这四种方案对土工格栅减载进行了系统的研究和探讨，推导了单层格栅和多层格栅减载下土压力计算公式。研究结果显示，布设“减载孔”的减载效果更好，更有利于格栅发挥“提兜”作用；方案③中单层格栅的最佳效果达到54%，方案④中达到59%，且推导的理论计算公式与试验拟合较好，具有一定的可信度。（3）通过：①不布设EPS板（即，不减载）；②布设5cm厚EPS板；③布设7.5cm厚EPS板；④布设10cm厚EPS板；四种方案研究EPS板的减载效率，分析了不同EPS板厚度对明洞顶土压力的影响及其减载效果。结果显示，EPS板的减载效率在1/3-1/2之间，且随着EPS板厚度的增加减载效果越发的明显。（4）通过：①69m现场不减载黄土试验段；②20m现场土工格栅减载试验段；分别研究了两种方案下，明洞顶土压力变化规律及土工格栅的减载效果。结果表明，当填土高度达到13m时，方案①明洞顶并未产生明显的“拱效应”，这与室内模型试验得到的结论相印证。虽然前期土压力与土柱法稍有偏差，但随着时间的增长土压力值逐渐靠拢γh，“拱效应”逐渐消失，证实了“拱效应”的不稳定性；方案②中得到格栅减载效率为40%，虽然不及室内模型试验，但仍旧能够达到很好的效果。（5）建立了平面有限元数值计算模型，通过：①不减载；②土工格栅减载；两种方案分别模拟现场实际回填，从数值分析方面对室内模型试验和现场试验进行两两对比，两两印证。结果显示，方案①在填土15m以下，土压力值与γh基本一致，大于15m时，呈曲线变化，，且增量逐渐减小，曲线趋于平缓。方案②得到其减载效果为42%，与现场得到的40%相印证。（6）在前文研究了高回填明洞顶土压力变化规律及其减载的基础上，对明洞结构、裂缝以及复合地基承载力进行了判定。研究结果表明，两种情况下，明洞衬砌结构安全系数均满足《规范》要求。不减载情况下，当填土高度达到50m时，裂缝宽度超限，最大裂缝宽度为0.21mm，证实了减载的必要性。根据提供的复合地基承载力发现，不减载情况下当填土高度达到13m时，明洞地基最大竖向应力略超过限值304kPa；而土工格栅减载情况下，虽然有所缓解，但当填土高度达到30m时地基应力也已然超限。因此本文得出结论，目标明洞在现有填土基础上和现有地基承载力304kPa下，不建议继续回填，在地基承载力足够的情况下，按建议中给出的方案进行回填，便可达到预想效果。
[Abstract]:In the current design code, the soil pressure, especially the vertical earth pressure in the Ming cave, is still calculated by the soil column method, that is, P= gamma H., but the existing research shows that the calculation method has some limitations. This paper is mainly based on the high backfill project of a Ming cave, through the indoor shrinkage model test, the actual field engineering test and the numerical value. In the three aspects, the change law of the earth pressure and the load reduction effect of the geogrid are studied. In order to ensure the safety and economy of the structure, the best way to achieve the target height (64M) is sought. The work and research results completed in this paper are as follows:
(1) according to the actual Ming cave, a (1: 30) reduction ratio model was made in the test room, and the simulated backfilling was carried out on the site of the Ming cave. Through: (1) no arch; (2) the arch; two kinds of schemes were discussed respectively. When the backfill soil was compacted different (75%, 80%, 85%), the law of the earth pressure on the top of the Ming cave. The results showed that with the change of the height of the fill, when the filling height was changed, the fill soil was filled in the soil. After the height of 0.5m (simulated height 15m), the earth pressure in the top of the Ming cave rises in a curvilinear form, and the curve gradually tends to be gentle. With the increase of the compaction degree of the fill, the soil pressure of the Ming cave gradually decreases, that is, the compaction degree of the fill is beneficial to the formation of the "soil arch effect" of the Ming cave.
(2) through: (1) not setting grille (that is, no load reducing); (2) setting up a multi-layer grille without "load reducing hole"; (3) laying a single layer grille + "load reducing hole"; (4) laying a multi-layer grid + "load reducing hole"; these schemes have carried out a systematic study and Discussion on the load reduction of geogrid, and the soil pressure under the load reduction of single layer grille and multi-layer grille is derived. The results show that the load reducing hole is better to reduce the load, and it is more favorable for the grille to play the role of "pulling". The optimal effect of the scheme is 54%, the scheme is 59%, and the deduced theoretical calculation formula is better than the test, and has certain reliability.
(3) through: (1) not set up EPS board (that is, no load reducing); 2. Set up 5cm thick EPS plate; 3. Set up 7.5cm thick EPS board; 4. Set up 10cm thick EPS plate; the load reducing efficiency of EPS board is studied. The effect of different EPS plate thickness on the top soil pressure of the Ming cave and the effect of load reduction are analyzed. The results show that the load reducing efficiency of the EPS plate is between 1/3-1/2 and along with the 1/3-1/2. The increase of the load reduction effect of the EPS plate is more obvious.
(4) through: (1) 69m site unloaded loess test section; (2) 20m site geogrid load reduction test section; under two schemes, the change law of the top soil pressure of Ming cave and the load reduction effect of geogrid are studied. The results show that when the height of the fill is up to 13m, there is no obvious "arch effect" in the top of the Ming cave, which is with the indoor model. The result of the experiment proves that although the initial soil pressure is slightly deviant from the soil column method, the soil pressure value gradually draws close to gamma h with the increase of time, and the "arch effect" gradually disappears, which confirms the instability of the "arch effect", and the scheme has obtained the grid load reduction efficiency of 40%, although it is still less than the indoor model test, but it still can reach very good. Good effect.
(5) the numerical calculation model of plane finite element is set up. Through: (1) no load reduction; (2) geogrid load reduction; two schemes are used to simulate actual backfilling in the field. 22 comparison and 22 proof are made for indoor model test and field test from numerical analysis. The results show that the value of earth pressure is basically the same as gamma h under 15m. When the value is greater than 15m, the curve changes, and the increment decreases gradually, and the curve tends to be gentle. The second is that the load reduction effect is 42%, which is verified by 40% phases obtained from the scene.
(6) on the basis of the study of the change law of the earth pressure and the load reduction of the high backfilling cave roof, the bearing capacity of the structure, crack and composite foundation of the Ming cave is determined. The results show that the safety factor of the lining structure of the Ming cave meets the requirements of the standard under the two circumstances. When the height of the fill is up to 50m, the width of the crack is the width of the crack. The maximum crack width is 0.21mm, which confirms the necessity of loading reduction. According to the bearing capacity of the composite foundation provided, the maximum vertical stress of the foundation of the Ming cave is slightly more than 304kPa when the height of the fill is up to 13m in the case of load reduction, while the earth grille is relieved, but the foundation stress is when the height of the fill is up to 30m. Therefore, it is concluded that under the existing fill foundation and the existing foundation bearing capacity 304kPa, it is not recommended to continue backfilling. Under the condition of sufficient foundation bearing capacity, the expected effect can be achieved by backfilling the proposed scheme.

【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U451

【参考文献】