本文選題：高回填明洞 + 土壓力　； 參考：《蘭州交通大學(xué)》2014年碩士論文

【摘要】：現(xiàn)行的設(shè)計規(guī)范中明洞各部位土壓力尤其是垂直土壓力計算仍采用土柱法計算，即P=γh。但是，已有研究表明這種計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項目，通過室內(nèi)縮小比例模型試驗、現(xiàn)場實際工程試驗及數(shù)值模擬三方面，研究了明洞頂土壓力的變化規(guī)律及土工格柵減載的減載效果，意在保證結(jié)構(gòu)安全性、經(jīng)濟性的前提下，尋求能讓目標(biāo)明洞回填達(dá)到目標(biāo)高度（64m）的最佳方式。本論文所完成的工作和研究成果如下： （1）根據(jù)實際明洞在試驗室制作了（1∶30）縮小比例模型，對現(xiàn)場明洞進(jìn)行模擬回填。通過：①不放拱；②放拱；兩種方案分別探討了，回填土壓實不同（75%、80%、85%）時，對明洞頂土壓力的影響規(guī)律。研究結(jié)果表明，隨著填土高度的變化，當(dāng)填土高度達(dá)到0.5m（模擬高度15m）后，明洞頂土壓力呈曲線形式上漲，且曲線逐漸趨于平緩；隨著填土壓實度的增加明洞頂土壓力逐漸減小，即填土壓實度有利于明洞頂“土拱效應(yīng)”的形成。 （2）通過：①不布設(shè)格柵（即，不減載）；②布設(shè)多層格柵，不布設(shè)“減載孔”；③布設(shè)單層格柵+“減載孔”；④布設(shè)多層格柵+“減載孔”；這四種方案對土工格柵減載進(jìn)行了系統(tǒng)的研究和探討，推導(dǎo)了單層格柵和多層格柵減載下土壓力計算公式。研究結(jié)果顯示，布設(shè)“減載孔”的減載效果更好，更有利于格柵發(fā)揮“提兜”作用；方案③中單層格柵的最佳效果達(dá)到54%，方案④中達(dá)到59%，且推導(dǎo)的理論計算公式與試驗擬合較好，具有一定的可信度。 （3）通過：①不布設(shè)EPS板（即，不減載）；②布設(shè)5cm厚EPS板；③布設(shè)7.5cm厚EPS板；④布設(shè)10cm厚EPS板；四種方案研究EPS板的減載效率，分析了不同EPS板厚度對明洞頂土壓力的影響及其減載效果。結(jié)果顯示，EPS板的減載效率在1/3-1/2之間，且隨著EPS板厚度的增加減載效果越發(fā)的明顯。 （4）通過：①69m現(xiàn)場不減載黃土試驗段；②20m現(xiàn)場土工格柵減載試驗段；分別研究了兩種方案下，明洞頂土壓力變化規(guī)律及土工格柵的減載效果。結(jié)果表明，當(dāng)填土高度達(dá)到13m時，方案①明洞頂并未產(chǎn)生明顯的“拱效應(yīng)”，這與室內(nèi)模型試驗得到的結(jié)論相印證。雖然前期土壓力與土柱法稍有偏差，但隨著時間的增長土壓力值逐漸靠攏γh，“拱效應(yīng)”逐漸消失，證實了“拱效應(yīng)”的不穩(wěn)定性；方案②中得到格柵減載效率為40%，雖然不及室內(nèi)模型試驗，但仍舊能夠達(dá)到很好的效果。 （5）建立了平面有限元數(shù)值計算模型，通過：①不減載；②土工格柵減載；兩種方案分別模擬現(xiàn)場實際回填，從數(shù)值分析方面對室內(nèi)模型試驗和現(xiàn)場試驗進(jìn)行兩兩對比，兩兩印證。結(jié)果顯示，方案①在填土15m以下，土壓力值與γh基本一致，大于15m時，呈曲線變化，，且增量逐漸減小，曲線趨于平緩。方案②得到其減載效果為42%，與現(xiàn)場得到的40%相印證。 （6）在前文研究了高回填明洞頂土壓力變化規(guī)律及其減載的基礎(chǔ)上，對明洞結(jié)構(gòu)、裂縫以及復(fù)合地基承載力進(jìn)行了判定。研究結(jié)果表明，兩種情況下，明洞襯砌結(jié)構(gòu)安全系數(shù)均滿足《規(guī)范》要求。不減載情況下，當(dāng)填土高度達(dá)到50m時，裂縫寬度超限，最大裂縫寬度為0.21mm，證實了減載的必要性。根據(jù)提供的復(fù)合地基承載力發(fā)現(xiàn)，不減載情況下當(dāng)填土高度達(dá)到13m時，明洞地基最大豎向應(yīng)力略超過限值304kPa；而土工格柵減載情況下，雖然有所緩解，但當(dāng)填土高度達(dá)到30m時地基應(yīng)力也已然超限。因此本文得出結(jié)論，目標(biāo)明洞在現(xiàn)有填土基礎(chǔ)上和現(xiàn)有地基承載力304kPa下，不建議繼續(xù)回填，在地基承載力足夠的情況下，按建議中給出的方案進(jìn)行回填，便可達(dá)到預(yù)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.

【學(xué)位授予單位】：蘭州交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：U451

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