發(fā)布時(shí)間：2019-02-28 15:09

【摘要】：隨著大量城市隧道的開發(fā)利用使得穿越砂卵石地層而造成的安全問題日益引起了人們的注意。砂卵石土是由不同粒徑的卵石和砂土構(gòu)成的松散顆粒堆積體,其顆粒排列復(fù)雜且具有明顯的離散特征。本文采用顆粒篩分試驗(yàn)、室內(nèi)大型三軸試驗(yàn)和PFC三軸數(shù)值模擬試驗(yàn)相結(jié)合的手段,深入研究砂卵石土的力學(xué)特征及工程特性,定量地分析了主要細(xì)觀參數(shù)對(duì)砂卵石土特性的影響規(guī)律,并獲得砂卵石土的宏細(xì)觀力學(xué)參數(shù),為研究隧道砂卵石圍巖穩(wěn)定性分析奠定了基礎(chǔ)。主要得到了以下成果:(1)對(duì)不同含水率、密度和粗粒含量的砂卵石土進(jìn)行了不排水不固結(jié)大型三軸試驗(yàn)研究,分析不同物理狀態(tài)下的應(yīng)力-應(yīng)變關(guān)系曲線變化規(guī)律和抗剪強(qiáng)度的規(guī)律;(2)基于顆粒流點(diǎn)接觸連接本構(gòu)模型(未考慮顆粒破碎),通過PFC內(nèi)嵌fish語(yǔ)言程序,得到PFC3D數(shù)值模擬平臺(tái)并完成數(shù)值模擬三軸試驗(yàn);數(shù)值模擬三軸試驗(yàn)和室內(nèi)大型三軸試驗(yàn)得到的應(yīng)力—應(yīng)變曲線總體上比較吻合,抗剪強(qiáng)度參數(shù)與室內(nèi)試驗(yàn)得到的強(qiáng)度參數(shù)相對(duì)誤差很小,此次數(shù)值模擬具有較高的吻合度;(3)從細(xì)觀角度研究影響砂卵石土變形特性和抗剪強(qiáng)度的相關(guān)因素,對(duì)顆粒接觸模量、摩擦系數(shù)和剛度比這三個(gè)主要細(xì)觀參數(shù)對(duì)砂卵石土宏觀力學(xué)性質(zhì)的影響做了詳細(xì)的分析。分析結(jié)果表明:隨著顆粒接觸模量的增加,砂卵石土的初始變形模量也有增大的趨勢(shì),峰值強(qiáng)度也有所越高,破壞時(shí)的軸向應(yīng)變則減小,剪縮變形越來越小,數(shù)值模型由剪縮轉(zhuǎn)向剪脹時(shí)相應(yīng)的軸向應(yīng)變也越小;隨著顆粒摩擦系數(shù)的增大,砂卵石土的峰值強(qiáng)度也隨著增大,峰值強(qiáng)度與摩擦系數(shù)大致呈正比例關(guān)系,砂卵石土的初始變形模量也隨摩擦系數(shù)增大有稍微增大的趨勢(shì),但顆粒的摩擦系數(shù)只對(duì)變形的影響不大;顆粒剛度比值越大峰值應(yīng)力越小,初始模量越小,體積應(yīng)變減小到最小時(shí)應(yīng)變?cè)叫?但是剛度比對(duì)砂卵石土的特性影響不明顯。這些結(jié)論一定程度上定量的揭示了影響砂卵石土工程特性的細(xì)觀因素。為研究砂卵石土特性提供了一定的參考。(4)砂卵石地層隧道開挖后,掌子面正前方土體最先發(fā)生破壞,且距離掌子面越近隧道拱頂?shù)耐馏w變形越大,從而引起地表沉降;應(yīng)力松弛區(qū)域由掌子面正前方逐漸向右上方擴(kuò)散,最終導(dǎo)致開挖面失穩(wěn)。
[Abstract]:With the development and utilization of a large number of urban tunnels, people pay more and more attention to the safety problems caused by traversing sand and pebbles. Sand-pebble soil is a loose particle accumulation composed of pebbles and sandy soil with different particle sizes, and its particle arrangement is complex and has obvious discrete characteristics. In this paper, the mechanical and engineering characteristics of sandy pebble soil are studied by means of particle sieving test, large-scale triaxial test in laboratory and PFC triaxial numerical simulation test. The effects of main micro-parameters on the characteristics of sand-pebble soil are quantitatively analyzed, and the macro-and micro-mechanical parameters of sand-gravel soil are obtained, which lays a foundation for studying the stability of surrounding rock of sand-pebble in tunnel. The main results are as follows: (1) the large-scale triaxial test of undrained and unconsolidated sandy pebble soil with different moisture content, density and coarse grain content was carried out. The variation law of stress-strain relation curve and the law of shear strength under different physical conditions are analyzed. (2) based on the constitutive model of particle flow point contact connection (without considering particle breaking), the PFC3D numerical simulation platform is obtained by PFC embedded in fish program, and the numerical simulation triaxial test is completed. The stress-strain curves obtained by numerical simulation triaxial test and indoor large-scale triaxial test are generally in good agreement, and the relative error between shear strength parameters and the strength parameters obtained from indoor tests is very small, so the numerical simulation has a high degree of coincidence. (3) the relative factors affecting the deformation characteristics and shear strength of sand-pebble soil are studied from the view of meso-view, and the contact modulus of particles is also studied. The effects of friction coefficient and stiffness ratio on the macro-mechanical properties of sand-pebble soil are analyzed in detail. The results show that with the increase of particle contact modulus, the initial deformation modulus of sand-pebble soil also increases, the peak strength is also higher, the axial strain decreases and the shear deformation becomes smaller and smaller. The corresponding axial strain is smaller when the numerical model changes from shear to dilatancy. With the increase of particle friction coefficient, the peak strength of sand-pebble soil increases, and the peak strength and friction coefficient show a positive proportional relationship. The initial deformation modulus of sand-gravel soil also increases slightly with the increase of friction coefficient, and the initial deformation modulus of sand-pebble soil increases slightly with the increase of friction coefficient. However, the friction coefficient of the particles has little effect on the deformation. The larger the particle stiffness ratio, the smaller the peak stress, the smaller the initial modulus and the smaller the volume strain is, but the stiffness ratio has no obvious effect on the characteristics of sandy pebble soil. To some extent, these conclusions reveal the micro-factors that affect the engineering characteristics of sand-pebble soil. It provides some reference for studying the characteristics of sand-pebble soil. (4) after the excavation of the sand-gravel stratum tunnel, the soil in front of the palm surface is destroyed first, and the deformation of the soil body closer to the palm surface is greater, which leads to the settlement of the earth surface. The stress relaxation region gradually diffuses from the front of the palm to the upper right, and finally leads to the instability of the excavation surface.
【學(xué)位授予單位】：成都理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：U451.2

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