【摘要】：軟弱圍巖在公路隧道施工中所占的比重較大,且多呈現(xiàn)節(jié)理發(fā)育和高地應力等特點。目前,對軟弱圍巖小凈距隧道施工過程中的圍巖特性與變形機制認識不清。因此,研究軟弱圍巖隧道變形特性具有重要的意義。論文分析了軟弱圍巖隧道的變形機理及圍巖-支護結構平衡穩(wěn)定體系。依據(jù)新意法,研究了掌子面擠出變形、預收斂變形與收斂變形之間的關系。針對現(xiàn)場監(jiān)測數(shù)據(jù)進行回歸分析,利用位移反分析法反演側壓力系數(shù)λ。運用FLAC3D數(shù)值模擬,分析在不同λ下小凈距隧道軟弱圍巖的變形特性,得到以下主要結論：(1)對現(xiàn)場監(jiān)測數(shù)據(jù)進行回歸分析,確定拱頂下沉與水平凈空收斂最佳時態(tài)曲線方程分別為U=T/(0.1154+0.0271×T)和U=39.5276×e(-24498/T)。推算出拱頂與洞周極限位移值分別為36.96 mm和39.53mm。通過12次迭代收斂運算確定側壓力系數(shù)λ值為1.1305,滿足收斂精度要求,且誤差△=20.95%,目標函數(shù)f(λ)=31.431.7。(2)隧道開挖導致沿軸線方向圍巖的變形呈逐步降低趨勢,且存在擠出變形與軸向距離為線性關系。當λ1.0時,擠出變形與頂?shù)最A收斂近似線性,而與水平預收斂不呈線性；當λ=1.0時,擠出變形與頂?shù)最A收斂和水平預收斂均呈線性關系；當λ1.0時,擠出變形與水平預收斂為線性,比與頂?shù)最A收斂的線性關系更為顯著。(3)考慮在襯砌施加前軟弱圍巖己發(fā)生較大的變形,數(shù)值試驗施加襯砌的時機應選擇在圍巖發(fā)揮一定的自承能力后,試驗結果表明襯砌施加前圍巖變形約為極限位移值的1/3-2/3；當λ=1.0時,襯砌剛度選定為10.5GPa,在合理的支護時機下,能夠提供足夠的支護抗力,充分發(fā)揮圍巖自承能力,防止軟弱圍巖發(fā)生大變形。(4)擠出變形與預收斂變形可呈線性關系,預收斂變形影響掌子面后方的收斂變形大小。襯砌支護后,掌子面后方圍巖的收斂變形降低約50%,預收斂變形降低約25%,擠出變形降低約10%。于掌子面后方1m的范圍內(nèi),圍巖變形發(fā)生了較大幅度的改變。由于掌子面固端效應和地應力場的影響,于掌子面前方圍巖可能出現(xiàn)位移方向相反的現(xiàn)象。(5)雙行洞開挖與先行洞單獨開挖相比,引起后者內(nèi)幫水平位移減小而外幫水平位移增加,且內(nèi)幫減小量大于外幫增加量。隨λ值增加,拱頂與仰拱豎向位移相對增加,當λ=0.5時,位移增量曲線的對稱效果顯著；當λ0.5時,相同距離對應的拱頂位移增量絕對值大于仰拱位移增量絕對值：當λ≥1.0時,相同距離對應的仰拱位移增量絕對值則大于拱頂?shù)摹?6)后行洞擾動與雙行洞開挖相比,水平位移變化量與垂直位移變化量曲線基本呈對稱狀。當λ=0.5時,基本上認為后行洞擾動與雙行洞開挖產(chǎn)生的圍巖變形一致;相對于雙行洞開挖,后行洞擾動令右?guī)团c拱頂產(chǎn)生相對較大的位移變化量。不同λ下的擠出變形并不相同,當λ=0.5時,擠出變形最小,且隨λ增加,側壓力系數(shù)與擠出變形近似為線性。
[Abstract]:Soft surrounding rock occupies a large proportion in the construction of highway tunnel, and most of them show the characteristics of joint development and high ground stress. At present, the characteristics and deformation mechanism of soft surrounding rock in the construction of small clear distance tunnel are not clear. Therefore, it is of great significance to study the deformation characteristics of soft surrounding rock tunnel. The deformation mechanism of soft surrounding rock tunnel and the balance and stability system of surrounding rock-support structure are analyzed in this paper. According to the new method, the relationship among extrusion deformation, preconvergent deformation and convergent deformation is studied. Based on the field monitoring data, regression analysis is carried out, and the displacement inverse analysis method is used to retrieve the lateral pressure coefficient 位. By using FLAC3D numerical simulation, the deformation characteristics of soft surrounding rock in small clear distance tunnel under different 位 are analyzed. The main conclusions are as follows: (1) regression analysis of field monitoring data is carried out. The optimal temporal curve equations of vault subsidence and horizontal clearance convergence are determined to be U=T/ (0.1154 0.0271 脳 T) and U (39.5276 脳 e) (-24498T), respectively. The limit displacement values of arch and hole are 36.96 mm and 39.53 mm. respectively. The lateral pressure coefficient 位 is determined to be 1.1305 by 12 iterative convergent operations, which satisfies the requirement of convergence accuracy, and the error is 20.95. The objective function f (位) = 31.431.7. (2) the deformation of surrounding rock along the axis of tunnel excavation is decreasing gradually, and there is a linear relationship between extrusion deformation and axial distance. At 位 1.0, the extrusion deformation is approximately linear with the top and bottom preconvergence, but not with the horizontal preconvergence, and when 位 = 1.0, the extrusion deformation is linearly related to the top and bottom preconvergence and the horizontal preconvergence. When 位 1.0, the linear relation between extrusion deformation and horizontal preconvergence is more obvious than that between pre-convergence of roof and bottom. (3) considering that the deformation of weak surrounding rock has occurred before the lining is applied, The test results show that the deformation of surrounding rock before the application of the lining is about 1 / 3 / 2 / 3 of the limit displacement value. When 位 = 1.0, the lining stiffness is chosen as 10.5 GPA, which can provide sufficient support resistance and give full play to the self-supporting capacity of surrounding rock under the reasonable timbering opportunity. (4) there is a linear relationship between extrusion deformation and preconvergent deformation, and preconvergent deformation affects the magnitude of convergence deformation behind the face of the palm. After lining support, the convergence deformation of surrounding rock behind the face of the face is reduced by about 50%, the pre-convergence deformation is reduced by about 25%, and the extrusion deformation is reduced by about 10%. Within 1 m behind the face, the deformation of surrounding rock has changed greatly. Due to the effect of the fixed end effect and the in-situ stress field, the displacement direction of the surrounding rock in front of the face may be opposite. (5) the excavation of double-row tunnel is compared with the excavation of the first hole alone. As a result, the horizontal displacement of the inner side decreases while the horizontal displacement of the outer side increases, and the decrease of the inner side is larger than the increase of the external side. With the increase of 位 value, the vertical displacement of arch and inverted arch increases relatively. When 位 = 0.5, the symmetry effect of displacement increment curve is remarkable. When 位 0.5, the absolute increment of arch displacement corresponding to the same distance is greater than that of inverted arch displacement: when 位 鈮，

本文編號：2366667