围压对横观各向同性砂岩弹性参数的影响
|
摘要
通过层理面角度为0°、45°和90°的长方体砂岩试样的单轴和三轴试验,直接测量了不同围压下砂岩的5个独立的横观各向同性弹性参数:弹性模量E,E';泊松比ν,ν';剪切模量G'。测得了前人难以测量的不同围压下的ν和G'值,得到了横观各向同性弹性参数与围压之间的函数关系,并揭示了弹性参数随围压变化的力学机制。试验结果表明,随着围压增大,弹性模量增大,泊松比减小,剪切模量增大。当围压超过30 MPa时,2个垂直方向的弹性模量、泊松比和剪切模量分别趋于相同值,表现为各向同性。由此可以推断:该砂岩的横观各向同性由内部微裂纹在平行于和垂直于层理面方向分布不均引起,围压升高造成裂纹闭合,最终导致各向异性消失。岩石的裂纹闭合效应可以用裂纹密度来定量评价与描述。
Uniaxial and triaxial compression tests were performed on prismatic specimens with bedding angles of 0°,45° and 90° to directly measure the five independent transversely isotropic elastic parameters,i. e.,Young's modulus E,E',Poisson's ratio ν,ν',and shear modulus G',under different confining pressures. Particularly,νand G' under different confining pressures have never been measured by former researchers. The functional relationships between the confining pressure and the transversely isotropic elastic parameters were obtained,and the mechanism of confining pressure dependency of elastic parameters was explained. Experimental results show that as confining pressure increases,Young's moduli increases,Poisson's ratios decreases,and shear moduli increases.Moreover,Young's moduli,Poisson's ratios,and shear moduli in two perpendicular directions tend to become the same constant value respectively when confining pressure is beyond 30 MPa,implying that the sandstone exhibits isotropic behavior. It is inferred that the transversely isotropy of the sandstone is due to the different distributions of microcracks in two directions of parallel and perpendicular to bedding,and the anisotropy is vanishing as more microcracks are closed,with the increase of confining pressure. The crack closure effect of rock can be quantitatively characterized and described by the concept of crack density.
Uniaxial and triaxial compression tests were performed on prismatic specimens with bedding angles of 0°,45° and 90° to directly measure the five independent transversely isotropic elastic parameters,i. e.,Young's modulus E,E',Poisson's ratio ν,ν',and shear modulus G',under different confining pressures. Particularly,νand G' under different confining pressures have never been measured by former researchers. The functional relationships between the confining pressure and the transversely isotropic elastic parameters were obtained,and the mechanism of confining pressure dependency of elastic parameters was explained. Experimental results show that as confining pressure increases,Young's moduli increases,Poisson's ratios decreases,and shear moduli increases.Moreover,Young's moduli,Poisson's ratios,and shear moduli in two perpendicular directions tend to become the same constant value respectively when confining pressure is beyond 30 MPa,implying that the sandstone exhibits isotropic behavior. It is inferred that the transversely isotropy of the sandstone is due to the different distributions of microcracks in two directions of parallel and perpendicular to bedding,and the anisotropy is vanishing as more microcracks are closed,with the increase of confining pressure. The crack closure effect of rock can be quantitatively characterized and described by the concept of crack density.
引文
[1]Jaeger J C,Cook N G W,Zimmerman R.Fundamentals of rock mechanics[M].John Wiley and Sons,2009.
[2]Barla G.Rock anisotropy:Theory and laboratory testing in rock mechanics[M].Udine,Italy,1974.
[3]Amadei B.Importance of anisotropy when estimating and measuring in situ stresses in rock[J].International Journal of Rock Mechanics and Mining Sciences,1996,33(3):293-325.
[4]Saint-Venant B.Sur la distribution desélasticités autour de chaque point d’un solide ou d’un milieu de contexture quelconque,particulierement lorsqu’il estamorphe sans etre isotrope[J].Journal of Pure and Applied Mathematics,1863(7-8):353-430.
[5]Cho J W,Kim H,Jeon S,et al.Deformation and strength anisotropy of Asan gneiss,Boryeong shale,and Yeoncheon schist[J].International Journal of Rock Mechanics and Mining Sciences,2012,50:158-169.
[6]席道瑛,陈林,张涛.砂岩的变形各向异性[J].岩石力学与工程学报,1995,14(1):49-58.(Xi Daoying,Chen Lin,Zhang Tao.Anisotropic deformation of sandstone[J].Chinese Journal of Rock Mechanics and Engineering,1995,14(1):49-58.(in Chinese))
[7]高春玉,徐进,李忠洪,等.雪峰山隧道砂板岩各向异性力学特性的试验研究[J].岩土力学,2011,32(5):1360-1364.(Gao Chunyu,Xu Jing,Li Zhonghong,et al.Experimental study of anisotropically mechanical characteristics of sandy slate in Xuefeng mountain tunnel[J].Rock and Soil Mechanics,2011,32(5):1360-1364.(in Chinese))
[8]刘胜利,陈善雄,余飞,等.绿泥石片岩各向异性特性研究[J].岩土力学,2012,33(12):3616-3623.(Liu Shengli,Chen Shanxiong,Yu Fei,et al.Anisotropic properties study of chlorite schist[J].Rock and Soil Mechanics,2012,33(12):3616-3623.(in Chinese))
[9]刘运思,傅鹤林,伍毅敏,等.横观各向同性岩石弹性参数及抗压强度的试验研究[J].中南大学学报(自然科学版),2013,44(8):3398-3404.(Liu Yunsi,Fu Helin,Wu Yimin,et al.Experimental study of elastic parameters and compressive strength for transversely isotropic rocks[J].Journal of Central South University(Science and Technology Edition),2013,44(8):3398-3404.(in Chinese))
[10]衡帅,杨春和,张保平,等.页岩各向异性特征的试验研究[J].岩土力学,2015,36(3):609-616.(Heng Shuai,Yang Chunhe,Zhang Baoping,et al.Experimental research on anisotropic properties of shale[J].Rock and Soil Mechanics,2015,36(3):609-616.(in Chinese))
[11]Kulhawy F H.Stress deformation properties of rock and rock discontinuities[J].Engineering Geology,1975,9(4):327-350.
[12]许江,王维忠,杨秀贵,等.细粒砂岩在循环加,卸载条件下变形实验[J].重庆大学学报(自然科学版),2004,27(12),60-62.(Xu Jiang,Wang Weizhong,Yang Xiugui,et al.Experimental study on the deformation characteristics of fine-sandstone under the loading and unloading conditions[J].Journal of Chongqing University(Science and Technology Edition),2004,27(12),60-62.(in Chinese))
[13]张媛,许江,杨红伟,等.循环荷载作用下围压对砂岩滞回环演化规律的影响[J].岩石力学与工程学报,2011,30(2),320-326.(Zhang Yuan,Xu Jiang,Yang Hongwei,et al.Effect of confining pressure on evolution law of hysteresis loop of sandstone under cyclic loading[J].Chinese Journal of Rock Mechanics and Engineering,2011,30(2):320-326.(in Chinese))
[14]Gustkiewic J.Deformation and failure of the Nowa Ruda sandstone in a three-axial state of stress with gas under pressure in the pores[J].Archiwum Górnictwa,1985,30(3):401-424.
[15]Verman M,Singh B,Viladkar M N,et al.Effect of tunnel depth on modulus of deformation of rock mass[J].Rock Mechanics and Rock Engineering,1997,30(3):121-127.
[16]Asef M R,Reddish D J.The impact of confining stress on the rock mass deformation modulus[J].Geotechnique,2002,52(4):235-241.
[17]刘斌,席道瑛,葛宁洁,等.不同围压下岩石中泊松比的各向异性[J].地球物理学报,2002,45(6):880-890.(Liu Bin,Xi Daoying,Ge Ningjie,et al.Anisotropy of Poisson’s ratio in rock samples under confining pressures[J].Chinese Journal of Geophysics,2002,45(6):880-890.(in Chinese))
[18]Walsh J B.The effect of cracks on the compressibility of rock[J].Journal of Geophysical Research,1965,70(2):381-389.
[19]彭俊,荣冠,周创兵,等.岩石裂纹闭合效应及其定量模型研究[J].岩土力学,2016,37(1):126-132.(Peng Jun,Rong Guan,Zhou Chuangbing,et al.Astudy of crack closure effect of rocks and its quantitative model[J].Rock and Soil Mechanics,2016,37(1):126-132.(in Chinese))
[20]Kachanov M.Elastic solids with many cracks and related problems[A]//Advances in Applied Mechanics[C].Hutchinson J,Wu T.Academic Press,1994:259-445.
[2]Barla G.Rock anisotropy:Theory and laboratory testing in rock mechanics[M].Udine,Italy,1974.
[3]Amadei B.Importance of anisotropy when estimating and measuring in situ stresses in rock[J].International Journal of Rock Mechanics and Mining Sciences,1996,33(3):293-325.
[4]Saint-Venant B.Sur la distribution desélasticités autour de chaque point d’un solide ou d’un milieu de contexture quelconque,particulierement lorsqu’il estamorphe sans etre isotrope[J].Journal of Pure and Applied Mathematics,1863(7-8):353-430.
[5]Cho J W,Kim H,Jeon S,et al.Deformation and strength anisotropy of Asan gneiss,Boryeong shale,and Yeoncheon schist[J].International Journal of Rock Mechanics and Mining Sciences,2012,50:158-169.
[6]席道瑛,陈林,张涛.砂岩的变形各向异性[J].岩石力学与工程学报,1995,14(1):49-58.(Xi Daoying,Chen Lin,Zhang Tao.Anisotropic deformation of sandstone[J].Chinese Journal of Rock Mechanics and Engineering,1995,14(1):49-58.(in Chinese))
[7]高春玉,徐进,李忠洪,等.雪峰山隧道砂板岩各向异性力学特性的试验研究[J].岩土力学,2011,32(5):1360-1364.(Gao Chunyu,Xu Jing,Li Zhonghong,et al.Experimental study of anisotropically mechanical characteristics of sandy slate in Xuefeng mountain tunnel[J].Rock and Soil Mechanics,2011,32(5):1360-1364.(in Chinese))
[8]刘胜利,陈善雄,余飞,等.绿泥石片岩各向异性特性研究[J].岩土力学,2012,33(12):3616-3623.(Liu Shengli,Chen Shanxiong,Yu Fei,et al.Anisotropic properties study of chlorite schist[J].Rock and Soil Mechanics,2012,33(12):3616-3623.(in Chinese))
[9]刘运思,傅鹤林,伍毅敏,等.横观各向同性岩石弹性参数及抗压强度的试验研究[J].中南大学学报(自然科学版),2013,44(8):3398-3404.(Liu Yunsi,Fu Helin,Wu Yimin,et al.Experimental study of elastic parameters and compressive strength for transversely isotropic rocks[J].Journal of Central South University(Science and Technology Edition),2013,44(8):3398-3404.(in Chinese))
[10]衡帅,杨春和,张保平,等.页岩各向异性特征的试验研究[J].岩土力学,2015,36(3):609-616.(Heng Shuai,Yang Chunhe,Zhang Baoping,et al.Experimental research on anisotropic properties of shale[J].Rock and Soil Mechanics,2015,36(3):609-616.(in Chinese))
[11]Kulhawy F H.Stress deformation properties of rock and rock discontinuities[J].Engineering Geology,1975,9(4):327-350.
[12]许江,王维忠,杨秀贵,等.细粒砂岩在循环加,卸载条件下变形实验[J].重庆大学学报(自然科学版),2004,27(12),60-62.(Xu Jiang,Wang Weizhong,Yang Xiugui,et al.Experimental study on the deformation characteristics of fine-sandstone under the loading and unloading conditions[J].Journal of Chongqing University(Science and Technology Edition),2004,27(12),60-62.(in Chinese))
[13]张媛,许江,杨红伟,等.循环荷载作用下围压对砂岩滞回环演化规律的影响[J].岩石力学与工程学报,2011,30(2),320-326.(Zhang Yuan,Xu Jiang,Yang Hongwei,et al.Effect of confining pressure on evolution law of hysteresis loop of sandstone under cyclic loading[J].Chinese Journal of Rock Mechanics and Engineering,2011,30(2):320-326.(in Chinese))
[14]Gustkiewic J.Deformation and failure of the Nowa Ruda sandstone in a three-axial state of stress with gas under pressure in the pores[J].Archiwum Górnictwa,1985,30(3):401-424.
[15]Verman M,Singh B,Viladkar M N,et al.Effect of tunnel depth on modulus of deformation of rock mass[J].Rock Mechanics and Rock Engineering,1997,30(3):121-127.
[16]Asef M R,Reddish D J.The impact of confining stress on the rock mass deformation modulus[J].Geotechnique,2002,52(4):235-241.
[17]刘斌,席道瑛,葛宁洁,等.不同围压下岩石中泊松比的各向异性[J].地球物理学报,2002,45(6):880-890.(Liu Bin,Xi Daoying,Ge Ningjie,et al.Anisotropy of Poisson’s ratio in rock samples under confining pressures[J].Chinese Journal of Geophysics,2002,45(6):880-890.(in Chinese))
[18]Walsh J B.The effect of cracks on the compressibility of rock[J].Journal of Geophysical Research,1965,70(2):381-389.
[19]彭俊,荣冠,周创兵,等.岩石裂纹闭合效应及其定量模型研究[J].岩土力学,2016,37(1):126-132.(Peng Jun,Rong Guan,Zhou Chuangbing,et al.Astudy of crack closure effect of rocks and its quantitative model[J].Rock and Soil Mechanics,2016,37(1):126-132.(in Chinese))
[20]Kachanov M.Elastic solids with many cracks and related problems[A]//Advances in Applied Mechanics[C].Hutchinson J,Wu T.Academic Press,1994:259-445.