为探究深厚冲积层冻结井筒外壁早期开裂机理,以丁集煤矿第二副井为工程背景,开展外壁混凝土早龄期力学特性试验和热-力耦合分析.首先,通过对不同龄期C70外壁混凝土开展立方体抗压强度、轴心抗压强度、弹性模量和劈裂抗拉强度试验,获得了强度指标和弹性模量复合指数时变模型和早期力学特性;然后,基于外壁混凝土弹性模量复合指数时变模型,利用FLAC3D软件建立外壁混凝土热-力耦合分析模型,对外壁混凝土早期温度场和应力场演化特征进行了研究分析.结果表明:外壁混凝土浇筑初期水化升温,其核心区峰值温度达到了 55.96℃;随后外壁混凝土开始降温,短时间内井壁外缘温差达到了 34.95℃;外壁混凝土在4~28 h升温阶段整体受压,降温阶段,井壁受冻结壁约束,竖向受拉严重,其中井壁外缘拉应力最大,达到了 5.08 MPa,当拉应力超过外壁混凝土早龄期抗拉强度时,外壁混凝土将产生环向裂缝,从而揭示了深厚冲积层冻结井筒外壁早期开裂机理.
In order to explore the early cracking mechanism of outer wall of freezing shaft in deep allu-vium,the early mechanical property test and thermal-mechanical coupling analysis of outer wall con-crete were carried out with the second auxiliary shaft of Dingji coal mine as the research object.Firstly,the time-dependent model of strength index and elastic modulus composite index is obtained by con-ducting cubic compressive strength,axial compressive strength,elastic modulus tests and Splitting ten-sion strength tests on C70 outer wall concrete of different ages.Then,based on the composite exponen-tial time-varying model of elastic modulus and early mechanical properties of outer wall concrete,the thermal-mechanical coupling analysis model of outer wall concrete is established by FLAC3D software,and the early temperature field and stress field evolution characteristics of outer wall concrete are exam-ined and analyzed.The results show that at the beginning of concrete placing,the hydration tempera-ture of outer wall rises,and the peak temperature of core area reaches 55.96℃.Then it begins to cool down,and the temperature difference of the outer edge of the well wall reaches 34.95 ℃ in a short time.The outer wall concrete is under pressure in the whole at the stage of 4~28 h temperature rise and is restrained by freezing wall in the stage of temperature reduction.Vertical tension is severe,in which the tensile stress of outer wall is the highest,reaching 5.08 MPa.When the tensile stress ex-ceeds the early-age tensile strength of outer wall concrete,annular cracks will occur in outer wall con-crete,thus revealing the early cracking mechanism of outer wall of freezing shaft in deep alluvium.