| The dolomite sandification problem in Yuxi section of the Central Yunnan Water Diversion Project seriously affects the construction safety of the water conveyance tunnel.In order to prevent and reduce the stability of strong and violent dolomite sandy soft rock tunnels,it is necessary to divert water from central Yunnan.Research on the regional geological characteristics and spatial distribution and development characteristics of dolomite sandification in the Yuxi section of the project,combined with indoor and outdoor physical and mechanical experimental research on dolomite sandification,reveals the macro and micro material structure characteristics of strong and violent dolomite sandification,which is further reasonable Select the mechanical parameters of dolomite sanding to provide the basis.Therefore,research on the physical and mechanical properties of dolomite sanding in central Yunnan has important engineering benefits and practical value for revealing the stability of tunnel surrounding rock and the evolution mechanism of dolomite sanding.The main results and conclusions of the paper are as follows:(1)The on-site investigation of the geological phenomenon of dolomite sandification shows that the structure of dolomite sandy rock mass mainly develops into block structure,layered structure,mosaic structure,fragmented structure,scattered structure,etc.;according to the above sandification of dolomite The structural characteristics of the rock mass of the rock mass,the macroscopic classification of dolomite sanding,the sanding intensity from weak to strong are:micro-new rock mass,weak(medium)sanding,strong sanding sanding and severe sanding sanding.grade.(2)Through the five typical water tunnels in the investigation and design stage of the dolomite sandification phenomenon,the dolomite sandification phenomenon revealed by the current construction and excavation and the characteristics of the drilled dolomite sand core,the research area is summarized and summarized.Spatial distribution characteristics of dolomite sandification:Zbdn and Zbd stratum lithology distribution,the influence of the fracture structure that the tunnel crosses,and the uneven distribution of sanded tunnel sections.At the same time,groundwater activity conditions and weathering have played a role in the occurrence of dolomite sanding.Promote synergy.(3)The water content,density and particle screening tests conducted on the typical strong and severe dolomite sanding in the study area show that the severe dolomite can be named as fine-grained soil sand,and the strong dolomite sanding is named as well-graded gravel.From weak to strong,the material composition is composed of fine-grained minerals such as dolomite gravel,dolomite sand and dolomite powder.(4)Through the study of the microscopic characteristics of dolomite sanding by SEM electron microscope scanning,it is found that the sanded surface of medium dolomite is broken into irregular particles without obvious grain structure.The overall degree of dolomite is good,and the sanded surface of strong dolomite has crystals.Granules and fine-grained particles are produced and attached to the dolomite framework.The severe dolomite sanding surface is mainly distributed with grains and fine-grained particles,and the existence of massive dolomite or dolomite framework is basically not found.Sandy pores of dolomite are characterized by intra-dolomite pores,intra-granular pores in dolomite,and inter-grain pores.The particle arrangement and contact features are edge-edge superimposition,edge-face and face-face superimposition,which provide water flow and storage.A good channel affects the permeability of the rock to a certain extent and reflects the differences in the macroscopic physical and mechanical properties of dolomite with different degrees of sanding.The EDS micro-element energy spectrum analysis of strong and violent dolomite sanding shows that during the process from intensive sanding to violent sanding,it is mainly the loss of Ca and Mg elements,the accumulation of Si and Fe elements,and the migration of meso-chemical elements.,That is,the mineral composition has changed.The change in the mineral composition also illustrates the macroscopic difference in the color of dolomite with different sanding degrees,which is reflected in the off-white to gray-yellow dolomite sand,dolomite powder and other color dolomite fine-grained minerals..(5)Through indoor and outdoor needle penetrating tests on strong and severe dolomite sanding,it can be known from the rock hardness that severe dolomite sanding can be classified as extremely soft rock,and strong dolomite sanding can be classified as soft rock.In general,the NPI of the indoor needle penetration test is smaller than the NPI of the field needle penetration test,which may be related to the homogeneity of the rock mass,water content,and pore density.(6)Most of the structure of the strong and violently sanded dolomite rock mass is destroyed,and it is difficult to achieve high-standard rock sample production.Complete the indoor uniaxial compressive strength test and obtain the complete uniaxial compressive strength of the rock.Therefore,the needle penetration field test is adopted.The result is calculated by converting the uniaxial compressive strength value?cmof the rock mass.The mivalue is determined to be 9±3through the rock empirical parameter table through strong and violent dolomite sanding.Based on the analysis of rock mass structure characteristics,the recommended GSI value for severe dolomite sandy rocks is 20±5;the recommended GSI value for strongly dolomite sandy rocks is35±5.Severe dolomite sanding c estimated by the generalized Hoek-Brown strength criterion:0.25?0.29MPa,?:28.04°?33.55°,En:0.63?0.87GPa;intense dolomite sanding c:0.34?0.71MPa,?:38.59°?50.96°,En:1.15?2.61GPa.(7)The results of estimation by empirical models of cohesion and needle penetration ratio(NPI-c),internal friction angle and needle penetration ratio(NPI-?)show that severe dolomite sanding c:0.086?0.17MPa,?:16.17°?19.08°;strong dolomite sanding c:0.30?1.60MPa,?:22.13°?33.64°.(8)Compared with the results of on-site flat tunnel rock mass shear and deformation tests,the generalized Hoek-Brown strength criterion and the needle penetration ratio NPI estimation results will deviate from the field test results,but in order to quickly obtain strong and violent dolomite sand in the field For the mechanical parameters of chemical rock mass,the needle penetration test is a method worth considering.The sharp dolomite sanding value estimated by needle penetration is closer to the recommended value than NPI.The estimated strong dolomite sanding value is close to and partially equal to the field rock mass direct shear test data,which indirectly proves the needle penetration ratio.The advantage of NPI in estimating the mechanical parameters of rock masses.It is also worth considering that the needle penetration ratio NPI is used to characterize the sandification development degree of the strong and violent dolomite sandy rock.It is recommended that the needle penetration ratio of the intensive sanding is0.7?7N/mm,the penetration ratio of intense sanding needle is 7?45N/mm. |
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