| The developments of altered-rock were controlled and affected by the structural planes,(gas)hydrothermal properties and the difference between the physical and chemical properties of wall rocks.The altered-rock bands which were the combination of the altered rocks of the different types and had a certain zoning feature were formed.Due to the alteration effect on the physical and mechanical properties of the rocks usually playing a role in the degradation,the altered-rock zones often became the main engineering geological defects.Because the granodiorite masses in dam area of Mengdigou hydropower station commonly had the altered-rock zones which were formed by the hydrothermal alteration,and the altered-rock bands were transformed by the late tectonic activities,the main fault structures of the dam site area were form and leaded to the altered-rock zones become the main engineering geological problems of the dam site area.In this paper,the altered-rock masses of the dam foundation of this hydropower station were as the study object,based on the analysis of the development characteristics of the altered-rock zones,the combination method of macro and micro was applied to study the zoning characteristics of the altered-rock bands and the petrological characteristics,the test method of physical and mechanical was adopted to study the physical and mechanical properties of the altered rocks of the different types;then the types of the engineering properties of the altered-rock zones were divided,and applying to a variety of methods to study the mechanical properties of the altered rocks(zones)of the different types.On this basis,the engineering geological classification schemes of the altered rocks were established,and the preliminary analysis of the availability of the foundation surface altered-rock zones was obtained.The main research results were as follows:(1)On the basis of the geological background analysis of the altered rocks of the dam area and the system researches of the altered-rock zones,according to the output characteristics,altered-rock zones were divided into the two major categories of fault type and fracture type.And the altered-rock zones of the fracture type were further divided into five subtypes of "ribbon" alteration,"layered" alteration,a single "vein" alteration,"grid" alteration and "dendritic" alteration.The study determined the spatial distribution and geological characteristics of 8 "fault" alteration zones(AZ)and 5 "fracture intensive" alteration zones(ACZ)of the dam area.(2)The mineralogical studies of the altered rocks shown that altered-rock zones from the center to both sides had different degrees of kaolinization,illitization,chloritization,sericitization,silication and carbonatation,and the clay from the center to the sides had gradually enhanced.Based on that,combing with the macro geological features of the altered-rock zones,the altered-rock zones from the center to both sides were divided into three zones,which were respectively the strong metasomatic weak clay zones,weak metasomatic strong clay zones and thermal contact softening zones.From the engineering geological view,the altered rocks were known as the granodiorite,the strong metasomatic weak clay altered rocks,the weak metasomatic strong clay altered rocks and the clay altered rocks respectively.(3)The methods of physical and mechanical test were adopted to obtain systematically the physical and mechanical properties of the altered rocks of the different types.The results showed that: the physical and mechanical properties of the minor metasomatic granodiorite were mainly influenced by the weathering alteration;the physical and mechanical properties of the rocks from weak weathering to micro-new were from good to better and their saturated uniaxial compressive strength were 67.7MPa and 92.0MPa respectively,the physical and mechanical properties of the strong weathering rocks were poor and its saturated uniaxial compressive strength was 21.8MPa.The rocks of each altered-rock zone were mainly affected by metasomatic alteration,the physical and mechanical properties increased with the increase of the clay minerals and reduced with the decrease of feldspar and heavy crystalline quartz,and the physical and mechanical properties of the altered rocks of the weak-weathering strong metasomatic weak clay were good and its saturated uniaxial compressive strength was 45.7MPa.The physical and mechanical properties of weak-weathering weak metasomatic strong clay and strong-weathering strong metasomatic weak clay altered rocks were poor and their saturated uniaxial compressive strength were 19.9MPa and 16.7MPa respectively.The physical and mechanical properties of the clay altered rocks were of equal to the fault argillaceous.The good functional relationship of rebound test,uniaxial compressive strength and point load strength was adopted to determine the standards which divided the soft and hard degree by rebound value.(4)Through combing with the geological zoning patters of the altered-rock zones,the physical and mechanical properties of each altered-rock zones and the comprehensive strength,the engineering characters of the altered-rock zones were divided into four categories(S1~S4),the mechanical properties of the altered rocks of various types and granodiorites were systematically studied.Where,the comprehensive rebound value of S1 type altered-rock zones was greater than 42,the saturated compressive strength of the comprehensive rebound was more than 60 MPa,the perforation wave velocity was more than 4500m/s,the deformation modulus was greater than 10 GPa.The S2 type comprehensive rebound value was 35~42,the saturated compressive strength of the comprehensive rebound was 45~60MPa,the perforation wave velocity was 3800~4500m/s,the deformation modulus was 4.5~8.0GPa.The S3 type comprehensive rebound value was 27~35,the saturated compressive strength of the comprehensive rebound was 30~45MPa,the perforation wave velocity was 3200~3800m/s,the deformation modulus was 3.0~4.5GPa.The comprehensive rebound value of S4 type altered rock zone was less than 27,the saturated compressive strength of the comprehensive rebound was less than 30 MPa,the perforation wave velocity was less than 3200m/s,the deformation modulus was less than 2.0GPa.The physical and mechanical properties of S1~S4 type altered-rock zones were respectively consistent with that of micro-new sub-block structure,the mosaic structure,the fracture-fragmentation structure and the fragmentation-dispersion structure granodiorite.(5)According to the correspondence of the developmental characteristics,zoning and engineering characteristics types of the altered-rock zones and the structural types and mechanical properties of the granodiorites,selecting saturated uniaxial compressive strength,rock integrity and the engineering characteristics types as the main indexes of the rock mass quality evaluation,the engineering geological classification schemes of altered-rock masses were established.The left micro-new weathering zones of the internal-fault altered-rock zones were determined for VI type rocks.Through the evaluation of the comprehensive deformation modulus and wave velocity of the right "fractured intensive" alteration zones,the "fractured intensive" alteration zones of ACZ01~ACZ04 and ACZ05 in micro-new,and no unloading belts were respectively divided into III1 and VI rock.The availability of the left ? right bank fault and "fractured intensive" alteration zones in the building surface was preliminary analyzed. |
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