Study On Actual Working Performance Of High Cemented Sand And Gravel Cofferdam

Many theoretical studies have been carried out at home and abroad on Cemented Sand and Gravel(CSG)dams,which are mainly based on the material parameters and constitutive relations obtained from laboratory tests.Thus,there is a lack of studies analyzing the actual working performance based on monitoring data from real prototypes working in practice.Dahuaqiao overwater cofferdam is the highest CSG cofferdam at present.In this thesis,on the basis of measured data from Dahuaqiao cofferdam,the actual working performance of stress,seepage,temperature and thermal stress are analyzed.Aiming at the design of high CSG cofferdam,the section symmetry,material partition and temperature control standard are discussed.Main contents and achievements are as follows:(1)Combined with actual construction and operation conditions,the monitoring data of hign CSG cofferdam are analyzed comprehensively,including strain,seepage water-head and temperature.The distribution and variation characteristics are explored.In terms of the processing of measured strain data,an analytical method suitable for the analysis of CSG is proposed,as well as the statistical model of stress-strain in the form of increment with the corresponding component factors.(2)Based on the strain component isolated from strain monitoring data,and the inverse analysis method suitable for the operation characteristics of CSG cofferdam,the real mechanical parameters of the material are inversed.The reason for the difference between the actual mechanical parameters and the test values is analyzed.The dynamic change process of the elastic modulus was fitted with the multi-engineering data.using the working performance of the stress and strain obtained from the reverse analysis,the deformation and stress stability of the high cofferdam structure under the conditions of water retaining and water flowing are analyzed.The whole section of the dam is basically compressed,with a relatively high stress triangle at the dam heel.The safety coefficient of stress intensity and the safety coefficient of anti-slip stability both meet the requirements and have larger safety margin.(3)On the basis of measured water-head from Dahuaqiao cofferdam,an inversion analysis method for unsteady seepage fields covering different time periods within a time sequence are established.The results indicate an effective dynamic change law for the material permeability coefficient and the real dynamic evolution characteristics of seepage fields.Abnormal CSG anti-seepage layer can meet the running requirements of cofferdams,along with simplified seepage prevention and drainage of dam foundation.Under the long-term action of water pressure,the seepage behavior of the dam body shows no obvious deterioration,suggesting that CSG can satisfy the required anti-corrosion property expected of dam construction materials.Thus,(4)On the basis of measured temperature from Dahuaqiao cofferdam,the thermal parameters of CSG are inversed,including adiabatic temperature rise,thermal coefficient and so on.From the perspective of the difference between the infiltration water temperature and the material temperature in transient conditions,the heat conduction equation of the temperature field with consideration of seepage field and the finite element calculation formula with its settlement is obtained.Accordingly,the numerical calculation method of temperature field is put forward for CSG cofferdam.The result of finite element calculations shows that,the seepage water causes a large temperature drop rate and drop range in areas below the infiltration line and produces a larger temperature difference of dam foundation in advance.(5)In combination with the measured strain and the calculated temperature field,the creep parameters of CSG are inversed,as well as the real working performance of thermal stress.The results show that under the action of the foundation temperature difference,there also has a large temperature stress caused by the strong transverse constraint,thus,it should be considered together with the stress along the river as the control stress.For the upstream,the control stress of the temperature difference between interior and surface is the stress along the river direction and along the slope direction(6)Whether high CSG cofferdams still need to adopt symmetrical sections has investigated.Within a wide and reasonable range of foundation and dam materials,The loss of safety for asymmetric profiles is discussed from the point of stress strength and anti-slip stability.It is emphasized that the low material strength requirement and the high safety brought by the symmetrical section are the advantages of CSG dam type,which obviously different from the traditional dam.The optimization of section design should not be over-emphasized(7)Based on the compressive stress partition,the method of dividing into high stress area,low stress area and local strengthening area is put forward.Thus,it can make full use of local materials with a poor raw,reduce the processing of materials,reduce mixing and construction requirements,and give full play to the economy,construction convenience and environmental protection.(8)A practical calculation method for temperature field in construction period is put forward.The significant temperature can be obtained by simple hand calculation,including average temperature of pouring layer,temperature at any point in pouring layer and average maximum temperature that can be reached.In terms of material thermal and mechanical parameters,structure characteristics,construction and operation characteristics,the difference between CSG cofferdam and the normal concrete dam is analyzed.The temperature control standard applicable to CSG cofferdam is formulated.