Study On Long Term Stability Of Geotechnical Prestressed Anchor System

Based on literature research and practice,wherewith the field testing data of Jinan round city express-way,the long term stability of the geotechnical prestressed anchor system had been lucubrated entirely by utilizing such research means as theory analysis, field examination,indoor experiment,etc.By relating to the actual engineering,the application research about the study thought was carried out,then determining the service life of the actual engineering,obtaining a series of research production which were beneficial to the theory and practice.(1) Based on entire study of the operation mechanism,types and failure mechanism of geotechnical prestressed anchor system,the fire-new conception of the geotechnical prestressed anchor system and it's long term stability were defined from dynamic viewpoint,it revealed that the stress corrosion of pole materials was the fundamental factor which would determine it's long term stability.It constructed the collectivity research frame of long term stability for the geotechnical prestressed anchor system,ascertained the basic theory aspect of research.(2) By means of the long term tracking field-monitoring,it revealed the characteristic and regularity of the anchor cable prestress variation under the different influence factors and during different period.The prestress variation,which caused by the rain,temperature change day and night,temperature change every year,had obviously undulation characteristic,which was like approximatively close loop,these loop were called separately "the big recurrence","the small recurrence" and "the additive recurrence".The undulation variation chronically existed and lag behind the change of the influence factors.By means of combining the rehological mechanics and the actual monitoring rule,based on the Kelvin model and Burgers model,it found the four parameter constitutive model,which could reflect the coupled characteristic of the geotechnical creep and the relaxation of the pole materials.For the first time,it put forward the mechanism of "placidly attenuation superposing undulation variation",the experiential model was established by utilizing the formula "P=Ae^-a(t-b)+B+Dsin(w₂t+φ₂)+F+Ce^-ct sin(w₁t+φ₁)",which could forecast the long term prestress variation.(3) By means of making certain the principal influence factors and orthogonal combinatory analysis,it creatively manufactured the indoor full-scale experimentation technic and equipments,which could simulate the corrosion of the metal pole materials as actual geotechnical condition.Based on the indoor examination,it ascertained the development rule of the stress corrosion,it was first time to found the quantificational formula "C_l=p₁·x₁^p₂·e^-p₃x₂·(p₄+x₃^p₅)",which represented the stress corrosion rule, the theoretical foundation of the geotechnical prestressed anchor system service life research was established.In terms of the field-testing,it primarily revealed the typical distribution and cross-section characteristic of the stress corrosion in the actual circumstance.The indoor experiment rule was modified by utilizing field-testing data,it could be used to forecast the service life of the actual prestressed anchor engineering.(4) Through first contrastive research on the full-scale field-striping examination and the numerical simulation of the prestressed anchor cable,it revealed the invalidation effect of the single anchor cable and the regulative rule of interior stress,and put forward the formula "δ=f(L)",which expressed the relationship of the influence modulus and space on the different location.The invalidation effect of group anchor cable and the instability expanding rule was researched by means of the numerical simulation of the three dimension continua fast Lagrangian calculation method,it revealed that the quantity of the failure anchor cable reached a critical scale,interior longitudinal plastic zone would connect to face of slope,the local instability occurred. The relative distance and quantity of the local instability had obviously different influence on the integral stability.For actual engineering,it made such important conclusion as the part slope become unsteady when the failure anchor cable exceed to 8 or the plastic area of the slope surface exceed to 200 m²,when two local instability on the adjacent step of same vertical section occurred,or when more than three local instability could mutually joined up,the whole slope become unsteady.(5) It put forward the systemic control conception and combination control method of the geotechnical prestressed anchor system stability,it was first time to raise the dynamic optimizing design method based on the most critical scale due to the different combination of prestress and space,at the same time the stress corrosion was considered. It entirely analyzed the three criterion of the geotechnical prestressed anchor system stability,it creatively found the method of ascertaining service life based on the prestress variation rule and stress corrosion rule.The actual engineering service life would be 41 years,the different body of the slope would have different life range.By means of associating the different stress corrosion quantization characteristic and field-monitoring result,it was first time to put forward the warning and reinforcing opportunity for the different failure situation,and reinforcing measure which aimed at the different warning prestressed anchor system.