Mechanism Research On Compound Tunnel Anchorage Of Suspension Bridge

As a kind of new stnicture form of anchorage system of suspension bridge, tunnel anchorage compound with prestressed anchorage cable possess inavailability advantage of tunnel anchorage: reasonable structure stress distribution, reliable safety, low construction, ecological condition conservancy, realizing sustainable development, enlarging field of application and engineering condition of tunnel anchorage, increasing competitive power of suspension bridge, filling up the blank that made the most of nature host dielectric powerful self-supporting in deed meaning, foreground engineering practice and great economic benefit.Limited by geologic conditions, application of tunnel anchorage was localized in geologic environment of intact rock with less joint at presen. It was difficult and worst risk that tunnel anchorage compound with prestressed anchorage cable was designed and constructed in engineering boundary condition with abundant joint fissure or break ground, the research was blank both domestic and abroad. At the same time, as one of the system bearing main body, it was not perfect only considering the prestressed anchor cable as safety margin of system.. It was incommensurate with the engineering practice that design and construction gave priority to empirical analogism method because of no related theory guide.Anchorage optimum design can generate enormous eonomic benefits, improve system stress, ensure engineering safety reliability and endurance. On the one hand, under definitive condition of load, satisfy static equilibrium, compatibility of deformation, constitutive law as well as boundary condition, system stability affected by topological parameter and initial stress of back anchorage cable change, thereby supervise and modify design;On the other hand, numerical method can't be adopt by majority designer although it can comprehensively consider discontinuity, anisotropy, nonlinear constitutive law and characteristic cubic of expansion, soften, large deformation, etc. of rock and soil matter, while structure was destroyed. Sometimes in engineering practice, how stress and strain of structure change with external load didn't be demand, only ultimately critical load or structure safety factor corresponding to plastic flow state need to be find out, itprovides a simplified calculation and an overall design thought for engineers that look for a simplified calculation formulae reflect basic engineering condition.Research state and prospect were argumented by literature overview and science and technology originality innovation approval;Theoretical analysis, numerical simulation, processing study, experimental verification (field model test and in-shu test) were synthetical adopt in research methodology. Primary coverage and achievements as follows:1. The ultimate anti-pulling capacity and failure mode affected by anchor-length, free-length, grouting quality and interface mode between grout-cable and rock mass were analyzed. Stress distribution modality in rock mass and root effect was illustrated The concept of safety storage coefficient was put forwardFree-length has key effect to effectively transfer and disperse stress to wall rock;The failure mode of anchor cable is controlled by free and anchor length;Contribution value and occasion of anchor cable is determined by its free-length and initial stress while they share the load together with anchorage system. Strands stubble or grout-cable- pour slippage were mostly two kind of single anchor cable destroy model, integral reversed cone failure of rock mass wont occur. Failure of anchorage cable was progressive: bearing capacity won't loss at once following destroy occuring before, higher peak instead under a certainty condition of loading until limiting destructive system. Domino offect occurs while the prestressed anchor cable group is destroyed2. Inclination, length, clamping angle of anchorage, interface roughness concentration and bonding capacity of interface ,etc. affect the displacement of anchorage and repose stability of rock mass. It indicates by multiplex load contrastive analysis, that anti-pulling capacity increase depend on effective projected area (axial direction projection component along main cable) of anchorage-wall rock interface increasing, gravity anchorage resist three-dimensional load depend on base friction, mat anti-slippage capacity increase mostly depend on anchorage volume gain;compound tunnel anchorage transfer and leveling foci stress, confine displacement by dip-holdup effect of tunnel anchorage and counterforce of prestressed anchor cable, spread systemic bearing depth and sphere. inclination of anchorage should be controlled in the field;Axial length L presence critical value, clamping angle of anchorage dominated displacement, and length influenced and "disturb " stress distribution on interface. The application of compound tunnelanchorage should be restricted at certain range and geologic conditioa3. Clip-holdup effect of rock mass and anti-pulling effect of anchorage cable system were self-balanceable, while they participate withstanding the load applied on tunnel anchorage system. Intial stress value of anchorage cable determined resource(carrying capacity that can be manoeuvred from rock mass) distribution: oversize initial stress generates unprofitable distortion and secondary stress in rock mass;undersize initial stress only generates reinforced effect and it was of no service to system stress redistributioa Initial stress of anchor cable ought to be controlled at the range of [(0.75~0.85)x0.75^k], thereby, value and occasion contributed by anchor cable will correspond with anchorage. If anchorage occur axial displacement corresponding with external load acting direction, the negative direction displacement and distortion of the anchorage must be overcame result in rock anchor stretching phase first of all.While initial stress was less, the anchorage cable stress enhanced only after rock mass clip-holdup being overcame.4. Based on field test results for compound tunnel anchorage system of suspension bridge, the failure model and failure condition are analyzed. The equilibrium equation of the anchorage system is established based on limit theorem. According to the actual construction technology and design scheme, the anchorage-rock mass interface is generalized into four types of mechanics model, and the failure criterion is correspondingly presented based on rock mass joint mechanics theorem and test achievements. The meaning and option method of subentry coefficient in simplified formula for bearing capacity estimation are discussed. The simplified formula for calculation of bearing capacity of anchorage was validated by practical engineering case. The proposed method provides a simplified calculation and an overall design thought for engineers.It's key core which leads theory harvest in a position to engineering practice by marriaging rock mechanics and engineering, both serving and supervising construction practice, and looking forward to provide rationale and guide for optimum design and construction of compound tunnel anchorage used in mutable landform and geology environment <.