Study On Lifetime Maximization Model Of Tunnel Structure Based On Probability

There are a lot of mountains in China.With the high developing pace of high speed railway,high standard railway tunnels emerge and it becomes a sign that tunneling construction faces a new peak.However,even though it's new railway tunnel,disaster also happens as existed tunnel.It reveals that during the operation period tunnel structure also has a huge security risk.At present,tunnel design work still focuses on the constructing period and yet hasn't thought of the whole lifetime of a tunnel.Precedent achievement on tunnel durability and reliability are mostly based on narrow durability of material and they haven't considered the characteristics of the tunnel construction.Although it has its meaning for long security of the tunnel,it's not suitable for tunnel structure.Tunnel structure is consisted of rock mass and support structure,during the operation period,tunnel is affected by the environment,stratum,and atmosphere,and thus deterioration happens and causes security of the structure is lessen and even tunnel is destroyed.Influence of the environment and interaction of inner structure of the tunnel needs to be studied thoroughly,and thus it could be a theoretical foundation and reference of strengthening the security of tunnel,extending the lifetime of the tunnel and lowering the total operation cost.Attached to the major project of MOR-study on durability and design work of tunnel structure system,study methods such as literature review,site investigation,indoor model experiment and numerical simulation are adopted to study the long period security under possible conditions.Achievements and conclusions are attained as follow:1.Distribution law of tunnel construction variation has been proposed.The probability of variation doesn't grow with the operation duration.The extension and range of variation grow within time in a linear way.The variation probability is distributed as exponential function in the rock mass classification.In the environmental classification,distribution is in a linear way,when rock is more difficult,the probability of variation is higher;when environment condition is worse,probability of variation is higher.The distribution shape of lining amount,variation amount and length in both rock mass and environment classification are polynomial.Properties of rock mass(mainly the quality after softening when it meets water)influence distribution of variation,probability of variation is higher when the rock mass could be easily deteriorated.On the other side,those constructions in a good quality,probability of variation is relatively low.Overall,tunnels in IV and V level rock,and in the D2 to D4 environment vary the most.Thus,IV and V rock,D2 to D4 environment are the study focuses.2.The reasons of variation have been analyzed.They are external and internal causes.The external factors exist objectively.They are classification of rock mass,environment level,topography,depth of tunnel and self-deterioration of rock mass.The internal factors are mostly caused by people.These factors are in design,construct and operation maintenance periods.The design work is the foundation,and quality of constructing is key point.3.The main influence factors of lifetime to a tunnel are established and their impact rules are also given.The most influential one is the deterioration of rock mass,which is also the most significant objective reason.On the construction element,deterioration of primary support or even ineffectiveness would not lead to final failure of the whole construction,and to some extend crack on the secondary lining doesn't influence the safety of tunnel structure.4.The load distribution and diversion principles which load distributes first with time then with stiffness,and the displacement in post-peak is favorable for the tunnel structure.After excavation,the earlier support is on,the more force tunnel structure will bear.When the support timing is the same,the stiffer structure is,the more force tunnel structure will bear.In the long period of operation,extra load will be bear by elements which have a both strong stiffness and capacity.If extra load is large enough,large displacement happens on the secondary lining,then rock mass will take the extra load that secondary lining cannot bear.5.Influence rule of first support deterioration to limit bearing capacity of secondary lining and tunnel structure is given.Failure of bolts influences safety of secondary lining less compared to inefficiency of steel frame and sprayed concrete,but failure of bolts affect limit bearing capacity more.6.After taking model experiments of different secondary linings which have varied stiffness and bearing capacity.The large stiffness secondary lining has,the lower limit bearing capacity it will has.When the stiffness of secondary lining is the same,larger intensity means limit bearing capacity.With the help of numerical simulation,we suggest that the thickness of secondary lining in V level rock mass could be lessened to 30 cm,relatively enhancing intensity of concrete,preventing brittle failure,an appropriate amount of fiber could be added or constructional reinforcement could be done.7.Maximum lifetime model system of tunnel structure focused on maximum stability is developed,maximum probability formula of tunnel stability:MAX[P(T)]=1-PC|PR)·XR.Relations of all the factors and entire function of tunnel structure are analyzed,strategies are proposed in design,construction and maintenance factors to guarantee tunnel to maintain a longer lifetime.