Theoretical And Experimental Study On Structural Performance Of The Sprayed-on Cement Mortor Liners Rehabilitaing Precast Concrete Drainage Pipe

Plain concrete pipe and steel reinforced concrete pipe have been widely buried to transport sewage and rainwater.Because of the excessive external load,uneven settlement of foundation,disqualification of the pipe and the construction,the concrete pipe failed with longitional cracks,or collapse,or corrosion and other kinds of structural damage.The structural damage,on the one hand,plunge the pipe into critical state and induce the collapse of the above vehicles and pedestrian;on the other hand,result in the outfilteration of the sewage and the rainwater causing the pollution and washing of the surround soils,or causing groundwater infilteration adding the operating burden.Consensus of the industry is the trenchless rehabilitation,including cement mortar spraying,slip lining,mechanical spiral wound lining,splice segment lining,et al.The cement mortar spraying method rehabilitate the failed host pipe just using the cement mortar;the slip lining,the mechanical spiral wound lining and the splice segment lining rehabilitate the host pipe using the chemical pipes firstly and then grouted the annulars between the host pipe and the liner.There are four common unsolved problems in these methods: the first one is the soil load on the rehabilitated pipe and the transformed load on the liner;the second one is the judgement condition of the strain compatibility between the cement mortar liner and the host pipe,compatible strain leading to one neutral axis,uncompatible strain leading to two two neutral axis;the third one is the bearing capacity of the rehabilited pipe,especially the residual bearing capacity of the host pipe;the forth one is the structural design method of the cement mortar liner.Extensive literature research,theoretical analysis,closed form equation,experimental study,and finite element models were used to solve these problems.The primary research contents and results are listed:1.The soil load on the rehabilitated pipe.Firstly,three dirrerent soil load model are established based on the history soil load in stage of design and service as well as experimental and analystical researches for the three kinds of structural failure: cracking,collapse and corrosion.Secondly,the transmitted soil load to the cement liner are established based on the structural form.Additional surface load could be calculated as a new pipe.2.The structural for of the rehabilitataed pipe.Firstly,one neutral axis structural model and two neutral axis structural model are proposed after the analysis of shear stress and radial stress in curved beams,and the formulas are deduced.Then,the shear stress and radial stress of different diameters are calculated and compared with the shear resistance and radial resistance at the cement and the host pipe interface.3.The bearing capacity of the rehabilited pipe.Firstly,flexural capacity equations for two kinds of structural form of straight beams are established,and then is the the equatiuons for the curved beams,after this is the compression bearing capacity equations.The bearing capacity of the two neutral axis structural model is determined by the rigidity ratio of the up beam and the down beam,and the ultimate bearing capacity is determined by the beam of which failure firstly.The bearing capacity of the one neutral axis structural model is calculated as the variable cross-section width single material beam and neglecting the “secondary stress” effect.The ultimate bearing capacity is determined by the firstly failure of the interface,up beam or the down beam.4.The residual bearing capacity model.The residual bearing capacity model are established according to the host pipe failure model and the structural form of the rehabilited pipe.For cracked and collapsed host pipe,if it is calculated as the two neutral axis model,the residual bearing capacity were neglected,while if it is calculated as the one neutral axis,the residual bearing capacity in positive bending moment areas were included,and the residual bearing capacity in negative bending moment areas were overlooked.For corroded host pipe,the residual bearing capacity is calculated using the traditional structural mechanics based the the extent of corrosion.5.Two kinds of strength cement and different structural form lateral force bending tests,compression tests,split tensile tests are executed.The test results reval that,for the two neutral axis structural model,the gap in the interface weakened the load shearing effect,the test results are just 0.6~0.9 times of the theoretical values.For the one neutral axis structural model,the local shear slip at the interface reduces the bearing capacity from 4 of theoretical values to 3~3.8.The split tensile tests results reveal that: the split tensile strength were about 0.95~1.86 MPa,0.47~0.73 times of the strength of themselves.6.Commercial software ABAQUS is used to simulate the straight beam under lateral force bending tests and the bearing capacity of the rehabilitated pipe.The simulation reveals that: for the two neutral axis structural model,the down beam begains to work just after the upper beam bend,and it`s action likes the upper beam.For the cracked and collapsed rehabilitated host pipe,just the residual capacity at positive bending moment areas worked.5.The structural design method of the cement mortar liner could be executed depending on the damage types of the host pipe and the structural form of the rehabilitated pipe using the limit state design method.Upon the defferent of the rehabilation materals,fiber concrete design method and steel fiber concrete design method could be used depending on the limit state of bearing capacity and the serviceability limit state.