| Trenchless technique is used for detecting,checking,renovating,changingand laying all kinds of underground public service(pipeline and cable) whenthe ground surface is not excavated.As a rising technology,it has not onlywide developing foreground but also especially high developing speed,theapplication field is extending increasingly.Horizontal Directional Drilling isone of the tenchless technique that is highly developed in recent years.HDD drill stem is the key part enduring the most complex force and themost execrable work conditions,so it is necessary to find out the stressdistribution state in the drill stem and the reason of destoried by simulatingand imitating analysis of the drill stem under all kinds of work conditions.Onthe basis of it,the structure of the drill stem,intension and bore track can beimproved and this technology can be perfectde as well.During Horizontal Directional Drilling,the form of bore tracks arevarious,they are may be two-dimensional or three-dimensional.Sometimesthey are more complex in order to go around the barrier.At the curvesegment,the drill stem must be bended by the restrict of the bore.When drillstem rotate especially when the drill stem is back-pulled,it will endured bothpressure ,pulling and vast torque, it is easily be destroied.So the drill stemmechanics and FEM model under the acted of axial force and torque wasbuilded.The distributing rule of stress and the relationship between themaximum axial load and the maximum curve radius was found out after theFEM static analysis was carried out.1,with the curve radius increasing,the maximum axial load increase aswell if the drill stem has the same length.2,When the curve radius is less than 60m,the increase speed ofmaximum axial load is fast.So it can be seen,the stress in the drill stem issensitive to the change of the curve radius.For example,when the drill stemdrilling but not rotating,the maximum axial load increase from 784KN of 30mto 939.1KN of 60m,the increment is 155.1KN。But in the range of the curveradius 30m to 60m, the maximum axial load only increased by 39.7KN.Theformer is as four times as the latter.3,Increasing the torque can raise the stress level in the drill stem.When100KN.m is applied on the drill stem,the maximum axial load decreasegreatly.For example,when the curve radius is 30m,the maximum axial loaddecreased by 17%。When the curve radius is 60m,the maximum axial loaddecreased by 19%.Usually the effect of the pipe connection is ignored when deformationof the drill stem is researched,only regard drill stem as a smooth pipe. On theassumption that the deformation curvature of the drill stem is as same as thehole's. This hypothesis is suit to vertical hole,but to horizontal directionaldrilling pipe with bigger connections ,its maximum curvature is not equal tothe hole's,especially to horizontal directional hole with little radius itscurvature is usually very big,it will not meet the project need if the effects ofthe connection are ignored any more.In order to investigate the influence law done to the drilling stem by theconnections,a drilling stem's stress and strain calculating model that effect ofthe connections are considered under action of axial load isestablished,structure static and buckling analysis have been done to it.Byanalyzing,some conclusions are drawn:1,After the horizontal directional drilling stem with connectionsdeformed restricted by the hole under the action of axial load,the maximumstress is located at the joint.2,With the increasing of the drilling stem connection diameter,themaximum bending stress in the drilling stem and the vertical deformation ofthe drilling stem will decrease accordingly.3,The critical load of initial buckling of the drilling stem withconnection is bigger than the one without connection.4,With the increasing of the drilling stem connection diameter, thecritical load of initial buckling will be increased too,which indicate thatbuckling can be restricted and frictional resistance will be decreased so thedrilling effect will be raised and the life of the drilling stem will be prolongedif the connection diameter increased.5,Though the stress in the drilling stem and the vertical deformation ofthe drilling stem will be decreased with increasing of the connectiondiameter,the flexibility will be decreased,which will bring difficulty todrilling.By analysing it is reasonable that the diameter of the connection isregarded as 66.7mm.In Horizontal Directional well,the stress state of drilling stem becamesvery complex.Frictional resistance influence the axial force and torquedirectly and it also determin the drilling effect.So many reasons can producefrictional resistance such as diameter shrink, well collapse,keyway ,thewell is not cleaned and blocked by the stone.So ,to know the stress anddeformation of the drill stem is key to choose drilling facilities and make acorrect drilling plan.The frictional resistance of the drill stem during drilling is analysed byusing ANASYS strong non-linear analysis function.Face-Face contactanalysis method is used.The soil is regarded as DP material,its plasticbehavior is presumed real elastic and plastic,at the same time the drill stem isregarded as a rigid body, a contact pair between the drill stem and the soil iscreated,by non-linear calculating the parameters such as frictional resistancecan be given.Through simulant calculating and contrast the calculating datawith the real one proves that the given frictional resistance calculating methodis feasible.In order to testify the validity of the results in chapter four,values ofstress in six important part in the drilling stem with different diameterconnections are obtained by using hydraulic omnipotence pressure machine.Itcan be seen after analysing the experimental data,under the action of sidepressure, the maximum bending stress in the drilling stem will decreaseaccordingly with the increasing of the drilling stem connection diameter,whichis accordant to the results in chapter four,and which testified it is scientific andrational to simulate by ANSYS.
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