| With the vigorously development of infrastructure,design,method and construction of New Technology of Engineering Foundations have been changing with each passing day.Feasible The feasible methods and technology of digging holes for piles are the key,considering that the pile foundation is the main form of deep foundation,besides,the pile foundation has been widely considered because of its advantages of settlement control and carrying capacity etc.However,the screw drivers is already applied to various types of formation,owing to that the screws drivers can at a lower cost,higher quality and faster speed to complete the pile hole construction comparing with the traditional way of pile.But,due to the complexity of the environment,the bit to impact intrusion and rotary cutting of the rock which is contacted with the screw driver,different lithology and construction parameters all have important influence on dynamic process of drilling rock into the hole.Therefore,research on the Mechanism of Rock Cracking of screw drivers is relatively less now,and most study is confined to research on the static and single factor.In order to more fully reflect the characteristics of dig rock and hole shape in the process of drilling,this paper mainly studies the dynamic process of rock fragmentation and Mechanism of Rock Cracking of screw drivers by the method of combining the engineering practice with theoretical analysis and numerical simulation.The main research content is as follows:? Rotary drilling parameters are analyzed,according to the working principle of the rotary drill and the force type of rock created by the pick cutting process can be got based on the Mechanical principles.And three-dimensional stress state of rock can be obtained by analyzing the stress state of rock under the cutter tooth cutting,which is based on the elastic semi-infinite element theory,then,the calculation formula of contact force between the cutter tooth and rock can be got by theoretical derivation,and the relationship between the normal load and displacement can also be obtained.? The three-dimensional numerical model of cutter tooth broken rock is set up.And the rock fragmentation process between vertical intrusion period of cutting tooth(Cutting tooth is without rotation and under vertical invasiveness pressure into the rock merely in this section)can be divided into five stages,which can be known by analysis of the contact force,contact area,crack,the plastic deformation of rock and damage evolvement etc.But the rock before tooth suffers the squeeze effect in rotarycutting section(cutter tooth is with rotation and suffers the effect of both vertical invasiveness and horizontal torque in this section),and the tooth rock suffers the action of both tensile and shearing,which illustrates screw drivers breaks rock is a process of extrusion,stretching and shearing coupling.? The effect of arrangement of cutter tooth on rock fragmentation process is analyzed under different rock strength,and the variation trend of obliquity of cutter tooth,slanting angle of cutter tooth and space width with the strength of rock.Moreover,the arrangement of cutter tooth has been optimized in this paper.? Three-dimensional model of rotary drilling process is established,the characteristics of breaking rock of different forms of bit under different drilling parameters are analyzed and the comparative analysis of the rock fragmentation process of drilling and the coring bit is conducted,the analysis result show that both the revolving speed and drilling speed of the bit have great influence on the broken asthenosphere.Besides,bearing layer decision model coordinated control by multifactor,namely the model of rock mass intensity,is put forward.The rationality and reliability of this mode is verified in this paper and the actual dynamic process of rock fragmentation created by the rotary drilling has been analyzed in greater detail. |
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