The Design Of Shallow Electro Mechanical Drill And Research On Ice Cuttings Auger Transportation

Ice caps and glaciers contain a rich store of information about climate in ancient times and carry important information about ancient microbiology,anthropogenic pollution,volcanic eruptions,and properties of natural ice.Glacier variations are sensitive indicators of changes in climate and may have direct impacts on processes of global importance such as sea-level rise,the hydrology of mountain-fed rivers,the freshwater balance of the oceans,natural disasters,and even the shape and rotation of the Earth.The information contained in the shallow ice cores can be used to reconstruct the climate change cycles,improve the accuracy of the oldest ice core position selection,and study the relationship between the dynamic characteristics of the ice sheet and the spatial and temporal changes of the stress and strain rate in the ice sheet.This thesis presents detailed research and analysis on shallow ice coring method and current development of cable-suspended electromechanical drill widely used in ice coring to the depths of 300-350 m.Based on which,rotary auger transportation theory and discrete element method simulation were applied to confirm the optimal parameters for ice cuttings auger transportation system in order to improve cuttings transportation efficiency.The Shallow Electro Mechanical Auger Drill(SEMA Drill)was designed and developed following the design concept of the modern shallow electromechanical drills.The lab and field experimental results prove the working reliability of ice cuttings auger transportation system and SEMA Drill,which provides important references for further modifications and optimizations of structural parameters of SEMA Drill to reach the best performance in a view of cuttings transportation efficiency,rate of penetration and ice core quality.The present study allowed to draw the following conclusions:1)Auger transportation of ice cuttings and its efficiency influencing factors were analyzed on the base of conventional rotary auger transportation theory.The friction coefficients between ice and various materials versus temperature were obtained as a result of measurements of the pulling force and weight of the ice samples using specifically developed testing stand.The relationships among auger angle,rotation speed and efficiency of cuttings auger transportation were estimated for cases with different material combinations.The optimal cuttings auger transportation efficiency can reach 87% using grooved inner surface of outer barrel and Teflon as inner barrel and flights with auger angle 13.7° and rotation speed 175 rpm.The feasibility of the application of the rotary auger transportation theory in the cuttings auger transportation system was verified by testing on the multi-function ice drilling testing stand.It is proved that the optimal cuttings auger transportation parameters estimated by the conventional rotary auger transportation theory cannot effectively convey the ice cuttings.Ice cuttings are clogged at the bottom of the flights and even crushed into pieces,causing the cuttings transport failure and eventually to be stopped rotating.It was concluded that conventional rotary auger transportation theory cannot be applied to the parameter design of ice cuttings auger transportation system.2)The granular particulate material analysis method-Discrete Element Method(DEM)was used to simulate the ice cuttings transportation performance in cuttings auger transportation system.DEM simulation showed that the nature of cuttings transportation in a coring auger is complex and sensitive to the operating parameters.Considering the size of cuttings,the following conclusions were drawn.At low rotation speed,cuttings accumulate at the lower end of flights.At higher speed over 100 rpm,cuttings transportation is more efficient.Maintaining an ordered track for the particles is an important factor in increasing transportation efficiency and energy saving.The reason why the cuttings tracks become disordered is probably that the clearance between the flights and jacket is larger than the diameter of the particles at high rotational speeds or that the weight of the particles is too light and the track easily becomes unstable at high rotation speed.To choose optimal parameters for a coring auger,many factors have to be considered(e.g.,particle sizes and their variability,ice temperature,material of core barrel and jacket).For the conditions assumed in the present study,the critical rotation speed between ordered tracking and disordered tracking is near 100 rpm at auger angles of 35° – 40°,and in conjunction with a comprehensive evaluation of various transportation characteristics(average particle velocity,average particle axial velocity,average particle height,average particles unit mass dissipated energy,energy ratio,and mass flow rate)these values can be recommended as the optimal auger parameters.3)The Test Shallow Electro-Mechanical Auger(Test SEMA)Drill and its testing stand were designed and manufactured to prove results of estimations based on DEM by drilling natural lake ice sample.Testing stand included components of the actual surface drilling facilities.The experimental results showed that during the drilling process,the cuttings were smoothly transported along the flights without any jamming,and the speed of rotation can obviously accelerate the speed and height of cuttings transportation.The drilling speed reached 10.2 m/h when the TestSEMA Drill became stable,which satisfies the average penetration rate requirement of electro-mechanical drills and proves the work stability and reliability of the cuttings transportation system.Smooth borehole and integral ice core was obtained during the tests,while sizes of cuttings were rather small and easily agglomerated with its high surface energy.The TestSEMA drill test verifies the feasibility of the Discrete Element Method in the application of the cuttings transportation system.Results of tests also proved the rationality of the design of Test SEMA Drill and testing stand which provides an important reference for the design and optimization of field SEMA Drill.4)Field SEMA Drill and corresponding surface equipment were designed and tested at elevation of 5600 m a.s.l.at Kuosesele glacier.Totally 55 runs were done.The drilling tests proved that the drill can transport ice cuttings with good performance and obtain ice cores with maximum core length 1.1 m,maximum penetration rate 18 m/h and average penetration rate 10.8 m/h.The field test of the SEMA Drill verified the feasibility and reliability of the drill,and additionally validated the applicability of the Discrete Element Method to design the cuttings transportation system.The entire facility can be carried out in the field into the glaciers or ice caps by two people with easy transportation,installation,disassembly and operation.