| Transmission lines are responsible for the tasks of transmitting and distributing electrical energy.It is necessary to ensure that the transmission tower foundation has sufficient adaptability to cope with complex and changing geological conditions.Screw anchor foundation has the advantages of fast installation,no need for excavation or curing,small environmental pollution,high construction mechanization,and no weather influence.It can be widely used in transmission line engineering.When installing the screw anchor,special engineering machinery is required to apply a certain torque on the anchor rod to screw it into soil layer,that involves installation torque.Therefore,research on the foundation of steel pipe screw anchor is of great significance for its application in practical engineering.In this thesis,the theoretical formula for installation torque of steel screw anchor in sand is firstly given,and it is verified by the model test.Secondly,the relationship between uplift capacity and installation torque of screw anchor in sand is analyzed,and the influence of structural and soil parameters on installation torque is further studied.Finally,the soil disturbance during the installation of screw anchor is investigated by using experimental test and theoretical analysis.The specific research is as follows:(1)The theoretical formulas of situ-in rotation and screw-in screw anchors in sand are given.At the same time,the steel screw anchor model test is performed to compare the theoretical torque value and measured torque value to verify the reliability of the calculation formula.The installation torque of the steel screw anchor is related to the anchor structure and the depth.The installation torque is more sensitive to the diameter of anchor plate.The larger is the screw plate diameter,the larger is the installation torque.In addition,there is a certain correlation between the installation torque and the pull-out bearing capacity,and the pull-out bearing capacity of the steel screw anchor can be predicted.(2)Based on the screw anchor plate bearing model,according to the relationship between the vertical pull-out bearing capacity and the resistance torque during the installation process,a more suitable calculation formula for the installation torque is obtained.The calculation formula is used to study the influence of the structural parameters of screw anchor and the soil compactness on the installation torque in sand.The obtained calculation formula shows that the increasing tendency of the installation torque decreases relatively with the screw-in depth when the critical depth is reached or exceeded.The diameter ratio(D/d)of screw anchor,the size of the anchor rod and the compactness of the soil have a greater impact on the installation torque.The larger is the size of the screw anchor or the denser the sand,the greater is the resistance torque generated by the anchor plate to the total installation torque.The number of anchor plates also has an important effect on the installation torque.However,when the number of anchor plates is greater than 3,the installation torque increases gradually weakened.The influence of the anchor plate inclination on the installation torque increases linearly.(3)The soil disturbance during the installation of screw anchor is studied.The screw advance rate is introduced,which is an indicator to measure soil disturbance.The screw advance rate is closely related to the rotation number of screw anchor.The results show that the ratio of plate pitch to diameter p/D has an important effect on soil disturbances,and p/D is more reasonable between 0.2 and 0.3.In this range,soil disturbance is relatively small.The influence of soil disturbance on the installation torque,the pull-up bearing capacity and the pressure around the anchor is analyzed through model tests. |
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