| Due to the region characteristic and the constraint of transmission line corridor, high-voltage transmission tower is often located right at the top of tunnel or near the top of the tunnel. Free-standing high-voltage transmission tower, as a towering space structure, has less rigidity. The foundations of tower are independent of each other. Tower is very sensitive to the settlement difference between two adjacent foundations. When tunnel constructed under or nearby the high-voltage transmission tower, the tunnel construction is easily result in uneven settlement of tower foundations. Serious uneven settlement may cause tower collapse. The collapse of tower may endanger the normal operation of the power lines, and it will not only cause significant economic losses, and can cause serious social influence.Lijiachong tunnel underneath500kV high-voltage transmission tower is used as engineering example. The numerical analysis and real-time monitoring are used as research methods. The influence of tunnel construction on transmission tower is analyzed. Based on the specific conditions of the Lijiachong tunnel and500kV transmission tower, the construction scheme and technical measures are studied, and the application effect is analyzed. The main research results and conclusions are as follows:1. The maximum stress of tower to the design compressive strength of steel is used as benchmark. The allowable value of foundation tilt and tower tilt are put forward, for typical free-standing high-voltage transmission towers with different height.2. The influence factors of the location of tower, diameter of tunnel, depth of tunnel, type of tower and external load of tower are studied, for the influence of tunnel construction on transmission tower. The influence of tunnel construction to towers at different position is compared, and the scope of influence is divided into several areas. By comparing calculation, the influence law of tunnel construction on tower is obtained, when the tunnel have different diameter and different deep, and when the tower have different external load. The influence law of tunnel construction on different height towers is obtained. 3. According to engineering example of Lijiachong tunnel under the high-voltage transmission tower, the damage to tower by the tunnel construction is analyzed. The advantages and disadvantages of several treatment plan of construction risk are compared. The construction scheme using the frame beams to reinforce the foundations of tower to avoid the risk of is suggested. The effectiveness of the treatment scheme is analyzed by numerical simulation method, and the feasibility of the treatment plan is proved by field test method.4. Analysis showed that the overall ability to resistance deformation is increased to the foundations of tower by using the frame beams to reinforce the foundations of tower and the independent foundations are connected as a whole. The uneven settlement and the difference of horizontal displacement of foundations are reduced effectively, at the same time, the stress increment of tower member and construction risk is reduced.5. Through the long-term monitoring of the construction of Lijiachong tunnel under the tower, the law of the deformation of tunnel, ground settlement, displacement and stress of tower is obtained. The engineering practice, which Lijiachong three lanes large-span tunnel under the high-voltage transmission tower constructed successfully, shows that the risk treatment plan and tunnel construction method are reasonable. The success engineering example provides analogy and reference to similar tunnel under tall buildings. |
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