Mechanical properties of pre-stressed linings with un-bonded annular anchors under high internal water pressure based on large-scale in-situ tests

The new type of pre-stressed lining with un-bonded annular anchors has the advantages of low prestress loss, small weak area and convenient construction. However, its mechanical properties are not clear because of its complex structure, which hinders its wide application. The first large-scale in-situ tests on the pre-stressed ring anchor linings are carried out for the Yinsong Diversion Project. The redistribution laws of the pre-stressed linings in the process of internal hydraulic loading are clarified. The variation laws of the ring anchor tension, steel bar stress and anchorage stress loss are revealed, and the combined bearing effects of the surrounding rock and linings are discussed. The in-situ tests show that the overall prestress distribution of ring anchor linings is uniform, the high-strength tension resistance of anchor cables and the compressive resistance of concrete are utilized efficiently, and the role of the conventional reinforcement bars is very small, so the reinforcement can not be distributed or constructed as a whole. The concrete prestress behind the anchor groove is slightly weak, which is the potential damage area of the structure under the action of high internal water pressure. In the process of internal water loading, the annular and longitudinal prestress values of linings tend to be consistent, which will effectively slow down the cracking tendency of the weak parts of prestressing force. The pre-stressed linings with un-bonded annular anchors have excellent tensile and impermeable properties and independent bearing capacity without depending on the surrounding rock conditions, or can use partial bearing capacity of the surrounding rock to reduce the design prestress value or increase the structural safety margin degree. It can provide a new way to solve the long-standing support problems of large-diameter pressure tunnels with thin overburden, poor geological conditions and high internal water pressure.