无黏结预应力环锚衬砌力学特性原位加载试验研究

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

新型无黏结环锚衬砌具备预应力损失低、薄弱区小、施工便捷等优势,但因结构复杂致使力学特性不明确,阻碍了其广泛应用。依托引松工程总干线压力隧洞,开展了首次预应力环锚衬砌大型原位加载试验,明确了内水压加载过程中衬砌预应力重分布特征,揭示了环锚拉力、钢筋应力以及锚固应力损失变化规律,并探讨了围岩和环锚衬砌联合承载作用。原位试验表明:环锚衬砌整体预应力分布均匀,高效地利用了锚索高强抗拉性和混凝土抗压性,常规钢筋作用极小,因而整体可不配筋或仅构造配筋;锚具槽背后混凝土预应力稍薄弱,是高内水压作用下结构潜在破坏区域,但内水加载过程中衬砌环向、纵向预应力值趋于一致,将有效减缓预应力薄弱部位开裂倾向;环锚衬砌具备优越的抗拉和抗渗性能,可不依赖于围岩条件而独立承载,也可利用围岩部分承载以降低预应力设计值或增加结构安全裕度,它能为覆盖层薄、地质条件差且内水压力高的大直径压力隧洞长期存在的支护难问题,提供解决新途径。

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.