砂土中隧洞开挖稳定机理及松动土压力研究

Study on Stability Mechanism and Relaxed soil Pressure in Sandy Soil during Excavation

为减轻在砂土地层中开挖隧洞的支护难度，通过离心模型试验，研究了隧洞内支护压力与地层位移的关系，以及砂层稳定与破坏的机理。结果表明，在砂土中开挖隧洞，由于砂土的拱效应，隧洞拱冠以上砂土在远小于原位上覆土压力的支护压力下仅发生一定的位移而不致塌落；若允许地表面发生少许沉降，隧洞内支护压力可以比原位上覆土压力有较大程度的降低。文中对太沙基的松动土压力理论及计算公式进行了讨论，用作者改进公式计算的松动土压力值与离心模型试验结果较为相近。

For reducing the degree of difficulty of support during excavating tunnel in sandy soil, the relations between the support pressure and stratum displacement, and between the stability and damage mechanism of sand layer, are studied by means of centrifugal model test. Test results show that, owing to the arching effect of sandy soil during tunnel excavation, the sandy soil above the tunnel arch crown merely produces certain displacement without collapse while the critical support pressure is much smaller than the original overburden pressure; if few depression of earth's surface may be allowed, the support pressure in tunnel compared with the original overburden pressure would be greatly decreased. The Terzaghi's relation pressure theory of sandy soil and his calculation formula are discussed in this paper. The calculation values of relaxation earth pressure by author's modified formula are close to the test results.