Model tests of road subsidence progress with underground cavities caused by cyclic dynamic load
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摘要:
在循环动荷载作用下，地下空洞会逐步发展成为路面塌陷。针对此问题，本文建立了模拟路面塌陷发生发展全过程的模型试验。试验结果表明，随着动荷载值的减小，土体所能承受的极限振动循环次数呈指数型增加。而当地下存在一定尺寸的地下空洞时，即使动荷载值较小，在足够多次数的振动循环作用后，也有可能引发路面塌陷。最大粒径较大、不均匀系数较高土体的静力稳定性较强，体现在其能承受的极限静荷载较大；但其动力稳定性较弱，体现在其能承受的极限振动循环次数较少。反之，最大粒径较小、不均匀系数较小土体的静力稳定性较弱，而动力稳定性较强。地下空洞上覆土层厚度越大，则其静力、动力稳定性均较强。同时，循环动荷载作用下地表沉降与土体裂缝的发展呈现出三阶段规律。阶段1为初始固结沉降阶段，持续时间较短，土体受到振动压密作用，地表发生整体沉降，土体裂缝未见明显发展；阶段2为等速沉降阶段，持续时间较长，中心土体受到振动剪切作用，地表中心沉降与土体裂缝随时间呈等速发展；阶段3为加速沉降阶段，持续时间最短，中心土体受到振动破坏作用，地表中心沉降与土体裂缝快速发展直至发生塌陷。
Abstract:Due to the cyclic dynamic load, the underground cavity will gradually develop into road subsidence. In view of this problem, this paper establishes model tests to simulate the whole developing process of road subsidence. The results show that as the cyclic dynamic load decreases, the limited cyclic loading times causing road subsidence increases exponentially. However, if there is a certain size of underground cavity, small cyclic dynamic load can also lead to road subsidence after sufficient cyclic loading times. The soil with larger maximum particle size and higher uneven coefficient has larger ultimate static strength and smaller ultimate dynamic strength. On the contrary, soil with smaller maximum particle size and smaller uneven coefficient has smaller ultimate static strength and larger ultimate dynamic strength. Larger thickness of the soil overlying the underground cavity will lead to larger ultimate static and dynamic strength. At the same time, the development of the road subsidence curve and the soil cracks under the cyclic dynamic load undergo three stages. Stage 1 is the initial consolidation settlement stage with short duration. In this stage, the soil is compacted by vibration and the ground surface has overall settlement with no obvious development of the observed soil cracks. Stage 2 is the uniform development stage with long duration and uniform development in settlement and soil cracks. The soil is subjected to the effect of shear vibrating. Stage 3 is the accelerated development stage with the shortest duration. The soil is subjected to vibration failure. The settlement and soil cracks develop rapidly until road subsidence occurs.
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Key words:
- cyclic dynamic load /
- ground subsidence /
- model tests
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表 1 循环动荷载试验工况汇总表
Table 1. Summary sheet of the cyclic dynamic loading tests
试验土体 空洞上方土层厚度 t/mm 加载
方式车辆荷载
W/kg极限振动循环次数 Nu 试验编号 标准
丰浦砂50 静荷载 W u=6.88 − Case 1-0 动荷载 Wu×100%=6.88 31 Case 1-1 Wu×90%=6.20 235 Case 1-2 Wu×85%=5.84 107 Case 1-3 Wu×80%=5.50 1385 Case 1-4 40 静荷载 Wu=5.95 − Case 2-0 动荷载 Wu×90%=5.36 31 Case 2-1 Wu×80%=4.76 238 Case 2-2 Wu×70%=4.17 113 Case 2-3 Wu×60%=3.57 1207 Case 2-4 连续级配硅砂-1 40 静荷载 Wu=8.67 − Case 3-0 动荷载 Wu×90%=7.80 1 Case 3-1 Wu×80%=6.94 1 Case 3-2 Wu×50%=4.33 40 Case 3-3 Wu×40%=3.47 860 Case 3-4 WuU×30%=2.60 1321 Case 3-5 连续级配硅砂-2 40 静荷载 Wu=6.75 − Case 4-0 动荷载 Wu×80%=5.40 15 Case 4-1 Wu×65%=4.39 34 Case 4-2 Wu×55%=3.71 330 Case 4-3 Wu×45%=3.04 1661 Case 4-4 
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