Feasibility of predicting settlement of medium compression soil foundation with centrifuge model tests
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摘要: 应用TLJ-2型土工离心试验机, 采用停机加载法与变加速度加载法, 研究了海南东环客运专线和胶济客运专线中等压缩性土地基的沉降特性, 并与现场填筑试验结果进行了对比, 分析了应用离心模型试验方法预测原型地基沉降的主要影响因素与预测精度。研究结果表明: 采用2种离心模型试验方法所得地基沉降比现场填筑试验值大, 且随着地基深度增大, 沉降修正系数减小, 沉降差异增大; 在现场填筑试验中, 地基表层6.0m范围内产生的沉降占地基总沉降的比例大于45%, 而离心模型试验的比例小于20%;2种离心模型试验方法产生的地基沉降具有相似的沉降特性, 路基填筑期完成的沉降占总沉降比例相同, 均为88%, 但采用停机加载法产生的地基沉降比变加速度法大1倍左右。可见, 采用2种离心模型试验方法均较难预测原型中等压缩性土地基的沉降, 但可进行定性分析。Abstract: Centrifuge-stopped loading method and acceleration-variable centrifuge-run loading method were carried out by using TLJ-2 geotechnical centrifuge, the settlement characteristics of medium compression soil foundations of Haidong High-speed Railway and Jiaoji High-speed Railway were researched and compared with that of field-filling tests, and the main factors influencing the precisions of predicting prototype foundation settlement with centrifuge tests were studied.Research result indicates that the settlements from centrifuge tests are larger than that from filling tests, and their correction factors decrease and the settlement differences increase with the increase of foundation depth.The settlements within 6.0 m from filling tests are more than 45% of total settlement, but the settlements from centrifuge tests are less than 20% of total settlement.The properties of the settlements from two centrifuge tests are similar, the settlements in subgrade filling are 88% of total settlements, but the settlement from the first method is about twice of that from the second method.Obviously, it is very hard to predict the foundation settlement of medium compression soil by using centrifuge tests, but the tests can be used for qualitative analysis.
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图 6 未扣除加载期沉降时荷载、沉降与时间关系
Figure 6. Relationships of loads, settlements and time with loading stage's settlements
图 7 扣除加载期沉降后荷载、沉降与时间关系
Figure 7. Relationships of loads, settlements and time without loading stage's settlements
表 1 地基土物理参数
Table 1. Physical parameters of foundation soils
断面 土名 参数 深度/m 含水量/% 干密度/(g·cm-3) DK67+620(停机加载法) 花岗岩全风化土(1) 0~6.0 26.52 1.53 花岗岩全风化土(2) 6.0~18.0 28.01 1.52 花岗岩全风化土(3) 18.0~24.0 35.37 1.46 DK67+630(变加速度加载法) 花岗岩全风化土(1) 0~6.0 25.45 1.55 花岗岩全风化土(2) 6.0~15.0 27.88 1.53 花岗岩全风化土(3) 15.0~21.0 32.08 1.49 DK218+950(停机加载法) 粉质粘土 0~11.2 9.11 1.80 粉土 11.2~18.2 14.98 1.70 黄土质粉质粘土 18.2~28.1 19.85 1.65 DK218+950(变加速度加载法) 粉质粘土 0~11.2 9.35 1.80 粉土 11.2~18.2 14.63 1.71 黄土质粉质粘土 18.2~28.1 19.94 1.65 
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表 2 恒载期地基应力对比
Table 2. Comparison of foundation stresses under constant loads
海东线 DK67+620(停机加载法) DK67+630(变加速度加载法) 距地基面深度/cm 0 3.8 8.0 0 4.0 8.0 地基应力/kPa 总应力 自重应力 总应力 自重应力 总应力 自重应力 总应力 自重应力 总应力 自重应力 总应力 自重应力 施加的路基荷载 第1级 24.0 0.0 65.4 42.6 114.4 91.2 20.4 0.0 33.0 11.3 44.5 22.9 第2级 41.4 0.0 82.1 42.6 128.3 91.2 34.7 0.0 52.5 22.4 70.2 45.6 第3级 57.3 0.0 96.1 42.6 139.5 91.2 53.4 0.0 81.5 33.7 108.3 68.4 第4级 82.6 0.0 118.0 42.6 158.1 91.2 79.5 0.0 117.0 45.0 154.4 91.3 胶济线 DK218+950(停机加载法) DK218+950(变加速度加载法) 距地基面深度/cm 0 4.0 14.7 0 4.0 14.7 地基应力/kPa 总应力 自重应力 总应力 自重应力 总应力 自重应力 总应力 自重应力 总应力 自重应力 总应力 自重应力 施加的路基荷载 第1级 31.2 0.0 87.7 61.8 244.9 236.1 26.5 0.0 38.1 15.5 71.7 59.0 第2级 73.4 0.0 126.6 61.8 279.8 236.1 56.9 0.0 82.4 30.8 154.1 117.7 第3级 88.9 0.0 141.7 61.8 283.4 236.1 81.0 0.0 119.6 46.2 220.0 176.6 第4级 103.6 0.0 153.2 61.8 288.0 236.1 99.7 0.0 152.3 61.6 294.5 235.4
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表 3 地基沉降对比
Table 3. Comparison of foundation settlements
试验断面 距地基面深度/m 离心模型试验 现场填筑试验[12] 沉降修正系数 未扣除加载期沉降 扣除加载期沉降 总沉降/mm 填筑期沉降占总沉降比例/% 未扣除加载期沉降 扣除加载期沉降 总沉降/mm 填筑期沉降占总沉降比例/% 总沉降/mm 填筑期沉降占总沉降比例/% 海东线DK67+620(停机加载法) 0 808.2 89 173.7 51 123.0 95 0.15 0.71 6.0 660.0 88 153.5 48 56.0 93 0.09 0.36 10.5 526.3 87 124.8 43 40.0 93 0.08 0.32 海东线DK67+630(变加速度加载法) 0 420.4 89 154.6 69 114.0 94 0.27 0.74 6.0 355.7 87 129.7 66 62.0 95 0.17 0.48 13.0 270.6 89 98.0 69 40.0 93 0.15 0.41 胶济线DK218+950(停机加载法) 0 438.4 89 107.0 54 96.0 92 0.22 0.90 胶济线DK218+950(变加速度加载法) 0 228.1 88 70.4 61 96.0 92 0.42 1.36 6.4 213.7 88 69.3 59 42.4 94 0.20 0.61 11.0 198.7 86 64.4 60 26.2 94 0.13 0.41
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表 4 地基压缩量对比
Table 4. Comparison of foundation compressions
试验断面 关键参数 离心模型试验 现场填筑试验[12] 未扣除加载期沉降 扣除加载期沉降 海东线DK67+620(停机加载法) 计算深度/m 0~6.0 0~10.5 0~6.0 0~10.5 0~6.0 0~10.5 压缩量占总沉降比例/% 18.3 34.9 11.6 28.2 54.5 67.5 计算深度/m 0~6.0 6.0~10.5 0~6.0 6.0~10.5 0~6.0 6.0~10.5 单位厚度压缩量/mm 24.7 29.7 3.4 6.4 11.2 3.6 海东线DK67+630(变加速度加载法) 计算深度/m 0~6.0 0~13.0 0~6.0 0~13.0 0~6.0 0~13.0 压缩量占总沉降比例/% 15.4 35.6 16.1 36.6 45.6 64.9 计算深度/m 0~6.0 6.0~13.0 0~6.0 6.0~13.0 0~6.0 6.0~13.0 单位厚度压缩量/mm 10.8 12.2 4.2 4.5 8.7 3.1 胶济线DK218+950(变加速度加载法) 计算深度/m 0~6.4 0~11.0 0~6.4 0~11.0 0~6.4 0~11.0 压缩量占总沉降比例/% 6.3 12.9 1.6 8.5 55.8 72.7 计算深度/m 0~6.4 6.4~11.0 0~6.4 6.4~11.0 0~6.4 6.4~11.0 单位厚度压缩量/mm 2.3 3.3 0.2 1.1 8.4 3.5
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