Engineering Characteristics and Road Performance of Cement-Stabilized Expansive Soil for Heavy Haul Railways
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摘要: 为了探究重载铁路水泥改良膨胀土路基填料的工程特性及路用性能,采用室内动三轴试验、微观结构试验、路基原位动力试验相结合的方法,揭示了膨胀土掺入水泥3%~5%改良前后静态指标与动态指标的变化特征,分析了水泥掺量5%和3%改良膨胀土分别用作重载铁路基床底层及以下路堤填料建设期的工作性能,评估了服役期列车动载作用下路基的动力稳定性. 研究结果表明:膨胀土掺入3%~5%水泥改良后,强度提高同时胀缩性显著降低,水稳定性提高3~4倍;相比重塑素膨胀土,水泥掺量3%~5%改良膨胀土临界动应力提高5~6倍;检测路基压密程度与强度指标满足规范且有较大富裕,监测路基中线地基沉降在铺轨前处于稳定状态;原位动力测试表明列车动载作用下路基的动应力沿深度逐渐衰减,在基床表层与基床底层范围内最大衰减量分别可达40%和80%以上,动应力影响深度是基床设计厚度的1.4~1.8倍,动应力影响深度范围内路基的动应力值远小于同位置填料的临界动应力,运营期路基动力稳定性满足安全服役要求. 研究成果能够为重载铁路水泥改良膨胀土路基精细化建设养修提供理论参考.Abstract: In order to explore the engineering characteristics and road performance of cement-stabilized expansive soil filler when it used as the subgrade filler of heavy haul railways, the dynamic triaxial tests, micro-structure tests and in-situ dynamic tests of subgrade were combined to reveal the variation characteristics of static and dynamic indexes when 3%−5% cement was added into expansive soil. The 5% and 3% modified expansive soil was analyzed in terms of their working performances when used as filler of subgrade bottom and embankment of heavy haul railways, and the dynamic stability of the subgrade in service period was evaluated under dynamic train load. The results show that the mix of 3%−5% cement can increase the strength of expansive soil, significantly reduce the swelling and shrinkage, and increase the water stability by 3−4 times. Compared with remolded expansive soil, the critical dynamic stress of the improved expansive soil with 3%−5% cement is increased by 5−6 times. The compaction degree and strength index of the test subgrade meet the standard with moderate margin. The foundation settlement of the middle line for the test subgrade is in the stable state before rail laying. In-situ dynamic tests show that the dynamic stress of subgrade gradually decreases along with the depth under the action of dynamic train load. The maximum attenuation can reach 40% and 80% respectively in the range of the surface layer and the bottom layer of the subgrade. The influence depth of dynamic stress is 1.4−1.8 times the design thickness of the subgrade. The dynamic stress value of roadbed in the influence depth of dynamic stress is far less than the critical dynamic stress of the filler at the same position, demonstrating that the dynamic stability of the subgrade meets the requirements of safe service.
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表 1 膨胀土掺水泥改良前后指标对比
Table 1. Indicator comparison of expansive soil before and after being mixed with cement
土样 颗粒含量/% 胀缩特性 强度指标 水稳系数 大于
0.075 mm
粒径0.075~
0.005 mm
粒径小于
0.005 mm
粒径自由
膨胀率有荷
膨胀率
(25 kPa)有荷
膨胀率
(50 kPa)膨胀
力/kPa收缩
系数缩限/
%黏聚
力/kPa内摩
擦角/
(°)7 d 饱和
无侧限
抗压强
度/kPa压实
度90%压实
度95%天然
土样5.4 50.3 44.3 66 6.80 6.7 129 0.91 10.2 45 21.4 44 0.18 0.25 水泥掺
量 3%20.5 52.2 27.3 32 0.10 < 0 14 0.73 10.2 183 24.6 866 0.81 0.85 水泥掺
量 4%21.1 55.8 23.1 28 0.06 < 0 10 0.62 11.9 201 33.2 1 018 0.84 0.88 水泥掺
量 5%23.0 55.0 22.0 23 < 0 < 0 1 0.52 11.2 291 35.5 1 170 0.83 0.89 表 2 水泥与石灰改良部分指标结果对比
Table 2. Comparison of cement and lime improvement indicators
土样 自由
膨胀率有荷膨胀
率(25 kPa)有荷膨胀
率(50 kPa)膨胀
力/kPa7 d 饱和
无侧限
强度/kPa天然
土样66 6.80 6.7 129 44 水泥掺
量 3%32 0.10 < 0 14 866 石灰掺
量 3%27 < 0 < 0 12 308 水泥掺
量 4%28 0.06 < 0 10 1 018 石灰掺
量 4%24 < 0 < 0 5 477 水泥掺
量 5%23 < 0 < 0 1 1 170 石灰掺
量 5%21 < 0 < 0 1 786 表 3 试验参数
Table 3. Test parameters
试验工况 频率/Hz 固结比 固结围压/kPa 重塑素膨胀土 1 1.0 15,30,60 2.0 15,30,60 5 1.0 15,30,60 2.0 15,30,60 3% 水泥改良膨胀土 1 1.0 15,30,60 5 1.0 15,30,60 5% 水泥改良膨胀土 1 1.0 15,30,60 5 1.0 15,30,60 表 4 临界动应力
Table 4. Critical dynamic stress
土样类型 围压/kPa 频率/Hz 临界动应力/kPa 土样类型 围压/kPa 频率/Hz 临界动应力/kPa 范围值 范围
平均值范围值 范围
平均值重塑素
膨胀土30 1 22.30~31.50 26.90 重塑素
膨胀土30 5 21.60~30.80 26.20 60 1 28.60~34.90 31.75 60 5 27.20~33.70 30.45 3% 水泥改
良膨胀土15 1 151.20~185.70 168.45 5% 水泥改
良膨胀土15 1 142.50~208.10 175.30 30 1 157.50~203.50 180.30 30 1 148.30~233.50 190.90 60 1 182.30~233.10 207.70 60 1 202.50~249.70 226.10 15 5 148.80~181.40 165.10 15 5 147.80~199.60 173.70 30 5 152.30~200.10 176.20 30 5 145.60~231.70 188.65 表 5 路基不同深处动应力与静应力汇总
Table 5. Summary of dynamic stress and static stress at different subgrade depths
深度/m 静应力/kPa 轴重 21 t 轴重 25 t 轴重 30 t 动应力/kPa 动、静应力比值 动应力/kPa 动、静应力比值 动应力/kPa 动、静应力比值 0 17.7 81.61 4.61 98.92 5.59 118.46 6.69 0.6 30.0 48.31 1.61 58.12 1.94 71.45 2.38 1.5 46.2 28.14 0.61 31.48 0.68 39.22 0.85 2.5 64.2 16.12 0.25 21.86 0.34 25.52 0.40 3.5 73.2 12.32 0.17 18.92 0.26 21.03 0.29 4.5 91.2 10.67 0.12 15.81 0.17 17.25 0.19 表 6 路基长期动力稳定性评估
Table 6. Long-term dynamic stability evaluation of subgrade
路基深度/m 路基动应力/kPa 临界动应力/kPa 评估结果 轴重 25 t 轴重 30 t 0~0.6 58.12~98.92 71.45~118.46 257.00~380.00 稳定 0.6~2.5 21.86~58.12 25.52~71.45 148.80~233.10 稳定 2.5~4.5 15.81~21.86 17.25~25.25 142.50~249.70 稳定 -
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