路基水泥改良膨胀土长期性能演变规律研究

Study on Long-term Property Evolution Law of Subgrade Cement Improved Expansive Soil

针对某公路路基改良膨胀土,模拟其在长期自然环境中受到的干湿循环和冻融循环作用,获取改良土自由膨胀率、无侧限抗压强度、抗剪强度的变化趋势,分析水泥改良效果的衰变特点,从长期性能角度出发探讨合理的水泥改良配比。研究表明:随着水泥掺量的增加,自由膨胀率逐渐下降,当掺量为10%时自由膨胀率最小,但掺量超过10%后,自由膨胀率又呈上升趋势;掺入水泥后,无侧限抗压强度qu抵抗干湿循环或冻融循环影响的能力明显增加,而且在较少的循环次数下qu趋于稳定;首次冻融循环时改良土的粘聚力和内摩擦角下降幅度最大,后续冻融循环的影响作用逐渐削弱;综合干湿循环试验及冻融循环试验考虑,对于水泥改良膨胀土,qu、c、各项指标在长期自然环境作用下衰减幅度均低于23%,该公路路基进行设计时应考虑这部分的衰减,同时从兼顾效果和成本的角度考虑,建议水泥掺量控制在10%左右。

Focused on a highway subgrade improved expansive soil,this paper simulated the dry-wet cycle and the freeze-thaw cycle effect in long-term natural environment.The variation trend of free expansion rate,unconfined compressive strength and shear strength was acquired.The decay characteristics of cement improvement effect was analyzed.From a long-term perspective,the reasonable ratio of cement to improve was discussed.The study shows that with the increase of cement content,the free expansion rate decreases gradually.When the cement content is 10%,the free expansion rate is the smallest.However,when the cement content exceeds 10%,the free expansion rate rises again.After cement addition,the ability of unconfined compression strength qu to resist the effects of dry-wet cycle or freeze-thaw cycles is significantly increased,and qu tends to stabilize with fewer cycles.During the first freeze-thaw cycle,the decreasing amplitude of cohesion and internal friction angle of the improved soil are the largest,while the influence of subsequent freeze-thaw cycle is gradually weakened.Considering the dry-wet cycle test and freeze-thaw cycle test for cement improved expansive soil comprehensively,qu and shear strength parameters attenuation in the long-term natural environment are less than 23%,the highway subgrade design should consider this part of attenuation.From the improvement effect and cost point,it is suggested that cement mixing ratio should be controlled at around 10%.