Influence of Preconsolidation on the Shear Strength of the Soft Soil in Floodplain Facies of Yangtze River
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摘要: 固结快剪试验是获取软土固结不排水抗剪强度的重要方法,长江漫滩相软土具有压缩性高、孔隙比大、含水率高、渗透率低、固结时间长等特点,严重影响了软土固结快剪试验的生产效率。为研究预固结对长江漫滩相软土抗剪强度的影响,并探索提高漫滩相软土固结快剪试验效率的方法,以南京长江漫滩相软土为研究对象,制定了预固结–卸载剪切、正常固结剪切、预固结–卸载–再固结剪切3种试验方案,开展了一系列固结和剪切试验。试验研究表明:长江漫滩相软土是一种前期固结迅速,后期固结稳定缓慢的软土;固结25 min时固结度可以达到95%,而完全固结稳定需要5~8 h;软土抗剪强度均随固结度U的增加呈增大趋势,其增长速度逐渐减缓,各荷载条件下抗剪强度随U提高的增长幅度基本相同;当固结度为70%~80%时,其抗剪强度达到完全固结时的90%~95%。研究成果可为软土固结快剪试验的方法改进提供参考。Abstract: The consolidation fast shear test is an important method to obtain the consolidation and undrained shear strength of soft soil, and the soft soil of the Yangtze floodplain has the characteristics of high compressibility, large pore ratio, high moisture content, low permeability, and long consolidation time, which seriously affects the production efficiency of soft soil consolidation fast shear test. To study the effect of preconsolidation on the shear strength of the Yangtze River floodplain facies soft soil and explore the method to improve the efficiency of fast shear tests for consolidation of floodplain soft soil, a series of consolidation and shear tests were carried out, taking the Nanjing Yangtze River floodplain soft soil as the research object. The results show that the Yangtze River floodplain facies soft soil is a kind of soft soil with rapid consolidation in the early stage and stable and slow consolidation in the later stage. The consolidation degree can reach 95% when consolidating for 25 minutes, while it takes 5~8 hours to fully consolidate and stabilize. The shear strength of soft soil increased with the increase of consolidation degree U, and its growth rate gradually slowed down. The increase of shear strength with the increase of U under each load condition was basically the same. When the degree of consolidation is 70%~80%, its shear strength reaches 90%~95% of that when fully consolidated. This study can provide a reference for improving the fast shear test method of soft soil consolidation.
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表 1 原状土基本物理力学性质指标
指标 含水率
/%密度
/(g·cm−3)孔隙比
e比重
Gs液限
wL/%塑限
wP/%压缩系数
/MPa−1均值 39.89 1.79 1.12 2.72 33.60 21.68 0.60 表 2 试验方案
试验压力/kPa 试验过程 50 预固结–
卸载剪切正常固结
剪切预固结–卸载–
再固结剪切100 150 200 表 3 固结度U及对应固结时间t
固结时间t 固结度U /% 固结时间t 固结度U /% 0:00:04 51 0:25:00 95 0:00:15 58 0:30:15 95 0:01:00 72 0:36:00 95 0:02:15 82 0:42:15 95 0:04:00 87 0:49:00 95 0:06:15 90 1:00:00 96 0:09:00 92 2:00:00 97 0:12:15 93 3:00:00 99 0:16:00 93 4:00:00 99 0:20:15 94 5:00:00 100 表 4 不同试验方案及压力下的抗剪强度平均值
固结压力/kPa 各试验方案抗剪强度平均值/kPa 预固结–
卸载剪切正常固结
剪切预固结–卸载–
再固结剪切50 32.00 31.56 32.82 100 61.30 64.85 68.82 150 84.30 87.84 91.70 200 103.60 109.18 112.83 -
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