掺细料砾石土的动孔压特性探讨

地震荷载作用下发生滑坡的滑动带通常由粗颗粒与细颗粒组成。滑带土的动力性质及动孔隙水压力的发展对边坡的稳定性至关重要。对掺细料砾石混合土进行动三轴试验来探讨细料(粒径小于0.5mm)含量对砾石(粒径6~20mm)混合土的动孔压特性的影响,进行细料含量为0%、20%和40%的三组试样的动三轴试验,采用固结围压为100kPa、固结应力比为1.0、频率为1.0Hz,施加轴向动应力分别为0.50、0.55、0.60和0.65kN,得到动孔压的变化规律。试验发现:(1)相同激振力作用下,随着细料含量的增加,动孔隙水压力增长速度逐渐变缓;相同细料含量时,随着激振力的增大,动孔隙水压力增长速度变快。(2)激振力较大和细料含量较少时,动孔隙水压力在较少的振次下达到较大值并趋于稳定。(3)细料含量为20%的砾石混合土试样在试验终止时的振动次数最大,细料含量为40%的砾石混合土在试验终止时的振动次数最小。(4)当细粒含量为0%和20%时,试验终止时最终的孔压都可以接近固结围压;当细粒含量为40%,激振力较大时,试验终止时最终的孔压才接近固结围压,而激振力较小时最终的孔压远远没有达到固结围压。

Discussion on Dynamic Pore Pressure Properties of GravellySoil Mixed with Fine Grains

Under seismic loading, sliding bands originating from landslides are usually composed of coarse and fine grains.The dynamic features of sliding-band soils and the development of dynamic pore water pressure during the cyclic loading process are extremely important to the stability of slopes.Dynamically cyclic triaxial tests on gravels including fine particles smaller than 0.5 mm were conducted to investigate the influence of fine particles on the dynamic pore water pressure features of these mixed soil gravels of 6~20 mm.Three groups of specimens with fine contents of 0%, 20%, and 40% were tested using a triaxial dynamic apparatus wherein the consolidation confining pressure was 100 kPa, the ratio of consolidation was 1.0, and the frequency was 1.0 Hz.Dynamic axially cyclic stress of 0.50 kN, 0.55 kN, 0.60 kN, and 0.65 kN was applied to each group.The specimen shape was cylindrical, and the specimen size was 100 mm × 200 mm.The dry densities of the specimens with fine contents of 0%, 20%, and 40% were 1.605 g/cm³;1.741 g/cm³, and 1.570 g/cm³, respectively.After the tests were concluded, the development of dynamic pore water pressure and its evolution laws were obtained and analyzed in detail. It was experimentally determined that under the same dynamic load, a more rapid increase in dynamic pore water pressure occurs when the fine soil particle content is small;when the content is high, the speed is lower.For the same fine grain content, a small dynamic load resulted in a low speed increase of dynamic pore water pressure; when the dynamic load was high, the increase was rapid. Moreover, a larger dynamic load and smaller fine grain content resulted in relatively larger dynamic pore water pressure of soil specimens that tended to be stable.The number of the dynamic cycles was largest (smallest) when the specimen with fine content of 20% (40%) was wreck.At the end of the experiment, the pore water pressure of the soil specimen was close to the consolidation confining pressure with fine contents of 0% and 20%.For the specimens of 40% fine content, the pore water pressure was close to the consolidation confining pressure under a high dynamic load.