改进的膨胀土侧限膨胀试验研究

Modified lateral confined swelling tests on expansive soils

为量测膨胀土在侧限浸水和不同上覆荷载下的竖向膨胀率和侧向膨胀力,通过改进常规侧限膨胀试验装置和方法,确保了施加上覆荷载后试样浸水前初始湿密状态不变,消除了制样产生的初始水平应力,并将侧向膨胀力从总的侧向力中区分出来。采用改进的试验装置和方法,以特定初始湿密状态下的广西百色中等膨胀土为研究对象,分别进行了常规侧限膨胀试验和改进的侧限膨胀平行性试验。试验结果表明:常规侧限膨胀试验中的上覆荷载会改变试样初始湿密状态,测得的竖向膨胀率偏小7%~95%;因制样产生的初始水平应力会使最终侧压力偏小16.1%~43.5%;分级加载和逐级卸载的改进侧限膨胀试验结果具有良好的一致性和可重复性;竖向膨胀率随着上覆荷载逐渐减小,引入相对膨胀率和相对压力,可建立反映极限膨胀状态的幂函数拟合公式;侧向膨胀力与上覆荷载相关并随之增大而逐渐增大,当上覆荷载增至竖向膨胀力时侧向膨胀力达到最大,两者之间可用双曲线较好拟合。研究成果可为膨胀模型的建立以及膨胀土地区支挡结构物设计计算提供参考。

In order to measure the vertical swelling ratio and lateral swelling pressure under different vertical loading and confined conditions during soaking, the conventional confined swelling test apparatus and method are modified to ensure the consistency of the initial water content and the dry density of specimens before soaking and loading, getting rid of the initial horizontal stress caused by specimen preparation and distinguishing the lateral swelling pressure from the total lateral pressure. Using the modified apparatus and method, the conventional and modified confined swelling parallel tests are respectively carried out on the expansive soils with medium swelling potential from Baise County in Guangxi Province with specific water content and dry density. The test results show that the initial water content and dry density will change due to vertical loading during conventional tests, resulting in underestimating vertical swelling ratio measured by 7% to 95%, and that the existence of the initial horizontal stress produced by specimen preparation will underestimate the lateral pressure measured by 16.1% to 43.5%. The results of multi-stage loading and step unloading tests show the great consistency and repeatability. The vertical swelling ratio decreases with the increase of the vertical loads, and a fitting formula performing the ultimate swelling state based on power function is set up by relative swelling ratio and relative swelling pressure. While the lateral swelling pressure increases with the increase of the vertical loads, reaching its maximum value with the increasing vertical loads to the vertical swelling pressure, a hyperbolic function can fit well between the upper loads and the lateral swelling pressures. The achievements may provide references for establishing a swelling model and designing retaining structures in expansive soil areas.