缩尺效应对粗颗粒土静止侧压力系数影响规律试验

准确把握粗颗粒土静止侧压力系数K₀对分析以及设计土石坝等岩土工程有十分重要的作用。由于缩尺效应的存在,室内试验结果往往无法正确反映原级配粗颗粒土静止侧压力系数。为研究分析缩尺效应对粗颗粒土静止侧压力系数影响规律,找出消除其影响的方法,利用自行研制的大型K₀测试仪对某砂卵砾石料及堆石料进行了大量K₀试验。通过改变试样的颗粒最大粒径、缩尺方法,相对密实度等初始条件,研究了不同密实度条件下粗颗粒土静止侧压力系数随级配的演化规律。试验结果表明：相对密实度及缩尺方法不变时,粗颗粒土静止侧压力系数会随着颗粒最大粒径的增加而显著减小,因此,缩尺效应对粗颗粒土静止侧压力系数的影响无法忽略；缩尺方法对粗颗粒土静止侧压力系数有一定影响,相对密实度及颗粒最大粒径相同时,采用等量替代法缩尺后试样静止侧压力系数值最小,因此,采用等量替代法缩尺可减小缩尺效应对粗颗粒土静止侧压力系数的影响；相比颗粒最大粒径,相对密实度对粗粒土静止侧压力系数的影响更为显著,相对密实度越大的土样,颗粒最大粒径对粗粒土静止侧压力系数影响更明显。基于静止侧压力系数试验结果及前人的研究,建立根据室内试验结果反推现场粗颗粒土料静止侧压力系数的公式,以消除缩尺效应对粗颗粒土静止侧压力系数的影响。最后,利用K₀试验结果验证了该经验公式的准确性及适用性。

Experimental Investigation on Scale Effect of the At-rest Earth Pressure Coefficient of Coarse-grained Soil

The accurate measurement of the at-rest earth pressure coefficient K₀ for coarse-grained soil is important in the analysis and design of geotechnical engineering such as the earth rockfill dam. The laboratory K₀ test results of the coarse-grained soil usually cannot accurately reflect its K₀ value due to scale effects. To investigate the scale effect of K₀ for coarse-grained soil, and propose a method to eliminate its influence, several K₀ tests for the sandy gravel and the rockfill were performed by using a special large-size K₀ testing apparatus. By changing the maximum grain size d_M, scale method, and relative density D_r0, 24 groups of specimens were designed. K₀ tests for all specimens were conducted by a large-size K₀ apparatus, to quantitatively study the multiple influences of d_M, scale method and D_r0 on the K₀ of coarse-grained soils, and investigate the method that can predict the K₀ behavior of sandy gravel in situ based on the laboratory test results and eliminate the influence of scale effects on K₀. The test data show that: when the scale method and D_r0 are the same, K₀ for coarse-grained soil trend to decrease observably with increasing d_M, therefore scale effect results in the obvious increasing value of K₀ for coarse-grained soil, and the smaller d_M for reducing scale soil, the stronger influence of scale effect on its K₀; Scale method have some influence on K₀ for coarse-grained soil with the same d_M and D_r0, and the increasing value of K₀ for test specimens prepared by replacement technique is the least, therefore adopting the replacement technique to prepare test specimen can reduce the influence of scale effect on K₀ for coarse-grained soil; Compared with d_M, D_r0 have a stronger influence on K₀ for coarse-grained soil, and the larger D_r0, the stronger influence of d_M on K₀ for coarse-grained soil. Based on the K₀ test data of sandy gravel and previous research results, an empire equation, which could predict the K₀ behavior of sandy gravel in situ based on the laboratory test results, was proposed to eliminate the influence of scale size on K₀ for coarse-grained soil. Furthermore, the accuracy and applicability of the empire equation were verified by the K₀ test data of the rockfill.