太原湿陷性黄土微观结构沿剖面变化特征研究

STUDY ON CHARACTERISTICS OF MICROSTRUCTURE VARIATIONS ALONG WITH THE DEPTH OF TAIYUAN COLLAPSIBLE LOESS

本研究对山西太原某地不同深度单线法室内自重湿陷后黄土样,通过压汞与扫描电镜观测相结合分析,描述了黄土颗粒、孔隙的形态特征并揭示其随深度的变化规律。得出如下结论:(1)黄土颗粒受风化等作用影响,随深度有细化的趋势。(2)不同深度孔隙稳定性与颗粒形态、颗粒间胶结状态等多因素相关。(3)将孔隙划分为大(>20μm)、中(5~20μm)、小(0.1~5μm)、微(<0.1μm)4种尺寸类型。大孔隙不稳定,随深度增加而减少,而微孔隙基本不受土层深度的影响。(4)中、小孔隙范围内,包括不同大小能承受一定荷载的亚稳定孔隙。在一定深度范围内,该孔隙随深度增加由大到小逐级被破坏、转化为更小的孔隙。该范围土层黄土依旧处于亚稳态结构,具有湿陷性。(5)深度增加至土体自重超过最后一级亚稳孔隙的强度界限时,小孔隙被压缩破坏,黄土结构趋于稳定,此深度以下黄土基本丧失湿陷性能。

In this study,a sample of loess saturated with water at different depths in Taiyuan,Shanxi,was analyzed through a combination of mercury intrusion and scanning electron microscopy.The morphological characteristics of loess particles and pores were described,and the law of change with depth was revealed.The following conclusions are drawn:(1)Loess particles are affected by weathering,tending to refine with depth.(2)The stability of pores at different depths is related to multiple factors such as particle morphology and inter-particle cementation state.(3)The pores at different depths are divided into four size types:large(>20-μm),medium(5~20-μm),small(0.1~5-μm),and micro(<0.1-μm).The large pores are unstable and decrease with the increase of depth,while the micro pores are hardly affected by the depth of the soil.(4)In the range of medium and small pores,there are metastable pores of different sizes that can withstand a certain load beyond which they will collapse.The pores from large to small are gradually destroyed and transformed into smaller pores as the depth and pressure increase.The loess in this condition is still in a metastable structure and is collapsible.(5)When the depth increases until the weight of the soil exceeds the strength limit of the last metastable pores,the small pores are compressed and destroyed,and the loess structure tends to be stable.Below this depth,the loess almost loses its collapsibility.