软黏土的结构性及压缩特性研究

Study on Soil Structure and Compressibility of Soft Clay

对天然土以及重塑土进行了压缩试验,分析了原状土和重塑土的压缩特征。结果表明,天然沉积软黏土具有明显的结构性特征,结构屈服应力与先期固结压力的比值σk/pc可以用来表征天然软黏土的结构性强弱程度;软黏土孔隙的组构特点是其压缩曲线不同于非结构性土的重要原因;淤泥土的结构性明显,黏质粉土结构性很弱;土体的宏观变形过程可以通过对微观结构的分析来描述,利用宏观与微观相结合的研究方法来论证土的基本特性;软黏土结构性的地域性很强,埋深较浅且处于不透水层的天然软黏土的先期固结压力较低,先期固结压力的作用使得软黏土形成结构强度,结构强度的大小是同类软黏土结构性程度强弱的重要体现;原状土和重塑土侧限压缩时的应力应变关系曲线呈上凹形,压缩模量随着荷载的增大而增长,对于成层分布的地基土而言,欲准确地计算地基沉降,应合理地选择使用随外荷载变化的压缩模量,使压缩模量随着深度的增加而增加,以符合地基土的压缩特性。得到的结论对软黏土结构性的研究和地基基础沉降计算具有一定的指导意义和工程实用价值。

Compression tests on undisturbed and reconstituted soil were applied to analyze compressibility.The results show that natural sediment soft clay has apparent character of soil structure,and the ratio ofσk/pcmeaning structural yield pressure to pre-consolidation pressure reflects the degree of structure.Pores of soft clay have the fabric which largely causes the differences between soft clay and non-structural soil on the aspect of compressibility.The structure of silt soil is obvious,by contrast clayey silt has little structure.The macroscopic deformation process of soil can be described by the analysis of the microstructure,and the basic characteristics of the soil can be demonstrated by the combination of the macroscopic and microscopic methods.The features of structure vary from region to region.The pre-consolidation pressure was low because of the buried depth of natural soft soil was shallow,as well as the soft soil layer lied in impervious bed.Furthermore,the effect of pre-consolidation pressure prompted the soft clay to have structural strength.The magnitude of structural strength is closely relevant to the level ofsoil structure.In the confined compression tests,the curve of'σ-ε'is concave upward,so,what can be inferred is that the modulus of compression increases due to the load increasing.With regard to layered subsoil,Esshould be reasonably selected so that foundation settlement can be correctly calculated.It means that the Esof foundation soil should increase with buried depth.The series of conclusions have significance to studying structure of soft clay,calculating foundation settlement and engineering practice.