Research On The Highway Embankment Granular Soil Fillings' Rheological Properties

Granular soil is used widely as highway embankment fillings in Hunan province, for its good engineering properties and extensive distribution, especially Redstone granular soil. However, the engineering practice shows that much pavement structure damage was caused by long-term rheological deformation. To solve this problem, the subject-Research on Highway Embankment Settlement with Affection on Pavement Structure was put forward by Hunan province Communication Science and Technology Development Fun. The main contents of this doctoral dissertation are the research results of this subject. In order to study the rheological properties of red stone granular soil, a series of rheological experiments were executed on the newly developed large tri-axial rheological apparatus. Laboratory experiment, in-situ tests and numerical calculation methods were synthetically adopted to analyze the soil-stone granular soil embankments' rheological deformation, and the main research contents and conclusions are as follows:(1) Sample tests of Redstone granular soil embankment fillings are carried out, and soil samples include dry Redstone granular soil and wet one. Experiments are consisted of compression test, direct simple shearing tests, and confining leash compressing rheological tests. In order to study the grain component percentage's changes, the sieve analysis tests for each soil samples are also carried out after these tests. The grain crushing effects of the red sandstone granular soil were studied under different stress types (compression stress, shearing stress), different load time (e.g. rheology test), and different humidity conditions (dry and wet). The tests showed that water had important effects on coarse grain crushing and final rheological values of red sandstone granular soil. For example, in the compression rheological tests, the average grain crushing rate (B_g) of wet soil samples was 145.04, while, the dry soil sample one was 88.44; the final rheological strain value of the wet soil sample was about 15.5%, while the dry soil sample one was about 9.86%. And, the tests showed that stress conditions also have great effects on coarse grain crushing rate of red sandstone granular soil. The average coarse grain crushing rate (B_g=49.14) in the confining leash compressing tests is smaller than the average coarse grain crushing rate (B_g=88.44) in rheological tests and bigger than the average coarse grain crushing rate (B_g=49.14) in the direct simple shearing tests.Through the tests studies and theory analysis, the rheological mechanism of the red sandstone granular soil was generalized as the coarse grain's crushing effects and the fine grain's filling effects. The rheological procedure of the red sandstone granular soil could be divided into three phases, in which water and stress conditions were two critical factors affecting rheology process.(2) According to the characteristic of fillings pressure in road embankments, a large tri-axial rheological apparatus (GSRT) are developed to study the rheological properties of granular soil fillings. This GSRT have four main parts, including the constant confining pressure providing part, the constant axial pressure providing part, confining pressure cell and soil sample cell, testing data measurement part. The axial pressure in GSRT is provided by the oil-gas energy depositing vessel's pressure oil with less than 5% axial pressure fluctuation during rheological tests procedure. The cell confining pressure in GSRT is provided by water head pressure in tube which could keep longtime constant during the rheological tests procedure. The confining pressure cell and soil sample cell in GSRT were directly adapted from the common large tri-axial apparatus's (SZ30-4) with the dimension (Φ=300mm, h=600mm). The axial force, the axial strain, the confining pressure, the volumetric strain, the drained water volume and the pore water pressure of the soil sample are measured. The common tri-axial tests and the tri-axial rheological tests of granular soil can be expediently executed on GSRT. The technical parameters of GSRT are as below: The constant axial pressure range with stepless free adjustment: 0～3.0MPa; The confining pressure range with four level adjustment: 50kPa, 100kPa, 150kPa, 200kPa; The granular soil samples with the large dimension (Φ=300mm, h=600mm) and large diameter grain (the maximum diameter of the grain, d_max=60mm) in the soil sample. This large triaxial rheological apparatus (GSRT) was firstly applied in road engineering research domain to study the granular soil embankment fillings in China. The development of GSRT presented the good testing tool for the granular soil embankment fillings' rheological properties and richen the soil test apparatus.(3) To study the rheological properties of granular soil embankment fillings, red stone granular soil samples were experimented on the GSRT, which were taken from the k20+240 embankment in Huaixin highway construction site.The experiment results showed that the stress condition, especially the principal stress level is the critical influencing factor of the rheological deformation properties. There were different rheological properties of the creep curves under different principal stress level. Under the low principal stress level (S=0.1), the granular soil showed the elastic properties, and there was no obvious rheological deformation. Under the principal stress level (0.2