Study On Soil Characteristics And Filling Performance Of Guangxi Red Clay

Due to the differences in geological and climatic conditions, resulting in the diversity of laterization process of soil in different regions, the final result is that red clay is of particularly strong regionality and nature of it quite differs in different regions. Only a detailed understanding of the characteristics of local red clay is helpful to better play its role in engineering applications. However, the research on the mineral composition and micro structure of red clay in Guangxi from the view of soil science is few, and previous studies have failed to conduct systematic analysis linking soil science and clay filling properties.Given the above, this paper on the red clay in Guangxi studied in the following three aspects:1, the basic physical and mechanical properties; 2, micro structure and composition; 3, clay filling properties under different soaking conditions and improved properties. It could be found that the red clay at different laterization stages has different engineering properties. The main conclusions are as follows:(1) Among red clay in Guangxi, physical properties of soil samples in Wuming, Guilin and Liuzhou, Tiebei, Lailiang vary greatly on the whole, which clearly are divided into two groups. In the indicators describing expansion or contraction properties (such as:free swell ratio, linear shrinkage ratio, volume shrinkage ratio, coefficient of contraction), red clay in Wuming and Guilin is smaller than that of Liuzhou, Tiebei, and Lailiang. For the permeability coefficient, red clay in Wuming and Guilin is much higher than that in Liuzhou, Tiebei, and Lailiang. The high liquid limit of red clay mainly caused by a larger water storage space inside the aggregates after soil granulation.(2) After a series of tests and analyses, it shows that:mineral compositions of red clay in Wuming are kaolinite, goethite and gibbsite; that of Guilin are kaolinite, goethite, gibbsite, and quartz; and that of Liuzhou, Tiebei and Lailiang are kaolinite, goethite, illite, and quartz those four kinds of minerals. Moreover, the soil layer of soil sectional in Tiebei near the bedrock also contains smectites minerals that makes themselves get higher free swell ratio. By means of the combination of Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS), it is found that the morphology of the same mineral of red clay in different places is different because of the different processes of laterization. with a mineral found in red clay in different locations in the morphology is different. In SEM picture with over 40,000 times enlargement ratio, the particle morphology cements can be saw.(3) No matter what the order of mineral evolution is, gibbsite is the important mark mineral to divide the stage of the laterization. The appearance of gibbsite means that has entered into the highest stage of the laterization. The content of quartz directly affects silica-alumina ratio and also reflects the laterization stage (that is the degree of desilication)in a certain extent. If the content of quartz is small, the possibility of entering the stage of the laterization may be higher. Red clays in Wuming and Guilin all contain gibbsite, and the content of quartz is low (that of Wuming not containing quartz), so it can be judged that red clays in Wuming and Guilin are on the third stage of laterization on the whole, that is the highest stage -- " allitic weathering desilication " stage; and red clays in Liuzhou, Tiebei and Lailiang do not contain gibbsite, and the content of quartz is higher than that of Wuming and Guilin. Therefore, red clays in Liuzhou, Tiebei and Lailiang shouid be on the second stage of laterization--" rich ferromanganese " stage. Compared the physical properties of red clay in Wuming and Guilin with that of Guilin Liuzhou, Tiebei and Lailiang, there exists remarkable differences in the overall, mainly resulting from different stage of laterization. Although red clays in Wuming and Guilin are both in the highest stage, after comprehensively analyzing the result of the particle size and the liquid plastic limit test, it can be found that red clay in Wuming contains a lot of iron concretion and pellets of silt fractionits whose granulation is stronger than red clay in Guilin. Thus, it can be concluded that the degree of laterization of red clay in Wuming is deeper than that of Guilin, and has a stronger lateritization effect.(4) The maximum dry density of red clay is mainly controlled by distribution of size, mineral composition and granulation degree (that is the depth of laterization). Red clays in Liuzhou, Tie Bei, and Lailiang has better distribution of size, much more quartz and lower granulation degree, so the maximum dry density is higher. While red clay in Wuming and Guilin are opposite to it, the maximum dry density is low. The degree of laterization of red clay in Wuming (granulation) is deeper than that of Guiliin, but due to the great richness of Fe and a lot of generation of Fe concretion, the maximum dry density of red clay in Wumibng is higher instead than that of Guilin.The CBR value of red clay is influenced by the maximum dry density, degree of swelling and the stage of lateritization. In the earlier period of lateritization, active cement failed to obviously show in the macro. The intensity of CBR is controlled by dry density and degree of swelling, such as red clays in Liuzhou, Tiebei and Lailiang. In the late stage of the late period, the strength of the CBR is mainly provided by the bonding strength of the cement, but it is not right that the deeper lateritization, the better red clay. Because the degree of lateritization is too deep and the cement is too old, it makes the standard CBR value of red clay in Wuming is lower than that of Guilin.Engineering properties of red clay in Wuming are mainly controlled by soil clay in the earth mass and silt fraction granular structure of clay characteristics in the high degree of saturation, resulting that the existence of coarse particle group in the earth mass>0.5mm (> 20% content) can’t improve CBR intensity after soaking and improve the range of water stability. In other words, it cannot produce similar improvement effect of adding coarse particle to the soil.(5) In the same sand content ratio, the decline range of plastic index of red clay in Wuming is obviously larger than that of the Guilin red clay. Mainly because of the deeper lateritization of red clay in Wuming, serious aging of the cement, and greatly decline of the specific surface area, its soil water effect is obviously weaken. While lateritization of red clay in Guilin is slightly lower, its cements are still of higher activity. It can give full play to the advantages of large specific surface area of active cement after mixing with adding sand, which makes the soil water effect less obvious and the plastic index decrease slightly.The CBR intensity of the red clay added sand is also affected by the aging of the cement. The cement of red clay in Guilin has a higher activity, and it can rebuild new connection by the disturbance after compaction and the establishment of this kind of connection is random, and has no rules. Therefore, it shows in the macro that the CBC peak value change a little with the increase of sand content ratio of red clay in Guilin. While excessive granulation of red clay in Wuming, intergranular cement has become aging and soil particle composition in the earth mass have tended to sand. The CBR peak value of red clay in Wuming becomes high only due to the increase of the coarse particles and shape the skeleton of earth mass. When the sand content ratio reaches 40%, the distribution of size is too coarse (distribution unreasonable), the CBR peak value is decreased instead.When the red clay is improved by mixing with lime, it will show different rule with ordinary high liquid limit soil mixing with lime:when lime content ratio of ordinary high liquid limit soil or expansive soil increases, coarse particles will increase, liquid limit will continuous decline, and the bearing capacity will get continuous improvement; while lime content ratio of red clay increases, coarse particles grow in number and the increase of bearing capacity of the red clay, liquid limit maintains at a relatively stable level. The main reason is that the water retention principle of the earth mass differs from the ordinary high liquid limit soil or expansive soil and red clay. The former mainly relys on thickening of the water film on the surface of clay to increase the water content.When fine particles are connected into coarse particles after adding lime, the specific surface area and water retention capacity decrease. While the latter mainly relys on internal pores of granular structure in the earth mass and pores of part of aggregate to store water, and small aggregates are connected into aggregates after adding lime, which has little effect on water storage volume of the internal pores of aggregates. Therefore, even the ratio of lime increases, it can’t decrease liquid limit.