CBR Experimental Study On Compacted Red Clay

The CBR test value is an indicator for assessing the strength of subgrade soil fillers and pavement materials.The section 3.3.3 of the “Highway Subgrade Design Specification”(JTJ D30—2015)embankment filling shall meet the following special conditions as specified in Article 4: fine-grained soils with a liquid limit greater than50% and a plasticity index greater than 26 shall not be directly As a embankment filler.Regulation 7.8.2 stipulates that red clay and high liquid limit soils should not be used directly as embankment fillings [1].If high liquid limit soils are used to fill embankments,they should be treated and put into production.Many scientific researchers in this profession have proposed different opinions on this provision,arguing that this provision regards the boundary moisture ratio as an important consideration,while ignoring the influence of soil particle characteristics on the nature of the soil,and is supported by several engineering examples.High liquid limited Red Clay is widely distributed along highways.If deep road excavation or tunnel construction is required during road construction,a large amount of earthwork is involved,whether it is modified with solidified material(such as lime)or replaced with non-high liquid limit soil.A large number of abandoned parties need to requisition land and build environmental protection projects.Both the construction progress and the project construction costs will be affected.Can red clay be used as subgrade filler? Therefore,this paper studies compacted red clay CBR test to provide reference for the construction of embankment in Red Clay area.This paper is based on the National Natural Science Foundation of “Study on the Attenuation Law of Red Clay Mechanical Properties under Wet-Dry Cycle”(No.51368010).The red clay soil sample from the new campus of Guizhou University was studied for the red clay subgrade disease in Guizhou.Subjects,through field sampling,geotechnical engineering testing techniques,indoor CBR testing,Excel data processing analysis and comparison,soil mechanics,geotechnical theory-based analysis,reference to the current highway engineering test procedures to improve,study and development The following results:(1)Test the basic physical indicators of red clay sample taken from soil:including moisture content,density,particle analysis test,specific gravity,liquid limit and plastic limit,and compaction characteristics(dry and wet methods).(2)Influence of sample preparation method on CBR value of red clay: Impact of compaction,static compaction and vibratory compaction on the CBR value of red clay.The CBR value is the highest at the optimum moisture content;the compaction degree decreases and the CBR value decreases;the CBR value of the vibro-compacted part is the highest,the CBR value of the compacted part is centered,and the CBR value of the statically compacted part is the smallest.(3)Impact of the test method on CBR value of red clay: Including the effect of water immersion mode,time of inundation,and overburden pressure on the CBR value of red clay.Lateral soaking of red clay can better reflect its true intensity;after 1day of soaking,its CBR value decays rapidly and decreases with the increase of soaking time,and basically stabilizes after 3 days of soaking;The overburden pressure during foaming can increase its CBR strength.(4)Effect of wet-dry cycle on CBR value of red clay: It includes the effects of different dry-wet cycle paths(dry and wet and dry before and after wet)and wet and dry cycles at different temperatures(300C and 1050C)on red clay CBR.During the first wet and dry cycle,the red clay CBR decayed the most.The higher the degree of compaction,the greater the attenuation of the sample CBR value,followed by a gentle,close to each curve.It is easier for the soil to be destroyed when it is dry and wet first than it is dried before it is wet.Dry-wet cycle test at high temperature is more likely to cause soil damage than normal temperature.(5)According to the "Highway Geotechnical Test Regulations"(JTG E40-2007)[2],the red clay CBR test value only meets the requirements for deep filling subgrade of 0.3~0.8m below the third and fourth grade highway road surface.In order to better match the actual conditions,the CBR test method needs to be improved.The upper immersion water is changed to lateral immersion,the overburden pressure is increased,and the wet-dry cycle is considered.The study results provide more references for the CBR value of subgrade design code in the red clay area,which is beneficial to propose an improved CBR test method suitable for evaluating the strength of the red clay filler.It has some practical engineering significance for highway subgrade construction in red clay area.For other professional direction to provide technical reference.(The body of the 5th or 4th small Arial)...