| Earth construction takes undisturbed soil as major structure or fender structure with no changes in chemical properties of materials.As an important constituent of traditional Chinese construction,the earth construction has advantages of low dissipation of energy,good thermal performance,acoustical absorption,radiation protection and environmental protection,and can serve as the model of"green construction".In recent years,the research on earth construction received much attention from the scholars,yet the absence of standard experimental method for test on mechanical properties of raw soil is a key factor hindering its development.The raw soil base material is a kind of constructional material with undisturbed raw soil as substrate which is added with some modifying adjuvants,and can be applied to building construction after simple processing without need for calcination.The paper is mainly about the standard method for test on strength of raw soil base.The compression test was done on 760 raw soil base test pieces,to make experimental investigation and theoretical analysis from the aspects of preparation of standard test piece,size of test piece,shape of test piece,setting loading parameters for the test,curing method and age of test piece,etc.The standard test method for raw soil base and setting method for strength value are suggested.The paper also studies the modifying technology to summarize the modifying formulation and figure out the design method of formulation for modifying composite admixing materials of raw soil base and calculation model,with main work and findings as follows:1.Research on the standard test method for raw soil base:as loess is widely distributed in China,the paper takes loess as main object to research the influence of different methods of test piece preparation,different processing of pressure-bearing interface,different size,shapes,different curing ages and methods on the compressive strength of test pieces by dint of a train of tests on substantive test pieces,proposes the standard test method for compression test on raw soil base cube,whose scientificaalness is verified via compressive strength test on earth materials in different regions.The summarizing finds that the test pieces was prepared by jack coMPaction method,the soil powder was laid on pressure-bearing surface in compressive strength test,the size of standard test piece adopted 100mm cube,loading speed of test was 1-3mm/min,and curing for test piece was done at 25-30 oC and under humidity of 50%-55%for 28 d.Under above conditions,the overall failure process of test piece in compressive strength test on raw soil has high reproducibility,with displacement curve of load showing consistent regularity,result data of compressive strength being stable,and discreteness being small,so this method can serve as the standard test method for compressive strength test on raw soil base.2.The research referred to Test Method for Wall Bricks to conduct compression test and bending test for 90 machine made bricks of raw soil base with different formulations and the same size and specification.The Nari and quadratically stable algorithm were introduced to analyze the discreteness and stability of result data for material strength and fracture surface appearance,etc.The compression and bending test method was tested on bricks,showing the stress distribution was even when machine made bricks of raw soil base were under stress,and the fracture surface appearance of test piece showed good reproducibility.The failure law is basically the same and has strong commonness.The discreteness and stability of test result were analyzed to find the data result was stable,reasonable and highly believable.Such method can recheck well,and is an ideal method to test the compressive and folding strength of machine made bricks of raw soil base.3.The CT scanning technique was applied to make a micromechanical analysis on the30 test pieces prepared by three preparation methods of coMPaction method(JS),jack coMPaction method(YS),machine coMPaction method(JYS)to research the weaving situation of interior materials,and compressive strength test was done to research the discreteness of data result and the relation between internal defect and actual failure morphology,thereby defining the scientific and reasonable standard method of preparing raw soil test pieces.The research found that the test pieces prepared by different methods have different internal defects,and the shaping quality of material is closely related to the strength of test piece,wherein the"jack coMPaction method"has convenient operation and convenient implementation of devices,good interior recombination of materials,small discreteness of materials of test piece,and a small influence on the test result.Maybe this preparation method is the method for preparing standard test piece of soil base material.4.Research on size effect and shape effect of compressive strength for raw soil base:The strength test was conducted on totally 300 cubic and cylindrical test pieces with different size to research the failure mechanism,strength and load displacement curve,and discreteness of data result,etc.The research found that the size effect and form effect were obvious in compression test on raw soil base,and the failure morphology and result of100mm cubic raw soil test pieces were concentrated and stable.The research also showed that the loading speed obviously influenced the test on raw soil base and the compressive strength of test piece decreased with increase of velocity.The screening method was applied to statistical data to calculate conversion coefficient for size effect strength so as to define the shape and size of test pieces as well as loading speed of equipment in standard test on compressive strength of raw soil base.5.Research on the curing mode and trial curing age of standard test piece:4 curing modes were adopted(natural curing,indoor curing,indoor+preservative film curing,curing in standard curing chamber)to make compressive strength test on totally 160 cubic raw soil test pieces at different ages(4d,14d,21d,28d),analyze the failure mechanism of test piece,failure mode,load-displacement curve and discreteness of strength data result,etc.The research found that the different curing conditions and curing time obviously influenced the failure mode of material,yet the load displacement curves were basically the same,showing high regularity.The compressive strength results of test pieces under 21d and 28d indoor curing and standard curing were basically the same,discreteness of test result was small and moisture percentage was stable.The recommended curing mode and standard curing age for standard test on raw soil test pieces are temperature of 25-30~oC,humidity of 50%-55%,and 28d.The least square method was introduced to make linear regression for the strength result of different test pieces maintained in standard curing chamber and to derive the relation,so as to provide calculation method for judging strength of test piece at different ages.6.Compressive strength test was done on totally 40 test pieces of raw soil base chosen from the area with concentration of earth construction,such as black soil in Northeast China,red soil in southeast China,loess in northwest,yellow sand soil in Xinjiang,to make a coMParative study on difference of soil in different areas,analyze the interior formation of material and the cause.The research showed that the standard test method formulated herein enabled the load displacement curve in compression test on raw soil base of different areas to show high reproducibility.Although the raw soil base has different strengths,this does not influence the feasibility of standard test method,thereby verifying the reasonableness of the this test method.The standard compressive strengths for raw soil base in different areas are ranked as follows in descending order:loess,black soil,yellow sand soil,red soil,which provides related reference for research on selection of materials of earth construction.7.Research on method of setting strength value for compressive strength test on raw soil base:Probability statistics analysis was done on test data.The function distribution was used to make estimate,hypothesis test and correlation studies as well as contrastive analysis on the similarities and differences between normal distribution estimate and Weibull distribution estimate.The result shows that Weibull distribution can more precisely describe the distribution characteristics of compressive strength of raw soil base cube,and adopting assurance rate of 95%can set and select strength standard value of raw soil base,thereby defining the method of setting standard value for strength test result of raw soil base.8.The test method and calculation method for composite admixing modifying formulation of raw soil base were researched according to preliminary study findings of the task group:The formulation design method of Montgomery and Voth single-lattice model were introduced to research modifying formulation of raw soil.The single-lattice mathematical model was used to conduct compression test on totally 120 raw soil test pieces,including 3 composite admixing materials of raw soil,gravel,fluvial sand,raw soil,gravel and cement.The strength,peak displacement and discreteness of test result was applied as reference standard to make indices regression analysis.The root of regression equation was solved using elimination method,and isogram of triangular material for raw soil base was drawn to figure out the optimal proportioning of modifying admixing amount,thereby establishing the standard test method in composite admixing situation of materials. |
PDF Full Text Request