Experimental Research On Treatmenttechnology And Stability Of Collapsible Loess High Embankment Foundation

With the full implementation of the western development strategy and the rapiddevelopment of the national economy，large scale development of the collapsibleloess mountain area is inexorable， and large numbers of collapsible loess highembankment formed by fill compaction will also appear. The deformation and stabilityproblems of such foundation receive an extensive concern from the engineeringtechnicians and the academia. On the basis of the related research achievements at homeand abroad, this paper mainly researches problems of reinforcement treatment ofcollapsible loess foundation, compaction of loess, deformation and strength property ofcompacted loess, deformation modes and stability of high sticking slope, anddeformation law of deep cutting fill foundation. Relying on the Lvliang airport testsection, the following research works are carried out.(1)Large scale geotechnical centrifuge model tests are carried out on models madeby intact loess and remolded loess. Under the condition of natural water content,problems about the collapsed loess high slope and deep-graben embankment, includingthe stability, the dominant factor of deformation, the post-construction settlement, thecharacteristics of deformation rate, the relation between post construction settlementand deformation stability time, and the failure modes of models and the reasons whensoil is saturated, are studied. On this basis, the reasonable gradient and the stabilityunder different moisture contents are analyzed by numerical methods.(2)With the use of dynamic sounding tests, loess collapsibility tests and fieldloading tests, this paper analyzes the change rule of physical and dynamical parametersof test area, including void ratio, dry density, modulus of compressibility and dynamicpenetration number, and then obtains deformation modulus of treated soil, characteristic number of ground bearing capacity and its corresponding settlement for the similarengineering.(3) A series of tests are conducted to study the dynamic compaction parameters andtheir effects on the deep collapsible loess foundation under super high fill in test area.Analyses are made on the average settlement of each test area before and after dynamiccompaction and on the regularity of the main physical and mechanical indexes of soil.The main parameters under the different energy levels of2000kN.m,3000kN.m or6000kN.m are gained, such as the centre distance of dynamic compaction points, thebest impact number, the standard of cutting out, and the effective reinforcement depth.Hence, the empirical formula of the effective reinforcement depth of dynamiccompaction is determined for the similar engineering.(4) Proctor compaction tests and a series of field tests are carried out to study thecompaction characteristics of Ma-lan loess in test area. The compaction effect of thesingle and the new combination technology is analyzed along with the influence ofwater content on it. The reference indexes of main physical and mechanical propertiesof compact Ma-Lan loess are gained. Meantime, this paper also gives out the referencevalue of ground bearing capacity feature value and elasticity modulus.(5) In order to study the deformation and the shearing strength characteristics ofcompacted Ma-lan loess in test area, compression tests and direct shear tests areconducted. Analyses are made on the relationship between the initial compaction degreeas well as the initial water content and the shear strength indexes, and also on theireffects on the compressive deformation of soil. By employing the secant modulusmethod, the modified formula of deformation is established when the initial compactiondegree and water content of compacted Ma-lan loess change. The modified formula ofdeformation can be used to analyze and calculate the deformation of foundation filledby compacted Malan loess.