Study On Mechanical Properties Of Fly Ash Cement Treated Marine Clay

Marine clay is widely found in the coastal areas.With the development of various engineering projects,marine geotechnical engineering has increasingly attracted people's research interest in recent years.On the other hand,our country is a coal-producing and coal-fired country,and the utilization of fly ash is a major issue in current economic and social development.In many geotechnical projects in marine clay?e.g.airport construction,deep excavation,and tunnelling?,soil stabilization is necessary prior to the constructions,with the aim to strengthen soil,and/or to decrease soil's permeability,and/or to decrease soil's compressibility and swelling potential.Ordinary Portland cement?OPC?is a commonly used binder,with which the stabilized soil can gain strength in a relatively fast manner;around 80%strength can be reached within a 28-day curing period.This feature enables the OPC being used in projects with a short construction period,such as tunnelling.However,many projects have a long construction period;for instance,when applying a cement-admixed slab in a deep excavation to resist the lateral displacement,the excavation may last half a year after the completion of the slab.In this circumstance,a low strength gaining rate is allowable.Fly ash will cause great pollution if not properly handled,which is common industrial waste.In view of the above situation,this paper mainly studies the micro-strengthening mechanism,strength characteristics,yield and deformation characteristics,small strain behavior and other mechanics of fly ash cement reinforced marine clay by using the experiments methods,as well as its influencing factors and changes in the law.The yield,strength and stiffness characteristics of the two kinds of cement treated clay are compared and analyzed,which provides basic experimental data and theoretical basis for the extensive application of fly ash cement.?1?Considering different cement content and different curing time,the unconfined compressive strength test of ordinary Portland cement treated clay and fly ash cement treated clay was carried out respectively.The effects of cement content and curing time on the strength of two kinds of cement treated clay were obtained respectively.The strength of ordinary Portland cement treated clay with 28 days is larger but the intensity of late growth is slow,however,the strength value of fly ash cement treated clay is small in 28 days but the strength of late stage is growing rapidly,which is nearly the same with OPCC in 90 days when the cement content is high.The micro-structures of two kinds of cement treated clay with different cement content and different curing time were analyzed by using SEM technique as well as the mechanism of the two kinds of cement treated clay.The strength,deformation and failure modes of the two kinds of cement treated clay were compared and analyzed.?2?Two sources of uncertainties were examined;that is,the uncertainty in cement fraction in binder,and the non-uniformity during the process of mixing binder slurry with in-situ soils;the latter is termed as binder concentration.These two uncertainties were quantitatively assessed as two random variables?and?,and the analyses were conducted through the Monte-Carlo simulation method.The model of the strength prediction of fly ash cement treated clay is established by introducing the uncertainty parameter?and parameter?.The prediction of the model was verified by the experimental data,and the error between the predicted results and the experimental results was less than 15%.The Monte-Carlo simulation method is used to simulate the effect of the variables?and?on the strength of the fly ash cement treated clay.The probabilistic density functions of the variables?and?are discussed herein.The variation of binder concentration is proposed to be linked up with the variation of strength through the operational parameter of blade rotation number.By using the operating parameters of the blade rotation number and the change of the intensity,the prediction model of the coefficient of variation used to evaluate the engineering practice site is constructed.?3?The triaxial isotropic compression tests of two kinds of cement treated clay were carried out respectively.The initial yield stress,the intermediate yield stress and the final yield stress of the two kinds of cement treated clay with different cement contents and different curing time were obtained.The linear relationship between initial yield stress and unconfined compressive strength of two kinds of cement treated clay was established.It is found that the initial yield strength and unconfined compressive strength of the two kinds of cement treated clay can be expressed by the same linear relation P'_py=0.55q_u;The logarithmic curves of effective confining pressure and specific volume of two kinds of cement treated clay under triaxial isotropic compression test were established respectively.?4?The triaxial drained shear tests of two kinds of cement treated clay were carried out respectively.The initial yield stress P'_py,the effective confining pressure p'and the deviator stress q are obtained as well as the initial yielding locus of two kinds of cement treated clay.It is found that the initial yielding locus of the two kinds of cement treated clay can be expressed by the same parabolic curve,except that the coefficient N is different:to OPCC,N=2.6,while to FACC,N=2.1.Based on the initial yield locus,the prediction model of the initial yield stress of two kinds of cement treated clay is established respectively.The initial yield strength of the two kinds of cement treated clay is predicted by this model.At the same time,using the prediction model established by unconfined compressive strength,the prediction and experimental values of the different prediction models are both less than 15%.?5?The bend element tests of two kinds of cement treated clay were carried out respectively and obtained the maximum shear modulus G_max of two kinds of cement treated clay with different cement contents and different curing time.The relationship between the maximum shear modulus G_max of the two kinds of cement treated clay and the initial yield stress P'_py is established.The maximum shear modulus G_max and the initial yield stress P'_py of the two kinds of cement treated clay can be expressed by the same function.The relationship between the maximum shear modulus G_max and the unconfined compressive strength q_u of two kinds of cement treated clay is established indirectly,and can be expressed by the above variables?and?.?6?The local strain tests of two kinds of cement treated clay were carried out respectively and obtained the local stress-strain curves and the small strain shear modulus G of two kinds of cement treated clay with different cement contents and different curing time.The changes of the local strain strength of the two kinds of cement treated clay with the change of cement content and curing as well as attenuation trend of the small strain shear modulus G of were discussed respectively.The two kinds of cement treated clay were compared and analyzed.?7?An empirical model for strengthening the initial yield of marine soil in Singapore was established by fly ash cement.For some structures with very high requirements for deformation control?such as subways and tunnels?,the initial yield stress is very significant for structural design.The purpose and significance of the initial yield experience model are introduced,and the error between the prediction results of the empirical model and the test results is compared and analyzed.