| Soft soil foundation is widely distributed in Chinese coastal areas and inland with rivers and lakes, due to the low shear strength, compression properties of high containing water higher negative to the earthquake resistant engineering with soft soil, even the upper load of construction foundation is small, the soft foundation shows large displacement of the settlement, cement mixing piles reinforcement technique is a common method in soft soil foundation treatment. Soft soil and cement are mixed by mixing machinery, using cement and soft soil occurs between a series of physical and chemical reaction, changing the soft to cemented soil, which has the advantage of high strength, low compressibility, low permeability.The dynamic characteristics of cement soil have a significant influence on the seismic behavior of cement mixing pile foundation, and it is also an essential part of the engineering seismic safety evaluation. Dynamic shear modulus and damping ratio of soil are two important parameters of soil dynamic characteristics, and the dynamic characteristics of small strain range can be studied by resonant column test. In this paper, the following research is mainly carried out by using the GDS resonant column test:(1)Studying the resonant column based on testing on different diameter and height calibration bars by using resonant column shows that aluminum calibration rods of torsional vibration resonance frequency along with the resonant column drive the increase of quality of the system decreases with the increase of the diameter of the specimen increases by calibration resonant column drive system of the moment of inertia of I0 values for 0.0037kg·m2. The flexural resonance frequency increases with the increase of diameter and the decrease with height. The dynamic elastic modulus values of samples are close calculated through Rayleigh method,which proofs the reliability of this method. Calibrating on five different height calibration bars and offer the calculation method based on Rayleigh method that take consideration of the size.(2)The influence of different cement mixing ratio, curing days and confining on small strain dynamic properties of aging cemented clay was studied through GDS resonance column.The research shows: the more cement mixed and the longer curing days, the higher the initial shear modulus of cemented clay was. Under the same confining, the primary consolidation become longer the initial shear modulus of cemented clay enlarge,and the small strain normalization dynamic shear modulus increase after consolidation.As the confining become increase,the aging cemented clay shows obviously,the small strain dynamic shear modulus more obvious under high confining. During the secondary consolidation, the small strain dynamic shear modulus was linear growth, in the short term, the small strain dynamic shear modulus can be corrected after getting the normalization dynamic shear modulus by using resonance column.(3)Studying the dynamic properties of clay and cemented clay-clay composite samples by using GDS resonant column. Research shows, the dynamic modulus G and damping ratio of clay and cemented clay-clay composite samples have the same change trend with shear strain γ. The replacement of the cement clay in the composite sample increases the strength of the whole sample.In small strain range, the influence of replacement ratio of cemented clay and cell pressure on dynamic shear modulus G and damping ratio D is remarkable, with the shear strain increases, the effect of replacement ratio on dynamic shear modulus G and damping ratio D is reduced. The Gmax of composite samples linear relationship with cell pressure and the replacement ratio of cemented clay.The greater the cell pressure, increasing the replacement ratio of cemented soil to Gmax enhancement effect is more obvious.Modified Hardin-Drnevich hyperbolic curve model can predict the dynamic stress-strain relation of different replacement ratio composite samples. |
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