On Settlement Of Dry-Jet-Mixing Composite Ground

The settlement of composite ground is a key parameter for engineering design, and is generally calculated using the specification method. However, experiences indicated that the difference exist extensively between the calculated settlement of the composite ground which are calculated using the specification method with the field measured settlement. So, analysis of the influencing factors of the specification method is being significant sense. The main works as follows:(1)History and research status of calculation method of the settlement of the composite ground is reviewed. The influencing factors on calculating the settlement of Dry-Jet-Mixing composite ground with the specification method are analyzed and summarized. Then, the problems need to be solved in the paper are brought out.(2)Based on lots of investigation, design, testing and settlement data of constructed and constructing highways, the settlement of the Dry Jet Mixing composite ground are calculated with the specification method. Comparing the results with the measured settlement show that their relationship are very messy and calculated settlement are 0.2~3.5 times the measured settlement.(3)The effects of the strength of pile or soil on the calculated settlement of composite ground with the specification method are analyzed. It is found that the main influencing factor is the modulus of compressibility of sub-layer soil. Nowadays, the shortage of the modulus of compressibility of soil provided by the engineering geologic investigation report are summarized as follows: firstly, the modulus of compressibility of soil is calculated without considering the influence of stress level; secondly, the modulus of compressibility is distorted badly because of sample disturbance.(4)The influencing factors and main phenomenon of sample disturbance on nature sedimentary clay are summarized. The methods of quantitatively evaluate the degree of sample disturbance (Dsd) of soil are reviewed. Furthermore, one of those methods which named"pore index method"is validated by a series of consolidation tests which conducted on artificially disturbed samples of Lian Yungang soft clay in the laboratory, so as the linear relationship between the Dsd with the consolidation yield stress of disturbed samples.(5)Shape of original compression curves and the effect of soil structure on the natural sediment clay are described. Then, several classical methods of forming original compressing curve are summarized. Furthermore, a new method named"modified Schmertmann method"is proposed in the paper based on quantitatively evaluation of the Dsd and the linear relationship between the Dsd and consolidation yield stress. Later, an engineering example is used to validate its applicability and feasibility.(6)Based on the original compression curve of soil, and considering the effect of stress level, a calculating formula of the modified modulus of compressibility which represents the in-situ compression properties of nature sedimentary clay is deduced. The modulus can reflect the practical deformation character of soil better than E1-2 which provided by engineering geologic investigation report.(7)The modified moduli of compressibility of soil are applied in calculating the settlement of sub-layer of Dry-Jet-Mixing composite ground. Comparing the calculated settlement with the corresponding field measured settlement gets a high-quality fitting degree, which validate the applicability and reasonability of the method proposed in the paper.(8)Finite element method combined with trail-and-error method is used to back calculating the modulus of compressibility of soil. It is found that the relationship between the results of back calculating with the modified modulus of compressibility is much better than that between the results with E1-2, which confirm the veracity of the method proposed in the paper again.