| This paper describes the characteristics, the formation mechanism, engineering mechanical properties and microstructure characteristics of marine soft soil in Tianjin Binhai new developed area. The existed applicable condition of ground treatment methods and the major factors that influence the intensity of soft soil solidified by cement are discussed and analyzed. For improving physical chemistry environment of soft soil, a new idea has been put forward, in which the soft soil can be solidified by cement with agents in addition. Two new curing agents were invented by a large number of laboratory tests.Through in-site application, it was found that the new curing agents not only have wonderful effects on solidifying soft soil but also can be used conveniently and economically. Meanwhile, the solidified mechanism of new curing agents has been discussed from the microstructure and physical chemistry reaction of the soft soil.The main results of this paper are as follows:1. The structural characteristics of the soft soil in Tianjin Binhai new developed area have been analyzed. It is found that the soft soil in this area is all structural soil; in Dagang district it is relatively strong; in Tanggu district it is relatively weak; and in Hangu district it is located between the former two. In the aspect of fabric characteristic, the soft soil in Tanggu district belongs to the typical flocculent form structure. The skeleton of the soil is incompact and the pore is relatively large in size. The soft soil in Hangu district belongs to granule-flocculate form structure. Its unit body is slice structural and the granulous particles are relatively close-knit in tactic modality.The soft soil in Dagang district is similar to Hangu district, but it has closer arrangement between unit body and particle than the former one. The difference of the fabric structure characteristic is the main reason leading to the difference of mechanics property of soft soil among the three districts.2. By introducing multi-fractals algorithm into a study of marine soft soil's microstructure, multi-fractals spectrum of pore characteristic parameters f(α)max are found as evaluation indexes of the looseness and the compacity of the soft soil. The higher of the f(α)max value, the looser of the soil.3. An evaluation index which is a reflection of marine soft soil pore's breaking trend -pore structure factor (PSF) is proposed. PSF is a synthetical reflection of the pore's size, shape, distribution and directivity. The higher of the PSF' s value, the greater of the tendency of the soil to disrepair and the lower of the soil's structure intensity.4. The major factors affecting the intensity of soil solidified by cement in Tianjin Binhai new developed area have been analysed. It is pointed out that water content, organic matter content and PH value of soft soil are key influencing factors besides common factors. It has been shown that the intensity of soil solidified by cement weakens with the increasement of moisture content and organic matter content , but weakens with the decreasement of the PH value. Therefore, all of them are called "the intensity of cement soil weakening factor". Special attention must be paid to the factors when making investigations in coast area so that some corresponding measures should be taken.5. The cement saturation effect existing in mixing law of cement soil has been found: in the condition of the same age period, the compression strength of soil solidified by cement increases obviously with the increasement of cement adulterated content. At the same time, with the optimum cement content, the intensity of soil solidified by cement reaches the maximum value. As long as the cement adulterated content is over optimum content, the intensity of the pile and the ultimate bearing capacity of the single pile can't be improved obviously no matter how much of the increasing of the cement content. The economic meaning of existence, discovery, and confirmation of the saturated phenomenon of cement is self-evident because it plays an important role in saving a large amount of fund on the premise of guaranteeing the project quality.6. The anisotropism of intensity increasement of cement soil has been put forward firstly by experimental study on the strength of soil-cement with different sites, multi-hole location, multi-stratum and different cement adulterated contents. In the condition of the same adulterating content and mixture ratio, the law of intensity increasement with age period of each layer varies with soil property and physical mechanical character. The growth of intensity of cement soil of each layer is out of step. It has vertical isometric in intensity increasement. If the stratums are veried different in horizontal direction, it has horizontal isometric possibly because of the great difference of soil property in horizontal direction. The vertical isometric and horizontal isometric of the intensity increasement of cement soil are called by a joint name anisotropic intensity increasement. This anisotropism indicates the otherness of intensity and bearing capability of single pile and bearing capability of compound-ground.7. The new curing agents have been invented, which is the conjugate of cement with sodium hydroxide and combination of cement with sodium carbonate. According to the engineering application and practical experience, it was proved to be an effective and economical method and it should be spreading used.8. The curing mechanism of curing agents in soft soil has been discussed. It is indicated that sodium hydroxide and sodium carbonate as cement additives can make cement soil maintain strong alkalescence and increase concentrations of hydronium. It makes large amounts of hydrate calcium silicate crystals of needle-like rod-shaped or fibrous and inhibits the generation of calcic alum crystal which would bring expansile action, At the same time, it can separate out hydrate calcium. All of them constitute the filling and inclusions together among soil particles and on the surface of soil particles, which cut down the interstices of cement soil obviously. Therefore, soil mass has been reinforced, and its intensity has been improved.
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