On The Soil-Cement Mixing Method Adaptation In Special Regional Soft Ground

In order to investigate the effects of water content, curing time, cement content, salt content, organic content on the strength behavior of the cemented clays, a series of physical tests and unconfined compressive tests were performed on cemented clays which composed of reconstituted Lianyungang clays or the Yancheng lagoonal soft clays mixed with powder cement or slurry cement The quantitative methods of strength prediction are proposed for assessing the unconfined compressive strength of cemented clays. In addition, the applicability of dry mixing method and slurry deep mixing method is discussed based on lab and field test results of cemented clay. The main results are conclude as follows:1.For non-organic original clays with high water contents, a concept of quasi-water-cement ratio is proposed for predicting the unconfined compressive strength of cemented clays. The strength prediction formula proposed in this study can be used for predicting the change in unconfined compressive strength with the variation of water content, cement content and curing time, based on the laboratory test results of the cemented clays with 28days of curing time for only a given quasi-water-cement ratio. The proposed strength prediction formula can be also well applied for the available data of the cemented clays published by other independent researchers.2. For original clays with high organic contents, a quantitative way to predict the unconfined compressive strength of cement-mixed clays with a given organic content is proposed. The Yancheng lagoonal soft clays were used an original clay to form cement-mixed clays through mixing with powder cement or slurry cement and organic matters. A series of tests were performed on the cement-mixed clays with various organic contents. A quantitative relationship is proposed between the strength ratio of the strength with a given organic content of y to the experimental strength with an organic content of y₀ and the organic contents of y and y₀. The quantitative expression proposed in this study can be effectively to predict quantitatively the effect of organic content on the unconfined compressive strength of cement-mixed clays within the organic contents of 5.5%～17.5%.3. For non-organic original clays with high salt contents, the effect of salt content on unconfined compressive strength of cemented clays is investigated. A pick value of 3.5% is acquired, which reflects influence of salt content on cemented soil strength's promotion or decline. When salt content is lower than this value, the strength of cement-soil will increase with salt content (due to salt's dissolvable crystallinity and expansion). Conversely, when the soil have a higher salt content, the strength of cemented clays will highly decrease with salt content due to structural destruction of cemented clays. In addition, the corrosion mechanism of cemented clays is also discussed and the anti-influence of organic content on cemented soils strength is proposed.4 The applicability of the dry mixing method and slurry deep mixing method is illustrated, based on the field and lab test results. The slurry deep mixing method is better than that of the dry mixing method when water content ratio defined as the ratio of water content to liquid limit is lower than 0.9. When the range of water content is between 0.9 and 1.0, both methods have almost the same strength. When this ratio is large than 1.0, the dry mixing method is better.