| Soft soil treatment has been a prominent issue on the construction of infrastructural facilities in the Pearl River Delta Region and the Yangtze River Delta region. The soft soil treatment technology and design theory have been developed greatly in recent year. But for various reasons differential settlement,bridge-head and post-construction settlement still exist to some extent in the operation of road. So according to the characteristics of T-shaped mixing pile, Panyu District, Guangzhou City, Huanglan fast road is selected and acted as representative of the soft soil of Pearl River Delta area. The fast road is treated by T-shaped mixing pile. Through combination of construction and Situ test, T-shaped mixing pile force characteristics and the composite foundation settlement are analyzed.Through soft soil engineering survey datas are extensive collected in the typical area of Nansha, the engineering geological characteristics of soft soil are summarized. The nansha compression lines of soft soil is shown:softening phenomenon is occurred under lower pressure, and hardening curve appear under higher pressure; Nansha'soft soil have some typical features such as high water content, high porosity, High permeability of compressibility, consolidation, low shear strength low bearing capacity and so on, which impact the reinforcement of city road seriously.Though strain gauges are equiped in the body of T-shape cement-soil mixing pile and single pile load tests are did, the law between axial force transmission, stress transmission and distribution of skin friction with depth are analyzed. The study is shown:due to the stress concentration the cross-section of pile body stress increased, and the pile body below the cross-section stress diminishes quickly. Along the depth of pile shaft force gradually attenuation, and in expanding heads above the pile attenuation rate is lower fast, expand the head the following3m-9m of pile shaft force reduce gradually, because the following9m formation conditions are good, so when the pile body with a small amount of the axial force growth; The same depths pile body stress (pile body axial force) with the load increases, expand the head of a larger extent increase of stress, under the stress of pile of basic unchanged. Based on the nail form stirring pile body quality testing results and pile body load transfer law, judge nail form mixing pile of single pile failure mode for pile quality damage, puts forward the nail form of mixing pile bearing capacity of single pile limit calculation method (Qu=ηfcuπD2/4, suggest the value of η is0.5～0.7). The curve of depth-soil settlement located in roadbed can be roughly divided into two sections:the first section above9.0m depth of pile that occur main settlement of all have lager settlement, and settlement value is gradul decreasing with increasing depth. The second section below9.0depth of pile have small settlement, only a few mm. The settlements of composite foundation of T-shape cement-soil mixing pile are considered from three aspects:strengthening regional settlements S1above cross-section of pile, strengthening regional settlements S2below cross-section of pile and subjacent bed of composite foundation S3respectively. All the theoretical settlement of composite foundation is to376.738mm. Though the foundation of city roads are reinforced by T-shape cement-soil mixing piles in Nansha'area, the actual engineering meaning and effect are obtained.
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