Field Study On The Cast-in-situ Concrete Thin-wall Pipe Pile Composite Foundation

As a new foundation improvement technology, the cast-in-situ concrete thin-wall pipe pile (PCC pile) has greater superiority over traditional method of foundation improvement in the effect of improvement, construction time limit, cost of engineering and environment protection etc. Therefore it has a great prospect of application in foundation improvement. Based on the application of this new technology in soft soil improvement of Yan-Tong expressway, the construction techniques of this new technology, method of quality control during construction, method of quality detecting of PCC pile, calculation theory, characteristic of loading and deformation are studied in the thesis. The effect of foundation improvement is also analyzed in the paper. For details, the main contents are as follows:1.The background of manufacture, principle of design, construction techniques of pile sinking, theory of working and mechanism of construction of PCC pile are analyzed in details. Advantages of PCC pile are also evaluated and the main methods of design at present are gathered.2. The construction techniques of PCC pile, method of quality control and influence on surroundings during pile construction and method of quality detecting of PCC pile are studied and some useful conclusion are obtained through field test, which can be popularized in similar engineering as empirical technology.3. Characteristics of loading on single PCC pile and composite foundation, especially that of settlement curve of single PCC pile, which is divided in elastic settlement phase and elastic -plastic settlement phase, are studied through static load test. It is pointed out that the PCC pile enters elastic settlement phase firstly under load and the settlement has a linear relationship with load. With the increase of settlement, there also comes an increase in pile wall friction. The pile wall friction reaches the maximum when the settlement of pile achieves elastic settlement limit and the pile enters elastic-plastic settlement phase hereafter. It is proposed that the shape of the curve of load and settlement in elastic-plastic settlement phase can be simulated by hyperbola and the bearing capacity of PCC pile can be obtained by extrapolation, which offers a simple method to determine the bearing capacity of PCC pile.4. The characteristics of bearing and deformation under embankment load and the effect of soft soil improvement of PCC pile composite foundation are analyzed based on the related datum obtained during load on the spot.5.The parameter of pile diameter, space between piles, thickness of pile wall are discussed through comparing with the effect of PCC pile composite foundation on the basis of different pile diameter, space between piles, thickness of pile wall and bed course.6.Characters of bearing of PCC pile are analyzed and the calculation method of bearing capacity of PCC pile is proposed through comparing the result of theoretical calculation with the datum of static load test.7.The result that the method of composite modulus does not fits the settlement calculation of PCC pile composite foundation is obtained and the effectiveness of stress ratio method for the settlement calculation of PCC pile composite foundation based on the real share in total load of pile and soil is affirmed by means of verification of the test settlement datum.