Study On Design Method Of Pile-Plank Embankment Of Ballastless Track In High-Speed Railway By Tests

Pile-plank embankment is a kind of new-type form of ballastless truck in high-speed railway, it is composed with the reinforced concrete plank at its upside and reinforced concrete piles, subgrade and subground at its downside, and plank directly connectes with the track structure, the piles fixedly link to plank and together with the subgrade compose a bearing load structure system. It synthesizes respective characteristic with the ballastless truck and the piles, fully depends on pile-soil and plank-soil interaction to satisfy with the intensity and the settlement requests. This paper unified Ministry science and technology development project 'study on the key technology under the line of ballestless truck in the Suining-chongqing high speed railway' ,with the topic pile-plank embankment in the Suining-chongqing high speed railway , domestically took the lead to carry out pile-plank embankment thorough research. The design and the calculation method of pile-plank embankment were summarized, through method of model test,field test and number simulation, received some innovation results,mainly obtained the following several conclusions.1. Pile-plank embankment is not only a kind of new-type form of ballastless truck, but also an independent subground processing technology system, pile-plank embankment definition and its suitable situation are given.2. The design theory and calculation method of pile-plank embankment are proposed, the crucial specification which under each kind of load combination condition and various component designs are summarized. Based on overseas ballaseless truck design, the design control target of pile-plank embankment is given, carried on the optimized design, the reasonable design size of pile-plank embankment is received.3. Through centrifugal model test of pile-plank embankment for ballastless truck, the settlement and pile-soil interaction of pile-plank embankment are studied. It is shown that the settlement of pile-plank embankment is completed when pile-plank embankment is laid for five months; By using the steel plate counterweight to simulate the train load, the settlement of ballastless truck is completed when it is used for seven months; and the pile of the structure is rock-socketed bored cast-in-place frictional pile whose diameter is small in proportion to its length.4. Based on Suining-chongqing high speed railway, the large scale dynamic model test is established, the loading frequency is 5Hz and 10Hz, and the loading time is 200000, receives the dynamic interaction and settlement change rules. Test results indicate that the amplitude of vertical dynamic stress is approximately " K" form to distribute with depth in soil between piles and soil under the middle-span plank, piles share most dynamic stress compared with soil, dynamic stress is affected by loading position and loading frequency. Pile structure expanded the depth of dynamic response of the subgrade and improve the stress of roadbed soil, the settlements of the pile-plank embankment remain constant after 10000 times of vibrant loading, post-construction settlements satisfy with the settlement control request to build ballastless truck in high-speed railway.5. Based on the field test in Suining-chongqing high-speed Railway, the dynamic responses of pile-plank embankment on which a disperse impetus locomotive CRH₂ and freight train with high speed is running are studied, changes the dynamic responses with the speed of train and the wheel load are analyzed. The analysis indicates that the acceleration and dynamic stress grow in varying degrees with the speed of train increased. The dynamic responses of subgrade are less affected by speed of train, but are significantly affected by the wheel load. The dynamic stresses attenuate with increasing the depth of subgrade, with increase in the depth, dynamic stresses are closer to the static stress. Dynamic stress at pile-bottom soil is biggish, and is one of the key dynamic design of subgrade.6. A tri-dimensional element model has been founded, which involves the ballastless track and pile-plank system. It can provide dynamic responses of the system with changes of wheel load, vehicle velocity, frequency, irregularities, and distribution of dynamic responses in the subgrade etc. by changed the wheel load, vehicle velocity, pile-span, the dynamic response of the system were studied systematically, some results were stated as followings:(1) Dynamic stress and displacement were less affected by vehicle velocity, but acceleration was significantly affected by vehicle velocity, and dynamic stress in the pile is mostly affectd at 2/3 pile length under the pile top, and is less affected at bottom of pile, dynamic response decreases with the vertical depth increase(2) The dynamic response increases along with the wheel load increase near linearity.(3) In the 5～10m span scope,the dynamic stress and displacement increase with the span increase,but acceleration reduced with the span increase.These studies show that the results are in good agreement with the datum from tests. It proves that the dynamic model is practical and reliable.7. Studied on the theory and the test of settlement and post-construction settlement of pile-plank embankment, discussed on the calculation settlement method of pile-plank embankment, calculated the post-construction settlement in Suining-chongqing high-speed railway and carries on the contrast analysis with the long test. The result indicated that pile-plank embankment was effective control post-construction settlements of roadbed, was one kind of effective roadbed and subground reinforcement measures.