Device for simulating full-scale pile-sinking process of static pressure pile by air bag preloading and test method thereof

1. A device for simulating a full-scale pile-sinking process of a static pressure pile by air bag preloading, comprising a frame formed by surrounding a plurality of counter-force frames ( 1 ), a beam ( 3 ) connected between adjacent counter-force frames ( 1 ), a hydraulic jack ( 2 ) mounted on the beam ( 3 ), a model box ( 4 ) located inside the frame, a model pile ( 5 ) pressed by the hydraulic jack ( 2 ), a first sand layer ( 71 ), an undisturbed soil mass ( 13 ), a second sand layer ( 72 ), a rubber pad ( 6 ), a forcing air bag ( 10 ), a counter-force steel plate ( 9 ), a model box top cover ( 15 ) covered on an upper surface of the model box ( 4 ), a forcing pipe ( 11 ) and a pressure relief pipe ( 12 ) which are both connected with the forcing air bag ( 10 ), a steel casing ( 8 ), and a control system ( 14 ) connected with both the hydraulic jack ( 2 ) and the forcing air bag ( 10 ), wherein the first sand layer ( 71 ), the undisturbed soil mass ( 13 ), the second sand layer ( 72 ), the rubber pad ( 6 ), the forcing air bag ( 10 ) and the counter-force steel plate ( 9 ) are laid in the model box ( 4 ) in sequence; the steel casing ( 8 ) passes through the model box top cover ( 15 ), the counter-force steel plate ( 9 ), the forcing air bag ( 10 ) and the rubber pad ( 6 ) in sequence and then reaches a bottom portion of the second sand layer ( 72 ); and the model pile ( 5 ) is inserted into the steel casing ( 8 ) to contact with a surface layer of the undisturbed soil mass ( 13 ).

2. The device for simulating the full-scale pile-sinking process of the static pressure pile by air bag preloading according to claim 1 , wherein the beam ( 3 ) is connected between adjacent counter-force frames ( 1 ) through a guide sliding sleeve.

3. The device for simulating the full-scale pile-sinking process of the static pressure pile by air bag preloading according to claim 1 , wherein two forcing pipes ( 11 ) and two pressure relief pipes ( 12 ) which are oppositely arranged and extend in opposite directions are both provided.

4. The device for simulating the full-scale pile-sinking process of the static pressure pile by air bag preloading according to claim 1 , wherein the rubber pad ( 6 ), the forcing air bag ( 10 ), the counter-force steel plate ( 9 ) and the model casing top cover ( 15 ) are all provided with a pile position hole ( 5 - 1 ) for the model pile ( 5 ) to pass through.

5. The device for simulating the full-scale pile-sinking process of the static pressure pile by air bag preloading according to claim 1 , wherein the counter-force steel plate ( 9 ) and the model casing top cover ( 15 ) are both provided with a forcing pipe position hole ( 11 - 1 ) and a pressure relief pipe position hole ( 12 - 1 ) for the forcing pipe ( 11 ) and the pressure relief pipe ( 12 ) to pass through respectively.

6. The device for simulating the full-scale pile-sinking process of the static pressure pile by air bag preloading according to claim 1 , wherein the first sand layer ( 71 ) and the second sand layer ( 72 ) are both a sand layer with a thickness no less than 50 mm.

7. A test method of the device for simulating the full-scale pile-sinking process of the static pressure pile by air bag preloading according to claim, comprising the following steps of:

surrounding the plurality of counter-force frames ( 1 ) to form the frame, slidably connecting the beam ( 3 ) between adjacent counter-force frames ( 1 ), placing the model box ( 4 ) in the frame, and fixing the hydraulic jack ( 2 ) on the beam ( 3 ) and positioning the hydraulic jack above the model box ( 4 );

paving the first sand layer ( 71 ) on the bottom portion of the model box ( 4 ) firstly, then placing the undisturbed soil mass ( 13 ) in the model box ( 4 ), and finally covering the second sand layer ( 72 ) on the undisturbed soil mass ( 13 );

covering the rubber pad ( 6 ), the forcing air bag ( 10 ) and the counter-force steel plate ( 9 ) on a surface of the second sand layer ( 72 ) in sequence firstly, and then respectively penetrating the forcing pipe ( 11 ) and the pressure relief pipe ( 12 ) which are connected with the forcing air bag ( 10 ) through the counter-force steel plate ( 9 );

arranging the model box top cover ( 15 ) on the model box ( 4 ), and respectively penetrating the forcing pipe ( 11 ) and the pressure relief pipe ( 12 ) through the model box top cover ( 15 );

coating lubricating oil on an inner wall of the steel casing ( 8 ) firstly, penetrating the steel casing ( 8 ) through the model box top cover ( 15 ), the counter-force steel plate ( 9 ), the forcing air bag ( 10 ) and the rubber pad ( 6 ) in sequence to reach the bottom portion of the second sand layer ( 72 ); then grabbing the sand layer in the steel casing ( 8 ) and avoiding disturbing the undisturbed soil mass ( 13 ) below the second sand layer ( 72 ); and finally inserting the model pile ( 5 ) into the steel casing ( 8 ) to contact with the surface layer of the undisturbed soil mass ( 13 ); and

connecting both the hydraulic jack ( 2 ) and the forcing air bag ( 10 ) with the control system ( 14 ), and controlling a pile pressing force and an upper layer soil weight in the pile-sinking process.

8. The test method of the device for simulating the full-scale pile-sinking process of the static pressure pile by air bag preloading according to claim 7 , wherein the undisturbed soil mass ( 13 ) is placed in the model box ( 4 ) and avoided from being disturbed.

9. The test method of the device for simulating the full-scale pile-sinking process of the static pressure pile by air bag preloading according to claim 7 , further comprising the step of: through multiple tests, simulating pile pressing processes at different depths by changing the undisturbed soil mass in the model box ( 4 ) and a pressure of the forcing air bag ( 10 ), and finally simulating the whole pile pressing process by superimposing results of the multiple tests.