| As a green and environment-friendly new energy industry,photovoltaic industry has ushered in new development opportunities under the background of"carbon peak and carbon neutrality".The foundation of the photovoltaic support is an important infrastructure of the photovoltaic power station,which plays the role of bearing the self-weight of the support and photovoltaic modules and resisting loads such as wind load,snow load,and earthquake load.At present,some domestic photovoltaic power generation projects,such as agriculture-photovoltaic complementation projects,fishery-photovoltaic complementation projects,and other photovoltaic projects,mostly use prestressed high-strength concrete pipe piles as support foundations.The pile diameter of this kind of photovoltaic PHC pipe pile is generally 300 mm,the pile length is short,the buried depth is relatively shallow,and the height of the exposed ground is relatively long.Most of the supports are in the form of a single column and generally do not have a cap.It bears a small vertical compressive load and large vertical uplift load and horizontal load,and it belongs to a kind of micro short pile.The mechanical mode and bearing mechanism of this kind of micro short piles are quite different from those of conventional piles,and the theoretical support is not clear at present.Under the action of wind load,if the quality control of micro short pile foundation is not proper,the photovoltaic support may be inclined,displaced,pulled up,or even broken,which will seriously affect the normal operation and service life of photovoltaic power station.In view of this,in this paper,by carrying out the field horizontal and uplift tests of the photovoltaic support of micro PHC short piles,combined with numerical simulation,the bearing characteristics of the micro PHC short piles under different working conditions such as horizontal load,uplift load,horizontal and uplift combined loads are systematically studied.The main conclusions are as follows:(1)Through the field horizontal test of photovoltaic micro PHC short piles,the results show that the photovoltaic micro PHC short piles in this test are rigid short piles,and the proportional coefficient m of the horizontal resistance coefficient of the soil is nonlinearly decreasing with the increase of horizontal load and horizontal displacement.The calculated m value of the test piles is 2.2 MN/m~4,which is within the range of 2～4.5 MN/m~4recommended by the specification.(2)Through the field uplift test of photovoltaic micro PHC short piles,the results show that the uplift load-displacement curves of the test piles are steep.The hyperbolic model can better fit the uplift load-displacement curves of photovoltaic micro PHC short piles in the test site,and the correlation coefficient R~2is 0.9954.The predicted value of ultimate uplift bearing capacity of micro PHC short piles obtained from the hyperbolic model should be corrected,and it is suggested to take the correction coefficient of 0.82.(3)The three-dimensional pile-soil model is established based on the field horizontal test,and firstly,the simulation calculation results are compared with the field test results to verify the reasonableness of the proposed model and related parameters,and then the horizontal bearing characteristics of the photovoltaic micro PHC short pile are analyzed by finite element method.The results show that under different horizontal loads,the horizontal displacement distribution of the photovoltaic micro PHC short pile presents the characteristics of the rigid pile,and the center of rotation of the pile is located at 0.6 times the depth of the pile into the soil.Reasonably increasing the depth of pile into the soil,pile diameter,and reducing the length of the free section at the top of the pile can appropriately increase the horizontal bearing capacity of the photovoltaic micro PHC short pile.Under a large horizontal load,the photovoltaic micro PHC short pile conforms to the failure form of a rigid pile.The horizontal bearing capacity of the single pile can be obtained by a theoretical formula when the distribution of the soil resistance p(y,z)around the pile is known.(4)Through the finite element analysis of the uplift bearing characteristics of the photovoltaic micro PHC short pile,the results show that the axial force of the photovoltaic micro PHC short pile under each level of uplift load decreases with the increase of the depth.When the uplift load is small,the lateral friction resistance of the upper soil layer around the pile body is first played,as the load increases,the increased load is transferred to the lower part of the pile body,which is borne by the lateral friction resistance of the lower soil layer.Reasonably increasing the pile depth,pile diameter,and pile-soil interface friction coefficient can effectively improve the ultimate uplift bearing capacity of the micro PHC short pile.Under the action of a large uplift load,the uplift failure mode of the photovoltaic micro PHC short pile is cylindrical shear failure along the pile-soil contact surface.The ultimate uplift bearing capacity can be calculated accurately by using the standard model theoretical calculation formula.(5)Through finite element analysis of the bearing characteristics of the photovoltaic micro PHC short pile under combined horizontal and uplift loads,the results show that the pre-imposed uplift load mainly affects the horizontal displacement of the pile above the ground,and can slightly reduce the horizontal displacement of the pile above the ground.The pre-imposed horizontal load can increase the lateral friction resistance of the pile within 1.5 m below the ground,thereby increasing the ultimate uplift bearing capacity of the single pile.Under the same inclined load,the greater the load inclination is,the greater the pile top combined displacement is.Under the same inclined load,with the increase of load inclination,the horizontal displacement of the pile,bending moment,normal soil pressure,and soil stress at the same depth increase. |
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