| The stratigraphic structure distribution of the parts of Qingdao is that the upper part is the soil layer and the bottom is the strong weathering mudstone layer,and it is mainly distributed in Jiaozhou,Chengyang and High-tech Zone.At present,there are more pile foundations in the area,and the piles are usually driven into the strong weathering mudstone to act as the “rock-socketed-driven-pile” by the hammering method of pile construction technology.However,due to the wide distribution of the strong weathering mudstone,the rock properties vary greatly.As the pile end bearing layer,some engineering problems often occur,which can affect the progress of the whole project.Based on the collection and collation of the literature and combined with foundation piling of the Qingdao strong weathering mudstone,the bearing capacity of this rock socketed pile was studied,and the common engineering problems of the driving pile foundation in the area were discussed.The following work has been carried out in this paper:(1)The definition and classification of rock-socketed piles were summarized,and on the basis the law of vertical load transfer of rock-socketed piles was analyzed.The process of axial load of rock-socketed pile was the gradual process of the pile-soil lateral resistance,the pile-rock side resistance and the pile end resistance.And it was analyzed separately.The pile-soil lateral resistance and the pile-rock side resistance were the function of the relative displacement of them,but the displacement of the pile-rock side resistance researched the limited value was smaller than the pile-soil relative displacement,and for the prefabricated rock-socketed pile,the shear failure surface often occurred in the pile-rock interface when the resistance researched the limit.(2)The vertical bearing capacity of the rock-socketed pile included the pile-soil lateral resistance,the pile-rock side resistance and the pile end resistance.It was a comprehensive reflection of the pile-soil-rock interaction,and the determination of the vertical bearing capacity of the pile rock-socketed pile was the key in the whole design and construction.The commonly used calculation methods of vertical bearing capacity of rock-socketed pile were synthesized,and the various methods of calculation model of it were given,and the static load test of pile was similar to the actual load state of the pile and it was still the most commonly used and the most reliable method.(3)Taking a pile driving project(Engineering A)on the strong weathered mudstone in Qingdao as an example,this paper analyzed the problems that the pile foundation construction was difficult to penetrate into the rock formation.The results showed that the bearing capacity of strong weathered mudstone was larger in actual engineering,and the reason for the static load test load to the emergence of a sudden drop was that the pile head concrete was crushed instead of the damage of the pile end rock.The static load test curve was quite different from the traditional static load curve of the pile when the pile tip penetration failure,and the steep drop could not judge the destruction of the mudstone according to the static load test only.The static test itself should be also judged correctly.(4)Combined with the static load test of the pile(Engineering B)into the strong mudstone,the bearing capacity and settlement characteristics of the rock-socketed driven pile were analyzed under the failure load.The ultimate bearing capacity of individual engineer of the static load test did not meet the design requirement.The analysis showed that although the natural state of strong weathering mudstone had good bearing capacity,the groundwater could penetrate into the fracture of the mudstone along the pile surface after the construction,which caused the mudstone soften and strength decreased.When the piling work on the strong weathering mudstone were studied,the specific analysis of the specific project should be done. |
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