The Research On Bearing Characteristics And Design Method Of Group Piles Foundation Of High Pile Pier Type Wharf In Inland River In Steep Rock Area

In the pile foundation engineering,the research of the slope pile foundation is always a hot spot and a difficult point.Compared with the flat rock-socketed pile,there are obvious differences in the bearing mechanism of slope rock-socketed pile.At present,the bearing capacity and behavior analysis of rock-socketed pile and related calculation theories are mostly based on the basic assumption that pile foundation is at the horizontal ground.There is not enough knowledge and solution for slope rock-socketed pile.Especially for the port pile foundation in the steep rock river bank(often in the form of group piles foundation),the working condition is extremely complex(superstructure(or mechanical)load,ship impact force(cable force),flow force and so on),and its research work has important engineering significance.Steep rock single pile and group piles foundation under vertical / horizontal /bidirectional / combined load.The lack of rock mass before slope and the increase of rock mass behind slope affect the vertical / horizontal / bidirectional / combined bearing capacity of single pile and group piles foundation in steep rock,and the related bearing mechanism researches are very few;In the study of group piles effect,it is usually only considered the case that the bearing platform is rigid,and the overall working ability of group piles is estimated too high;For the group piles effect of steep rock group piles foundation,there is no clear definition in port engineering standard.To solve the above problems,the vertical / horizontal / bidirectional / combined load characteristics of steep rock single pile / group piles are researched step by step.By adopting the numerical simulation method of drilling hole in rock slope,pouring concrete of pile and platform,loading process of group piles foundation,bearing capacity /bahavior of steep rock single pile / group piles under vertical / horizontal /bidirectional / combined load is analyzed theoretically(change of slope angle,pile spacing,pile diameter and rock-socketed depth is taken into account).The main conclusions are as follows:(1)Under vertical load,loss effect of rock mass before pile and enhancement effect of rock mass behind pile exist in single pile in steep rock.The vertical bearing behavior of rock-socketed pile is affected by the effect of rock loss before pile and rock increase behind pile.With the increase of slope angle and vertical load on pile top,the horizontal displacement of pile will disturb the loss effect of rock mass before pile and enhancement effect of rock mass behind pile.(2)Under horizontal load,critical value fluctuation of rock-socketed depth exists in single pile in steep rock.When rock-socketed depth is increased to a certain degree,the contribution of rock mass resistance to horizontal bearing of slope rock-socketed pile is relatively limited;If the depth of rock-socketed pile is increased continually,the slope rock-socketed pile tend to developement of elastic long pile,the flexural deformation of the pile is further exerting,the negative displacement of rock socketed section increases and the horizontal displacement of pile top increases,that is,the horizontal bearing capacity of pile foundation decreases relatively.(3)Under vertical load,group piles radial expansion exists in group piles in steep rock.Under vertical load,the bearing platform is compressed and deformed.Due to the transmission of force,the four piles / the five piles connected with the bearing platform produce external buckling deformation(group pile radial expansion).The evolution process of the effect of rock loss before pile and rock increase behind pile in group piles in steep rock is further influenced by the group piles radial expansion(the quadrangle four piles / plum blossom five piles).(4)Under vertical load,stress local effect(Saint Venant principle)interpretation in group piles in steep rock.Through a lot of numerical simulation and theoretical analysis,this thesis holds that the sudden change of axial force near the pile top is mainly related to the degree of pressure at the pile top(the complexity of the force).For example,the larger the vertical load and the larger pile spacing,the greater the deformation of the bearing platform and the greater the degree of pressure at the pile top,the more complex the force of the pile top is.The main reason for the sudden change of the axial force near the pile bottom lies in that the rock mass around the pile bottom and the pile bottom is extruded violently,and the stress concentration is aggravated.Arching effect exists in the rock mass around the pile bottom,which results in the sudden change of the axial force near the pile bottom.(5)Under horizontal load,group piles space effect exists in group piles in steep rock.Under the conditions of different slope angle/ pile spacing/ pile diameter /rock-socketed depth,there is a certain degree of deflection in the bearing platform,and the horizontal displacement state of each pile top under the bearing platform is different,and the stress state of each pile is also different(the degree of extrusion between rock mass and each pile),the transmission of force will change on the whole group piles foundation(space effect of pile group foundation).(6)Under horizontal load,exertion degree of horizontal bearing capacity of eachpile top in group piles in steep rock(without considering stress local effect(Saint Venant principle)).From the two aspects,the proportion of maximum positive moment near the pile top and the proportion of maximum positive shear near the pile top.(1)Steep rock group piles under different slope angle / pile spacing / pile diameter conditions.With the gradual increase of slope angle / pile spacing / pile diameter,exertion degree of horizontal bearing capacity of the front row piles top decreases gradually,and that of the back row piles top increases.(2)Steep rock group piles under different rock-socketed depth conditions.With the gradual increase of rock-socketed depth,exertion degree of horizontal bearing capacity of the front row piles top increases roughly,and that of the back row piles top decreases(but compared with pile 1 and pile2,the proportion of the largest positive moment or the largest positive shear near pile top of pile 3 and pile 4 is still larger.).(7)Under horizontal load,exertion degree of horizontal bearing capacity of each pile top in group piles in steep rock(with considering stress local effect(Saint Venant principle)).From the aspect of the proportion of the shear force distribution on the each pile top.(1)Under different slope angle(R=15°,R=30°and R=45°)/ pile spacing /pile diameter / rock-socketed depth conditions,exertion degree of horizontal bearing capacity of the front row piles top is smaller,that of the back row piles top is larger.(8)Bidirectional load condition--influence of vertical load variation(horizontal load invariant)and horizontal load variation(vertical load invariant)on bidirectional bearing capacity and characteristics of steep rock single pile / group piles foundation.(9)Combined load condition--influence of five loading schemes(five load conditions of port engineering)on combined bearing capacity and characteristics of steep rock single pile / group piles foundation.(10)The design method of “double controls of single pile--double controls of group piles” for group piles foundation of high pile pier type wharf in inland river in steep rock area under vertical / horizontal / bidirectional / combined load is proposed.Among them,“ double controls” refers to first control--bearing capacity(inclined to be macroscopic),second control – bearing behavior(inclined to be microcosmic).