Settlement Deformation Characteristics Of Soft Soil And Its Control Measures On The Fourth Runway Of Pudong Airpor

The thickness of soft soil in Pudong Airport area is very large.The thickness of soft soil is generally more than 30m.The area where ancient river flows through is even up to 60m.The deformation of soft soil is very large under load.The deformation control of deep soft soil becomes the primary problem to be solved in engineering construction.The existing runway first,second and third of Pudong Airport have spent great efforts in soft foundation treatment during the construction process to solve the deformation problem of deep soft soil.The first runway adopts dynamic compaction method,the second runway adopts "deep preloading + shallow dynamic compaction"method,the third runway adopts impact rolling method,and after the three runways are put into operation.Long-term settlement observation has been carried out,and it is found that large settlement deformation still occurs after runway navigation.The average settlement of one runway is about 62 cm in 14 years of navigation,and that of the second runway is about 36 cm in 8 years of navigation.The new four runways are adjacent to the sea embankment.Compared with the first,second and third runways of the airport,the geological conditions are worse and the treatment of soft foundation is very difficult.Settlement deformation occurs in the process of deformation and strength treatment of soft soil,and under the influence of aircraft load after navigation.Settlement deformation runs through the whole process.Only by mastering the deformation characteristics of soft soil can appropriate deformation control countermeasures be formulated.Therefore,this paper studies the deformation characteristics of soft soil in the process of soft foundation treatment,studies the deformation characteristics of soft soil under aircraft load,and then formulates the deformation control measures of soft soil in four runways.The main research work in this paper is as follows:Firstly,this paper studies the characteristics of soft soil in different runway areas of Pudong Airport,especially the characteristics of silty clay in layer 4.Through the study,it is found that the engineering characteristics of soft soil layer are getting worse and the difficulty of settlement and deformation control is increasing gradually from three runway to four runway(from West to east).The four runway is more difficult to deal with in soft ground than other runways.After the runway is opened to traffic,the soft soil foundation will still undergo great settlement deformation under the influence of aircraft dynamic load.The settlement caused by aircraft dynamic load can not be ignored.In this paper,the variation of additional stress in the soil foundation under the action of aircraft dynamic load and the depth of influence are analyzed.The deformation characteristics of aircraft under dynamic load are studied.It is found that the main influence depth of aircraft load is less than 10 m.especially for the shallow soft soil layer within 5 m.The settlement deformation caused by aircraft load on existing runway in Pudong Airport is less than 160 m M.The ratio of-aircraft dynamic load settlement to total settlement after construction is larger at the initial stage of navigation,but with the increase of runway navigation time,the foundation soil is consolidated,the soil strength is gradually increased,the influence of aircraft dynamic load is gradually reduced,and the proportion of aircraft dynamic load induced settlement in total settlement is gradually reduced.Aiming at the problem of large deformation of deep soft soil layer in the four-runway area,this paper carries out the surcharge test and studies the deformation characteristics of soft soil under the action of large-area surcharge.Through the test,it is found that the settlement deformation of soft soil in the four-runway area is veiy large under the action of large-area surcharge.This test combined surcharge with plastic drainage plate area.The average settlement deformation of the soft soil in the "insertion plate area" is 1187.9 mm,and that of the "non-insertion plate area" in the direct surcharge area is 662.4 mm.Among them,the settlement deformation of the soft soil in the depth of 10-18 m is large,and the influence depth of large area surcharge is very large.The settlement measured at the depth of 38 m is still 107 mm..After loading,the porosity ratio of the main soil layer decreases,and the compressive modulus and the number of standard penetration strikes are increased to varying degrees.It shows that the deformation of the soil layer decreases and the strength increases.In this paper,the method of numerical simulation is used to study the deformation of large-area soft clay.The creep model of soft clay is used to simulate the consolidation and creep of clay and silty clay.The results of numerical simulation are very close to the field test data,which better reflects the actual situation in the field and achieves the desired results.It is found that there is uneven settlement on the surface of the loading area,and the settlement in the middle part of the loading area is large and the edge is small.In this experiment,the settlement at the top of the edge slope is about 76%～80%of the settlement in the middle part of the loading body,5 m from the top of the loading body,84.7%～88.8%of the settlement in the middle part of the loading area and 84.7%～88.8%from the slope.At the top 10m,the ratio of settlement to central area settlement exceeds 90%.Therefore,when carrying out the design of surcharge,the influence of the boundary effect can not be ignored.Although the problem of large deformation of soft soil foundation is solved under the action of large-area surcharge,the strength of soil layer is still very low.Combined with the strength treatment test of surface soil,the deformation characteristics of soft soil under impact load are summarized,and the construction method suitable for shallow strength treatment of four runways is summarized.Through the above research,the deformation characteristics of soft soil under large area load,under impact vibration load and under aircraft load are mastered.On this basis,the deformation control measures of soft soil in four runways are put forward.Finally,according to the analysis of settlement deformation data of four runways after navigation,the control effect of settlement deformation of four runways is evaluated.