| Affected by terrain and climate conditions,many gullies are widly developed in mountainous areas,the bottom of the gully is easy to deposit and soft soil and the thickness is quite different.The physical and mechanical characteristics are not uniform influenced by topographic and climatic conditions.On the one hand,building highways in mountain areas will not avoid a large number of high fill culverts.On the other hand,if directly in the gully bottom construction of culvert in soft soil area prone to insufficient bearing capacity or settlement amount is too large which directly affect the construction of highway engineering structures.In addition,when the foundation soil is poor,the thickness is larger and on the high demand of settlement,it is obvious that it is uneconomical to take other foundation treatment methods or can not reach the treatment effect.At this time,it is an inevitable choice to use pipe pile to treat the soft foundation of the bottom of the culvert.But the mechanism of high fill culvert is complex,which is opposite to the design ideas of foundation and foundation of bridges and buildings.The greater the stiffness of foundation and foundation,the more obvious the stress concentration of the culvert,and the greater the actual external load of the structure.Therefore,how to reduce the stress concentration of culvert top as far as possible under the premise of reinforcement of soft soil is worth further studying.In this paper,based on the T6 elevation culvert solid project of Bao Mao Expressway(Guangdong section),the engineering survey and field test are used to monitor the soil pressure and fill settlement characteristics.By using the method of numerical simulation,the influence of the pile treatment range,depth,pile distance and the length of the lateral pile on the stress concentration of the culvert and the settlement of the foundation under the height of 5~50m are studied.The main results are as follows:(1)There is a great difference between the soil pressure of the culvert and the culvert of the high fill cover culvert with the current standard.The concrete manifestation is that the pressure of the culvert and the vertical earth pressure of the culvert is"U",and the horizontal earth pressure of the side wall is"3",which is different from the linear and trapezoidal distribution in the standard.Due to the asymmetric influence of the topography and geomorphologic condition,the lateral pressure and the settlement distribution rule of the culvert top fill have a significant bias load effect;(2)The vertical earth pressure,the vertical earth pressure coefficient,the differential settlement of the fill and the base settlement are negatively related to the pipe pile treatment range,the pile distance and the side pipe pile length,and there is a positive correlation with the depth of pipe pile treatment;(3)It is suggested that when the pipe pile is used to treat the soft foundation cover culvert of the high fill cover culvert,the width of the pipe pile is 3D(D as the culvert span)the depth of the pipe pile treatment is strictly controlled under the premise of guaranteeing the pile crossing of the soft soil.In addition,the"unequal length pile"layout is suitable for pipe pile placement,that is,the length of culvert side pipe pile should be as long as the length of bottom pipe pile,and at the same time,the spacing between piles should be increased properly.If set up properly,when compared with the natural foundation,the foundation settlement of the high fill culvert decreases nearly 50%after using the pipe pile composite foundation,and the average vertical soil pressure concentration coefficient K_s of the culvert is not more than 10%. |
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