Centrifuge Modeling Tests On Slip Surfaces In Backfill And Earth Pressure Characteristics Against Balance Weight Retaining Wall

Balance weight retaining wall is a kind of retaining structure widely used in railway and highway engineering in mountainous areas.The wall has a good effect of closing the slope under the condition of steeper transverse slope.Existence of balance weight platform greatly enhances the stability of the wall,improves the distribution of foundation stress,and reduces the amount of foundation excavation and backfill.In practical engineering,the balance weight retaining wall can effectively maintain slope stability,control roadbed diseases such as landslide collapse,intercept rockfall from high cutting slopes,and reduce vehicle driving threat.A series of good engineering effects will appear such as low cost or convenient construction when the wall is used with bridges and other structures.Due to the unique back shape,the interaction between balance weight retaining wall and soil is particularly complex.The existing design standards ignore the mutual influence between soil pressure of the upper and lower walls.Design results have a large deviation from the actual date,resulting in shear failure along the heel of the upper wall.At present,the soil deformation characteristics,earth pressure action characteristics,and structural failure mechanism of the balance weight retaining wall are unclear,and there is a lack of corresponding engineering countermeasures.Therefore,it is urgent to establish a set of earth pressure calculation methods suitable for complex wall back conditions.Based on domestic and foreign research,five groups of centrifugal model tests of different embankment slope height,filling strength and size of balance weight platform are designed and conducted.Soil slip surface,earth pressure characteristics and structural design calculation method are systematically studied.The main research results are as follows:(1)The soil deformation and fracture characteristics of the balance weight retaining wall under translation mode are revealed.Through the soil deformation photogrammetry device and image processing technology,the deformation vector of backfill before and after the test was obtained.The results show when the active limit state is reached,the slip surface towards the lower wall and the second slip surface towards the upper wall occur in the backfill of the balance weight retaining wall,which is divided into three regions:translational soil,sliding soil and immobile soil.Only the slip surface towards the lower wall occurs in backfill of the broken-line retaining wall,which is divided into sliding soil and immobile soil.The shear deformation inside the sliding soil is basically coordinated,and the first slip surface towards the upper wall assumed by the design calculation no formed.(2)The mechanism of diagonal tension failure at the upper wall heel of the balance weight retaining wall is clarified.The comparison between the test data and the design calculation value shows that shear stress of the first slip surface towards the upper wall does not reach the shear strength of soil,resulting in the earth pressure test value on the upper wall to be 32.16%larger than the design calculation value but 40.39%smaller for the lower wall,and resultant force point of earth pressure on the upper wall is about 21.03%higher.The larger earth pressure test value and higher force point of earth pressure on the upper wall are the key factors causing shear stress of the balance weight retaining wall along the oblique section at the upper wall heel to be too large and form the shear failure disease.(3)Modified calculation method is proposed for earth pressure of the balance weight retaining wall based on the shearing state of the first slip surface towards the upper wall.According to the experimental phenomenon that the first slip surface towards the upper wall no occur,and introducing a mobilization coefficient(η≤1)of internal friction angle(φ)for the first slip surface towards the upper wall,a modified pattern based on the stress declination angle(φ_η=ηφ)for calculating earth pressure against balance weight retaining wall is proposed,and the corresponding modified formula is deduced.The analysis shows that theηvalue mainly affects the distribution of the earth pressure on the upper and lower walls.Compared with the design results of the existing specification,the calculated modified value of earth pressure and slip surface dips are closer to test data.