On The Behaviour Of Composite Soil Nailing

Combined with two research projects of the construction department of hunan province in 2001 and 2003, which are study on deformation of soil nailing and study on optimum design of composite soil nailing , two kinds of composite soil nailing , which are "bolts + composite soil nailing " and "soil -cement mixing piles + composite soil nailing " are studied . A finite element method of plane problem is used to analyze the function of composite soil nailing in this paper, which provide theoretical base and engineering guidance for the wide use of composite soil nailing .The main research workings are as follows:1. Based on the Duncan-Chang non-linear E-B model, a finite element programmed-SCSN1 has been developed to analyze the deformation of composite soil nailing which include the calculation of the settling of ground and horizontal displacement of the structure of soil nailing and heaving of pit. And the problems of internal force distribution of soil nailing, the moment and shear force of soil-cement mixing piles and their performance are discussed, too.2. As a result of the pre-stress of bolts and stiffness of soil-cement mixing piles , the deformation of pit reduced to great extent and the stability and the maximum degree of depth of nailing have also improved greatly when compares with soil nailing . The horizontal displacement of wall of pit is usually measured on the middle or upper part of the wall, the earth pressure behind the soil-cement mixing piles is in the state of motionless in the "soil-cement mixing piles + composite soil nailing ", and the pressure on the surface of wall is less than that of motionless in "bolts + composite soil nailing".3. Considering the effects of small pre-stress by soil nailing ,the small pre-stress soil method , which is a method of lessening the deformation of wall , has been put forward according to the study of the relationship between piles and soil nailing in the "soil-cement mixing piles + composite soil nailing ". And this method has far-reaching significance on the practice of engineering.4. The pre-stress of bolts confined the deformation of soil nails nearby and its effect of reinforcement in "bolts + composite soil nailing". In order to make full use of the effect of reinforcement of these nails and lessen the deformation of wall, the delaying bolts pre-stress method has been put forward based on the process of calculation and contrast in this paper.5. In the "soil-cement mixing piles + composite soil nailing ", the maximumpositive moment of the soil-cement mixing piles is distributed in the middle of the wall of pit, and the negative one keep close to the ground ,and the maximum shear stress is distributed on the surface . It is concluded that, the stiffness of soil-cement mixing piles can be used to reduce the horizontal displacement of wall of pit efficiently, while it is not so to the length of soil nails. The deeper the soft soil layer, the greater the settling of ground and the deformation of pit and the heaving of pit. The narrow down soil of pit base would cause to make much greater deformation and settling of pit.6. Considering the shearing effects of soil nails and soil-cement mixing piles, a stable analytic method of composite soil nailing has been put forward. Through analyzing the length and distribution density of soil nails , the diameter of soil-cement mixing piles , the depth of soft soil and the coefficient of safety , we come to the conclusion that the efficient length of nail is (1.0~1.2)H . Sliding surface of soil mass has much relationship with the distribution density of soil nails, the characteristics of soil and the depth of soft soil.7. The concept of critical density is firstly put forward to distinguish soil nailing from soil nailed wall in this paper. The coefficient of safety is used to comment the stability of soil nailing, which increased with the distribution density of soil nails. However, when the distribution density of soil nails comes to the critical, the stability of soil nailing is decided by the outer stability, the...