Study On Two-parameter Design Theory Of Lattice Frame And Its Application

Slope stability is one of very important research subjects in geotechnical engineering. With the development of economic and society, large scaled infrastructure move to mountains, which lead to the slope stability becoming more and more significant, and great attention was payed to reinforcement project as an effective method to prevent destroy. It can supply enough anti-slide force when Lattice frame was applied combining with anchor-rope, and more beautiful than other structure. So it applied widely in diversified fields, but its design theory lags behind the practice.Two-parameter foundation model was introduced to calculate the force of lattice frame. By means of rational hypothesis on distribution coefficient of soil stress, the parameters was acquired. Several examples were calculated to prove the model's rationality, and FLAC^3D was carried out to demonstrate the reaction of horizontal foundation and slope toward load and the internal force distribution law of beam, finally the application of two-parameter method model was introduced. Results are as follow:1. Force of lattice frame is analyzed to derive the control equation: E_bI_b(d⁴y)/(dx⁴)=q(x)-p(x)·Three typical calculation methods were analyzed, which including inverse beam method, Winkler method and semi- infinity elastic space mehtod. The result indicates that inverse beam method, which simply based on hypothesis of distributed load, is suitable for the situation that beam and base have relative great stiffness, the homogeneous foundation and symmetrical load in proper space only. Winkler method ignores the stress diffuseness in foundation, it is applicable to cracked, low strength and less elasticity foundation. Semi-infinity elastic space mehtod regards the foundation as homogeneous, consecutive and stretchy semi- infinity body, the contact pressure can be calculated according to static equilibrium and deformation compatibility, and ordinary suitable for rock foundation.2. Two-parameter foundation model was applied to calculate the force of lattice frame. Beginning with the stress and strain state of foundation, the manipulative equation of the beam was achieved under the help of equilibrium conditions on z axes, the expression of the equation is -k_Hâ–½²Ï‰(x,y) + k_vω(x,y)=q(x,y), it was controlled by two parameters k_v and k_H, which respectively representate contace presure modulus and lateral modulus influenced by vertical stressσ_z and shearing strengthÏ„_xz,Ï„_yz . Rational hypothesis on characteristic of foundation stress distribution coefficient helps to infer calculation method and analytic solution of lattice frame. Comparing to Winkler method, semi- infinity elastic space mehtod, indoor test and field test, the result indicates that two-parameter method is closer to test data and it is of more comprehensive application.3. The numerical simulation is carried out by FLAC^3D. The mechanism of SEL-pile is analyzed. The characteristic of internal force of single beam on horizontal foundation and slope were anaylzed, so did the distribution of stress and displacement. The principal result of simulation includes difference between internal forces brought by single beam on horizontal foundation and slope, which internal force on slope is 10% smaller than that on horizontal foundation. Likely there is difference between strain diffuseness characteristics, owing to friction of slope girder to sloping face and difference in gravity strain field of slope and strain field of horizontal foundation.when lattice frame is composed with beam and carling they bear the load at the same time, which reduces the internal force of beam as concentration degree of strain at the bottom of beam foundation and average the strain diffuseness to enlarge its extent, therefore the design of lattice flame has prior consideration in actual project depending on its notable effect.4. Taking the slope in the Three Gorges Reservoir area of Zigui as an example, the application of two-parameter was detailedly introduced. The beam structure was designed by inverse beam method, Winkler method, semi- infinity elastic space mehtod and two-parameter method, the compared result indicated that the structure which based on two-parameter method could save investment at a certain extent.