A Study On The Effect Of Filling Properties And Groove Slope To The Earth Pressure Of High Fill Loess Open Cut Tunnel

The urban of loess plateau shortage of land, cutting and cultivation has become an important way to alleviate this situation, it is inevitable to back fill the existing highway(railway) open cut tunnel in the process of cutting and cultivation, it also making open cut tunnel construction increasing, unreasonable calculation of earth pressure will cause a variety of problems to design and application of these projects, including projects investment waste and Structure security concerns etc. The current design specifications rules that still using soil column method( ? = ?H)while calculating the vertical earth pressures on the top of high fill open cut tunnel. This formula only applies to earth pressure calculation while the back filling height is relatively low, during the design of high fill open cut tunnel, if use this formula to calculate the earth pressure unconditional will lead to the size of the structure too conservative thus making the cost of open cut tunnel structure and construction costs of infrastructure projects increase, resulting in economic waste. Based on the above analysis, the effcetion of filling properties, slope angle, bottom width ratio of the groove to the distribution of earth pressure have made overall and deep study through earth pressure calculation theoretical derivation, laboratory model test and finite element numerical analysis, The main work and conclusions are as follows:(1) The experimental study on the filling element that were used in laboratory model test,it can get the cohesion c and internal friction angle?of loess and improved loess by using triaxial compression test and consolidation test; get the liquid limit wl and plastic limit wp of loess and improved loess by using liquid plastic limit joint measurement; by using light compaction test, the test data is plotted the relation curve between dry density ?d and moisture content w then get the maximum dry density ?dmax and the optimum moisture content of loess and improved loess; and finally tested the compression coe·fficient and deformation modulus of loess and improved loess. These physical and mechanical parameters provided basis for choice of the theoretical formula and finite element model parameters.(2) Through finite element numerical analysis of the earth pressure on the top and arch foot of open cut tunnel for the working conditions of different slope angle, bottom width ratio of the groove and filling properties. using Mohr-Coulomb ideal elasto-plastic model to simulate the loess, using linear elastic materials to simulate the open cut tunnel and rigid foundation. Analysis obtained: With the increase of the slope angle, the earth pressure of the top and arch foot of open cut tunnel decreases; With the increase of bottom width ratio of the groove, the earth pressure of the top and arch foot of open cut tunnel increases; With the increase of cement content in cement improved loess, the earth pressure of the top of open cuttunnel decreases, while the arch foot earth pressure increases, improved loess is best used as filling in the process of high backfill loess open cut tunnel.(3) The laboratory model test adopts to study the distribution regularity of earth pressure for high fill loess open cut tunnel, six kinds of working condition is established under the combination of two factors such as the slope angle and bottom width ratio of the groove. The results showed that: when the bottom width ratio of the groove is certain, the greater the slope,the total width and gravity of the lateral soil column decreases, the effect of slope is relatively increased, while with the increase of slope angle the vertical component of friction increases,the earth pressure of the top of open cut tunnel decreases, and with the filling height increases,the effect is more obvious; when the slope is constant, with the gradual increase of bottom width ratio of the groove the effect of slope to lateral soil column gradually decrease, and the earth pressure of the top of open cut tunnel gradually increase.(4) Five classical earth pressure theory and its scope are summarized, including earth pressure coefficient method, soil column method, unloading arch theory, dispersion limit equilibrium method and Terzaghi theory. And based on the Coulomb earth pressure theory,limit equilibrium method theory, a earth pressure mechanical model of high fill loess open cut tunnel is established, the earth pressure calculation formula on the top of open cut tunnel is derived which is consider the influence of slope, it can provide theoretical reference for structural design and construction on high fill open cut tunnel.(5) By the results of laboratory model test, the results of finite element numerical analysis with the formulas derived in this paper comparing mutual authentication, can get:when the fill height is less than 30cm(simulate fill 7.5m), the results of this theoretical formula calculation, finite element numerical analysis, laboratory model test are consistent with the calculated values of soil column method(?h), with filling height continues to increase, the results of theoretical formula, finite element numerical analysis are consistent with the result of ?h and theoretical calculations and finite element results average difference of 8%. The model test results gradually deviated from theory and finite element values from the non-linear growth, mainly because in the process of model test, in order to prevent open cut tunnel by man-made destruction, the compaction degree of loess on the top of open cut tunnel is low, causing generate soil arching effect.