Research On Calculating Methods Of Earth Pressure On Gravity Retaining Wall With Cohesive Backfill

It is a key to ascertain earth pressure correctly in retaining wall design. The linear earth stress distribution result of classical theory like Rankine and Coulomb is not correspondent with the practice. A scholar named M.EKarah in Soviet Russia adopted differential level layer unit to analyze equilibrium condition of forces for retaining wall with sandy backfill firstly and confirmed that earth stress distribution is nonlinear in theory, then some domestic scholars modified the method to apply it to retaining wall with cohesive backfill and arbitrary wall back angle and fill surface, considering friction effect and adhesive force on the soil-wall interface ,and the theory is thought of as the method of layer analysis.Though the method is relatively complete, there are two problems when using it to calculate active earth pressure on retailing wall with cohesive backfill. Firstly, the result of earth stress near the top of wall may be negative, and this leads to that the strained condition there during the formula is being deduced is not consistent to that when the result have being got . Secondly, the height near the top where the earth stress is negative is thought of as crack depth, but the value is too bigger.Aiming at these problems, the impact of cracking course of cohesive backfill for earth stress is considered and the method is modified, then the formulas on crack depth and earth stress distribution are deduced again. In order to verify its rationality, the crack depth formula adopted and equilibrium condition of forces on sliding wedge behind wall combined with, a resultant force formula on earth pressure is deduced and the distribution is assumed to be linear, which is the Coulomb Theory with Crack Depth Formula of the Modified Method of Layer Analysis.Corresponding programs developed, influences like cohesion and internal friction angle and adhesive force and external friction angle and fill surface angle and back angle and surcharge on the results of the two modified methods and the available methods like Generalized Coulomb Theory and Coulomb Theory with Crack Depth Formula of Rankine and the method of layer analysis are analyzed, and the results are compared, verifying rationality of the modified method of layer analysis.The results shows that, firstly, the modified method of layer analysis avoids the phenomenon that the earth stress near the top is negative, and its active earth pressure and overturning moment are even larger comparison with the method of layer analysis, the cohesion and adhesive force larger and external friction angle and back angle less, the difference more obvious, but internal friction angle and fill surface angle and surcharge have a relatively less influence on the difference. Secondly, the active earth pressure results of the two modified methods are in good agreement, and the crack depth results are equal, which are least comparison with those of the other methods. In addition, the overturning moment result of the modified method of layer analysis is largest.In short, the modified method of layer analysis is most reasonable theoretically, and its earth stress distribution result is consistent with the test, and it is most safe to adopt this method to design retaining with cohesive backfill, which can be used as a reference for engineers.