【導(dǎo)讀】面各個教學(xué)環(huán)節(jié)的繼續(xù)、深化和拓展，是培養(yǎng)我們綜合素質(zhì)和工程實踐能力的重要階段。分析和解決實際問題的能力。和以往的理論教學(xué)不同，畢業(yè)設(shè)計要求我們在教師指導(dǎo)下，獨立地、系統(tǒng)地完成一個工程設(shè)計，以及能掌握一個工程設(shè)計的全過程，學(xué)會考慮問題，分析問題和解決問題，并可以繼續(xù)學(xué)習(xí)到一些新的專業(yè)知識，有所創(chuàng)新。在路基工程中，擋土墻可用以穩(wěn)定路堤和路塹邊坡，減少土石方工程量和占地面積，防止水流沖刷路基，并經(jīng)常用于整治坍方、滑坡等路基病害。在山區(qū)公路中，擋土墻的。為避免大量挖方及降低邊坡高度的路塹地段；為節(jié)約用地、減少拆遷或少占農(nóng)田的地段。在考慮擋土墻的設(shè)計方案時，應(yīng)與其他方案進(jìn)行技術(shù)經(jīng)濟(jì)比較。技術(shù)經(jīng)濟(jì)條件及當(dāng)?shù)氐慕?jīng)濟(jì)等因素。重力式擋土墻一般由塊石或混凝土材料砌筑。重力式擋土墻是靠墻身自重保證墻身。筋以承受拉應(yīng)力，故墻身截面較小。在現(xiàn)場拼裝而成，依靠填土與結(jié)構(gòu)的相互作用力維持其自身穩(wěn)定。與重力式擋土墻相比，

　　

【正文】 e relationship. Limit analysis takes advantage of the upperand lowerbound theorems of plasticity theory to bound the rigorous solution to a stability problem from below and above. Limit analysis solutions are rigorous in the sense that the stress field associated with a lowerbound solution is in equilibrium with imposed loads at every point in the soil mass, while the velocity field associated with an upperbound solution is patible with imposed displacements. In simple terms, under lowerbound loadings, collapse is not in progress, but it may be imminent if the lower bound coincides with the true solution lies can be narrowed down by finding the highest possible lowerbound solution and the lowest possible upperbound solution. For slope stability analysis, the solution is in terms of either a critical slope height or a collapse loading applied on some portion of the slope boundary, for given soil properties and/or given slope geometry. In the past, for slope stability applications, most research concentrated on the upperbound method. This is due to the fact that the construction of proper statically admissible stress fields for finding lowerbound solutions is a difficult task. Most previous work was based on total stresses. For effective stress analysis, it is necessary to calculate porewater pressures. In the limitequilibrium method, porewater pressures are estimated from groundwater conditions simulated by defining a phreatic surface, and possibly a flow , or by a porewater pressure ratio. Similar methods can be used to specify porewater pressure for limit analysis. The effects of porewater pressure have been considered in some studies focusing on calculation of upperbound solutions to the slope stability problem. Miller and Hamilton examined two types of failure mechanism: (1) rigid body rotation。 and (2) a bination of rigid rotation and continuous deformation. Porewater pressure was assumed to be hydrostatic beneath a parabolic free water surface. Although their calculations led to correct answers, the physical interpretation of their calculation of energy dissipation, where the porewater pressures were considered as internal forces and had the effect of reducing internal energy dissipation for a given collapse mechanism, has been disputed. Porewater pressures may also be regarded as external force. In a study by Michalowski, rigid body rotation along a logspiral failure surface was assumed, and porewater pressure was calculated using the porewater pressure ratio ru=u/ǐz, where u=porewater pressure, ǐ=total unit weight of soil, and z=depth of the point below the soil surface. It was showed that the porewater pressure has no influence on the analysis when the internal friction angle is equal to zero, which validates the use of total stress analysis with Φ =0. In another study, Michalowski followed the same approach, except for the use of failure surface with different shapes to incorporate the effect of porewater pressure on upperbound analysis of slopes, the writers are not aware 30 of any lowerbound limit analysis done in term of effective stresses. This is probably due to the increased in constructing statically admissible stress fields accounting also for the porewater pressures. The objectives of this paper are (1) present a finiteelement formulation in terms of effective stresses for limit analysis of soil slopes subjected to porewater pressures。 and (2) to check the accuracy of Bishop’s simplified method for slope stability analysis by paring Bishop’s solution with lowerand upperbound solution. The present study is an extension of previous research, where Bishop’s simplified limitequilibrium solutions are pared with lowerand upperbund solutions for simple slopes without considering the effect of porewater pressure. In the present paper, the effect of porewater pressure is considered in both lowerand upperbound limit analysis under planestrain conditions. Porewater pressures are accounted for by making modifications to the numerical algorithm for lowerand upperbound calculations using linear threenoded triangles developed by Sloan and Sloan and Kleeman. To model the stress field criterion, flow of linear equations in terms of nodal stresses and porewater pressures, or velocities, the problem of finding optimum lower and upperbound solutions can be set up as a linear programming problem. Lower and upperbound collapse loadings are calculated for several simple slope configurations and groundwater patterns, and the solutions are presented in the form of chart. LIMIT ANALYSIS WITH POREWATER PRESSURE Assumptions and Their implementation Limit analysis uses an idealized yield criterion and stressstrain relation: soil is assumed to follow perfect plasticity with an associated flow rule. The assumption of perfect plasticity expresses the possible states of stress in the form F( 39。ij? ) = 0 (1) Where F( 39。ij? ) = yield function。 and 39。ij? = effective stress tensor. Associated flow rule defines the plastic strain rate by assuming the yield function F to coincide with the plastic potential function G, from which the plastic strain rate pij? can be obtained though 39。39。pij ij ijGF? ? ??????? （ 2） where ? = nonnegative plastic multiplier rate that is positive only when plastic deformations occur. Eq. (2) is often referred to as the normality condition, which states that the direction of plastic strain rate is perpendicular to the yield surface. Perfect plasticity with an associated with very large displacements are of concern. In addition, theoretical studies show that the collapse loads for earth slopes, where soils are not heavily constrained, are quite insensitive to whether the flow rule is associated or nonass