| Land leveling is the important measure in the construction of high and stable yield in order to do well the land grading, and has great influence on the reasonable irrigation, water saving, labor productivity increasing, mechanical operation efficiency exertion, soil improvement, and water, land, and fertilizer retention, etc. Transforming slope into terrace is the main form of land leveling in the hilly area, which includes slope-reducing treatment, soil ridge and retaining rock wall construction. However, with large-area development of land consolidation in the program of farmland regulation, it emerges a serious problem from the program which has been carried out, especially in the sloughing control of soil ridge and retaining rock wall in the hilly area. The construction of soil ridge and retaining rock wall must take into account of several factors, such as properties of soil mechanics, slope and rainfall. In the design of soil ridge and retaining rock wall, it mainly uses the design parameters by means of range value, which is provided for the project design codes of land development and consolidation, instead of reference value in the specific environment. Therefore, this paper makes use of the Stress Control Triaxial Compression Apparatus to study soil shear strengths of loess, calcareous purple soil, and neutral purple soil in hilly areas of Chongqing, which is in different water contents, dry densities and dry-wet cycles. Meanwhile, based on the demand of soil ridge and retaining rock wall's stability, it combines with the theory of soil mechanics for the sake of making sure of slope stable angle of soil ridge in the different soil types and different environments. Furthermore, through VB programming, it calculates the optimal cross section of retaining rock wall. In that case, it can achieve the design optimization of soil ridge and retaining rock wall in the land consolidation project. And it can provide the scientific evidence of design for land engineering in hilly areas of Chongqing so as to promote the land consolidation efficiently. The main results are as the following:1. Influences of soil shear strengths on soil dry densities, water contents and dry-wet cyclesIn the same dry densities, c shows a trend of first increase and then decrease along with water contents increasing; in the same soil water contents, c increases with dry densities increase as a whole. Andφall takes on a clear reductive tendency towards water contents increasing. The interaction of water contents and soil dry densities produces a great effect on c in order that c can increase with soil dry densities increase within the limit of 1.3 g/cm3-1.7 g/cm3. And each soil dry density corresponds to single water content. So c can reach to the maximal value in this interaction. Nevertheless, the interaction of water contents and soil dry densities has the minor influence onφ. In the same dry densities,φgoes up with dry densities increase slowly and the value has a little change. On the contrary, water contents make an important impact onφ. With the respect to sands, clays represent the relative large conditions of c andφ. And c andφin the loess and calcareous purple soil are greater than those of neutral purple soil. In three soil types, c values decrease with times of dry-wet cycle increase. And twice through top cycles attenuate greatly. From the third time to the fifth time, attenuating ranges of c values tend to stabilize from reducing. After the fifth time of dry-wet cycle, c of yellow soil is slightly bigger than that of calcareous purple soil. Both of them are larger than neutral purple soil. In the three different kinds of soil,φshows a trend of decreasing, but the differences are among them. And after the final cycle,φof yellow soil is 24.6°, the biggest. The second is 22.6°, theφof neutral purple soil. The least is 19.3°, theφof calcareous purple soil.2. The optimal design of soil ridge in the land consolidation project through the different shear strengthsFor sands, the allowable value ofθwill reach the maximum 34°, if the soil ridge does not experience the dry-wet cycle. The first time of dry-wet cycle has no effect onβ, the second to the fourth start to reduce, and the last time comes to the minimum. After the fifth of dry-wet cycle,φwill not decrease fast with the ongoing times of dry-wet cycle and basically reaches to stability. Thus the construction of neutral purple soil'sθcan be designed as 21°.MoreoverΚof cohesionless soils has some connection withφandθ, but has nothing to do with slope height and severe soil erosion.As for clays, under the same condition,θof soil ridge tends to decrease with the increasing of ridge height. Within 1.5m of height,θof loess and calcareous purple soil are the same. When the height is greater than 1.5m, the allowable value of calcareous purple soil'sβis smaller than that of loess. In other words,θof soil ridge demands gentle slope angles to meet requirement of their stability. In consideration of land occupation and stability, soil ridge can be built on the basis of theβdesign when the ridge height of loess is within 3m. However, in calcareous purple soil of Suining, the height of soil ridge should be controlled within 2.5m.3. The optimal design of retaining wall of retaining rock wall in the land consolidation project through the different shear strengthsThe earth pressure of retaining wall depends on the drainage facilities, for example, the loess, whose active earth pressure is going up with the height of retaining wall increases. And the retaining wall with the drainage facilities gets the smaller pressure than that of no ones. The difference value is 17%.With the height of retaining wall increases, the active earth pressure of it goes up like the parabolic curve. The height increase from 0.5m to 2m, and the active earth pressure of 2m wall is 16 times as much as that of 5m wall. When the height rises from 2m to 5m, the soil pressure augments slowly, and the active earth pressure of 5m wall is 6 times as much as that of 2m wall. On the other hand, under otherwise equal conditions, when the slope angleβof the filling soil on the surface of the wall behind is fixed, the earth pressure of s reclining on the slight slope (ε>0) is larger thanεadvancing to the rise (ε<0). So the earth pressure diminishes withεdecreases.The results of optimal designs in the three kinds of soil regions reveal that the structures of retaining walls are designed to the wall reclining on the slight slope. In the meantime, when the height andβis the same, the size of retaining wall in the calcareous purple soil area is bigger than that of loess area. And by comparison among the three soils, the retaining wall of neutral purple soil area is the least.To sum up, the differences of shear strengths in complicated environmental hilly areas, which manifest the interactions among the external conditions, such as the soil dry densities, water contents, and dry-wet cycles. Recently, the range value, offered by the design criteria of land consolidation program, is deficient in appropriateness, and overlooks the specific influences of different environments on the design parameters so that it is difficult to economize the investments, not to mention the optimal design. The ensuring of design parameters of soil ridge largely depends on the stable value, which is affected by dry-wet cycle so as to rapidly decrease the soil shear strengths. Soil physical properties and the filling-slope behind the wall are not so identical in diverse conditions, which codetermine the design parameters of cross sections of retaining rock wall's retaining walls. The design of soil ridge and retaining rock wall is system engineering. For the soil ridge, in the construction of soil ridge, it can add the lime to improve the soil physical and mechanical properties, which can obtain the larger shear strength and eliminate the functions of dry-wet cycle. Whereas for the retaining rock wall, it can go deep into studying on other structures and materials in the light of demands of engineering practice in future research. So it is necessary to do the intensive study in order to further improve the design system of soil and retaining rock wall of land consolidation project in the hilly and mountains' areas of Chongqing.
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