重庆丘陵区梯田规划与工程设计分析
摘要
人多、人均耕地少和耕地后备资源紧缺是我国的基本国情。由于土壤贫瘠化、盐渍化、酸化、污染等原因,不少地方耕地质量又有进一步下降的趋势,已对我国的粮食安全、生活质量和社会可持续发展构成严重的威胁。目前,国内外学者主要是从施肥、耕作、栽培等农业管理措施角度探讨对耕地质量的影响及耕地地力的提升,然而,土壤资源一旦遭到污染或破坏自身难以在短时间内恢复,这些传统农业管理措施也难以在短期内达到耕地地力提升的要求。随着对粮食安全的恐慌、生态安全意识的增强,如何解决耕地质量下降、提升耕地地力,已成为土壤学的研究热点,现代土壤工程学随之应用而生。目前,关于现代土壤工程的研究均处于经验阶段,因此,有必要加强现代土壤工程设计和实施的量化、程序化和标准化的研究。
作为现代土壤工程组成部分的梯田工程是我国坡耕地治理的一项重要措施。就重庆丘陵区而言,实施梯田工程有助于实现农业增产、发展农村经济,同时也有助于防止农田水土流失、改善生态环境。但目前关于重庆丘陵区梯田工程的研究,主要集中于成效以及后期培肥的研究,而对梯田工程本身较少进行深入研究探讨。因此,本文以重庆市合川区大石镇和开县厚坝镇的梯田工程为例,对研究区的梯田布局和设计进行了分析,探讨了水系、土壤性质以及岩层性状等自然因素对其的影响。获得的主要研究结果如下：
(1)旱地梯田规划的制定主要依据研究区的地形条件及坡面水系情况进行的。本文依据临界坡度和主观分级坡度方法,确定0°-3°,3°-5°,5°-15°,15°-25°四级坡度分级标准,提取研究区的坡度分区图,选定能代表坡耕地平均坡度的纵向基线和横向基线,进行矩形或者梯形区域的划分。梯田规划要正确地设置耕作田块的长边方向,从而保障机械化作业的方向,提高机械的作业效率,降低土壤侵蚀速度,提高作物产量。同时,针对重庆丘陵区坡耕地主要存在的排灌问题：骨干渠系垮塌严重,其他渠系分布零散,排水能力不足,耕地水土流失严重,本文基于数字高程模型(DEM)生成的水系图,对现状水系进行有效整合和优化设计。
水田梯田规划综合考虑地形、灌溉、排水、机械化耕作等多个因素的制约作用。开县厚坝镇耕作田块的布置是以现状道路和沟渠分割的格田为基础,规划一定数量的田间道路和排灌沟渠,修筑成一定规模的耕作田块。研究区虽有控制地下水的任务,但由于土质较轻,现状排水沟距在150m-300m,排水断面比较大,因此,排除地表水和控制地下水的排水农沟可以结合使用,农沟沿着等高线布置,或者与等高线有个较小的夹角,直接承受或排泄农田积水。斗沟垂直于等高线布置,直接承接农沟的排水。合川区大石镇以现有田块为基础,田块长边大致沿等高线方向,宽度根据实地调查结果,进行上下田块的合并。排灌系统则是以天然河沟作为骨干排水沟道,承接农沟(渠)的积水,农沟(渠)垂直于等高线布置,保证排水通畅。
(2)在旱地梯田设计中,本文分析了研究区岩层倾角、厚度和岩性与坡耕地形成和利用的关系,探讨了基于岩层分析的坡改梯设计方案。同时,为了避免实践中典型田块选取的主观性,采用数字高程模型(DEM)的坡度分析作为研究区坡度分析方法。结果表明：5°以下的缓坡地,田面宽度一般为20m-38m,既能适应机耕和灌溉,又能最大限度地节省土方量和需功量。15°-25°的丘陵陡坡地区,田面宽度最好在10m左右,或者先修筑成4m-7m小块地,作为过渡。介于5°-150之间的中坡地,田面一般采取9m-14m的宽度。
在水田梯田设计中,本文调查分析了研究区土壤状况、地形和现状排水情况等,设计排水农沟(渠)深度为0.6m-1.5m,间距在100m-200m。基于研究区数字高程模型(DEM)生成的坡度图和现状机械化水平,以及适应工程实施后畜力耕作和机械作业的需求,研究区梯田设计侧重于机修梯田的设计标准,平整田块面积较大。厚坝镇田块设计长度为100m-150m,宽度20m-50m,大石镇田块长度为50m-100m,宽度10m-30m。土地平整中高程的设计和土方量大小不仅与工程总投资直接相关,而且对梯田工程实施后的耕地质量产生重要的影响。因此,针对两个研究区各自的特点,本文选取了不同的计算方法。厚坝镇为现代河流冲积平坝区,地形变化简单,先运用数字高程模型(DEM)模拟整个区域的地形状况,分析得出合理的设计高程。然后,结合方格网法,进行土石方量计算,计算原理简单,操作容易,计算速度快,但是工程量偏大,单位挖填方量为0.44万m3。大石镇为中丘地貌类型,微地形变化复杂,存在一定的高差,因此,土方量的计算采用等高线法,数据准确度较高,单位挖填方量为0.27万m3,但是,该法量算工作会比较繁琐,工程量大,并且对地形图的精度要求比较高。因此,为实现研究区梯田工程的最大综合效益,土地平整土石方的计算需要一种具有广泛用户基础、操作简单、能充分运用现有数据资源且计算结果精度较高的方法。
1.8m高,0.3m宽的早地石坎需砌筑一轮30×30×100cm的丁字石,才能达到其稳定性要求。在水田石坎设计中,为保证其稳定性,厚坝镇在石坎高度为2.25m和2.5m时,要分别设置一轮丁字石,其工程量占石坎总量的5.26%、4.76%。否则,石坎会发生倾覆失稳现象。大石镇石坎高度1.75m、2.0m、2.25m和2.5m需分别设计一轮、一轮、二轮、三轮丁字石来提高石坎稳定性,其工程量分别占石坎总量的6.67%、5.88%、10.0%、13.04%。由于丁字石的附加设计,石坎自身重量增加,增强了自身的稳定性,原需要进行换基处理的≥1.5m高石坎理论上不需进行混凝土垫层处理。然而,仅由安全系数不能完全保证石坎结构的稳定性,因此,大石镇在石坎高度大于1.0m时,均进行混凝土垫层处理,垫层厚度为10cm。同时,通过占地分析发现,条石坎占地损失远远少于块石坎,田坎外坡越缓,安全稳定性越好,但占地增大速率也越快。不同地区不同石坎高度具有其不同的临界值,比如,在采用2m田面高差的情况下,大石镇1.8m高块石坎的临界坡度为64°。确定了临界坡度角,在保证了田坎稳定的同时,还能尽量减少田坎占地。
本文以重庆市合川区大石镇以及开县厚坝镇梯田工程为例,对该区域梯田的布局和设计进行了分析,其结果可为重庆丘陵区梯田工程的设计和实施量化、程序化和标准化提供参考。但是由于重庆丘陵区土壤和岩层性质差异大、地形地貌复杂,决定了梯田工程布局分析中难以实现全面考虑,设计参数难以确定。因此,实现重庆丘陵区梯田工程实施和设计的量化、程序化和标准化仍需要进行大量的研究。
Our country is characterized by a large population with relatively arable land and a shortage of mothball farmland resource. More over, the cultivated land quality has a decreasing tend in many areas on account of soil leanness, salinization, acidification and pollution and so on, which pose a great threat to food safety, people's living quality and social sustainable development of our country. Many scholars, native and overseas, have studied dynamic changes of cultivated land quality and influencing factors. However, soil resource was polluted or destroyed, it can't renew at short time. And the traditional agriculture management measures are hardly to improve cultivated land quality at short time. For the increasing scare for food and ecology safety, how to resolve the decreasing land plantation ability and improve farming plantation ability is becoming a new study hotspot, so modern soil engineering science appeared. At present, the research on modern soil engineering science is still at experience stage, thus, it is necessary to do more researches for realization of quantitative, programmed and standardized development of engineering design and implementation.
As a component of modern soil engineering, the project of transformation of slope land into terrace is an important measure. As for hilly region, in Chongqing, it is in favor of increasing agriculture production and developing rural economics, as well as preventing soil and water loss and improving ecological environment. However, at present, study of transformation of slope land into terrace in hilly region, Chongqing were mainly concentrated on fertilization, and there were little relevant literatures on the project itself. So, in this paper, taking the project of transformation of slope land into terrace in Dashi Town, Hechuan District and Houba Town, Kaixian County, Chongqing for two typical examples, the planning and engineering design of terrace in these two regions were analysized, and drainage system, soil properties and rock stratum were discussed. The main results were as follows:
(1)The planning of dry land terrace was mainly based on the conditions of topography and slope drainage system. According to critical slope method and subjective classification method, a system of four categories of slope classification was determined, which was 0°-3°,3°-5°,5°-15°and 15°-25°. Furthermore, slope maps of study areas were picked up, and rectangular or trapezoid parcel of rice field were to divide, which designed the orient of longer-side accurately, especially, to ensure the direction of mechanized farming, increase efficiency of mechanization farming, decrease soil erosion rate and enhance crop yield. Meanwhile, the main problem of irrigation and drainage in hilly region, Chongqing were the severely collapse of main trench, scattered distribution of the others, deficiency of drainage ability, and serious soil erosion. Therefore, based on slope maps, water system were designed anew.
In the planning of paddy field terrace, topography, irrigation, drainage, mechanized farming and so on were taken account of. The collocation of parcel of rice field in Houba town, Kaixian County was that based on the situation of roads and ditches, an amount of roads and irrigation and drainage ditches were programed, and then a certain scale of cultivation areas were built. Although there existed tasks of controlling ground water, because of the light soil property, the distance of the drainage ditch ranges from 150 to 300 meters, and big discharge section, thus the farming drainage ditches of removing the surface water and controlling the underground water can be used integrated, which was arranged along the contour line or having a small angle with it, and directly discharged the seeper of farmland. The lather drainage ditch should be designed vertically to the counter line, and directly receives the drainage water. The programing of combination the up and low fields in Dashi Town, Hechuan District was based on the existence farming field, the longer side of which approximately along the counter line, but the width was according to the results of field survey. The irrigation and drainage system was based on the natural ditches as main drainage ditch, received the seeper of farming ditches or trenches, which were designed vertical to the counter line, making sure of a smoothly drainage.
(2) The relationships between strata obliquity, bed thickness, lithological characters and the formation & utilization of slope land were analyzed in the study area, and the design of the transformation of slope land into terrace was further discussed based on the analysis of rock stratum. At the same time, digital elevation model (DEM) was used to study change of slope, so that the subjectivity of choosing representative farming lands could be avoided. The results showed that:with slope of 0°-5°,5°-15°, 15°-25°, field width was in range of 20m-38m、9m-14m、7m-10m, respectively, which could not only be to adapt to mechanical tillage and irrigation, but also to decrease the amount of earthworks farthest.
In the design of level terrace, soil conditions, topography and drainage status were analyzed. The depth of farming ditch was designed 0.6m-1.5m, and distance between farming ditches was 100m-200m.Based on DEM and mechanization level, parcel of rice field in Kaixian County and Dashi Town, were length of 100m-150m, width of 20m-50m and length of 50m-100m, width of 10m-30m respectively.At the same time, the terrace design of paddy had the advantages of large area, integrated management, high machinery degree, high industrial degree, and earthwork calculation was convenient and accurate, compared with terrace design of dry land.Therefore, different methods of earthwork calculation were selected based on the two study areas. By means of DEM, land leveling earthworks was 4,400 m~3 hm~(-2) in Kaixian County, but the results were relatively large, and the accuracy was not high. At the same time, based on contour method and field observation, land leveling earthworks was 2,700 m~3hm~(-2) in Dashi Town. The results were accurate, but this method caused the waste of human and material resources. Therefore, we could choose simple, fast earthwork calculation method, and improve the accuracy to achieve the maximum of comprehensive benefit.
The design of stone dikes was studied based on strata, topography and engineering properties. What is more, due to non-entirety of field surface and stone dikes in dry land, T-shaped stones of 30×30×100cm were of masonry for stone dikes of 1.8m, in order to meet the need of the anti-gliding stability and bearing capacity of foundation soil. While in the paddy field in Kaixian County, T-shaped stones of 30×30×100 cm were of masonry for stone dikes of 2.25m and 2.5m, accounted for 5.26% and 4.76% of the total amount of stone dikes, respectively. Meanwhile, in Dashi Town, T-shaped stones of one-layer, two-layers and three-layers were built for stone dikes of 1.75m,2.0m,2.25m and 2.5m, respectively, the amount of which accounted for 6.67%,5.88%,10.0%,13.04% of the total amount of stone dikes, respectively. In addition, due to foundation settlement existed at some degree, foundation treatment of concrete cushion was in need, when the stone dikes height was larger than 1.5m. However, the masonry of T-shaped stone enhanced the stability of stone dikes, and eccentricity and bearing capacity of foundation soil of stone dikes has met the need of their stability, without foundation treatment of concrete cushion. Based on Du Yongfeng's reliability theory, the stone dikes of≥1.0m were performed foundation treatment of concrete cushion in Dashi Town, whose thickness was 10cm, in order to reduce instability probability of stone dikes.Meanwhile, land occupation ratio of boulder strip dikes is far less than that of dimension stone dikes by comparative analysis. Gradient angle for each region has its appropriate critical value. For example, in the case of altitude difference of 2m, critical gradient angle of stone dikes of 1.8m was 64°in Dashi Town, so as to guarantee the stability of stone dikes, and decrease land occupation ratio of different field dikes.
Taking engineering of the transformation of slope land into terrace in Houba Town, Kaixian County and Dashi Town, Hechuan District as examples, planning and engineering design of terrace were analyzed in the study areas, and the results can offer reference for quantitative, programmed and standardized development of engineering design and implementation in hilly region, Chongqing. However, due to great difference of soil and rock, complex terrain, many factors had association with planning of project of the transformation of slope land into terrace, and the design parameters was difficult to determine. Therefore, more researches are still to do for realization of quantitative, programmed and standardized development of engineering design and implementation in hilly region, Chongqing.
作为现代土壤工程组成部分的梯田工程是我国坡耕地治理的一项重要措施。就重庆丘陵区而言,实施梯田工程有助于实现农业增产、发展农村经济,同时也有助于防止农田水土流失、改善生态环境。但目前关于重庆丘陵区梯田工程的研究,主要集中于成效以及后期培肥的研究,而对梯田工程本身较少进行深入研究探讨。因此,本文以重庆市合川区大石镇和开县厚坝镇的梯田工程为例,对研究区的梯田布局和设计进行了分析,探讨了水系、土壤性质以及岩层性状等自然因素对其的影响。获得的主要研究结果如下：
(1)旱地梯田规划的制定主要依据研究区的地形条件及坡面水系情况进行的。本文依据临界坡度和主观分级坡度方法,确定0°-3°,3°-5°,5°-15°,15°-25°四级坡度分级标准,提取研究区的坡度分区图,选定能代表坡耕地平均坡度的纵向基线和横向基线,进行矩形或者梯形区域的划分。梯田规划要正确地设置耕作田块的长边方向,从而保障机械化作业的方向,提高机械的作业效率,降低土壤侵蚀速度,提高作物产量。同时,针对重庆丘陵区坡耕地主要存在的排灌问题：骨干渠系垮塌严重,其他渠系分布零散,排水能力不足,耕地水土流失严重,本文基于数字高程模型(DEM)生成的水系图,对现状水系进行有效整合和优化设计。
水田梯田规划综合考虑地形、灌溉、排水、机械化耕作等多个因素的制约作用。开县厚坝镇耕作田块的布置是以现状道路和沟渠分割的格田为基础,规划一定数量的田间道路和排灌沟渠,修筑成一定规模的耕作田块。研究区虽有控制地下水的任务,但由于土质较轻,现状排水沟距在150m-300m,排水断面比较大,因此,排除地表水和控制地下水的排水农沟可以结合使用,农沟沿着等高线布置,或者与等高线有个较小的夹角,直接承受或排泄农田积水。斗沟垂直于等高线布置,直接承接农沟的排水。合川区大石镇以现有田块为基础,田块长边大致沿等高线方向,宽度根据实地调查结果,进行上下田块的合并。排灌系统则是以天然河沟作为骨干排水沟道,承接农沟(渠)的积水,农沟(渠)垂直于等高线布置,保证排水通畅。
(2)在旱地梯田设计中,本文分析了研究区岩层倾角、厚度和岩性与坡耕地形成和利用的关系,探讨了基于岩层分析的坡改梯设计方案。同时,为了避免实践中典型田块选取的主观性,采用数字高程模型(DEM)的坡度分析作为研究区坡度分析方法。结果表明：5°以下的缓坡地,田面宽度一般为20m-38m,既能适应机耕和灌溉,又能最大限度地节省土方量和需功量。15°-25°的丘陵陡坡地区,田面宽度最好在10m左右,或者先修筑成4m-7m小块地,作为过渡。介于5°-150之间的中坡地,田面一般采取9m-14m的宽度。
在水田梯田设计中,本文调查分析了研究区土壤状况、地形和现状排水情况等,设计排水农沟(渠)深度为0.6m-1.5m,间距在100m-200m。基于研究区数字高程模型(DEM)生成的坡度图和现状机械化水平,以及适应工程实施后畜力耕作和机械作业的需求,研究区梯田设计侧重于机修梯田的设计标准,平整田块面积较大。厚坝镇田块设计长度为100m-150m,宽度20m-50m,大石镇田块长度为50m-100m,宽度10m-30m。土地平整中高程的设计和土方量大小不仅与工程总投资直接相关,而且对梯田工程实施后的耕地质量产生重要的影响。因此,针对两个研究区各自的特点,本文选取了不同的计算方法。厚坝镇为现代河流冲积平坝区,地形变化简单,先运用数字高程模型(DEM)模拟整个区域的地形状况,分析得出合理的设计高程。然后,结合方格网法,进行土石方量计算,计算原理简单,操作容易,计算速度快,但是工程量偏大,单位挖填方量为0.44万m3。大石镇为中丘地貌类型,微地形变化复杂,存在一定的高差,因此,土方量的计算采用等高线法,数据准确度较高,单位挖填方量为0.27万m3,但是,该法量算工作会比较繁琐,工程量大,并且对地形图的精度要求比较高。因此,为实现研究区梯田工程的最大综合效益,土地平整土石方的计算需要一种具有广泛用户基础、操作简单、能充分运用现有数据资源且计算结果精度较高的方法。
1.8m高,0.3m宽的早地石坎需砌筑一轮30×30×100cm的丁字石,才能达到其稳定性要求。在水田石坎设计中,为保证其稳定性,厚坝镇在石坎高度为2.25m和2.5m时,要分别设置一轮丁字石,其工程量占石坎总量的5.26%、4.76%。否则,石坎会发生倾覆失稳现象。大石镇石坎高度1.75m、2.0m、2.25m和2.5m需分别设计一轮、一轮、二轮、三轮丁字石来提高石坎稳定性,其工程量分别占石坎总量的6.67%、5.88%、10.0%、13.04%。由于丁字石的附加设计,石坎自身重量增加,增强了自身的稳定性,原需要进行换基处理的≥1.5m高石坎理论上不需进行混凝土垫层处理。然而,仅由安全系数不能完全保证石坎结构的稳定性,因此,大石镇在石坎高度大于1.0m时,均进行混凝土垫层处理,垫层厚度为10cm。同时,通过占地分析发现,条石坎占地损失远远少于块石坎,田坎外坡越缓,安全稳定性越好,但占地增大速率也越快。不同地区不同石坎高度具有其不同的临界值,比如,在采用2m田面高差的情况下,大石镇1.8m高块石坎的临界坡度为64°。确定了临界坡度角,在保证了田坎稳定的同时,还能尽量减少田坎占地。
本文以重庆市合川区大石镇以及开县厚坝镇梯田工程为例,对该区域梯田的布局和设计进行了分析,其结果可为重庆丘陵区梯田工程的设计和实施量化、程序化和标准化提供参考。但是由于重庆丘陵区土壤和岩层性质差异大、地形地貌复杂,决定了梯田工程布局分析中难以实现全面考虑,设计参数难以确定。因此,实现重庆丘陵区梯田工程实施和设计的量化、程序化和标准化仍需要进行大量的研究。
Our country is characterized by a large population with relatively arable land and a shortage of mothball farmland resource. More over, the cultivated land quality has a decreasing tend in many areas on account of soil leanness, salinization, acidification and pollution and so on, which pose a great threat to food safety, people's living quality and social sustainable development of our country. Many scholars, native and overseas, have studied dynamic changes of cultivated land quality and influencing factors. However, soil resource was polluted or destroyed, it can't renew at short time. And the traditional agriculture management measures are hardly to improve cultivated land quality at short time. For the increasing scare for food and ecology safety, how to resolve the decreasing land plantation ability and improve farming plantation ability is becoming a new study hotspot, so modern soil engineering science appeared. At present, the research on modern soil engineering science is still at experience stage, thus, it is necessary to do more researches for realization of quantitative, programmed and standardized development of engineering design and implementation.
As a component of modern soil engineering, the project of transformation of slope land into terrace is an important measure. As for hilly region, in Chongqing, it is in favor of increasing agriculture production and developing rural economics, as well as preventing soil and water loss and improving ecological environment. However, at present, study of transformation of slope land into terrace in hilly region, Chongqing were mainly concentrated on fertilization, and there were little relevant literatures on the project itself. So, in this paper, taking the project of transformation of slope land into terrace in Dashi Town, Hechuan District and Houba Town, Kaixian County, Chongqing for two typical examples, the planning and engineering design of terrace in these two regions were analysized, and drainage system, soil properties and rock stratum were discussed. The main results were as follows:
(1)The planning of dry land terrace was mainly based on the conditions of topography and slope drainage system. According to critical slope method and subjective classification method, a system of four categories of slope classification was determined, which was 0°-3°,3°-5°,5°-15°and 15°-25°. Furthermore, slope maps of study areas were picked up, and rectangular or trapezoid parcel of rice field were to divide, which designed the orient of longer-side accurately, especially, to ensure the direction of mechanized farming, increase efficiency of mechanization farming, decrease soil erosion rate and enhance crop yield. Meanwhile, the main problem of irrigation and drainage in hilly region, Chongqing were the severely collapse of main trench, scattered distribution of the others, deficiency of drainage ability, and serious soil erosion. Therefore, based on slope maps, water system were designed anew.
In the planning of paddy field terrace, topography, irrigation, drainage, mechanized farming and so on were taken account of. The collocation of parcel of rice field in Houba town, Kaixian County was that based on the situation of roads and ditches, an amount of roads and irrigation and drainage ditches were programed, and then a certain scale of cultivation areas were built. Although there existed tasks of controlling ground water, because of the light soil property, the distance of the drainage ditch ranges from 150 to 300 meters, and big discharge section, thus the farming drainage ditches of removing the surface water and controlling the underground water can be used integrated, which was arranged along the contour line or having a small angle with it, and directly discharged the seeper of farmland. The lather drainage ditch should be designed vertically to the counter line, and directly receives the drainage water. The programing of combination the up and low fields in Dashi Town, Hechuan District was based on the existence farming field, the longer side of which approximately along the counter line, but the width was according to the results of field survey. The irrigation and drainage system was based on the natural ditches as main drainage ditch, received the seeper of farming ditches or trenches, which were designed vertical to the counter line, making sure of a smoothly drainage.
(2) The relationships between strata obliquity, bed thickness, lithological characters and the formation & utilization of slope land were analyzed in the study area, and the design of the transformation of slope land into terrace was further discussed based on the analysis of rock stratum. At the same time, digital elevation model (DEM) was used to study change of slope, so that the subjectivity of choosing representative farming lands could be avoided. The results showed that:with slope of 0°-5°,5°-15°, 15°-25°, field width was in range of 20m-38m、9m-14m、7m-10m, respectively, which could not only be to adapt to mechanical tillage and irrigation, but also to decrease the amount of earthworks farthest.
In the design of level terrace, soil conditions, topography and drainage status were analyzed. The depth of farming ditch was designed 0.6m-1.5m, and distance between farming ditches was 100m-200m.Based on DEM and mechanization level, parcel of rice field in Kaixian County and Dashi Town, were length of 100m-150m, width of 20m-50m and length of 50m-100m, width of 10m-30m respectively.At the same time, the terrace design of paddy had the advantages of large area, integrated management, high machinery degree, high industrial degree, and earthwork calculation was convenient and accurate, compared with terrace design of dry land.Therefore, different methods of earthwork calculation were selected based on the two study areas. By means of DEM, land leveling earthworks was 4,400 m~3 hm~(-2) in Kaixian County, but the results were relatively large, and the accuracy was not high. At the same time, based on contour method and field observation, land leveling earthworks was 2,700 m~3hm~(-2) in Dashi Town. The results were accurate, but this method caused the waste of human and material resources. Therefore, we could choose simple, fast earthwork calculation method, and improve the accuracy to achieve the maximum of comprehensive benefit.
The design of stone dikes was studied based on strata, topography and engineering properties. What is more, due to non-entirety of field surface and stone dikes in dry land, T-shaped stones of 30×30×100cm were of masonry for stone dikes of 1.8m, in order to meet the need of the anti-gliding stability and bearing capacity of foundation soil. While in the paddy field in Kaixian County, T-shaped stones of 30×30×100 cm were of masonry for stone dikes of 2.25m and 2.5m, accounted for 5.26% and 4.76% of the total amount of stone dikes, respectively. Meanwhile, in Dashi Town, T-shaped stones of one-layer, two-layers and three-layers were built for stone dikes of 1.75m,2.0m,2.25m and 2.5m, respectively, the amount of which accounted for 6.67%,5.88%,10.0%,13.04% of the total amount of stone dikes, respectively. In addition, due to foundation settlement existed at some degree, foundation treatment of concrete cushion was in need, when the stone dikes height was larger than 1.5m. However, the masonry of T-shaped stone enhanced the stability of stone dikes, and eccentricity and bearing capacity of foundation soil of stone dikes has met the need of their stability, without foundation treatment of concrete cushion. Based on Du Yongfeng's reliability theory, the stone dikes of≥1.0m were performed foundation treatment of concrete cushion in Dashi Town, whose thickness was 10cm, in order to reduce instability probability of stone dikes.Meanwhile, land occupation ratio of boulder strip dikes is far less than that of dimension stone dikes by comparative analysis. Gradient angle for each region has its appropriate critical value. For example, in the case of altitude difference of 2m, critical gradient angle of stone dikes of 1.8m was 64°in Dashi Town, so as to guarantee the stability of stone dikes, and decrease land occupation ratio of different field dikes.
Taking engineering of the transformation of slope land into terrace in Houba Town, Kaixian County and Dashi Town, Hechuan District as examples, planning and engineering design of terrace were analyzed in the study areas, and the results can offer reference for quantitative, programmed and standardized development of engineering design and implementation in hilly region, Chongqing. However, due to great difference of soil and rock, complex terrain, many factors had association with planning of project of the transformation of slope land into terrace, and the design parameters was difficult to determine. Therefore, more researches are still to do for realization of quantitative, programmed and standardized development of engineering design and implementation in hilly region, Chongqing.
引文
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