Rural Roads Construction And Its Landscape Effect In Hilly-mountainous Region Of Southwestern China

As one of the key rural infrastructure, rural roads has got rapid expansion recently basing on the comprehensive land consolidation, the new countryside construction and urban and rural harmonious development. Current researches focus on high-grade road system in the large geomorphic unit, like the gathering and radiation of logistics and the exchange of information coming from coherent road network such as highways, railways, state (province) road or county road, and "channel - blocking " effect driving on heterogeneity and diversity of landscape use and land cover in large geomorphic unit and its impact on ecosystems. Low-grade rural roads are concentrated in the layout and evaluation of road network, design and cost control of road construction, engineering construction, quality control and maintenance management, surface drainage, slope erosion and road erosion control and so on. However, the rural roads distributed widely in the Hilly-mountainous Region of Southwestern China are restricted not only by human economic activities, but also by natural conditions. Its construction and operation provide a protection for social development and a promoting economic development, while cause a division, disturbance, destruction and degradation of natural landscape and ecosystems and so on. Considering this, picking 14 administrative villages from Sichuan Province(areaⅠ), Guizhou Province(areaⅡ) and Chongqing City(areaⅢ,ⅣandⅤ) as 5 study areas, this paper analyzed the type and function of rural roads in different geographical environment combining with socio-economic levels including topography, hydrogeology, climate, soil, vegetation, rural population, cultivated land, per capita arable land, infrastructure, agricultural production conditions, farming systems and the socio-economic.It also cleared the requirement for rural roads according to the economic development status and future development trend in the Hilly-mountainous Region of Southwestern China. And it researched the engineering technology of rural roads such as surface and subgrade combining with the usage of local agricultural machinery and characteristics of common building materials. Moreover, it built the rural road system in Hilly-mountainous Region of Southwestern, and analyzed features of the rural road network systems and its landscape effect so that provided a support on theory and technical to rural road system layout and design in Hilly-mountainous Region of Southwestern China.(1) The layout of rural roadRural roads can be divided into field roads and production roads by function and road pavement width. Field road is a road contacting rural residential area with piece of paddy fields, which mainly services for cargo transporting, transferring of operating machinery to field and fueling the machine, adding water, adding seed and other production operation. It is better to adopt orthogonal when field road intersect to facilitate turning of farm machinery. Field roads should be laid along the short edge of the piece of paddy field, whereas it can be laid in the middle of field operation area in the dry farming region, along the long side of the piece of paddy field so that farm machinery can enter the work area on both sides to reduce the blank line. It should be arranged according to specific terrain in the terrace area shall, laid by the method of walking along the edge of the trench. Field road is usually set beside the gutter, deep in ditch or on the mountain ridge. It presents a bias shape when the mountains are low and slopes are even; it presents an "S" shape or a spiral shape winding up the mountain when the mountains are high and slopes are steep. Production road is the kind of road to link each piece of paddy fields for field production operations and mainly services for manual field work and harvesting agricultural products. It should be criss-cross laid to form a network with field road. It often locates in the long side of the piece of paddy field and presents different ways in dry lands and paddy fields. One horizontal production road in dry lands farmland separates another from 40 to 200 meters. It can be laid combining with gallet bank in areas gallet is widely spread to save space. Vertical production roads are often arranged on the hilly ridges and one separates another from 200 to 500 meters according to the length of the field surface. If the production roads and ditches are not conducive to drain off water or traffic when combined settings, they will be arranged separately. Production roads in paddy can be set outside the agricultural ditch and directly connected with paddy fields. Horizontal production road can be arranged an interval of 100 to 300m, vertical one can be arranged an interval of 200 to 500m; It should avoid areas like erosion around the depressions, cave development zones and large fault fracture zone in soluble limestone regimen which with complex geological conditions. Rural roads should be laid combining topography conditions and production methods as far as possible. What is more, field roads can be laid combining branch canal and lateral canal, production roads can be laid with field ditch. In sum, the layout rural roads in the Hilly-mountainous Region of Southwestern China should not only consider the distribution of rural settlements, facilities of irrigation and settings of farming plots, but also harmonize with the natural environmental conditions, agricultural and human landscape.(2) Engineering design of rural roadsRural road surface is designed above the original ground surface about 20 to 30cm in purple rock area, and the pavement bed course is built by hand placed stones of 20cm. The foundation course is a stable layer of gravel mud of 10 to 15cm, and road surface is covered by 15 to 20cm thick cement concrete of C25～C30. The soil base in this area has a high intensity so the subgrade can be compacted directly with a degree of compaction above 90%. The width of subgrade is 4.5 to 5.0m, slope ratio is 1:1.5. Taking into account the long rainfall period and large rainwater harvesting area in the region, the ditch can be laid at the runoff side of the subgrade, the width of it is 0.25 to 0.30m, and the net depth of it is 0.3 to 0.4m. The trench wall of it is built by cement mortar boulder strip of M10-M15 or mortar block stone, and the bottom is paved by cement concrete of C15-C20 with 8～10cm. To ensure the stability of the subgrade, the road shoulder is adopted on the other side of the field road using stone curb, precast concrete or soil; Due to the frequent water and soil erosion from both sides of the hill in the soluble limestone region, the subgrade and pavement in this region are designed thicker than the purple soil region, and exceed the ground of 30 to 40cm. The pavement bed course is built by hand placed stones of 20cm, and the foundation course is a stable layer of gravel mud of 15cm, and road surface is covered by 18 to 20cm thick cement concrete of C30. Clear width of the road is 3.5 to 4.5m with cross slope of 0.3% to 0.5%. The flat curve of field road has a radius (turning radius) not less than 15m, on special difficulties not less than 10m, and its length cannot be less than 15m. When the radius of flat curve is equal to or less than 150m, the curve should be set ultra-high and the inside of the curve should be widened. Meantime the ultra-high eased segment not less than 10m should be set at both ends of a flat curve. The ultra-high cross slope value does not exceed 8% and not more than 6% in snow frozen area. The maximum longitudinal slope of field road should take 6% to 8%. Under special circumstances, it's not more than 11% in hilly area, not more than 13% in the mountain area, and not more than 8% in an altitude of 2000m above areas or freezing cold region. Whether in purple rock area or soluble limestone area, the passing bay should be set in the appropriate distance when the road surface width of field road is less than 4.0m, Passing bay should be located in vantage point, and make the driver can see the approaching vehicles from two adjacent passing bay. The section of pavement setting the passing bay has a road surface width of not less than 6.5m, the interval should be of 300 to 600m, the effective length shall be 15 to 25m; Production road in purple rock area should adopt rubble, stone block cushion, and its subgrade width should be 0.6 to 2.7 m. The width of the road is designed from 0.6 to 2.5m. Soil can be used to compact subgrade in free water and erosion areas, and the subgrade of production road should be higher than the road surface 0.1 to 0.2m. The grouting stone subgrade should be adopted in soluble limestone area, above the field surface 0.2 to 0.5m. The pavement of production road can be produced by cast-in-situ concrete, precast concrete board, green flag and other materials. The concrete road surface should be of 5 to 20cm thick, the precast concrete board and flag should be of 6～15cm, and other materials are desirable of 8～20cm. Agricultural bridge can be arranged where field road and production road crossing ditches or gully which falls into for field road and for pedestrian. Its structural design safety level is not less than the third grade. Types of agriculture bridges can be the beam type and the vault type, and building materials usually are brick, stone, concrete and reinforced concrete etc. Culvert should be built under the canal, road or the ground when the road crossing the canal. There should be a certain distance of 20 to 30cm away from the top of the culvert to the subgrade. Culvert water direction should be orthogonal with fill ditches on roof or roads, in accordance with the original direction. The culvert can be made by concrete or reinforced concrete pipe, and the form of it can be round, box, cover type and vault type etc. In a word, the engineering design of rural roads in Hilly-mountainous Region of Southwestern China should consider the geological topography, hydrology, land use and soil characteristics of the road sections passing, meanwhile make use of local materials to reduce costs.(3) Characteristics of the rural road network systemOn the one hand, the differences of natural conditions and socio-economic in these study areas intensified the differences of focus on building in regional road system. On the other hand, the whole road systems had become more comprehensive, and the differences in the network characteristics had narrowed. Like the index of view from the corridor, the total length and density of rural roads in all cease areas had increased. Before building, total length of the road in these villages ranged from 6.73km to 76.36 km, the longest was 11.4 times longer than the shortest. The network density of road ranged from 38.18 m/hm2 to 149.6 m/hm2, and the biggest was 11.4 times bigger than the smallest. After building, the length ranged from 7.88 km to 82.15 km and the gap narrowed to 10.4 times; the density ranged from 65.87 m/hm2 to 159.6 m/hm2 and the gap was only 2.4 times. In addition, there was a remarkable structural change in the type of road consisting systems. Although increased greatly the proportion of field road, the production of road still occupied the main parts in the entire road system. Before building, the ratio of high road, Field Road and production ratio in areaⅠ, areaⅡ, areaⅢ, areaⅣ, areaⅤwere 11:15:74,0:31:69,9:12:79,3:17: 80,8:28:64 respectively. After building, those were 9:17:74,0:27:73,7:23:70,3: 16:81,6:25:69.Considering the index of the rural road network, the network density index (d), the network closure index (α), the line point rate (β) and the network connectivity index (γ) were higher, while costs rate index (C) reduced in some extent. Before building, a ranged from 0.126 to 0.361:βranged from 1.242 to 1.681:y ranged from 0.419 to 0.577:C ranged from 0.9908 to 0.9971. After building, a index ranged from 0.312 to 0.370, (3 index ranged from 1.614 to 1.707, y index ranged from 0.542 to 0.582, C ranged from 0.9913 to 0.9956.Meanwhile, in the Hilly-mountainous Region of Southwestern, there were an increasing trend in the number of nodes and corridors of the road network with the road expansion. The differences of road density in these regions were attributed to the differences of the number of nodes and corridors between the different regions. In addition, a, (3, y were positively correlated whereas were significantly negatively correlated with C, that is, the cost ratio decreased with the expansion of road network. Moran index further indicated that:before the construction, the road density inⅤwas decentralized, whereas they were relatively gathered inⅠ,Ⅱ,ⅢandⅣ. After the construction, the road density inⅠ,ⅢandⅤincreased significantly, while they increased slightly inⅡandⅣ. The reason for this is that the terrain ofⅡandⅥis relatively steep, while it is relatively flat inⅠ,ⅢandⅤ. So we found that:as a rural agricultural landscape corridor or channel for material flow and value flow, the rural roads can be evaluated by the network structure analysis, moreover by it can attain the rural road system network optimization.(4) The landscape effect of rural road systemAccording the type, using the road as centerline, the degree of interference of rural roads on the surrounding land use pattern generally shows a gradual decay to both sides of the road. Across the paddy field, dry land and the regions which are the human settlements in, the field road make the most significant interference with the fragmentation of those regions. The results indicated:it made the most significant degree of interference with landscape connectivity within 25m, and the interference gradually weakened beyond 25m. Meantime, it brought severe interference with land use disturbance in 10-25m and the hugest one was within 10m. Exceeding 25m, the degree of interference gradually decayed away as the distance increased. In 0-25m interference band, degree of fragmentation of the land-use types from field road showed:dry land> paddy> settlement water> woodland, and in 25m-250m band showed:paddy field> dry> settlement> water> woodland. The intensity of interference pattern of land use from production path increased with distance adding within 2.5m, while it decreased with distance adding and the severest disturbance happened within 2.5-10m. It changed less in 10-30m and gradual decayed over 30m. In 0-20m interference band, degree of fragmentation of the land-use types from production road showed:paddy fields> dry> settlement> water> woodland, and in 25m-250m band showed:dry land> paddy> settlement> water> woodland.According the landscape, using the road as centerline, the degree of interference of field roads on the surrounding landscape pattern also shows a gradual decay to both sides of the road, while interference of the production shows an increasing trend at first and then gradually decayed. The results indicated:the strongest intensity of disturbance on land use landscape from field road was in 5m, and it decreased with distance increasing beyond 5m. After the construction of field road, except IV which had a slightly increased of landscape fragmentation in the 0-10m, the landscape fragmentation in other four regions were improved or mitigated, they were almost same in the 10-250m. The complex bending degree of landscape border raised slight in a certain extent, and the degree of regular shape of the landscape types increased. The continuity of adjacent plots of preponderant land use in study areas increased overall, and the dominant landscape types was not threatened or even increased. The disturbance on landscape from production road increased with distance adding within 5 m, and the most severe of interference came from 2.5 to 5m band. In the 5-10m band, the disturbance was still large. Over 10m, however, the degree of interference gradually decayed away as the distance increased. The degree of the landscape fragmentation within the 0-30m was improved due to the construction of production road. Although it kept same within 30-120m, the complexity of landscape boundaries rose slightly while the degree of regular shape of the landscape types reduced slightly. Therefore, as a landscape type, the rural roads can optimize the reconstruction of local rural land use so that the efficient use can be achieved.In summary, this paper demonstrated the idea about the hierarchy system of rural roads in Hilly-mountainous Region of Southwestern China by the layout and the structural design of production road and field road. It analyzed features of the network system of rural road in Hilly-mountainous Region of Southwestern China pre and post construction by indexes of corridor structure, network structure and the spatial autocorrelation (Moran). Basing on those, it discussed what influence on the surrounding land use pattern from the formation and development of rural roads. Thus it revealed the landscape effect pre and post construction of the rural road system in Hilly-mountainous Region of Southwestern. However, the landscape effect from road is not just in the impact on the surrounding land use, it also includes impact on regional transportation, human activity, community structure and organization and function and succession of ecosystems and so on. What is more, this effect works in the whole process of road building. Therefore, it is necessary to strengthen the research on human activity, community structure and organization, the dynamics of social and economic development which correlate with construction process of rural road system from multi-angle.