Assessing Suitability of Rural Settlements Using an Improved Technique for Order Preference by Similarity to Ideal Solution

Land suitability assessment is a prerequisite phase in land use planning; it guides toward optimal land use by providing information on the opportunities and constraints involved in the use of a given land area. A geographic information system-based procedure, known as rural settlement suitability evaluation(RSSE) using an improved technique for order preference by similarity to ideal solution(TOPSIS), was adopted to determine the most suitable area for constructing rural settlements in different geographical locations. Given the distribution and independence of rural settlements, a distinctive evaluation criteria system that differed from that of urban suitability was established by considering the level of rural infrastructure services as well as living and working conditions. The unpredictable mutual interference among evaluation factors has been found in practical works. An improved TOPSIS using Mahalanobis distance was applied to solve the unpredictable correlation among the criteria in a suitability evaluation. Uncertainty and sensitivity analyses obtained via Monte Carlo simulation were performed to examine the robustness of the model. Daye, a resource-based city with rapid economic development, unsatisfied rural development, and geological environmental problems caused by mining, was used as a case study. Results indicate the following findings: 1) The RSSE model using the improved TOPSIS can assess the suitability of rural settlements, and the suitability maps generated using the improved TOPSIS have higher information density than those generated using traditional TOPSIS. The robustness of the model is improved, and the uncertainty is reduced in the suitability results. 2) Highly suitable land is mainly distributed in the northeast of the study area, and the majority of which is cultivated land, thereby leading to tremendous pressure on the loss of cultivated land. 3) Lastly, 12.54% of the constructive expansion permitted zone and 8.36% of the constructive expansion conditionally permitted zone are situated in an unsuitable area, which indicates that the general planning of Daye lacks the necessary verification of suitability evaluation. Guidance is provided on the development strategy of rural settlement patches to support decision making in general land use planning.

Long-term tunnel behaviour and ground movements after tunnelling in clayey soils

Long term ground movements above a tunnel may continue to increase with time after tunnelling in clayey soils as the tunnellinginduced excess pore water pressures dissipate,whilst the changing earth pressure acting on the tunnel leads to further tunnel deformation during consolidation.Furthermore the tunnel itself introduces new drainage conditions;that is,depending on the drainage condition of the tunnel lining,the effective stresses around the tunnel change with time,inducing further soil consolidation.A seepage rate from low permeability clayey soil is often very small and the groundwater seeping into the tunnel can evaporate quickly.Although a tunnel may look impermeable because the surface looks dry,it is possible that the tunnel drainage conditions are actually permeable.This paper summarises the investigation of soil-tunnel consolidation interaction,particularly focusing on ground surface movements and tunnel lining deformation in the interest of engineering concerns.Analysis results show that tunnel lining permittivity relative to the permeability of the surrounding ground plays an important role on both long-term ground movements as well as tunnel lining behaviour.The findings published in literature are reviewed step by step starting from a single tunnel,twin tunnels to complex cross passage structures.The mechanisms of tunnelling-induced soil consolidation for these structures are identified and,where applicable,possible engineering methodologies to assess the magnitude of long-term ground surface settlements and tunnel lining loads are proposed.