A healthy ecosystem provides various ecological services for human beings and it is the foundation for the sustainable development of human society. However, human activities and natural disasters inevitably interfere with the evolution of an ecosystem at different scales [1-2]. Ecological risk refers to the possibility that the ecosystem structure and function will be degenerated under external pressure [3]. Ecological risk assessment (ERA) is an effective method for quantifying
The construction of a slurry shield tunnel produces large amount of excavated soil. Direct discharge of the excavated soil by transportation not only increases the overall construction cost but also raises environmental concerns of pollution. In this study, we explore in-situ recycle of excavated soil in the Nanjing Yangtze River tunnel project as the back-fill grout. A series of laboratory were carried out to determine the synchronous grout parameters, including compression strength and shear strength, initial setting time, fluidity, consistency, and bleeding rate. The mixture ratio of the back-fill grout is also discussed to optimize the grout performance. It is found that: (1) the excavated soil produced from the construction of slurry shield tunnel in this project can be reused as the material of back-fill grout in the sand stratum; (2) Proper selection of binder/sand ratio and fly ash/cement ratio improves the performance of the synchronous grout. The test results demonstrated that the discharged soil can be recycled in-situ as the grouting material in the sand stratum.
Biomass is important in monitoring global carbon storage and the carbon cycle, which quickly and accurately estimates forest biomass. Precision forestry and forest modeling place high requirements on obtaining the individual parameters of various tree species in complex stands, and studies have included both the overall stand and individual trees. Most of the existing literature focuses on calculating the individual tree speciesโ biomass in a single stand, and there is little research on calculating the individual tree biomass in complex stands. This paper calculates the individual tree biomass of various tree species in complex stands by combining multispectral and light detection and ranging (LIDAR) data. The main research steps are as follows. First, tree species are classified through multispectral data combined with field investigations. Second, multispectral classification data are combined with LIDAR point cloud data to classify point cloud tree species. Finally, the divided point cloud tree species are used to compare the diameter at breast height (DBH) and height of each tree species to calculate the individual tree biomass and classify the overall stand and individual measurements. The results show that under suitable conditions, it is feasible to identify tree species through multispectral classification and calculate the individual tree biomass of each species in conjunction with point-cloud data. The overall accuracy of identifying tree species in multispectral classification is 52%. Comparing the DBH of the classified tree species after terrestrial laser scanning (TLS) and unmanned aerial vehicle laser scanning (UAV-LS) to give UAV-LS+TLS, the concordance correlation coefficient (CCC) is 0.87 and the root-mean-square error (RMSE) is 10.45. The CCC and RMSE are 0.92 and 1.41 compared with the tree height after UAV-LS and UAV-LS+TLS.
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