Study on Influence of Joint Distribution on Surrounding Rock Failure of an Underground Tunnel

Due to geological structure and artificial disturbance, a large number of joints and fissures are formed in the surrounding rock of an underground tunnel. In order to study the influence of joints on the failure characteristics of tunnels, three test schemes with different joint lengths, joint spacing, and joint positions are designed. The results show that the bearing capacity of the tunnel decreases with the increase in the joint length. With the increase in joint spacing, the bearing capacity of the tunnel decreases first and then increases. The crack propagation law of the three test schemes has experienced four stages: no crack, crack initiation, crack rapid development, and crack gradual reduction. The location of joints has the greatest influence on the failure mode of the tunnel. The crack is most likely to appear at the top of the tunnel and expand along the joint, mainly because it is easy to form tensile stress at the top of the tunnel and compressive stress concentration at the joint tip. Therefore, when excavating the tunnel in the underground space, the influence of joints on the tunnel should be considered. Analyzing the relationship between the tunnel and joints has important practical guiding significance for the control of the surrounding rock of the tunnel. Finally, the failure results of the indoor physical model and numerical model are compared and analyzed. They are in good agreement, which also reflects the rationality of numerical simulation.

Runoff-associated nitrogen and phosphorus losses under natural rainfall events in purple soil area: the role of land disturbance and slope length

Land disturbance and slope length play key roles in affecting runoff-associated nitrogen (N) and phosphorus (P) losses in different forms under natural rainfall. Field monitoring was conducted in nine plots located parallel on a 15° purple slope in southwest China. Three slope lengths (20-, 40-, 60-m) combined with measures of artificial disturbance and natural restoration were implemented. The highest N concentration was observed in soft rainfall events across all plots. The highest P concentration was recorded in heavy rainfall events for the artificially disturbed plots and in soft rainfall events for the naturally restored plots. Land disturbance differed orthophosphate concentration in 20-m plot, and affected N and P loss amounts in different forms. Slope length differed total dissolved phosphorus concentration in naturally restored plots, and also differed the loss amounts of total dissolved nitrogen and orthophosphate in artificially disturbed plots. Naturally restoration reduced loss amounts of total nitrogen and total phosphorus by 62.14–79.05% and 79.28–83.43% relative to artificial disturbance, respectively. Concentrations of nitrate-nitrogen, total phosphorus and dissolved phosphorus were closely correlated with rainfall and runoff variables, respectively, in artificially disturbed plots. Our results highlight the dominant role of natural restoration in reducing erosion and nutrient loss in sloping land.

Naturally rainfall-induced changes in runoff-associated nitrogen and phosphorus losses in purple soil area: roles of land disturbance and plot length

<p>Severe soil erosion occurs in southwestern China owing to the large expanses of human disturbance and sloping land. This field monitoring study was conducted during the rainy season to record the rainfall events, runoff, sediment yield, nitrogen, and phosphorous loss in 20-, 40-, and 60-m plots under conditions of artificial disturbance or natural restoration on a 15° slope in the purple soil area of southwestern China. The concentrations and loss amounts of total nitrogen (TN), total dissolved nitrogen (TDN), ammonium-nitrogen (NH4-N) and nitrate-nitrogen (NO<sub>3</sub>-N), total phosphorus (TP), total dissolved phosphorus (TDP) and orthophosphate (PO<sub>4</sub>-P) were comparatively determined. The highest N concentration was observed in long duration and soft rainfall events across all plots. The highest P concentration in artificial disturbed plots was found in long duration and intensive rainfall events while it was recordeds for measured variables were dominantly recorded under the long duration and lowest soft rainfall events in naturally restored plots intensity., while The the highest loss amounts for N and P in different forms for these variablesalmostmostly appeared under high rainfall intensity. Land disturbances differed orthophosphate PO<sub>4</sub>-P concentration in 20--m plot and and loss amounts of of measured variables N and P with different forms across in all plots. Plot lengths differed total dissolved phosphorus TDP concentration in natural restored plot and loss amounts of total dissolved nitrogenTDN and orthophosphate PO<sub>4</sub>-P in artificially disturbed plots. Naturally restoration reduced loss amounts of total nitrogen and total phosphorus by 69.4%62.14-79.05% and 79.28-83.43% TN, 68.8% TDN, 71.2% NH<sub>4</sub>-N, 74.3% NO<sub>3</sub>-N, 81.5% TP, 71.9% TDP and 70.0% PO<sub>4</sub>-P loss amounts comparedrelative to artificial disturbance, respectively. There were significant interrelationships among N and P concentrations in different forms in two land disturbance plots, while nitrate-NO<sub>3</sub>-nitrogenN concentration hadwas significantly negatively negative correlatedion with rainfall intensity and runoff rate in artificialally disturbanceed plots. Rainfall intensity was logarithmically correlated with TN, NO<sub>3</sub>-N concentrations in artificially disturbed plots and with NO<sub>3</sub>-N concentration in naturally restored plots. Runoff rate was logarithmically correlated with TN, TDN and NO<sub>3</sub>-N concentrations in artificially disturbed plots. Our results highlight the effects of land disturbance and plot length on nutrient losses in sloping land.</p>

The Effect of Submergence and Eutrophication on the Trait’s Performance of Wedelia Trilobata over Its Congener Native Wedelia Chinensis

Climate change and artificial disturbance may lead to increased submergence and eutrophication near a riparian zone and the shift of terrestrial plants into a riparian zone. In this study, the responses of terrestrial invasive Wedelia trilobata (WT) and congener native Wedelia chinensis (WC) plants were examined under submergence and eutrophication. A greenhouse experiment was conducted in which ramets of WT and WC were investigated under two levels of submergence (S1 and S2) and three levels of nutrients (N1, N2 and N3) along with two cultures (mono and mixed). Submergence (S) did not affect the morphological traits of both the species but nutrients (N), culture (C) and their interaction, along with submergence, had a significant effect on the morphological traits of both the species. The growth of WC under high submergence and high nutrients was decreased compared with low nutrients (N1, N2) but WT maintained its growth in monoculture. In mixed culture, low submergence (S1) and low nutrients (N1, N2) made WC more dominant but high submergence (S2) and high nutrients (N3) made WT more successful than WC due to its high phenotypic plasticity and negative effect of competition intensity. It was concluded that both species survive and grow well under submergence and eutrophication, but high submergence and eutrophication provide better conditions for WT to grow well.

Evolution of localized artificial disturbance in 2D and 3D supersonic boundary layers

The evolution of a controlled broadband wave packet in flat-plate and swept-wing supersonic boundary layers was experimentally investigated at Mach number M = 2. The wave packet was introduced into the boundary layer by a localized pulse electrical discharge. The structure and evolution downstream of the wave packet were studied by hot-wire measurements. It was found that the wave packet has a symmetric shape in a flat-plate boundary layer, whereas there is asymmetry in case of a swept-wing one. The spectral analysis of the development of different modes of the wave packet was provided.