Community phylogenetic diversity and abiotic site characteristics influence abundance of the invasive plant Rhamnus cathartica L.

Aims Theory predicts that the success of introduced species is related to the diversity of native species through trait-based processes.Abiotic site characteristics may also affect a site’s susceptibility to invasion.We quantified resident plant species richness,phylogenetic diversity and several abiotic site characteristics for 24 oak forests in Minnesota,USA,to assess their impact on the abundance of a widespread,introduced terrestrial plant species,common buckthorn(Rhamnus cathartica L.).Specifically,we asked(1)whether resident species richness and phylogenetic diversity affected the abundance of R.cathartica and(2)what site characteristics explained the overall abundance of R.cathartica.Methods Our survey included 24 oak-dominated stands in Minnesota’s deciduous forests.In each stand,we identified all species in 16 plots.We also measured a series of environmental site characteristics,including canopy openness(a proxy for light availability),percent bare soil,soil pH,percent sand,an index of propagule availability,duff layer thickness(a proxy for earthworm activity),an index of insolation and slope.For all species present in at least one site,we estimated a community phylogeny.We combined all sitelevel characteristics,including phylogenetic diversity of the resident plant species,in a multiple regression model to examine site-level drivers of community invasibility.Important Findings Results indicate that sites with higher overall plant phylogenetic diversity harbor less R.cathartica,even though native species richness was not significantly related to R.cathartica abundance.Regression analyses indicated that,in addition to resident species phylogenetic diversity,the most important predictors of R.cathartica abundance were canopy openness and the amount of bare soil,both positively related to the abundance of the invader.By combining the effects of abiotic site characteristics and resident species phylogenetic diversity in a model that predicted the abundance of R.cathartica,we were able to simultaneously account for a wide range of factors that might influence invasibility.Overall,our results suggest that management strategies aimed at reducing disturbances that lead to increased bare soil and light levels may be more successful if they also maximize phylogenetic diversity of the resident plant community.

Influence of earthquake ground motion incoherency on multi-support structures

A linear response history analysis method is used to determine the influence of three factors:geometric incoherency,wave-passage,and local site characteristics on the response of lnulti-support structures subjected to differential ground motions.A one-span frame and a reduced model of a 24-span bridge,located in Las Vegas,Nevada are studied,in which the influence of each of the three factors and their combinations are analyzed.It is revealed that the incoherency of earthquake ground motion can have a dramatic influence on structural response by modifying the dynamics response to uniform excitation and inducing pseudo-static response,which does not exist in structures subjected to uniform excitation.The total response when all three sources of ground motion incoherency are included is generally larger than that of uniform excitation.

Dynamic soil-tunnel interaction in layered half-space for incident plane SH waves

The dynamic soil-tunnel interaction is studied by indirect boundary element method （IBEM）, using the model of a rigid tunnel in layered half-space, which is simplified to a single soil layer on elastic bedrock, subjected to incident plane SH waves. The accuracy of the results is verified through comparison with the analytical solution. It is shown that soil-tunnel interaction in layered half-space is larger than that in homogeneous half-space and this interaction mechanism is essentially different from that of soil-foundation-superstructure interaction.

Dynamic soil-tunnel interaction in layered half-space for incident P-and SV-waves

The dynamic soil-tunnel interaction is studied by the model of a rigid tunnel embedded in layered half-space, which is simplified as a single soil layer on elastic bedrock to the excitation of P- and SV-waves. The indirect boundary element method is used, combined with the Green＇ s function of distributed loads acting on inclined lines. It is shown that the dynamic characteristics of soil-tunnel interaction in layered half-space are different much from that in homoge- neous half-space, and that the mechanism of soil-tunnel interaction is also different much from that of soil-founda- tion-superstructure interaction. For oblique incidence, the tunnel response for in-plane incident SV-waves is com- pletely different from that for incident SH-waves, while the tunnel response for vertically incident SV-wave is very similar to that of vertically incident SH-wave.

Ground motion amplification pattern with TBM tunnels crossing soil-rock interface:Shaking table test

The current aseismic design has seldom considered the effect caused by underlain tunnels.Previous studies focused on the scenarios of tunnels embedded in homogeneous soil under transverse seismic excitation.This paper aims to investigate the tunnel effect on the surface acceleration response in soil-rock strata by shaking table tests.Three sets of excitations are employed and input along the shaking table in both transverse and longitudinal directions.The soil-rock site is classified as four micro-zones with varying conditions,to mount observation stations of acceleration sensors.Dynamic characteristics of the four zones are identified by the transfer function(TF)method,and the tunnel effect on the ground acceleration response is obtained by comparing the spectral acceleration results between the free-field and ground-tunnel models.The test results indicate that the tunnel effect varies with the site conditions.Distinctively,a significant amplification effect is observed at the A4 zone,located on the soil deposit near the soil-rock interface.Then,it is proved that the scattering waves generated at the interface and the standing waves trapped between the tunnel and upper ground surface account for the amplification,revealed by the discrepancies of the TF results and acceleration details between the free-field and ground-tunnel models.