Sediment transport trends and cross-sectional stability of a lagoonal tidal inlet on the Central Coast of Vietnam

Lagoonal tidal inlets are a typical morphology of the Central Coast of Vietnam. Recently, navigation channels in these inlets have become increasingly threatened by siltation. This study analyses the relations between sediment distribution and transport trends (using the technique of Sediment Trend Analysis-STA■) in the lagoonal system of the De Gi inlet and then proposes appropriate countermeasures against sand deposition in the navigation channel. The STA identified three types of transport trends in the De Gi inlet, namely dynamic equilibrium, net accretion, and net erosion. Processes associated with the tidal prism have resulted in trends of sediment transport and deposition across the flood and ebb tidal shoals, which maintain a present cross-sectional area of about 1000m^2. However, longshore sediment transport from north to south resulting from northeast waves cause additional sand deposition in the channel. In addition, the effects of refraction associated with a nearby headland and jetty also increase sedimentation. These processes provide the main reasons for sediment deposition in the De Gi inlet. Short term and regular dredging helps to maintain the navigation channel. A system comprised of three jetties (north, south, and weir) is necessary to ensure the longterm cross-sectional stability of the navigation channel.     

Advance in the penetrometer test formulation to estimate allowable pressure in granular soils

In this paper, we present a modification of the existing mathematical formulation used to obtain the allowable bearing pressure from dynamic penetration tests in order to extend its applicability to the design of shallow foundations. The conventional relationships adopted to obtain the allowable bearing pressure from penetrometer tests have a discontinuous gradient, and they are limited to a depth less than the footing width. The aim of this work was to find a relationship that permits the estimation of this pressure in cohesionless soils, from the results of dynamic probing super heavy tests, through a single non-piecewise and continuous relationship that remains valid up to depths several times the footing width. This equation was applied as part of the geomechanical characterization survey undertaken for the construction of an elevated helipad in the centre of the Iberian Peninsula. The survey results were considered satisfactory, and the construction was completed without structural problems.     

The 2014 seismic hazard model of the Middle East: overview and results

The Earthquake Model of Middle East (EMME) Project aimed to develop regional scale seismic hazard and risk models uniformly throughout a region extending from the Eastern Mediterranean in the west to the Himalayas in the east and from the Gulf of Oman in the south to the Greater Caucasus in the North; a region which has been continuously devastated by large earthquakes throughout the history. The 2014 Seismic Hazard Model of Middle East (EMME-SHM14) was developed with the contribution of several institutions from ten countries. The present paper summarizes the efforts towards building a homogeneous seismic hazard model of the region and highlights some of the main results of this model. An important aim of the project was to transparently communicate the data and methods used and to obtain reproducible results. By doing so, the use of the model and results will be accessible by a wide community, further support the mitigation of seismic risks in the region and facilitate future improvements to the seismic hazard model. To this end all data, results and methods used are made available through the web-portal of the European Facilities for Earthquake Hazard and Risk (www.efehr.org).     

遥测电平中断快速自动控制电路的设计

在远距离遥测传输过程,被传输的讯号中断时,PTY—8遥测仪鉴频盘将输出幅度很大的脉冲干拢,严重地损害了记录图的质量,甚至有些已经记录到的地震波形被掩没在讯号中断后出现的高频脉冲干扰中。据此,我们设计了快速自动保护电路。使用此电路后,讯号中断和怀复在记录图上未出现任何脉冲,中断后记录呈一条直线。     

Estimating water fluxes in the critical zone using water stable isotope approaches in the Groundnut and Ferlo basins of Senegal

Sustainable water management in semi-arid agriculture practices requires quantitative knowledge of water fluxes within the soil-vegetation-atmosphere system. Therefore, we used stable-isotope approaches to evaluate evaporation (E_a), transpiration (T_a), and groundwater recharge (R) at sites in Senegal's Groundnut basin and Ferlo Valley pasture region during the pre-monsoon, monsoon, and post-monsoon seasons of 2021. The approaches were based upon (i) the isothermal evaporation model (for quantifying E_a); (ii) water and isotope mass balances (to partition E_a and T_a for groundnut and pasture); and (iii) the piston displacement method (for estimating R). E_a losses derived from the isothermal evaporation model corresponded primarily to Stage II evaporation, and ranged from 0.02 to 0.09 mm d⁻¹ in the Groundnut basin, versus 0.02–0.11 mm d⁻¹ in Ferlo. At the groundnut site, E_a rates ranged from 0.01 to 0.69 mm d⁻¹; T_a was in the range 0.55–2.29 mm d⁻¹; and the T_a/ET_a ratio was 74%–90%. At the pasture site, the ranges were 0.02–0.39 mm d⁻¹ for E_a; 0.9–1.69 mm d⁻¹ for T_a; and 62–90% for T_a/ET_a. The ET_a value derived for the groundnut site via the isotope approach was similar to those from eddy covariance measurements, and also to the results from the previous validated HYDRUS-1D model. However, the HYDRUS-1D model gave a lower T_a/ET_a ratio (23.2%). The computed groundwater recharge for the groundnut site amounted to less than 2% of the local annual precipitation. Recommendations are made regarding protocols for preventing changes to isotopic compositions of water in samples that are collected in remote arid regions, but must be analysed days later. The article ends with suggestions for studies to follow up on evidence that local aquifers are being recharged via preferential pathways.     

Climate-related variations in crustal trace elements in Dome C (East Antarctica) ice during the past 672 kyr

Cr, Fe, Rb, Ba and U were determined by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in various sections of the 3,270 m deep ice core recently drilled at Dome C on the high East Antarctic plateau as part of the EPICA program. The sections were dated from 263 kyr bp (depth of 2,368 m) to 672 kyr bp (depth of 3,062 m). When combined with the data previously obtained by Gabrielli and co-workers for the upper 2,193 m of the core, it gives a detailed record for these elements during a 672-kyr period from the Holocene back to Marine Isotopic Stage (MIS) 16.2. Concentrations and fallout fluxes of all elements are found to be highly variable with low values during the successive interglacial periods and much higher values during the coldest periods of the last eight climatic cycles. Crustal enrichment factors indicates that rock and soil dust is the dominant source for Fe, Rb, Ba and U whatever the period and for Cr during the glacial maxima. The relationship between Cr, Fe, Rb, Ba and U concentrations and the deuterium content of the ice appears to be similar before and after the Mid-Brunhes Event (MBE, around 430 kyr bp). Mean concentration values observed during the successive interglacials from the Holocene to MIS 15.5 appear to vary from one interglacial to another at least for part of the elements. Concentrations observed during the successive glacial maxima suggest a decreasing trend from the most recent glacial maxima (MIS 2.2 and 4.2) to the oldest glacial maxima such as MIS 14.2, 14.4 and 16.2, which could be linked with changes in the size distribution of dust particles transported from mid-latitude areas to the East Antarctic ice cap.     

Monitoring precipitable water vapor in real-time using global navigation satellite systems

This paper addresses real-time monitoring of the precipitable water vapor (PWV) from GNSS measurements and presents some results obtained from 6-month long GNSS PWV experiments using international and domestic GNSS networks. In the real-time GNSS PWV monitoring system a server/client structure is employed to facilitate formation of PWV networks and single-differenced GNSS measurements are utilized to mitigate errors in GNSS satellites’ orbits and clocks. An issue relating to baseline length between the server and clients is discussed in detail and as a result the PWV monitor is configured to perform in two modes depending on the baseline length. The server estimates sequentially the zenith wet delay of the individual stations, which is then converted into the PWV of the stations. We evaluate system performance by comparing the real-time PWV solution with reference solutions including meteorological measurements obtained with radiosondes and deferred-time precision GNSS PWV solutions. Results showed that the standard deviation of difference between the real-time PWV and the reference solutions ranged from 2.1 to 3.4 mm in PWV for a 6-month long comparison, which was improved to 1.4 to 2.9 mm by reducing comparison period to 20 days in winter.     

Sr–Nd–Pb isotopic compositions of the Kovdor phoscorite–carbonatite complex, Kola Peninsula, NW Russia

The Sr, Nd and Pb isotopic compositions for the Kovdor phoscorite–carbonatite complex (PCC), Kola Peninsula, NW Russia, have been determined to characterize the mantle sources involved and to evaluate the relative contributions of a plume and subcontinental lithospheric mantle in the formation of the complex. The Kovdor PCC is a part of the Kovdor ultramafic–alkaline–carbonatite massif, and consists of six intrusions. The initial isotopic ratios of the analyzed samples, calculated at 380 Ma, display limited variations: ε_Nd, + 2.0 to + 4.7; ⁸⁷Sr/⁸⁶Sr, 0.70319 to 0.70361 (ε_Sr, − 12.2 to − 6.2); ²⁰⁶Pb/²⁰⁴Pb, 18.38 to 18.74; ²⁰⁷Pb/²⁰⁴Pb, 15.45 to 15.50; ²⁰⁸Pb/²⁰⁴Pb, 37.98 to 39.28. The Nd and Sr isotope data of the Kovdor PCC generally fit the patterns of the other phoscorites and carbonatites from the Kola Alkaline Province (KAP), but some data are slightly shifted from the mixing line defined as the Kola Carbonatite Line, having more radiogenic ⁸⁷Sr/⁸⁶Sr ratios. However, the less radiogenic Nd isotopic compositions and negative Δ7/4 values of Pb isotopes of the analyzed samples exclude crustal contamination, but imply the involvement of a metasomatized lithospheric mantle source. Isotopic variations indicate mixing of at least three distinct mantle components: FOZO-like primitive plume component, EMI-like enriched component and DMM-like depleted component. The isotopic nature of the EMI- and DMM-like mantle component observed in the Kovdor samples is considered to be inherited from metasomatized subcontinental lithospheric mantle. This supports the previous models invoking plume–lithosphere interaction to explain the origin of the Devonian alkaline carbonatite magmatism in the KAP.     

Three-dimensional numerical simulation for mechanized tunnelling in soft ground: the influence of the joint pattern

The main purpose of this study was to provide a three-dimensional numerical model, which would allow the tunnel lining behaviour and the displacement field surrounding the tunnel to be evaluated. Most of the processes that occur during mechanized excavation have been simulated in this model. The influence of the lining joint pattern, including segmental lining joints and their connections, has in particular been taken into consideration. The impact of the processes during mechanized excavation, such as the grouting pressure and the jacking forces in the structural forces induced in the tunnel lining, has been presented. These values depend on the tunnel advancement. However, a negligible influence of the joint pattern on the ground displacement field surrounding the tunnel has been observed. Generally, a variation in the structural forces in successive rings along the tunnel axis has been found in a staggered segmental lining, indicating the necessity of simulating the joints in the tunnel lining and using a full three-dimensional numerical model to obtain an accurate estimation. In addition, the considerable influence of the coupling effect between successive rings on the lining behaviour has been highlighted.