Ultimate uplift capacity of model rigid metal piles in clay

Summary Laboratory model test results for estimation of the ultimate uplift capacity of rigid metal piles embedded in a compacted near-saturated clayey soil are presented. The length-diameter ratio of the piles was varied from 10 to 15. The direction of the uplift load on the pile was varied from 0 to 50°. Based on the present test results and the results of existing model studies, an empirical relationship for estimating the pile uplift capacity has been presented.     

Coarse sediment supply sets the slope of bedrock channels in rapidly uplifting terrain: Field and topographic evidence from eastern Taiwan

The incision rate and steepness of bedrock channels depend on water discharge, uplift rate, substrate lithology, sediment flux, and bedload size. However, the relative role of these factors and the sensitivity of channel steepness to rapid (>1 mm yr⁻¹) uplift rates remain unclear. We conducted field and topographic analyses of fluvial bedrock channels with varying channel bed lithology and sediment source rock along the Coastal Range in eastern Taiwan, where uplift rates vary from 1.8 to 11.8 mm yr⁻¹ and precipitation is relatively consistent (1.5–2.7 m yr⁻¹), to evaluate the controls on bedrock channel steepness. We find that channel steepness is independent of rock uplift rate and annual precipitation but increases monotonically with sediment size and substrate strength. Furthermore, in reaches with uniform substrate lithology (mudstone and flysch), channel steepness systematically varies with sediment source rock but not with channel width. When applied to our data, a mechanistic incision model (saltation-abrasion model) suggests that the steepness of Coastal Range channels is set primarily by coarse-sediment supply. We also observe that larger particles are mainly composed of resistant lithologies derived from volcanic rocks and conglomerates. This result implies that hillslope bedrock properties in the source area exert a dominant control on the steepness of proximal channels through coarse-sediment production in this setting. We propose that channel steepness may be insensitive to uplift rate and flow discharge in fast-uplifting landscapes where incision processes are set by coarse sediment size and supply. Models assuming a proportionality between incision rate and basal shear stress (stream power) may not fully capture controls on fluvial channel profiles in landslide-dominated landscapes. Processes other than channel steepening, such as enhanced bedload impacts and debris-flow scour, may be required to balance rock uplift and incision in these transport-limited systems.     

Positioning with two satellites and known receiver clock,barometric pressure and radar elevation

GPS Solutions - We investigate the feasibility of completing an aircraft precision approach using two global navigation satellite systems (GNSS) satellites from different constellations in...     

Integrating hydrometeorological information for rainfall‐runoff modelling by artificial neural networks

The major purpose of this study is to effectively construct artificial neural networks‐based multistep ahead flood forecasting by using hydrometeorological and numerical weather prediction (NWP) information. To achieve this goal, we first compare three mean areal precipitation forecasts: radar/NWP multisource‐derived forecasts (P_r), NWP precipitation forecasts (P_n), and improved precipitation forecasts (P_m) by merging P_r and P_n. The analysis shows that the accuracy of P_m is higher than that of P_r and P_n. The analysis also indicates that the NWP precipitation forecasts do provide relative effectiveness to the merging procedure, particularly for forecast lead time of 4–6 h. In sum, the merged products performed well and captured the main tendency of rainfall pattern. Subsequently, a recurrent neural network (RNN)‐based multistep ahead flood forecasting techniques is produced by feeding in the merged precipitation. The evaluation of 1–6‐h flood forecasting schemes strongly shows that the proposed hydrological model provides accurate and stable flood forecasts in comparison with a conventional case, and significantly improves the peak flow forecasts and the time‐lag problem. An important finding is the hydrologic model responses which do not seem to be sensitive to precipitation predictions in lead times of 1–3 h, whereas the runoff forecasts are highly dependent on predicted precipitation information for longer lead times (4–6 h). Overall, the results demonstrate that accurate and consistent multistep ahead flood forecasting can be obtained by integrating predicted precipitation information into ANNs modelling. Copyright © 2009 John Wiley & Sons, Ltd.     

岩溶洞穴分类新思考

根据一固定流域范围内相对于岩溶合水层的水流运动方式,将洞穴划分为流入、流出和穿越含水层三种类型;并指出:只要外部环境相对稳定,洞穴在流域中所处位置,所执行功能和拥有水动力条件就会随之保持稳定,形成一定成因类型的洞穴,其发育就会表现出很好的延续性和系统性,并展示出相应的形态特征。      

Seismo-ionospheric precursor of the 2008 Mw7.9 Wenchuan earthquake observed by FORMOSAT-3/COSMIC

The seismo-ionospheric precursor prior to the Mw7.9 earthquake near Wenchuan, China, on 12 May 2008 was observed by the FORMOSAT-3/COSMIC satellite constellation. By binning radio occultation observations, the three-dimensional ionospheric structure can be obtained to monitor the ionospheric electron density variation prior to the earthquake. It has been determined that near the epicenter the F2-peak height, hmF2, descends about 25 km and the F2-peak electron density, NmF2, decreases about 2 × 10⁵ el/cm³ around noon within 5 days prior to the earthquake. The integrated electron content decreases more than 2 TECU between 250 and 300 km altitude.     

Determining elastic constants of transversely isotropic rocks using Brazilian test and iterative procedure

The elastic constants of rocks are the basic parameters for rock mechanics, and play a very important role in engineering design. There are many laboratory methods to determine the elastic constants of transversely isotropic rocks, and the Brazilian test is a popular method. This paper presented a method combination of the Brazilian test, back calculation, and iterative procedure to evaluate the five independent elastic constants of transversely isotropic rocks in laboratory. The strain data at the centre of discs were obtained using Brazilian test. The stresses at the centre of discs were computed using numerical programs. By using back calculation, the temporary elastic constants were computed after the stresses and stains were substituted into elastic mechanics equations. After iterative procedure, the convergent values of the elastic constants can be obtained. One numerical example and three experimental cases were proposed to show the applicability of this method. The convergent values of the five independent elastic constants can be obtained in no more than 10 iterative cycles. The results coming from numerical analysis method exhibited satisfactory outcome in accordance with those of generalized reduced gradient method. The merits of this method include convenient specimen preparation of the Brazilian test, simple iterative procedure, and readily available commercially numerical programs, so that this method can be easily popularized in research and engineering analysis. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental investigation on seismic behavior of scoured bridge pier with pile foundation

This study investigated the seismic performance and soil‐structure interaction of a scoured bridge models with pile foundation by shaking table tests using a biaxial laminar shear box. The bridge pier model with pile foundation comprised a lumped mass representing the superstructure, a steel pier, and a footing supported by a single aluminum pile within dry silica sand. End of the pile was fixed at the bottom of the shear box to simulate the scenario that the pile was embedded in a firm stratum of rock. The bridge pier model was subjected to one‐directional shakes, including white noise and earthquake records. The performance of the bridge pier model with pile foundation was discussed for different scoured conditions. It is found that the moment demand of pile increases with the increase of scoured depth whereas the moment demand of the bridge pier decreases, and this transition may induce the bridge failure mechanism transform from pier to pile. The seismic demand on scoured pile foundations may be underestimated and misinterpreted to a certain degree. When evaluating the system damping ratio with SSI, the system response may not be significantly changed even if the soil viscous damping contribution is varied. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation of code criteria for bridges with unequal pier heights

One of the challenges associated with Eurocode 8 and AASHTO-LRFD is predicting the failure of irregular bridges supported by piers of unequal heights. EC8 currently uses “moment demand-to-moment capacity” ratios to somewhat guarantee simultaneous failure of piers on bridges, while AASHTO-LRFD relies on the relative effective stiffness of the piers. These conditions are not entirely valid, in particular for piers with a relative height of 0.5 or less, where a possible combination of flexure and shear failure mode may occur. In this case, the shorter piers often result in brittle shear failure, while the longer piers are most likely to fail due to flexure, creating a combination of different failure modes experienced by the bridge. To evaluate the adequacy of EC8 design procedures for regular seismic behavior, various irregular bridges are simulated through a non-linear pushover analysis using shear-critical fiber-based beam-column elements. The paper investigates the behavior of irregular monolithic and bearing-type bridges experiencing different failure modes, and proposes different methods for regularizing the bridge performance to balance damage. The ultimate aim is to obtain a simultaneous or near-simultaneous failure of all piers irrespective of the different heights and failure mode experienced.