Proposed Bridge Site Research Articles

Experimental Study of Bearing Capacity Bridge Foundation Determination

Ethiopia is almost mountainous and hilly in topography, with many rivers flowing from the cities' centers. To facilitate transportation, a bridge across the Berbere Wonze River must be built. The bearing capacity of foundation soil is important for foundation design because it can carry heavy loads from the superstructure. The primary goal of this experimental geotechnical investigation is to determine the bearing capacity of foundation soil for the design of bridge foundation at Berbere Wonze River in Amahara Region South Wollo, Kombolcha, Ethiopia. The foundation investigation work includes a Dynamic Cone Penetration (DCP) test, a Standard Penetration Test (SPT), visual identification, groundwater monitoring, soil sampling, and subsequent laboratory tests on representative samples to determine the physical and engineering properties of the subsurface formations and soil underlying the proposed bridge sites. These are to provide safe and cost-effective foundations based on a combination of field data and laboratory test results.

Geotechnical Investigation of a Proposed Bridge Site Across Walva-Shirgaon, Sangli

Geotechnical Investigation of a Proposed Bridge Site Across Walva-Shirgaon, Sangli

Electrical resistivity as a binary classifier for bridge scour evaluation

Scour is responsible for approximately 60% of all bridge collapses in the United States. Evaluating scour using empirical equations has proven inaccurate, particularly in fine-grained soils. Furthermore, evaluating scour potential based on site specific erosion testing can be uneconomic as erosion testing is time consuming. Many soil characteristics that affect soil erosion also influence soil electrical resistivity (ER) which can be measured in the field or in the laboratory. The objectives of this study were to assess if field and laboratory ER measurements can be used interchangeably for characterizing soil erodibility and the impact of saturation as expected during a flood event, on the ER based soil erodibility model. Twenty-one bridge sites were used for in situ electrical resistivity tomography (ERT) surveys and erosion testing. Supplementary ER measurements at varying degrees of saturation were also conducted using a soil box in the laboratory. It was found that ER values do not differ significantly when ERT is conducted on streambanks as opposed to fully saturated conditions. A receiver operating characteristic curve and probability density function (PDF) were used to determine that soils with ER over 50 Ωm had an 87% probability of classifying as highly erodible based on this data set. Statistical tests also suggested that laboratory ER can be used as an alternative to field ERT surveys. While in situ ERT provides more information in terms of spatial variation in the subsurface, laboratory ER measurements on retrieved samples will allow transportation agencies to utilize the developed erodibility classifier model without the capital investment of an ERT system. Given the large number of bridges with scour susceptible foundations in the National Bridge Inventory, ER can be used to rapidly prioritize them for additional testing to measure the erosion potential or to characterize the soil erosion at proposed bridge sites.

Influence of elevated water levels on wind field characteristics at a bridge site

The influence of elevated water levels on wind field characteristics at bridge sites owing to hydroelectric power stations plays an important role in bridge engineering, particularly in mountainous valley regions. To investigate this issue, a comparative experimental study, which uses a topographic model with two water level states for determining the influence on wind field characteristics at the proposed bridge site located in a mountainous valley area, was conducted in the XNJD-3 wind tunnel at Southwest Jiaotong University, Chengdu, PR China. The altitude difference between the two water level states was approximately 200 m, whereas uniform and D-type boundary layer air inflow conditions were adopted during the wind tunnel test, respectively. The wind speed at the bridge girder and profile of the 1/4, mid, and 3/4 spans were recorded during the experiment. The test results indicated that after the water level was raised, the mean wind speed (or speed-up factor) along the bridge girder decreased by approximately 10%, and the values of the wind profile also decreased. However, the wind profile curve shapes remained approximately unchanged, and the wind attack angle was significantly transformed by approximately 5° in certain locations of the bridge girder. Moreover, the variation in the water level had a negligible influence on the turbulence intensities, turbulence integral length scales, probability distribution of fluctuating wind components, and turbulent wind spectra along the bridge girder. Therefore, as the water level in the canyon rises, the wind field characteristics at the bridge site tend to be conducive to bridge safety. Therefore, long-span bridges located in mountainous valley areas should be designed appropriately according to the expected minimum water level of the river.

Site-specific ground response analysis of a proposed bridge site over Barak River along Silchar Bypass Road, India

It is well known that the local soil condition is an important factor in changing the ground motion parameters during earthquake. Therefore, it becomes important to carry out site-specific earthquake risk study for the designing of earthquake-resistant structures due to future hazard. In the present study, a ground response analysis of a proposed bridge site over Barak River along Silchar Bypass Road is carried out to evaluate the local site effect with the real recorded earthquake ground motions available in this study area. Detailed soil investigation report in terms of SPT bore log profile is collected from the Government Agencies (Public Works Department, Govt. of Assam). In the absence of in situ shear wave velocity profile data, the Vs profiles are estimated from the known SPT-N value by proposing new empirical equations correlating Vs and SPT-N. After evaluation of the Vs 30 profiles, the site is then classified according to the provisions of National Earthquake Hazards Reduction Program (NEHRP). The input ground motions used for the analyses are in the form of acceleration time histories obtained from two recorded earthquakes such as Ms 7.2 (India–Burma Border earthquake, 1988) and Mw 6.4 (India–Burma Border earthquake, 1995). The modulus reduction and damping ratio curves are obtained from the different research works published considering the characteristics of subsurface profiles. The ground response analyses have resulted in the calculation of the ground motion parameters as well as the amplification factor, and response spectra at the ground surface for the site. The results have revealed that the ground motion at bed rock level has been highly amplified by the soil layers at three different frequency ranges from 2 to 8 Hz for both the earthquakes with a maximum amplification factor up to 4.6. The average surface level peak ground acceleration for the bridge site is found to be 0.25 and 0.18 g for the Ms = 7.2 and Mw = 6.4 earthquakes, respectively. Further, the averaged response spectrum of both the earthquakes for the bridge site is compared with the response spectrum of the Indian Standard (IS) 1893:2002. The design response spectrum for the bridge site is also developed considering NEHRP provisions. Therefore, the results would be very much useful for the designer, planner and the Govt. of Assam for the safety of such important bridge for earthquake-resistant design to mitigate seismic hazard.

Nonlinear Site Response Evaluation of Earthquakes: A Case Study from Sirdjan Balvavard Bridge, Kerman Province, Iran

The aim of this study is to illustrate the soil conditions encountered at the proposed bridge sites to analyze and evaluate the test conducted, submit recommendations regarding foundation design. At first by field investigation, the required data was collected and after primary processing the acceptable data was selected. For nonlinear analysis of elastic and rigid half space bed rock, standard hyperbolic model was selected and performed, and the results were compared. The study clearly showed that the effect of bed rock on soil behavior during earthquake is one of the main factors controlling prediction of ground response. A critical aspect of this work was to develop and use a computer code “Abbas Converter” developed by the authors that has several advantages, such as quick installation, acting as a connecter function between the used softwares which can generate the input data corresponding to a defined format and finally, the results of this computer code can be easily exported to the other softwares used in this study. Moreover this code can make it easy to solve the problems encountered.

台風シミュレーション・システムの開発と風向別最大風速の評価

The basic wind speed for a long-span bridge was examined using GIS-based typhoon simulation system. First, the recorded typhoons which generated strong wind at the proposed bridge site were extracted from the typhoon data by the Japan Meteorological Agency, and probabilistic models expressing the characteristics of the typhoons were created. Next, the surface wind speed and direction were calculated using the Meng's formula, and they were examined by comparing with wind observation records at the site. Based on these results, the probability distributions of the annual maximum wind speed for every 16-divided wind direction were computed by the Monte-Carlo method. Various analyses were efficiently performed making the best use of the functions of GIS.

Site-specific ground motion simulation and seismic response analysis at the proposed bridge sites within the city of Addis Ababa, Ethiopia

In this study synthetic ground motion time histories have been generated at rock sites simulating earthquakes of moment magnitudes 6.8, 6.0 and 5.2 and epicentral distances of 25, 50, 80, 120 and 200 km. Applying these rock time histories as input motions at the base of the soil columns determined using surface seismics, a one-dimensional, equivalent-linear analysis was used to propagate the input motions through the soil columns to determine the ground motions at the ground surface. The goal is to determine the seismic responses of the sites chosen for bridge construction in the framework of the Addis Ababa City Ring Road Project. The computed acceleration time histories, response spectra and amplification spectra will be most useful for design engineers.

Application of reflection seismology to foundation investigations at A5 Pont Melin Rûg, North Wales

A modern road bridge across the Afon Alwen is proposed to replace the existing A5 Pont Melin Rûg, a masonry arch structure built in 1792. However, progress on engineering design has been hampered by problematic ground conditions caused by a previously unrecorded, 40–50 m thick sequence of soft to very soft glaciolacustrine silts (Rûg Silts). The remarkable depth of the Rûg Silts and the need to locate a foundation stratum for the proposed new bridge prompted the application of geophysical techniques. A high-resolution seismic reflection survey was performed to image the subsurface conditions at the proposed bridge site to a depth of 100 m below ground level and provide a comprehensive understanding of the geological profile. The seismic survey successfully delineated the bottom of the Rûg Silts, identified a basal unit of very dense, heterogeneous glaciofluvial gravels and delimited bedrock of Silurian Nantglyn Flags. Subsequently, a single deep borehole confirmed the findings of the geophysical survey and importantly, the investigations proved a possible foundation horizon for the proposed new bridge at a depth of 45.80 m in the basal gravel unit. The seismology provided the largest and most continuous source of geological information across the site and consequently had the greatest influence on the deliberations on foundation selection and optimization. This case history illustrates the benefits of using reflection seismology in areas of complex glacial geology. It also demonstrates the benefits of geophysical investigations to geotechnical assessments of local ground conditions.

Archaeological Survey of Property for the Proposed Eagle Pass International Bridge, Maverick County, Texas

In May 1990, archaeologists for the Center of Archaeological Research, The University of Texas at San Antonio conducted a surface survey and subsurface testing program. at the site of the proposed Eagle Pass international bridge. The survey was conducted for Groves and Associates, Inc., consulting engineers and project planners, for the City of Eagle Pass. Survey and testing activities were performed in order to locate and evaluate any archaeological remains which might be affected by construction of the bridge and associated facilities. In addition, archival research was conducted at the Eagle Pass library and county courthouse in order to assess potential archaeological resources in the area of the proposed bridge site. The project area has been much disturbed by road, railroad, and water treatment facility constructions. No significant prehistoric or historic archaeological remains were identified during the survey and testing. However further machine and hand excavations within the river terraces to examine for deeply buried cultural deposits and conduct geomorphological recording will be required.

AN APPLIED GEOMORPHOLOGICAL STUDY ON THE SELECTED BRIDGE SITE ALONG THE BRAHMAPUTRA-JAMUNA RIVER IN BANGLADESH

Directly after the independence of Bangladesh, the government of Japan was requested to research the possibility of constructing a bridge across the Brahmaputra-Jamuna River. Constructing a bridge across the river, the most important thing to consider is the shifting of the river course and change of the banklines of the river. The shift from the Old Brahmaputra River to the present Brahmaputra-Jamuna River occurred 180 years ago. It is the fear of technical officials who govern the river in Bangladesh that the river may shift after construction of the bridge. The government of Japan was requested to fix the whole river course of the BrahmaputraJamuna River. This was, however, impossible for financial reasons because the river is both too long, and too wide. Bahadrabad, Gabargaon, Sirajganj and Nagarbari (Aricha) were selected as proposed bridge sites. The author was requested to select the most stable and suitable site among the four for the bridge based on applied geomorphological research. The main causes of the shifting of the river are remarkable crustal movement, deposition of sand, variation of discharge, and a bank completely consisting of sand. To make sure of the stability of the river at the four proposed bridge sites, the author investigated (1) the change of banklines and the location of thalwegs and prepared (2) a geomorphological map of the R. Brahmaputra-Jamuna Basin (1: 50, 000) and (3) a geomorphological map of the R. Brahmaputra-Jamuna and R. Ganges Plain (1: 1, 000, 000). (1) The author researched the change of banklines and the location of the thalweg from 1830 to the present. At the Bahadrabad site, due to the rising of the river bed, the expanding of river width and braiding of river channels are continuing. Nagarbari (Aricha) is located at the confluence between the Ganges and the Brahmaputra-Jamuna. The peak of the flood discharge of the Ganges generally occurs about one month later than that of the Brahmaputra-Jamuna. Due to the back-water, the bank erosion, change of river, and location of the thalweg are the largest among the the four proposed bridge sites. The change is smaller at the Gabargaon and Sirajganj sites. (2) The geomorphological map of the Brahmaputra-Jamuna River has been prepared by utilizing the mozaic of the aerial photographs which were taken in 1974 by the Japanese Reconnaissance Team as a base map. The author has prepared the map by utilizing the photographs and conducting field observation by boat and jeep (Fig. 5). The rivers from the border with India to Sirajganj, with a straight or meandering flow, are similar to rivers in natural levee regions. There are natural levees, back-swamp, and abandoned river courses in the alluvial fan around the Bahadrabad and Gabargaon. The author estimated that the natural levees and back-swamps were originally formed by the R. Tista, Jamuna, and Jhinai and that the alluvial fan by the Brahmaputra-Jamuna River had coverd partly the natural levees, back-swamps, and former river courses after the shifting of the Brahmaputra-Jamuna River. In the future, the area of the natural levee, back-swamp, and abandoned river courses in the fan will be buried by the future shifting of the river course. Sirajganj and Balktia (which is located across the river from Sirajganj) are situated on the old alluvial plain which was formed by the Tista, Jamuna, Jhinai, etc. more than 180 years ago. The old alluvial plain is separated from the present alluvial plain by the cliff, whose relative height is about 3 m. The narrowest point of the new plain between the old plains is 7 km in width.

Safe bearing capacity evaluation of the bridge site along Syafrubesi-Rasuwagadhi road, Central Nepal

The research work was carried out at the proposed bridge site along Syafrubesi-Rasuwagadhi Road, Central Nepal. The study was based on field SPT/DCPT and laboratory tests. N values were determined from SPT/DCPT test. The index and mechanical properties of granular soils were computed in laboratory. Then, ultimate and allowable bearing capacities with safety factor 3 for maximum tolerable limit of 40 mm settlement was estimated by empirical equations provided by Teng (1988) and Terzaghi and Peck (1978). It is recommended that safe bearing capacity for 6 m size open square foundation at left and right abutments are suitable within 4.5 to 6 m depth. doi: 10.3126/bdg.v12i0.2254 Bulletin of the Department of Geology, Vol. 12, 2009, pp. 95-100