An Integrated Geophysical and Geotechnical Assessment of Hazards Around The Abu Serga Church E-Book
Sayed Hemeda
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- Herausgeber: Bentham Science Publishers
- Kategorie: Geisteswissenschaft
- Sprache: Englisch
The Abu Serga Church is one of the oldest known Coptic churches in Egypt, with a history of almost 1700 years. This reference work presents a comprehensive geotechnical and geophysical survey of the vicinity of the Abu Serga Church. The book details the information of the survey using classical and modern methods of geotechnical engineering while keeping contemporary issues faced by site investigators in view. Chapters provide the data of the church site while covering topics of interest to students such as seismic analysis, 3-D modeling and historical preservation principles. Advanced methods of interest to engineers such as mathematical analysis using finite element methods are also covered.
This work provides key data about the Abu Sega Church site and is of interest to scholars and engineers involved in conservation engineering of architectural heritage (or built heritage), as well as readers interested in church studies.
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Seitenzahl: 189
Veröffentlichungsjahr: 2021
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PREFACE
This book is of interest to practical geotechnical engineers and experts in the Conservation Engineering of the architectural heritage or built heritage. It discusses some contemporary issues related to advanced geotechnical and geophysical techniques in preservation projects which are critical components in conservation planning and management of built heritage and often require detailed management techniques and unique solution methods to address failures and remedial measures. The geotechnical engineering community continues to find improved testing techniques for determining sensitive properties of bearing soils and structures, including stress-wave based non-destructive testing methods and techniques. Also to improve the foundation retrofitting intervention; the design and implementation. To minimize failure during conservation and preservation projects. Contemporary issues and data may reveal useful lessons and information to improve restoration project construction management and minimize economic losses. This book discusses these aspects using appropriate methods in a simple way.
This book discusses many interesting topics in Geophysical and geotechnical engineering like, Modern Geotechnical Practice, Geotechnical Earthquake Engineering, Principals and Practice in Foundation Design, and 3D Modeling in Geomechanics, Geotechnical investigation for Preservation of Historical Buildings and Archaeological Sites.
This book brings together a small collection of chapters but covering Geotechnical problems and solutions from a broadest to a narrowest sense.
Using this opportunity, I would like to express my gratitude to the publishers (Benthan Scientific Publishers) for their efforts in making this book published.
CONSENT FOR PUBLICATION
Not applicable.
CONFLICT OF INTEREST
The authors declare no conflict of interest, financial or otherwise.
ACKNOWLEDGEMENTS
Declared none.
Introduction and Scope of Work
Sayed Hemeda1. INTRODUCTION
Abu Serga Church in Coptic Cairo is one of the oldest Coptic churches in Egypt. The church was built in the 4th century and was probably finished during the 5th century.
Saints Sergius and Bacchus Church is traditionally believed to have been built on the spot where the Holy Family, Joseph, Mary, and the infant Jesus Christ, rested at the end of their journey into Egypt.
The church is of significant historical importance, and in fact, it is where many patriarchs of the Coptic Church were elected.
It was burned during the fire of Fustat, in the reign of Marwan II around 750. It was then restored during the 8th century and has been rebuilt and restored constantly since medieval times; however, it is still considered a model of the early Coptic churches. Again, the most precious and ancient of the icons are on the southern wall. A vast central hall is divided into three naves by two rows of pilasters.
The 12 October 1992 Dahshour earthquake south of Cairo, Egypt, was the most severe natural hazard to hit this area in more than 10 decades. The earthquake measured 5.3 in magnitude on the Richter scale (duration magnitude Md due to the seismic station at Helwan). The P-wave magnitude (mb) and the surface wave magnitude (Ms) determined from worldwide seismic records were equal to 5.9 and 5.3, respectively. The epicenter was about 18 km south of the center of Cairo, near the village of Dahshour, and located at an estimated depth of 25 km. Several aftershocks followed the main event and continued to occur during the month of November. One of Richter magnitude 4.2 occurred on 13 October another of magnitude 4.3 occurred on 22 October. On 5 November, three consecutive aftershocks ranging from 3.9 to 4.2 in magnitude occurred within half an hour, followed by several aftershocks of smaller magnitude.
The present report helps in understanding the amount of hazards and risks that Abu Serga Church suffers. Abu Serga Church is located within Cairo city and is considered one of the oldest Churches found in Egypt. The church suffers moderate hazards but high risk; it is very important to assess the amount of engineering and seismic risk for this important archeological structure. For this, the amount of hazards were evaluated carefully using all available source of information, including review of the pieces of literature in and around Abu Serga church, earthquake catalogues, expected water table level, and seismic strength. A GPR survey was held at Abu Serga church to detect any suspected archeological remains under the church. Finally, the resonance properties and expected design response spectrum were determined for the Abu Serga Church.
Previously published geological maps and literature on the geology of the Cairo area have been integrated within a regional framework and tectonic context of the area under investigation. Having done that, fault intersection has been defined in the area in and around the church.
2. SCOPE OF WORK
The present study is an integrated geophysical work to determine the following points:
Determining the possibility of near-surface groundwater and its expected depth.Determining the soil shear strength in terms of shear wave velocity versus depth.Determining the amount of expected probabilistic seismic hazard in terms of expected peak ground accelerations for exposure time periods of 50 & 100 years.Determining the soil and structure natural frequencies of vibrations.Determining design response spectrum for Abu Serga church,Making 2D geo-radar Multi-scanning for determining the possibility of old remains of any archaeologies features under the church.Task 1- Study the soil saturation and expected water depth.
Task 2- Study soil strength in terms of shear wave velocity.
Task 3- Study the resonance properties of the church.
Task 4- Study the neotectonic and geohazards issues in Abu Serga church.
Task 5- Study of neotectonic and paleoseismic issues in Abu Serga church and the surrounding region, and give the expected amount of shaking in terms of PGA. This is to address future surface and subsurface problems.
Task 6 - Regional tectonic framework study. This is to address fundamental problems or practical issues of tectonic evaluation and produce a seismic hazard model.
Task 7- Give the expected design spectrum based on the most important earthquakes that hit the region.
Task 8- Study the possibility of old archeological remains under the church.
3. METHODOLOGY & WORK PROCEDURE
In order to meet the above-mentioned objectives, the following work procedure was followed:
1- Reviewing available information, previous work, and maps (topographic, geologic, and seismicity data) related to Abu Serga church area and its surroundings.2- Satellite images were geo-referenced, processed for structure analysis.3- Analyzing and interpreting the collected data of resistivity imaging, refraction microtremors test, soil resonance test, and ground-penetrating radar data (GPR).4- A field visit was conducted to verify the interpretation and gather detailed features, principally those that might affect the Abu Serga church area.5- Collecting historical seismicity in and around Abu Serga church in the period 2200 BC. 1899 AD.6- Collecting recent instrumental earthquake catalogue in the period 1899 AD. 2006 AD.7- Performing regional seismic hazard analysis based on the most recent hazard parameters available in Egypt, such as PGA attenuation formulas, seismic source regionalization, recurrence relationships … etc.Finally, based on the previously collected data, the amount of hazard at Abu Serga church is accessed assessed, and possible archeological features are given.
Determining the S-Wave Velocity by Using Refraction Microtremors Technique
Sayed HemedaAbstract
The refraction microtremors technique is based on two fundamental ideas. The first one is that common seismic-refraction recording equipment, set out in a way almost identical to shallow P- wave refraction surveys, can effectively record surface waves at frequencies as low as 2 Hz (even lower if low-frequency phones are used). The second idea is that a simple, two-dimensional slowness-frequency (p-f) transform of a microtremors record can separate Rayleigh waves from other seismic arrivals and allow recognition of true phase velocity against apparent velocities. Two essential factors that allow exploration equipment to record surface-wave velocity dispersion, with a minimum field effort, are the use of a single geophone sensor at each channel, rather than a geophone “group array”, and the use of a linear spread of 12 or more geophone sensor channels. Single geophones are the most commonly available type and are typically used for refraction rather than reflection surveying. The advantages of ReMi from a seismic surveying point of view are several, including the following: It requires only standard refraction equipment already owned by most consultants and universities; it requires no triggered source of wave energy, and it will work best in a seismically noisy urban setting. Traffic and other vehicles, and possibly the wind responses of trees, buildings, and utility standards, provide the surface waves. The present study uses the ReMi method to determine the S-wave seismic velocity with depth for Abu Serga church. This is important to determine the depth of the bedrock (any solid rock underlying the soil with S-wave >765 m/s, USGS, 190) as well as other engineering applications.
1. DETERMINING THE S-WAVE VELOCITY USING REFRACTION MICROTREMORS TECHNIQUE
The present study uses the ReMi method to determine the S-wave seismic velocity with depth for Abu Serga church. This is important to determine the depth of the bedrock (any solid rock underlying the soil with S-wave >765 m/s, USGS, 190) and other engineering applications. The refraction microtremors technique is based on two fundamental ideas. The first is that common seismic-
refraction recording equipment, set out in a way almost identical to shallow P-wave refraction surveys, can effectively record surface waves at frequencies as low as 2 Hz (even lower if low frequency phones are used). The second idea is that a simple, two-dimensional slowness-frequency (p-f) transform of a microtremors record can separate Rayleigh waves from other seismic arrivals and allow recognition of true phase velocity against apparent velocities. Two essential factors that allow exploration equipment to record surface-wave velocity dispersion, with a minimum of field effort, are the use of a single geophone sensor at each channel, rather than a geophone “group array”, and the use of a linear spread of 12 or more geophone sensor channels. Single geophones are the most commonly available type, and are typically used for refraction rather than reflection surveying. The advantages of ReMi from a seismic surveying point of view are several, including the following:
It requires only standard refraction equipment already owned by most consultants and universities; it requires no triggered source of wave energy, and it will work best in a seismically noisy urban setting. Traffic and other vehicles and possibly the wind responses of trees, buildings, and utility standards provide the surface waves this method analyses (Louie, 2001; Pullammanappallilet al., 2003).
2. Theory
ReMi processing involves three steps: Velocity Spectral Analysis, Rayleigh Phase-Velocity Dispersion Picking, and Shear-Wave Velocity Modeling.
2.1. Velocity Spectral Analysis
The basis of the velocity spectral analysis is the p-tau transformation, or “slantstack,” described by Thorson and Claerbout (1985). This transformation takes a record section of multiple seismograms, with seismogram amplitudes relative to distance and time (x-t), and converts it to amplitudes relative to the ray parameter p (the inverse of apparent velocity) and an intercept time tau. It is familiar to array analysts as “beam forming” and has similar objectives to a two-dimensional Fourier-spectrum or “F-K” analysis as described by Horike (1985). Clayton and McMechan (1981) and Fuiset al. (1984) used the p-tau transformation as an initial step in P-wave refraction velocity analysis. McMechan and Yedlin (1981) developed the p-f technique and tested it against synthetic surface waves and reverberations seen on controlled-source multichannel seismic records. Parket al. (1998) applied the p-f technique to active-source MASW records. All phases in the record are present in the resulting (p-f) image that shows the power at each combination of phase slowness and frequency. Dispersive phases show the distinct curve of normal modes in low-velocity surface layers: sloping down from high phase velocities (low slowness) at low frequencies to lower phase velocities (high slowness) at higher frequencies. Milleret al. (2000) examine p-f-domain power spectra of MASW records along a profile to define lateral variations in dispersion curves and thus in shear velocities. The distinctive slope of dispersive waves is a real advantage of the p-f analysis. Other arrivals that appear in microtremor records, such as body waves and air waves, cannot have such a slope. The p-f spectral power image will show where such waves have significant energy. Even if most of the energy in a seismic record is a phase other than Rayleigh waves, the p-f analysis will separate that energy in the slowness-frequency plot away from the dispersion curves this technique interprets. By recording many channels, retaining complete vertical seismograms, and employing the p-f transform, this method can successfully analyze Rayleigh dispersion where SASW techniques cannot.
2.2. Rayleigh Phase-Velocity Dispersion Picking
This analysis adds only a spectral power-ratio calculation to McMechan and Yedlin's (1981) technique for spectral normalization of the noise records. The ability to pick and interpret dispersion curves directly from the p-f images of spectral ratio parallels the coherence checks in the SASW technique (Nazarian and Stokoe, 1984) and the power criterion in the MASW technique (Parket al
