Site Effects Estimation using Experimental and Numerical Methods in Karaj City

Nastaran Ehsani1*, Mohammad Reza Ghayamghamian2, Mohsen
Fazlavi3 And Ebrahim Haghshenas4
1, 2, 4. International Institute of Earthquake Engineerng &
Seismology
3. Imam Khomeini International University, Qazvin, Iran Extended Abstract
(Paper pages1-28)
Introduction
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

The earthquake is one of the most devastating natural disasters that always threats human societies in terms of health and financial issues. Iran is one of the most seismic prone countries of the world due to locating on Alpine- Himalayan Orogenic belt. On the other hand, growing population and increased construction of tall buildings, increases the damages caused by large earthquakes, especially in large cities. Karaj is one of the most populous cities in Iran which there has been considerable industrial and economic development in recent years. When an earthquake occurs, seismic waves radiate away from source and travel rapidly through the earth crust. When these waves reach the ground surface, they produce shaking that may last from several seconds to a few minutes. During earthquakes, different alluviums with different structures show various reactions. It is wellaccepted that, besides the earthquake magnitude and fault distance, local geologic conditions, known as site effects, can also exert significant influences on characteristics of the seismic waves such as amplitude, frequency content and duration of strong ground motion at a given location. The seismic ground motion at any site is influenced by the type of soil in that region. Younger and softer soils usually amplify ground motion more than older soils or bedrocks .
There are theoretical and experimental methods to evaluate the site response. In the present study, the Nakamura’s H/V spectral ratio method has been used to evaluate the resonance frequency in 37 locations at Karaj site.
In addition, a preliminary 1-D site response modelling has been conducted using Deepsoil program according to downhole, array and geology data. Site frequencies obtained from modelling are presented and compared with site frequencies obtained through microtremor measurements.
Materials and Methods
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Single station microtremor measurements at the Karaj site were carried out by the International Institute of Earthquake Engineering and Seismology (IIEES) in 2012 with a three-component broadband seismometer (Guralp CMG-6TD). In the present study, we have used 37 microtremor data along the north-southwest profile because at this profile, geological section was available and these stations contained geotechnical boreholes data. Dynamic range of sensor changes between 0.033 -50 Hz and has a natural period of 1 second. 24-bit analog-to-digital (A/D) converter digitized the recorded data. The recording system was operated continuously for about 30 minutes with sampling frequency of 100 Hz. The use of ambient vibrations for analysis of the local site effects has been studied in detail in the framework of the European research project SESAME (Site Effects Assessment Using Ambient Excitations). The recommended guidelines on the H/V spectral ratio technique are the result of the comprehensive and detailed analysis performed by the SESAME participants during three years of investigations (2001-2004).
H/V spectral ratio was carried out by the Geopsy software. The process starts by converting data from binary format to ASCII format. After DC offset removal, eighth order Butterworth band pass filter used within the range of 0.1 Hz to 50 Hz. The Anti-triggering algorithm STA/LTA has been selected to reject energetic transients from ambient vibration recordings, so STA and LTA were considered respectively 1 and 30 second. Minimum and maximum STA/LTA thresholds were selected between 0.2 and 2.5. For each station, the time-series of the record is divided into windows of 40 to 100 seconds in three components with an overlap of 50%. Also, a cosine taper with the length of 5% of the total window length was used at each end.
The amplitude spectra of each selected window is computed with a fast Fourier transform (FFT) and smoothed using the Konno-Ohmachi function (Bandwidth=40). Then, two horizontal components are merged by squared average. Finally, the H/V spectral ratio of Nakamura is applied for each individual window, and the final predominant frequency is obtained by averaging the H/V spectral ratio of all window. The presence of clear peak on H/V spectral ratio curve is indicative of the impedance contrast between the uppermost surface soil and the underlying hard rock, where large peak values are generally associated with sharp velocity contrasts, and is likely to amplify the ground motion. The H/V spectral ratio in some stations shows a clear peak and at the others might show two or multiple peaks which represents the geologically complex areas. Calculated dominant frequency changes between 0.4 and 2 Hz. These low values indicate the existence of basement at greater depths and large thickness of sediments on basement (Parolai et al., 2002).
Site modelling
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

The results of H/V spectral ratio are affected by the local geologic structure. Based on this assumption, we can produce theoretical H/V curve with knowledge of the geologic structure in the area. One-dimensional modelling is a suitable method to evaluation of the site response due to the local geology which requires geotechnical and geophysical data. In the onedimensional modelling, it is assumed that all boundaries are horizontal in the infinite media and the response of a soil deposit is predominantly caused by SH-wave propagating vertically from the underlying bedrock. In this present study, one-dimensional modelling was carried out using Deepsoil software. Due to the very small deformations in soils by microtremor and producing a low levels of strain, we applied the linear method to evaluate the ground seismic response during mild earthquake shakes. In this software, homogeneous and isotropic soil profile is considered as N horizontal layers. The site response (transfer function) is evaluated by parameters such as layer thickness (m), density (ρ), shear modulus (G), and damping factor of layers (β), which are obtained from available geotechnical boreholes.
Usually, engineering bedrock is considered for the purpose of numerical modelling. According to TC4 (1994), the seismic bedrock was defined as a layer with a shear wave velocity of more than 600 m/s. Shima (1978) recommended that the upper crust with a shear wave velocity of about 3000 m/s, is adopted as bedrock when large scale structures with longer vibration period are being considered. International building code (ICC2000) has defined the seismic bedrock by a shear wave velocity of more than 760 m/s. According to Unified Building Code (UBC97), bedrock is defined into two groups: A (very hard rock with a speed of more than 1500 m/s) and B (rock with a speed of 760 to 1500 m/s). Therefore, the proposed values of the shear wave velocity are different for considering seismic bedrock. In order to consider the uncertainty of the shear wave velocity in the present onedimensional modelling, three scenarios for the bedrock, were performed with three speeds of 760 m/s (based on engineering bedrock), 1300 m/s (bedrock geology), and 2500 m/s (corresponding to tuff-andesite of the Karaj basement) at different depths, according to the regional geological map. Then, three scenarios of the numerical modelling were compared with microtremor transfer function.
1. One-dimensional modelling at the Karaj site using downhole data for engineering bedrock (> 760 m/s)
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

In order to access the shear wave velocity profile for 1-D modelling, downhole data from 21 boreholes were used in nine sites which were available up to the maximum depth of 50 meters at 20 boreholes and 96 meters at A09 borehole. Low thickness of alluvium (about 17-85 meters) was considered with engineering bedrock (>760 m/s) for numerical modelling. The results represent higher frequency range compared with the microtremor data. In some previous studies where engineering bedrock had been defined by shear wave velocity values between 700 to 800 m/s in 1-D modelling, the results of the theoretical model is incompatible with experimental results. Thus, it seems that it is not suitable to consider the engineering bedrock in 1-D modelling.
2. One-dimensional modelling at Karaj site using microtremor array data for geology bedrock (> 1300 m/s)
By considering the seismic bedrock (>760 m/s) at depths of 17 to 85 meters and calculating the one-dimensional transfer function, the peaks in higher frequency compared with the experimental method is observed. According to reliability of experimental H/V results which has been proved by researchers around the world (Haghshenas et al., 2008), the difference between the transfer function results in experimental and theoretical methods indicates that two variables of shear wave velocity or depth of bedrock and alluvium thickness have not been properly modeled. It seems that in order to get better results, it’s necessary to analysis by considering the geology bedrock at greater depth. Tchalenko, et al., (1974) considered lower part of Plio-Quaternary sediments of Hezardareh Formation and Miocene marllimestone of Upper Red Formation as the bedrock in the Karaj plain. Shafiee and Azadi (2006) computed shear wave velocity characteristics of these geological units throughout Tehran city. Therefore, a mean velocity of 1300 m/s was considered for the geology bedrock during the modelling.
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

In order to access the shear wave velocity profiles at greater depths, microtremor array stations were designed by seven seismometer with 100 m radius at A09 (site 8) borehole. As it can bee seen, a clear contrast at a depth of about 230 m is observed. Therefore, the modelling was carried out by taking 230 m alluvial thickness on geology bedrock according to lithology of the region. The result of this modelling has shown a peak at frequency range of 0.87 Hz that is compatible with the microtremor peaks at this site. In other site this modelling was performed using array and downhole data. The results indicated that the first effective contrast occurs at depth of 200 to 300 meters.
3. One-dimensional modelling at the Karaj site for basement (> 2500 m/s)
Transfer functions obtained from the previous model, did not cover low frequency peaks in the experimental methods. Therefore, the presence of other low-frequency peaks is either due to the geometry of the sedimentary basin or deep contrast. It seems that due to the geology of the region, tuff- andesite of the Karaj Formation as basement plays an important role in the creation of low-frequency peaks. Therefore, to obtain a better model, deep contrast was considered about 2 kilometers due to differences in the type of bedrock with a shear wave velocity of 2500 m/s. For this purpose, according to the properties of the Upper Red Formation, an average constant speed of 1400 (m/s) was considered in modelling and by changing the thickness of this layer, the modelling was continued in a trial and error manner until the numerical model is consistent with microtremor peaks. The modelling results in nine site indicate that there is basement at the depth of 2000 to 2250 meters.
Two-dimensional model of the Karaj site
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Using the one-dimensional analysis and evaluation of the geological map of the area, two dimensional geological structure was rebuilt in studied profiles. Green and gray tuffs and igneous rocks of Karaj Formation outcrops in north of Karaj and constitute the Alborz Mountains. This Mountains eroded by the action of rivers and were deposited in the form of large alluvial fans. Coarse sandy sediments were deposited near mountains wherein energies of rivers and streams were extremely high (site 1 to 4). Furthermore, fine-grained sediments were deposited at far distances by decreasing in the energy of streams (site 5 to 9). Berberian et al (1985) divided B Formation in two parts: heterogeneous deposits of sand, gravel, rock and clay in north of Tehran (Qbn) and silts and clays of Kahrizak (Qbs) in south of Tehran. According to 1-D modelling, thickness of this layer is about 200 to 300 m which has been deposited on geology bedrock. As mentioned before, lower parts of Hezardareh Formation at the north of Karaj and Upper red Formation in the south west of Karaj are considered as geology bedrock. Upper Red Formation was deposited with unconformity on tuff-andesite of the Karaj basement at depths of 2000 to 2250 meters.
Conclusions
The use of empirical methods based on microtremor is an efficient way to estimate the site effects in Karaj city, although the use of earthquake records could provide better evidence of the depth and geometry of basement. Onedimensional modelling of shear wave velocity profiles obtained from downhole data and considering the engineering bedrock (> 760 m/s) at depths of 17 to 85 meters, is not a good way to estimate the dominant frequency of alluvium. By considering the greater depth of alluvium and using shear wave velocity profiles obtained from microtremor array, 1-D modelling was carried out for geology bedrock (1300 m/s). Therefore, peak frequency in transfer function at the range of 0.87 Hz has been associated with effective contrast at depths of 200 to 300 meters. It seems that Karaj basement (> 2500 m/s) with about 2 kilometers depth plays an important role in the production of low-frequency peaks in transfer function.
Keywords: Site effects, Microtremor, Spectral ratios H/V, 1D site modeling

*Corresponding author: [email protected]

Identification and Stabilization of Dispersive
Soils: Case Study of Water Transfer Canal of Simindasht-Garmsar

Abdolhosein Haddad1, Hamed Javdanian2*, Faezeh Ebrhimpour3 1, 3. Department of Civil Engineering, Semnan University.
2. Assistant Professor, Department of Civil Engineering, Shahrekord University.
Extended Abstract
(Paper pages 29-50)
Introduction
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

In some soils, special phenomena happen with increases in their moisture content that sometimes inflict major damages on development projects. Dispersive soils are one type of such soils. The physico-chemical properties of the particles in dispersive soils cause them to disperse and separate from each other upon contact with water. If dispersive clays are not accurately identified, they will cause damages and failures. In the Simin Dasht region of Semnan Province, some hydraulic structures have incurred serious damages because they are located on dispersive soils.
The present research studied the soils around the canal transferring water from the Simin Dasht to Garmsar. This 37-kilometer long canal is situated in Semnan Province between the Simin Dasht and the Garmsar diversion Dams. Scouring and soil erosion under the concrete lining of the canal has led to the destruction of the structure. After visiting the site and taking soil samples, double hydrometer and pinhole tests were performed. The effects of adding various amounts of cement, lime and aluminum nitrate on amending dispersive clays were studied and compared in the Simin Dasht region of Semnan Province.
Experiments
The effects of the quantities of cement, lime and aluminum amendment materials on stabilization of dispersive soils in the Simin Dasht region of Semnan Province were investigated. Two types of dispersive clayey soils were amended. Table 1 presents the characteristics of the soils. The effects of various amounts of lime, cement, and aluminum nitrate on reduction in the degree of dispersion in the tested soils were studied. The cement, lime, and soil samples were dried at 40˚C for 24 hours. It must be mentioned that the amount of added lime, cement, and aluminum nitrate were zero, 3, 5, and
7 percent.
Table1. Characteristics of dispersive soils used in this reserch
Soil Natural water content (%) Liquid limit, LL
(%) Plastic limit,
PL (%) Plasticity
Index, PI
(%) Optimum
Moisture
(%) Gs
A 13.84 17.63 15.09 2.54 15 2.72
B 3.02 22.44 16.11 6.33 11 2.66
Results
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Average changes in discharge passing through the dispersive soil samples A and B, and through samples of these soils amended with lime, cement, and aluminum nitrate in pinhole tests are presented in Figures 1(a-f), respectively. Figure 1a indicates that the behavior of the A soil samples amended with lime did not follow any specific trend, but we can cautiously say that soil A will become non-dispersive when lime is added at 4.5 percent at all moisture contents. Increases in the quantities of the cement added to the dispersive soils A and B to stabilize them independent of the moisture content of the soils were also investigated (Figure 1c, d). Behavior of the A soil samples stabilized with aluminum nitrate followed a specific trend (Figure 1 e, f) contrary to those amended with the other stabilizers.
Conclusions
Results of the tests show that dispersion in soil A was amended (without completely preventing the occurrence of the scouring phenomenon) by the addition of cement or lime at 5 percent or aluminum nitrate at 3 percent. Moreover, dispersion in soil B was amended by the addition of cement at 3 percent, lime at 5 percent, or aluminum nitrate at 3 percent. Aluminum nitrate was a better and more effective amendment material for the dispersive soils compared to lime. Therefore, aluminum ions replaced the other ions in the structure of dispersive clays more suitably compared to calcium ions. Comparison of the results obtained from the pinhole tests performed on soil samples amended with aluminum nitrate, lime, and cement suggests that it took a shorter time for the samples to be stabilized with aluminum nitrate compared to the other two amendment materials.
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017

.

Figure1 Variation of discharge due to soil stabilization, Lime (a and b), Cement
(d and c), Aluminum nitrate (e and f)

Keywords: Dispersive soil, Pinhole test, Double hydrometer test, Crumb test, Soil stabilization
-51815-15140

*Corresponding Author: [email protected]

Value Engineering Based on Monitoring During
Tunnel Excavation Phase-a Case Study of Hakim Tunnel
Majid Taromi1*, Maziar Hosseini2, Seyed Mahdi Pourhashemi3, Majid Sadeghi4
Young Researchers and Elite Club, South Tehran Branch, Islamic Azad University, Tehran, Iran.
Civil Engineering Department, College of Engineering, Islamic Azad University-South Tehran Branch, Tehran, Iran.
Engineering and Development Organization, Municipality of Tehran, Manager of Urban Tunneling Projects, Tehran, Iran.
Engineering and Development Organization, Municipality of Tehran, Project Manager of Hakim Tunnel, Tehran, Iran. Extended Abstract
(Paper pages 51-72)
1268732149348

Downloaded from jeg.khu.ac.ir at 11:32 IRST on Saturday October 28th 2017



قیمت: تومان

دسته بندی : زمین شناسی

دیدگاهتان را بنویسید