**3. Nonlinear site response of liquefied areas**

## **3.1 Introduction and studied area**

Japan, Chile, the USA, Italy, Iran, and Turkey are some of the most important earthquake-prone countries, and they have been exposed to devastating activities over the last decades causing damaged buildings and many fatalities. One of the most essential regions for liquefaction studies in the literature is the Duzce/Sakarya Region in Turkey which was immensely affected by Kocaeli and Adapazari (Duzce) earthquakes in 1999. Liquefaction susceptibility in structural design should be considered in zones consisting of loose sand soils because it may cause significant damages as excessive settlement and sinking of the structures. This can only be possible by the nonlinear site-specific analysis.

In this section, the nonlinear site response of liquefied areas will be investigated using the well-documented in situ data taken from the city of Sakarya which is surrounded by Istanbul, Yalova, Duzce, and Bilecik. The region lays on the extension of the North Anatolian Fault Zone [25], and it is neighboring two local faults (Sapanca and Duzce), and the map is presented in **Figure 8**. The area suffered a lot, and many liquefied zone were inspected during Duzce Earthquake in 1999.

Five different boring log data were used in the analyses to evaluate the ground response in a liquefied prone zone. The soil profiles consist of almost 90% of silty sands (SM), and some low-plasticity clays, gravelly sands, and clayey sands can be found in very shallow depths. A summary table showing the information about the logs is presented below.

All the borings are 20 m long having shear wave velocity (Vs) values changing from 145 to 290 m/s. The average Vs of upper 30 m for each profile was also determined to be able to use it in the estimation of the surface response spectra

cycles are needed to liquefy soil sample for different types of loading at a double

*Geotechnical Engineering - Advances in Soil Mechanics and Foundation Engineering*

One clear point can be made from the figure that the variety of loading and its dominant frequency are effective on the number of cycles that would initiate the liquefaction. Although the excess pore pressure buildups are similar for the first 5 cycles, Type 1 with the harmonic shape diverges from the rest of the group, and the number of cycles needed for liquefaction occurs to be at least 2.5 times later than the others. With regard to the irregular type of loadings, they even act differently, and the number of cycles to liquefy the soil varies between 10 and 40 which can be considered a wide interval. Thus, the potential of liquefaction triggering should be

The essence of the results in terms of number of cycles to liquefy soil samples is

It should be noted that the variation is a lot for different cyclic stress ratios. For

As a summary, three different stress levels at varying loading shapes were used to run dynamic triaxial tests in order to determine the generation of excess pore pressures under cyclic excitations. The desired relative density and confining pressure for all 18 tests were constant as 40% and 65 kPa, respectively. There are a few

parameter that influences the duration and the number of cycles to liquefy

ii. As the stress level increases, the number of cycles for soil to lose its stability decreases. For example, the needed time to liquefy soil at CSR = 0.15 changes

**CSR Type 1 Type 2 Type 3 Type 4 Type 5 Type 6** 0.15 1848 340 474 466 867 335 0.20 111 41 13 25 31 26 0.30 10 2 5 3 1 2

**Boring Depth (m) Vs (m/s) Vs,30 (m/s) FC (%)** B1 20 150–280 220 10–85 B2 20 180–190 185 5–42 B3 20 165–290 230 27–35 B4 20 145–195 175 8–32 B5 20 165–175 170 18–38

i. The pattern of the loading (harmonic vs. inharmonic) is an effective

example, Type 3 and Type 4 loading patters need similar number of cycles to liquefy the soil at CSR = 0.15, whereas it changes for increasing CSRs. Harmonic loading always takes more time/cycle to generate pore pressure than others, and every irregular loading type has its varying frequency-dependent characteristics at increasing stresses. Therefore, the excess pore pressure generation is not only affected by the frequency content of the loading alone, but also the stress levels

along with it play important role in estimating liquefaction triggering.

amplitude of 26 kPa stress, just to give an example.

studied with different types of loading when needed.

clear points that are worth to emphasize:

*Number of cycles to initiate liquefaction for different types of loading.*

same soil samples.

**Table 3.**

**Table 4.** *Soil profiles.*

**130**

shown in **Tables 3** and **4**.

20 years (Duzce, Kocaeli, and Van earthquakes) were chosen to produce possible regional earthquake scenarios. The details of the earthquakes used in the process are

*Estimation of Excess Pore Pressure Generation and Nonlinear Site Response of Liquefied Areas*

All of the earthquakes can be considered as the big magnitude earthquakes as seen in the table. Two of the events were taken from the Pacific Earthquake Engineering Research Center (PEER) [28] and one from the Strong Motion Data Base of Turkey (SMDB-TR) [29], and all of them were scaled to the local PGA accordingly. **Figure 9** shows the scaled versions of the earthquakes, in other words possible earthquake schemes for the studied area for the probability of 10% chance of being

The duration of the earthquakes differs from 25 to 85 seconds, and PGAs were set to be 0.72 g for all of them. More high-frequency content is seen from top to

**Earthquake Year Source Station Magnitude Rjb (km)** Duzce 1999 PEER Duzce 7.1 0 Kocaeli 1999 PEER Izmit 7.5 1.38 Van 2011 SMDB-TR Van 6.7 19.2

shown in **Table 5**.

*DOI: http://dx.doi.org/10.5772/intechopen.88682*

exceeded in 50 years.

*Reference earthquakes used in the analysis.*

**Table 5.**

**Figure 9.**

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*Scaled versions of the earthquake data.*

#### **Figure 8.** *Studied area and the active fault lines [29].*

offered by the building codes, and the soil type of two borings is classified as ZE, and three of them are ZD. The fine content for the layers were obtained as well, and the variation is listed in the table. Layers have water content of 11–25%, and the unit weight of the soils samples laid in a range of 17.6–18.9 kN/m<sup>3</sup> throughout the profiles. Some triaxial tests were run in the laboratory to evaluate the strength of the sandy soils, and 33–38 degrees of friction angle along with 0–5 kPa cohesion were detected.

The dynamic properties (modulus reduction and damping behavior of soils at varying strains) of clays and sands were calculated adopting proposed models by Darendeli [26]. During the analyses, pore pressure generation was let to build up during cyclic loading in nonlinear analyses; however it was not possible by the frequency-dependent equivalent linear simulations. With the available information of the soil index properties, the required parameters were derived to model the pore pressure generation behavior suggested by Matasovic and Vucetic [27].
