*3.1.3 Site condition*

There are three groups of parameters that govern the soil liquefaction phenom-

The vulnerability of any cohesionless soil to liquefaction during an earthquake depends on the magnitude and number of cycles of stresses or strains caused by the seismic excitation. These in turn are correlated to the intensity, duration of ground shaking and predominant frequency. The degree of soil liquefaction varies with the different earthquake magnitude. Based on on-site observations and a simple parametric study, Green and Bommer [19] have concluded that a small earthquake with a moment magnitude of 4.5 will trigger liquefaction in highly susceptible soil deposits. However, for soil profiles suitable for building structures, the minimum earthquake magnitude is about 5 that cause liquefaction. Tesfamariam and Liu [20] considered the Stark and Olson [21] earthquake liquefaction datasets and intuited that with increase in *M* and *a*max, the likelihood of liquefaction increases. Peak ground acceleration (PGA) is a function of earthquake magnitude, site to fault distance, fault type and soil type as per Boore et al. [22] and usually used to quantify

Pirhadi et al. [14] used closest distance to rupture surface which is among the other seismic parameters such as earthquake magnitude and peak ground acceleration as an influence factor and concluded that among the seismic parameters earthquake magnitude, peak ground acceleration and closest distance to rupture surface illustrate lesser effects on liquefaction triggering as compared to the cumulative absolute velocity. It is generally agreed, that earthquake magnitude, peak ground acceleration, and closest distance to rupture surface are the three major factors that

Liquefaction is usually observed in shallow, loose, saturated cohesionless soils subjected to strong ground motions. In case of in-situ cone penetration test, soil behavior type index is used to classify soils based on fines content presented by Robertson and Wride [23]. The liquefaction susceptibility depends on soil type,

The type of soil that is more prone to liquefaction is one in which deformation resistance is mobilized by particle friction. When other factors like grain shape, uniformity coefficient, and relative density are held constant, the frictional resistance of cohesion less soils decreases as grain size decreases. Gravelly soils mobilize more strength during shearing and dissipate excess pore pressures more quickly than sandy soils. There are some case histories [24–26] that show liquefaction in loose gravelly soils during severe ground shaking or when the gravel layer is

The strength of soil liquefaction may vary depending on the fines content. Several studies have found that fines content has a significant impact on soil susceptibility to liquefaction [24–26]. Soil liquefaction potential increases as fines content exceeds 30%. When fines content exceeds 50%, however, the soil's lique-

Zhou et al. [27] concluded that the cone tip resistance (*qc*) factor is sensitive

among the predictor variables in CPT in-situ test method, which provides

where fine-size particles are easier to liquefaction than coarse particles.

enon, according to published research papers, namely seismic parameters, site conditions, and soil parameters [13–18]. Each of these contains a wide range of factors that characterize liquefaction, to a varying degree of significance. The details

of these parameters are given below.

*Earthquakes - From Tectonics to Buildings*

*3.1.1 Seismic parameter*

the ground motion intensity.

*3.1.2 Soil parameter*

affect the seismic intensity at the site.

confined by an impervious layer.

faction potential is reduced [27].

**166**

It is widely known that the increase in the vertical effective stress increases the bearing capacity and shear strength of soil, and consequently increases the shear stress required to cause liquefaction and decreases the potential for liquefaction. Many researchers have reported that saturated sands deeper than 15 to 18 m are not probably to liquefy [29]. These depths are in general agreement to Kishada [30], who states that a saturated sandy soil is not liquefiable if the value of the vertical effective stress exceeds 190 kN/m<sup>2</sup> . It is reported that an increase in the overburden pressure the occurrence of liquefaction decreases [31, 32]. Tesfamariam and Liu [20] considered the Stark and Olson [21] earthquake liquefaction datasets and, intuited that, with a decrease in vertical effective stress, the likelihood of soil liquefaction increases. As vertical effective stress is conditioned on total vertical stress therefore accordingly, total and vertical effective stresses are included in the proposed model as governing factors.

In order to induce extensive damage at ground surface level due to liquefaction, the liquefied soil layer must be sufficient thick thereby resulting uplift pressure and amount of water expelled from the liquefied layer can result in ground damage such as sand boiling and fissuring (Ishihara [26]; Dobry [33]). If the liquefied sand layer is thin and deposited within the soil profile, the presence of a non-liquefiable surface layer may prevent the effects of the at-depth liquefaction from reaching the surface. Ishihara [26] established a standard that specifies a threshold value for the thickness of a non-liquefiable surface layer to avoid ground damage due to liquefaction.

It was intuited in the survey report prepared by Japan society of Civil Engineers that the big-sized earthquake liquefied the sand layer when the thickness is more than 3.0 m. When the thickness of the liquefied layer is very thin, the presence of a non-liquefiable surface layer may prevent the effects of the in-depth liquefaction from reaching the surface.

The resistance of soil to liquefaction is weakened as groundwater levels rise. The effect on soil liquefaction potential increases as groundwater levels rise above 2 m [34]. The water table regime must be minimized as one of the design criteria against seismic soil liquefaction [35]. The vertical effective stress is closely related to the depth of soil deposit. The vertical effective stress increases as the depth of the soil deposit increases. Increased vertical stress has been shown to improve the soil's bearing capacity and shear strength, reducing the risk of liquefaction. Even liquefaction from very loose sand is almost impossible for over 15 m of overburden, according to Florin and Ivanov [36], and Satyam [37] concluded the same for the preliminary assessment of the soil liquefaction potential in a seismically active region.

The significant factors of seismic soil liquefaction that are identified through SLR approach are presented in **Table 2**.

Field experts' examined and analyzed the preliminary list and they believed that the soil liquefaction factors retrieved from the literature were important for expanding exploratory research by developing structural self-interaction matrix for interpretive structural modeling. The set of liquefaction factors identified in **Table 2** for seismic soil liquefaction potential was used to develop the model which represented the correlation between eleven seismic soil liquefaction factors. In the ISM model, for the development of the structural self-interaction matrix (SSIM),


#### **Table 2.**

*List of significant factors of seismic soil liquefaction.*


*Note: V–row factor influences the column factor; A–column factor influences the row factor; O–no relationship between the row and column factors.*

#### **Table 3.**

*Structural self-interaction matrix for seismic soil liquefaction factors.*

pair-wise comparison were made by the correlation criteria and four symbols V, A, X, or O were used (see **Table 3**). For example, earthquake magnitude F1 (*M*)–row factor influences the peak ground acceleration, F2 (*a*max)– column factor so the symbol used is V. Groundwater table depth F9 (*Dw*)–column factor influences the vertical effective stress, F7 (*σ*<sup>0</sup> *<sup>v</sup>*)–row factor so the symbol used is A. Earthquake magnitude F1 (*M*)–row factor has no relation with the thickness of soil layer F11 (*Ts*)–column factor so the symbol used is O. Field experts' made consensus on the pair-wise comparison and the results are shown in **Table 3**.

when the initial reachability matrix has been obtained and is presented in final reachability matrix (**Table 5**), wherein entries marked (\*) show the transitivity. For example, in **Table 4**, the initial reachability matrix shows that F4 (*FC*) is related to F6 (*Ic*), and F6 (*Ic*) is related to F2 (*a*max), then the interaction F4 (*FC*) and F2 (*a*max) having 0 value is transformed into 1\* in **Table 5**. The reachability sets are determined from the factor itself and other factors which have influence in the horizontal direction, while the antecedent sets consist of the factor itself and other factors which have influence in the vertical direction for each significant soil liquefaction

Rank VI II VI VI II III IV V VI VI VI I VI/VI *Note: 1\* indicates the values after applying transitivity; Dep. represents dependence power; Dri. represents driving*

**F***<sup>i</sup>* **F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12** F1 1 10000000 0 0 1 F2 010000000 0 0 1 F3 01 1000000 0 0 1 F4 0001 1 1000 0 0 1 F5 000010000 0 0 1 F6 01001 1000 0 0 1 F7 00001 1 100 0 0 1 F8 000001 1 10 0 0 1 F9 000010101 0 0 1 F10 0000101 10 1 0 1 F11 000000000 0 1 1 F12 000000000 0 0 1

*Elucidation of Seismic Soil Liquefaction Significant Factors*

*DOI: http://dx.doi.org/10.5772/intechopen.97278*

**F***<sup>i</sup>* **F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 Dri. Rank** F1 1 1 0 0 0 0 0 0 0 0 0 1 3 III F2 0 1 0 0 0 0 0 0 0 0 0 1 2 II F3 0 1 1 0 0 0 0 0 0 0 0 1 3 III F4 0 1\* 0 1 1 1 0 0 0 0 0 1 5 V F5 0 0 0 0 1 0 0 0 0 0 0 1 2 II F6 0 1 0 0 1 1 0 0 0 0 0 1 4 IV F7 0 1\* 0 0 1 1 1 0 0 0 0 1 5 V F8 0 1\* 0 0 1\* 1 1 1 0 0 0 1 6 VI F9 0 0 0 0 1 1\* 1 0 1 0 0 1 5 V F10 0 0 0 0 1 1\* 1 1 0 1 0 1 6 VI F11 0 0 0 0 0 0 0 0 0 0 1 1 2 II F12 000000000 0 0 1 1 I Dep. 1 7 1 1 7 6 4 2 1 1 1 12 44/44

**Table 4.**

*power.*

**Table 5.**

**169**

*Final reachability matrix.*

*Initial reachability matrix.*

SSIM is converted to a binary matrix called the initial reachability matrix by replacing the original symbols V, A, X, and O with 1 or 0 (**Table 4**) as per the rule illustrated in **Table 1**. When pair of the same factor, i.e., F1 (*M*) with F1 (*M*) is formed, it is represented by 1. The concept of transitivity is introduced in **Table 4**
