The dynamic properties of soils influence seismic site response and liquefaction susceptibility. The previous

studies mostly worked on effect of natural fiber and synthetic fiber used in clayey soil to investigate its effect

on the dynamic properties of modified soil.This research deepens our understanding of the dynamic behaviour

of Niger Delta soils, which is important for evaluating the region's vulnerability to liquefaction and seismic

response. By combining experimental data with well-validated empirical models for small to medium-shear

strain behaviour in the area's common sandy soils.This study experimentally investigated the behavior of

damping ratio and shear modulus under the effects of confining pressure of sandy soils collected from

Igbogene Town in the Niger Delta region of Nigeria. Undisturbed samples were acquired from boreholes using

thin-walled tubes and consolidated anisotropically under effective stresses of 100, 200, 300, and 400kPa in a

depth. This work enhances geotechnical seismic hazard evaluations through validated empirical

characterizations of small to medium-shear strain behavior for sandy deposits prevalent in the Niger Delta.The

findings can be directly used in seismic ground response analysis. These results are expected to improve

geotechnical seismic hazard assessments and provide more accurate evaluations of seismic risk in the region.

The Niger Delta's complex geology presents unique challenges for soil mechanics, with Akpokodje [1]

emphasizing the importance of understanding sub-soil behavior for loss estimation. The study's focus on soil

hysteresis and energy dissipation under cyclic loads is particularly relevant given the region's seismic activity.

Amini [2] demonstrated the noteworthy impact of confining pressure on dynamic soil characteristics, which

conducted on the area's dynamic soil properties. This study addresses this gap by employing cyclic direct

simple shear tests, following best practices [6], to provide valuable data for seismic hazard assessment.

Undisturbed soil samples were acquired from boreholes representing various soil types in the Niger Delta.

Anisotropic consolidation was applied under diverse confining pressures [3], followed by cyclic torsional shear

tests to measure damping ratio and shear modulus at varying shear strain levels. Cyclic load-controlled triaxial

tests were conducted at effective confining pressures of 100-400 kPa [7], with a damping ratio computed using

Dobry et al.'s [8] equation. The study's findings on shear modulus reduction are consistent with established

theories [9] and extend to Niger Delta soil types. The nonlinear damping ratio-strain relationship aligns with

Głuchowski et al. [10] findings. Bender element tests [11] and resonant column tests offer comprehensive soil

characterization [12].

level, four load cycles were applied with maximum shear strain (γ) ranging from 0.001% to 2%

logarithmically. Using equation [Eq. 1] from Dobry et al.,[8] damping ratio (ξ) was computed by the

developed hysteresis loop during each cycle.

ξ = (ΔW/4πWE) × 100 (1)

During each loading cycle, ΔW is the energy dissipated and is equivalent to the area bounded by the hysteresis

loop. WE is the energy dissipated during each loading cycle and can be derived from the maximum shear

modulus of soil. Santos et al. [16] developed mathematical models to predict the variation in damping ratios

for various soil types under variable confining pressures and shear stresses.

Shear modulus (G) was calculated by determining the stress-strain curve slope at each strain level for a given

loading cycle.

were established by Dobry et al. [8].

The soil behavior at any location can be assessed by accurately determining the dynamic soil properties such

as shear modulus and damping ratio. The importance of these parameters can also be recognized as they help

predict the liquefaction potential and seismic ground motion. Several empirical and semi-empirical models

have been suggested [8], [16]to explain the variation of these properties with confining pressure and shear

strain. Nonetheless, due to the significant inconsistency of soil conditions, site-specific data remains crucial for

refining existing models and ensuring their applicability across diverse geological settings. Previously there are

fewer studies on the dynamic soil characteristics of the Niger Delta region. The present data is insufficient to

fully understand the variation of dynamic properties with depth and confining pressure. The Niger Delta region

silt, and clay deposited in fluvio-deltaic environments [17]. Specifically, Igbogene Town is underlain by sand

and interlayered sand/silt/clay sediments of the Benin Formation, which covers most of the southern Niger

Delta.

Undisturbed soil samples were collected from the site using thin-walled tube samplers with an outer diameter

of 54 mm as per ASTM standard D1587. This sampling procedure preserves the natural on-field structure and

properties of cohesive soils. Samples were extracted at the total depth intervals of 1.50 m from the ground

surface down to a maximum depth of 30.0 m. Special precautions were taken during sampling and

transportation to the laboratory to minimize sample disturbance. The samples were visually classified and

representative samples were selected from each stratum for laboratory testing.

To perform the cyclic direct simple shear (DSS) test undisturbed soil samples were arranged to calculate the

dynamic properties of soil. The DSS test was chosen due to its ability to subject soil samples to full reversal

cyclic shear stresses and strains while maintaining constant normal stress, simulating field conditions during

earthquakes.The DSS testing was performed as per American standards (ASTM D6528) using the bender

element system for sample preparation and test execution. Bender elements consist of piezoceramic

transducers that generate and detect shear waves to monitor the shear modulus continuously during the test.

The samples were trimmed to a diameter of 50.0mm and a height of 20.0mm for testing. Porous stones and

filter paper sheets were used at the top and bottom of the sample for drainage.

The samples were first consolidated anisotropically under the desired confining pressures of 100-400kPa with

an increment of 100kPa, selected to represent overburden stresses at different depths. Confining pressure was

logarithmic increments. At each strain level, at least 10 cycles were applied until a stable response was

achieved. The developed shear stresses and strains were recorded during testing to compute shear modulus and

damping ratio. From the shear stress-strain hysteresis loop during the loading phase, the shear modulus was

determined by calculating the secant modulus. Similarly, the energy dissipated within the loop represents the

This study considered the effect of confining pressure on the dynamic characteristics of soil in the region of the

Nigerian Niger Delta using Bender Element (BE), and Resonant Column (RC) testing. Samples were prepared

carefully to ensure consistency in initial conditions. The results show a good relationship between maximum

shear modulus and confining pressure as studied by Dobry et al., [8]

the shear modulus highlighted in previous studies.

like liquefaction assessment and seismic ground response modeling for Igbogene Town [6]. However, testing

Fig. 3: Shear Modulus of Sandy Soil at 200kPa of Igbogene Town

increasing strain, G reduced nonlinearly and followed an exponential decay trend consistent with the findings

of Santos and Correia [16].The data was fitted to the empirical model proposed by Santos et al. [4] to quantify

the shear modulus reduction behavior. A good correlation between the measured data and the model was

observed, validating the model's applicability for soils in the study area under 200 kPa stress conditions. This

confirms that confining pressure and shear strain influence shear modulus as emphasized by Dobry et al. [5].

The damping behavior of sandy soil under 200 kPa pressure was also investigated. Figure 4 depicts the

Fig. 4: Damping Ratio of Sandy Soil at 200kPa of Igbogene Town

The impact of 300 kPa confining pressure on the dynamic properties of sandy soils from Igbogene Town was

investigated. Cyclic DSS tests following ASTM D6528 were performed on undisturbed samples under 300 kPa

effective stress.

as suggested for site-specific soils.

Figure 6 presents the damping ratio variation with the shear strain curve obtained from DSS hysteresis loops

using the energy method recommended by Dobry et al. [8]. ξ increased nonlinearly with strain remaining

minimal (<5%) at small strains but rising beyond 0.01% strain, consistent with trends for liquefiable soils

(Santos et al., 2012). An empirical equation fitted the 300 kPa data to existing damping models [18],

corroborating these models.

Fig. 6: Damping Ratio of Sandy Soil at 300kPa of Igbogene Town

The impact of 400 kPa confining pressure on the dynamic properties of sandy soils from Igbogene Town was

analyzed. Cyclic DSS tests compliant with ASTM D6528 were conducted on undisturbed samples under 400

kPa effective normal stress.

Fig. 7: Shear Modulus of Sandy Soil at 400kPa of Igbogene Town

Figure 7 depicts a variation of normalized shear modulus (G/Gmax) with shear strain. At very small strains (γ