# Experimental and Analytical Evaluations of Ground Behaviors on Changing in Groundwater Level in Bangkok, Thailand

^{1}

^{2}

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## Abstract

**:**

## 1. Introduction

## 2. Geology and Hydrogeology in Bangkok Plain

## 3. Experimental Modelling by Centrifuge Test

^{3}[17]. Then, the Speswhite kaolin clay was compacted above the Toyoura sand layer. The arrangement of the soil layer was determined as the soil profile of Bangkok, Thailand. The Speswhite kaolin clay was prepared at 27% water content and compacted by controlling the density at 1.65 t/m

^{3}[18].

## 4. Analytical Modelling by Finite Element Method

#### 4.1. Geometric Model and Boundary Conditions

#### 4.2. Associated Parameters for Material

^{3}and 1.70 t/m

^{3}, respectively. Other parameters were adopted from the general properties of Speswhite kaolin clay in the model. The stiffness used in the model, such as the Secant stiffness in the standard drained triaxial test (E

_{50}

^{ref}) is 16,000 kN/m

^{2}, the tangent stiffness of the oedometer test (E

_{oed}

^{ref}) is 20,000 kN/m

^{2}, and the ratio of unloading and reloading stiffness (E

_{ur}

^{ref}) was 70,000 kN/m

^{2}. The shear strain (γ

_{0.7}) was equal to 0.001 which was considered at Gs = 0.722Go. The shear modulus (G

_{o}

^{ref}) was equal to 90,000 kN/m

^{2}at a very small strain. The Poisson’s ratio can be replaced by the name of ν

_{ur}′, which was about 0.2 for the Spestwhite Kaolin clay. The reference pressure (P

_{ref}) equals 100. The coefficient of lateral earth pressure for normally consolidated clay (K

_{0}

^{nc}) was 0.485. The failure ratio was given as 0.9, according to the default value. The interface reduction factor was 0.75. The value of the initial void ratio was 0.8 [24]. The input parameters of groundwater property were adopted for the unsaturated soil parameters which were obtained by using the fitting parameters from Van Genuchten such as g

_{n}, g

_{a}, and g

_{l}, the residual saturation (S

_{res}), and saturation (S

_{sat}). The permeability parameters were assumed in three dimensions such as K

_{x}, K

_{y}, and K

_{z,}which are equal to 8.64 × 10

^{−4}m/day for Speswhite kaolin clay, as shown in Table 2 [25].

^{3}. Due to the limitation of soil parameters, the other values for Mohr-Coulomb were modified based on the medium-dense sand of the Bangkok area [26]. The stiffness of soil was assumed to be equal to 85,000 kPa from the Triaxial test and 115,500 kPa from the Oedometer test. Cohesion was 0.1 kPa. The friction angle was 36 degrees. The Dilatancy angle is 5 degrees. The shear modulus was 33,000 kPa at a very small strain. The Poisson’s ratio is 0.3. The interface reduction factor was 0.75. The over consolidation ratio or OCR was 0.73 [24]. The permeability values used in three dimensions such as K

_{x}, K

_{y}, and K

_{z,}were equal to 1.25 × 10

^{−2}m/day from grain size distribution data in the software.

^{7}kN/m

^{2}and Poisson’s ratio was determined to be 0.15.

## 5. Result and Discussions

#### 5.1. Porewater Pressure

#### 5.2. Effective Stress

#### 5.3. Pile Capacity

#### 5.4. Ground Deformation

## 6. Conclusions

- (1)
- The ground deformation continues to occur in the condition of groundwater drawdown due to void between soil particles and self-weight consolidation in term of time. After groundwater begin to recover, ground deformation continues to occur but the rate of ground deformation was less than the period of groundwater drawdown. In the case of groundwater recovery to the ground surface, the ground deformation rate of PLAXIS3D was about 0.09 cm/year while the centrifuge test was about 0.001 cm/year. These values were different due to limitations of the PLAXIS3D model and the centrifuge model such as the time of the consolidation process, soil preparation in the centrifuge test, and input soil parameters in the PLAXIS3D model. However, the trend of the ground deformation from both results demonstrated that the results have similar trends to the previous data of the observation station in Bangkok, Thailand.
- (2)
- The bearing capacity demonstrated by using the pile load test depends on the state of the groundwater level. The PLAXIS3D result reveals the pile capacity increased during groundwater drawdown due to the effective stress increase. The clay layer also shows the unsaturated zone and suction zone in the model. For the same reason, the pile capacity decreases when the groundwater was on the ground surface. The clay layer found the suction value almost zero and the saturated zone is almost 100%. The loss of pile capacity occurred in PLAXIS3D and the centrifuge test by around 8 to 25%.

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Ground deformation in Bangkok and urban areas [1].

**Figure 3.**Location of the ground deformation measurement in Bangkok region [1].

**Figure 10.**Variation of groundwater level. (

**a**) Increasing groundwater level to ground surface. (

**b**) Decreasing groundwater level to soil interface (

**c**) Groundwater level recovered to ground surface.

**Figure 12.**Comparison of saturation stage. (

**a**) The first testing stage. (

**b**) The second testing stage. (

**c**) The third testing stage.

**Figure 13.**Comparison of suction value during the changing water levels. (

**a**) Suction of the first testing stage. (

**b**) Suction of the second testing stage. (

**c**) Suction of the third testing stage.

**Figure 14.**Schematic of the pile load test (

**a**) the first pile load test, (

**b**) the second pile load test, and (

**c**) the third pile load test.

**Figure 15.**Comparison of the load distribution results (

**a**) PLAXIS3D result. (

**b**) The centrifuge result.

Parameters | Speswhite Kaolin Clay | Toyoura Sand |
---|---|---|

The saturated unit weight (${\mathsf{\gamma}}_{\mathrm{s}\mathrm{a}\mathrm{t}}$), kN/m^{3} | 16.5 | 15.3 |

The unsaturated unit weight (${\mathsf{\gamma}}_{\mathrm{u}\mathrm{n}\mathrm{s}\mathrm{a}\mathrm{t}}$), kN/m^{3} | 17 | 15.3 |

Secant stiffness (${\mathrm{E}}_{50}^{\mathrm{r}\mathrm{e}\mathrm{f}}$), kN/m^{2} | 16,000 | E’ = 85,800 |

Tangent stiffness (${\mathrm{E}}_{\mathrm{o}\mathrm{e}\mathrm{d}}^{\mathrm{r}\mathrm{e}\mathrm{f}}$), kN/m^{2} | 20,000 | - |

The ratio of stiffness (${\mathrm{E}}_{\mathrm{u}\mathrm{r}}^{\mathrm{r}\mathrm{e}\mathrm{f}}$), kN/m^{2} | 70,000 | 115,500 |

Power for stress level | 1 | - |

Cohesion (${\mathrm{C}}_{\mathrm{r}\mathrm{e}\mathrm{f}}^{\prime}$), kN/m^{2} | 35 | 0.1 |

Friction angle (${\mathsf{\phi}}^{\prime}$), degree | 31 | 36 |

Dilatancy angle ($\psi $) | 0 | 5 |

Shear strain (${\mathsf{\gamma}}_{0.7}$), degree | 0.001 | - |

Shear modulus (${\mathrm{G}}_{0}^{\mathrm{r}\mathrm{e}\mathrm{f}}$), kN/m^{2} | 90,000 | 33,000 |

Poisson’s ratio (${\mathsf{\nu}}_{\mathrm{u}\mathrm{r}}^{\prime}$) | 0.2 | 0.3 |

Reference pressure | 100 | - |

Coefficient of lateral earth pressure (${\mathrm{K}}_{0}^{\mathrm{n}\mathrm{c}}$) | 0.485 | - |

Failure ratio (${\mathrm{R}}_{\mathrm{f}}$) | 0.9 | - |

Interface reduction factor (${\mathrm{R}}_{\mathrm{i}\mathrm{n}\mathrm{t}\mathrm{e}\mathrm{r}}$) | 0.75 | 0.75 |

OCR | 1 | - |

Initial void ratio (${\mathrm{e}}_{\mathrm{i}\mathrm{n}\mathrm{t}}$) | 0.8 | 0.73 |

References | Modified Benz (2006) [24] | Modified Likitlersuang et al. (2013) [26] |

Parameters | Speswhite Kaolin Clay |
---|---|

Residual saturation | 0.05 |

Saturated saturation | 1 |

Fitting parameters (g_{n}) | 1.6 |

Fitting parameters (g_{a}) | 0.04 |

Fitting parameters (g_{l}) | 0.5 |

Horizontal permeability, m/day | 8.64 × 10^{−4} |

Horizontal permeability, m/day | 8.64 × 10^{−4} |

Vertical permeability, m/day | 8.64 × 10^{−4} |

Description | Centrifuge Modeling | PLAXIS3D Modeling | ||||
---|---|---|---|---|---|---|

BP1 | BP2 | BP3 | BP1 | BP2 | BP3 | |

Time period of water level change | 157 | 192 | 49 | 157 | 16 | 94 |

Porewater pressure (kPa) | ||||||

At 20 m from ground surface | 194.64 | 33.10 | 195.32 | 202 | 26 | 185 |

At 35 m from ground surface | 348.48 | 136.11 | 349.33 | 352 | 159 | 344 |

Effective stress at interface of soil (kPa) | 184 | 277 | 184 | 205 | 300 | 205 |

Ground displacement rate (cm/year) | 0.14 | 0.02 | 0.001 | 0.4 | 0.28 | 0.09 |

Total ground displacement (cm) | 21.62 | 25.69 | 25.66 | 41.6 | 50.5 | 58.9 |

Maximum pile load (kN) | 100,000 | 120,000 | 100,000 | N/A | 1200 | 1800 |

Pile settlement (mm) | 346 | 339 | 346 | N/A | 75 | 200 |

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**MDPI and ACS Style**

Intui, S.; Inazumi, S.
Experimental and Analytical Evaluations of Ground Behaviors on Changing in Groundwater Level in Bangkok, Thailand. *Water* **2023**, *15*, 1825.
https://doi.org/10.3390/w15101825

**AMA Style**

Intui S, Inazumi S.
Experimental and Analytical Evaluations of Ground Behaviors on Changing in Groundwater Level in Bangkok, Thailand. *Water*. 2023; 15(10):1825.
https://doi.org/10.3390/w15101825

**Chicago/Turabian Style**

Intui, Sutasinee, and Shinya Inazumi.
2023. "Experimental and Analytical Evaluations of Ground Behaviors on Changing in Groundwater Level in Bangkok, Thailand" *Water* 15, no. 10: 1825.
https://doi.org/10.3390/w15101825