Settlements of Embankments on Different Types of Soils

doi:10.21203/rs.3.rs-2634581/v1

Foundation soils play an important role in which undergoing settlements of any structures based on the type of foundation. While constructing embankments on any type of foundation soil a geotechnical engineer faces a difficult problem.So, to overcome these problems, many stabilizing techniques such as adding admixtures, and ground improvement techniques like reinforcement are usedwhetherthe foundation soil is homogeneous or layered.The paper aims to determine the impact of geogrids andthe influence of reinforced granular bed stiffness of embankments founded on soft silty sandand silty sandby using Plaxis-2D software. By considering with and without a table the prediction of Embankment toe Horizontal displacementsand settlements beneath the Embankmentis explainedby varying modular rigidity on silty sand, soft soil, and silty sand.

Settlements

Horizontal displacements

Geogrid

Reinforced granular bed

plaxis-2D

Soft soil

Silty sand

Settlements of structures are common in all types of foundation soils. Montmorillonite minerals are present as a result settlements are more in the clayey type of foundation soils.Cohesive soils are like soft clay and silty sandhas low permeability. Pore water pressure is also one of the parameters for undergoing structural settlements.So,structures like embankments constructed on any type of foundation soil may lead to excessive settlements.Settlements of structure can be prevented by using manystabilizing techniques like Jet grouting,Expanded geopolymers, and geotextiles. Geotextiles can serve as multi purposes like reinforcement, drainage, and filtration. These stabilizing techniques may vary from place to place based on the site conditions. Here in this analysis settlements are reduced by reinforcement and also by using ground improvement techniques likeproviding areinforced granular bed andgeogrid in an Embankment.Settlements decreases as the depth increase. Geogrid is one of the geotextile materials and it can serve as reinforcement. By using these reinforcements settlements are reduced to a maximum extent and structured in a safe condition.

1.1 Literature review

Loganathan et.al, (1993) ¹explained the consolidation process utilizing the finite element technique.To determine the deformation at the toe and under the embankment many numerical and experimental studies are done.Chai et.al,(2002)²explained the behavior ofembankment with and without the provision of reinforcement, they found that the safety factor increases and Horizontal displacement reduce when reinforcement is provided.Haung et.al, (2006)³discussed aboutIncreased embankment soil elasticity reduces lateral displacement at the toe. Rankine et.al, (2007)⁴explained that an equation was proposed to determine lateral displacements and settlements at the toe. Based on the numerical analysis shorter distance at the toe of the embankment is also determined.Subramaniam et. al, (2010)⁵explained the solutions of analytical and numerical solutions of piled supported embankments by transferring several layers in geogrid. Faizi et.al, (2013)⁶explained the seismic stability level of an embankment under two different loads by using geotextile with different layers maximum displacements are reduced with an increase in geogrid stiffness.Safadoust et. al,(2013)⁷explained the improvement in reinforcement rigidity was explained.It leads to a decrease in lateral displacements but not settlements and increases the structures' stability.Chin et.al, (2016)⁸explained the effective ground treatment using prefabricated vertical drains and geogrids measured settlements more than the calculated settlements.Suresh et. al, (2020)⁹explainedthat the lateral pressures and deformation along the depth are analyzed in this paper.Fu et.al, (2021)¹⁰explained thata wide embankment has lower settlements than a narrow embankment. A wide embankment has more excess pore water pressure than a narrow embankment.Kommu et. al, (2022)¹¹explained study's investigation of several Embankment sections at various slope angles led to a decrease in entire construction costs while maintaining a safety factor of 1.5.Prasad et. al, (2022)¹²explained the applicability of recycled building demolition waste material for road embankments demonstrated in the laboratory.

To determine settlements without a water table for uniform and stratified soils by varying modular rigidity.
To determine settlements with water tables for uniform and stratified soils by varying modular rigidity

The effect of geogrid and granular beds on different types of foundation soil like silty sand and RGB + Siltysand + Soft clay is studied using the finite element method by using PLAXIS 2D. The following are the soil parameters that were considered.Plaxis − 2D software is used to determine the displacements and settlements on silty sand, silty sand + soft clay + Reinforced granular bed. A plane strain model with a 15-node setup is considered in this analysis. Half a section of an embankment is considered with an axis-symmetric model. The depth of foundation soil (Silty sand) was taken as 20m to eliminate boundary conditions.Mohr-Coulomb is utilized to stimulate soil activity. An embankment built on uniform silty sand is studied. An embankment's geometry and plaxis model with foundation soil as a homogeneous and two-layered soil. i.e., Reinforced Granular bed + Geogrid + Silty sand as shown below with and without considering the water table.

Table No:1 Parameters of soil

Parameters	Embankment soil	Layer-1(RGB)	Layer-2(soft clay)	Layer-2(Silty sand)
Material model	Mohr-coulomb	Mohr-coulomb	Mohr-coulomb	Mohr-coulomb
Γ_b(kN/m³)	18	20	17	19.70
Cohesion	1	5	15	1.00
𝛗( ̊)	33	38	0	38
Deformation modulus MPa	55	10–50	5	5
Poisson’s ratio, ν	0.400	0.300	0.350	0.35

CASE-1(SILTY SAND)

The height of an Embankment is 6m and the base width of the embankment is 16m with a slope ratio of 2H:1V. Embankment fill is carried out as 1m fill for each increment as the embankment extends the total height of 6 meters.

Geogrids are placed at alternate layers of embankment with stiffness of 5000kN/m. A two-layered soil with a 1m thick Reinforced Granular bed is set on top of Silty sand and is well-drained. on the other hand, Silty sand is considered an undrained state.

CASE-2(SOFT CLAY + SILTY SAND)

An embankment's geometry and plaxis model with foundation soil as a homogeneous and two-layered soil. i.e., Reinforced Granular bed + Geogrid + Silty sand + Soft clay as shown below with and without considering water table.A layered soil with a 1m thick Reinforced Granular bed is set on top of soft clay + Silty sand with a soft clay depth of 9m and a depth of silty sand of is10m.

Geogrids are placed at alternate layers of embankment with stiffness of 5000kN/m. Displacementsand settlements are determined for various modular rigidities of 1,2,5 and 10.µ₁/ µ₂ = 1 indicatingthe soil is homogeneous with the same modular ratio, and µ₁/ µ₂ > 1 RGB + Silty sand in case-1 and µ₁/ µ₂ > 1 RGB + Soft clay + Silty sand indicatesover a soft layer in case-2 with and withoutwater table.

Without water table

Silty sand:

4.1 Settlements

Surface settlement variations at the top as well as beneath the Embankment with increasing fill height for a homogeneous as (silty sand) andstratified structure(Silty sand + RGB)of various modular rigidities are illustrated in Figs. 6,7&8. Top surface settlements gradually decreased from 194mm to 155mm because of providing various soil modular rigidities.

From the above figure, settlements on the ground surface for homogeneous soil (µ₁/ µ₂ = 1) and layered soil (µ₁/ µ₂ > 1) indicate RGB soils over Silty sand.The thickness of the Embankment fill shows at the final result of construction, settlements increased linearly. Fill thickness settlements gradually decrease from 179mm to 160mm because of various soil modular rigidities anda geogrid.

4.2 Horizontal displacements

For homogeneous and two-layered soils, the variation of thehorizontal displacement of an embankment toe with fill thickness is shown in Fig. (9).

From the above figure, Horizontal displacements at an embankment toe for homogeneous soil (µ₁/ µ₂ = 1) and layered soil (µ₁/ µ₂ > 1) indicate RGB soils over Silty sand. The thickness of the Embankment fill shows at the final result of construction, settlements increased linearly. Fill thickness displacements are gradually decreased from 51mm to 17mm. withavariation in modular rigidity from 2 to 10. The horizontal displacement profileat the final result of construction under the Embankment toe is shown in Fig. 10.

µ₁/ µ₂ = 1 (homogeneous soil) for the modular ratios, with horizontal displacements at the ground surface of 42mm. With avariation in modular rigidity from 2 to 15, the displacements beneath the toe reduce from 34mm to 28mm. The horizontal displacements fall significantly from 42mm to 28mm at a depth of 3m, which is at the top of the Silty sand, with avariation in the modular ratio from 2 to 10.

4.3 With the water table

Settlements

Surface settlement variations at the top as well as beneath the Embankment with increasing fill height for a homogeneous as (silty sand) andstratifiedstructure (Silty sand + RGB) ofvarious modular rigidity are illustrated in Figs. 11,12 &13. Top surface settlements gradually decreased from 219mm to 178mm with an increase in modular ratios from 2 to 10.

From the above figure, settlements on the ground surface for homogeneous soil (µ₁/ µ₂ = 1) and layered soil (µ₁/ µ₂ > 1) indicate RGB soils over Silty sand. The thickness of the Embankment fill shows at the final result of construction, settlements increased linearly. Fill thickness settlements are gradually decreased from 204mm to 182mm with avariation of modular ratio from 2 to 10and also by considering a water table.

4.4 Horizontal displacements

For homogeneous and two-layered soils, the variation of the horizontal displacement at the Embankment toe with fill thickness is shown in Fig. (14).

From the above figure, Horizontal displacements at an embankment toe for homogeneous soil (µ₁/ µ₂ = 1) and layered soil (µ₁/ µ₂ > 1) indicate RGB soils over Silty sand. The thickness of the Embankment fill shows at the final result of construction, settlements increased linearly Fill thickness displacements gradually decreased from 57mm to 21mm. Withavariation in modular ratio from 2 to 10. The horizontal displacement profile at the final result of construction under the Embankment toe is shown in Fig. 15.

µ₁/ µ₂ = 1 (homogeneous soil) for the modular ratios, with horizontal displacements at the ground surface of 49mm. With avariation in modular ratio from 2 to 10, the displacements beneath the toe reduce from 40mm to 33mm. The horizontal displacements fall significantly from 49mm to 33mm at a depth of 3m, which is at the top of the Silty sand, with an increase in the modular ratio from 2 to 10 and also by considering the water table.

4.4 Soft soil + silty sand

Without water table

Settlements

Surface settlement variations at the top as well as beneath the Embankment with increasing fill height for a homogeneous as (silty sand + soft clay) and two-layer system (Soft clay + Silty sand + RGB) of different modular rigidity are shown in Figs. 16,17&18. Top surface settlements gradually decreased from 160mm to 134mm with an increase in modular ratios from 2 to 10.

From the above figure, settlements on the ground surface for homogeneous soil (µ₁/ µ₂ = 1) and layered soil (µ₁/ µ₂ > 1) indicate RGB soils over soft clay + Silty sand.

The thickness of the Embankment fill shows at the final result of construction, settlements increased linearly. Fill thickness settlements are gradually decreased from 154mm to 120mm with a variation in modular ratio from 2 to 10.

4.5 Horizontal displacements

For homogeneous and two-layered soils, the variation of the horizontal displacement at the Embankment toe with fill thickness is shown in Fig. (19). Horizontal displacements at an embankment toe for homogeneous soil (µ₁/ µ₂ = 1) and layered soil (µ₁/ µ₂ > 1) indicate RGB soils over soft clay + Silty sand. The thickness of the Embankment fill shows at the final result of construction, settlements increased linearly. Fill thickness displacements are gradually decreased from 29mm to 13mm. withavariation in modular rigidity from 2 to 10. The horizontal displacement profile at the final result of construction under the Embankment toe is shown in Fig. 20.

µ₁/ µ₂ = 1 (homogeneous soil) for the modular ratios, with horizontal displacements at the ground surface of 34mm. With an increase in modular ratio from 2 to 10, the displacements beneath the toe reduce from 32mm to 24mm. The horizontal displacements fall significantly from 34mm to 24mm at a height of 3m, RGB is at the top of the soft clay + Silty sand, with avariation in the modular ratio from 2 to 10.

4.6 With the Water table

Settlements

Surface settlement variations at the top as well as beneath the Embankment with increasing fill height for a homogeneous as (silty sand + soft clay) and two-layer system (Soft clay + Silty sand + RGB) of different modular rigidity are shown in Fig. 21,22&23. Top surface settlements gradually decreased from 165mm to 143mm with an increase in modular ratios from 2 to 10.

settlements on the ground surface for homogeneous soil (µ₁/ µ₂ = 1) and layered soil (µ₁/ µ₂ > 1) indicate RGB soils over soft clay + Silty sand.

The thickness of the Embankment fill shows at the final result of construction, settlements increased linearly. Fill thickness settlements are gradually decreased from 160mm to 147mm with avariation in modular ratio from 2 to 10 and also by considering the water table.

4.7 Horizontal displacements

For homogeneous and two-layered soils, the variation of the horizontal displacement at an Embankment toe with fill thickness is shown in Fig. (24).

Horizontal displacements at an embankment toe for homogeneous soil (µ₁/ µ₂ = 1) and layered soil (µ₁/ µ₂ > 1) indicate RGB soils over soft clay + Silty sand. The thickness of the Embankment fill shows at the final result of construction, settlements increased linearly. Fill thickness displacements are gradually decreased from 29mm to 13mm. With an increase in modular ratio from 2 to 10. The horizontal displacement profile at the final result of construction under the Embankment toe is shown in Fig. 25.

µ₁/ µ₂ = 1 (homogeneous soil) for the modular ratios, with horizontal displacements at the ground surface of 34mm. With avariation in modular ratio from 2 to 10, the displacementsbeneath the toe reduce from 32mm to24mm.The horizontal displacements fall significantly from 34mm to 24mm at a height of 3m, RGB is at the top of the soft clay + Silty sand, with avariation in the modular ratio from 2 to 10 and also by considering the water table.

The PLAXIS software uses a finite element method to estimate the impact of the granular layer and geogrid over soft layer + silty sand with and without water table on displacements and settlements underneath an embankment for various modular rigidity. The following are some of the findings:

Surface settlements for silty sand are reduced up to 23.71% by varying soil modular rigidity. With water table surface settlements are reduced by 22.69% by varying soil modular rigidity
Ground surface and fill depth settlements are reduced by 11.41% by varying soil modular rigidity and providing geogrids. With water table ground surface and fill depth settlements are reduced by 11.98%
Horizontal displacements are reduced by 45.09% by varying soil modular rigidity.With water table by varying soil, modular rigidity Horizontal displacements are reduced by 49.022%
Surface settlements for RGB + Soft, clay + silty sand are reduced up to 19.69% by varying soil modular rigidity. With water table surface settlements are reduced by 14.88% by varying soil modular rigidity
Ground surface and fill depth settlements are reduced by 27.611% by varying soil modular rigidity and providing geogrids. With water table ground surface and fill depth settlements are reduced by 8.23%
Horizontal displacements are reduced by 40.90% by varying soil modular rigidity. With water table by varying soil, modular rigidity Lateral displacements are reduced by 40.768%
With the provision of water table settlements are more in the case of silty sand and soft clay + Silty sand.
Horizontal displacements with the provision of a water table there is not much variation in displacements in silty sand + soft clay.

1. Conflict of interest

A) There is no conflict of interest in the manuscript.

2. Funding declaration

A) There is no funding declaration in this manuscript.

Loganathan, N., Balasubramanian, A. S., & Berg ado, D. T. (1993). Deformation analysis of embankments.
Chai, J. C., Miura, N., & Shen, S. L. (2002). Performance of embankments with and without reinforcement on soft subsoil.
Huang, W., Fityus, S., Bishop, D., Smith, D., & Sheng, D. (2006). Finite-element parametric study of the consolidation behavior of a trial embankment on soft clay.
Rankine, B., & Sivakugan, N. (2007). Short-term lateral deformations induced in an elastic medium through the application of rigid embankment loading.
Balasubramaniam, A. S., Cai, H., Zhu, D., Surarak, C., & Oh, E. Y. N. (2010). Settlement of embankments in soft soils.
Afadoust, J., Amiri, S. N., & Esmail, A. (2013). Numerical Analysis of Reinforced Embankment Over Soft Foundation.
Faizi, K., Armaghani, D. J., Kassim, A., & Lonbani, M. (2013). Evaluation of geotextiles on embankment displacement under seismic load.
Yean-Chin, T. A. N., Peir-Tien, L. E. E., & Kuan-Seng, K. O. O. (2016). The construction control chart developed from the instrumented trial embankment on soft ground
Suresh, B., & Suresh Kommu, S. S. (2020). Design of Mechanically Stabilized Earth Wall for Widened Embankment.
Jiang, X., Chen, X., Fu, Y., Gu, H., Hu, J., Qiu, X., & Qiu, Y. (2021). Analysis of Settlement Behavior of Soft Ground Under Wide Embankment.
Kommu, S., Kumaar, M. A., & Madhira, M. (2022). Optimization of Embankment Widening.
Shivaprasad, H., & Kommu, S. (2022, March). Geotechnical Laboratory Evaluation of Construction Demolition Recycled Material for Road Embankments.

No competing interests reported.

Settlements of Embankments on Different Types of Soils

Status:

Version 1

Abstract

Figures

1. Introduction

2. Objectives

3. Methodology

CASE-1(SILTY SAND)

CASE-2(SOFT CLAY + SILTY SAND)

4. Results And Discussions

Without water table

Silty sand:

4.1 Settlements

4.2 Horizontal displacements

4.3 With the water table

Settlements

4.4 Horizontal displacements

4.4 Soft soil + silty sand

Without water table

Settlements

4.5 Horizontal displacements

4.6 With the Water table

Settlements

4.7 Horizontal displacements

5. Conclusions

Declarations

References

Additional Declarations

Status:

Version 1