8. C O N C L U S I O N S AND R E C O M M E N D A T I O N S

8.1. Conclusions

> By using GRPS Embankment system the differential settlement, lateral moment

can be reduced while increasing the slope stability is increased. Reduction of

construction time is another advantage over other ground improvement methods.

> Road embankment construction over soft ground. Bridge approaches. Retaining

walls and Widening of roads over soft soil are some of the common application

of GRPS embankments in Sri Lanka.

> The main aims of this study can be listed as below.

Development of finite element models in Plaxis 2D and compare the

resuhs with BS8006 and German Draft Standard (EBGEO).

Development of graphs for the behavior of Axial load of piles.

Maximum SF & B M of piles. Maximum tensile force in the geo

reinforcement layers and overall settlement of the embankment due to

changes of various factors like pile size, pile spacing, embankment

height, number of GR layers, spacing between GR layers and surcharge

load etc.

> The finite element study shows that factors like tensile stiffness of the geogrid,

the pile Area, the height of the embankment, the position of the geogrid and the

properties of the embankment fill affect the GRPS system significantly.

However, these effects are not always considered by the other available methods.

> It is very difficult to find an analytical method to evaluate the lateral moment of

reinforcement embankments. Chapter 2 of this report discuss some methods used

for unreinforced piled embankments. However, focus in this report is on two

design procedures for reinforcement embankment on piles namely BS8006 and

EBGEO and compare the results with PLAXIS 8.2.

> The Plaxis 8.2 program is equipped with facilities to model several interacting

mechanisms in the GRPS system. The stresses and displacement of any point of

the system can be evaluated using this finite program. The impact on tensile

force in geogrid due to soil resistance provide by the underlying soil can be

evaluated. The lateral deformation of piles can be easily studied.

106

> For the analysis of slope stability, the BS8006 recommend the Bishop Circle

method. This method can handle short term stability analysis considering pore

water pressures and performing an Undrained analysis. For evaluation of slope

stability of a homogenous soil, the friction circle method was found most

convenient. However, this method also does not consider the geosynthetic

reinforcement.

> According to the Standard Deviation Tables for case 1 and case 2 show that

EBGEO gives calculation results that agree best with our Plaxis- 2D calculations

> When compare the currently available methods for analysis of GRPS

embankments, the numerical analysis is more reliable. This method considers

the effect of numerous variables like the tensile stiffness of the geosynthetic, the

pile modulus and the change in height of the embankment on the stress

concentration ratio which is neglected by all other methods. The tension in

geosynthetic reinforcement in a multi-layer reinforced fill can only be calculated

using this method.

> According to the Plain strain model analysis the following conclusions can be

derived. These conclusions were made considering optimum combination of

axial loads, SF, BM, Tension in GR, Settlement of embankment and FOS of

embankment.

The most efficient pile size is 350mmx350mm

Recommended pile spacing is 3.0 m

Efficient GR layer spacing is 300 mm

8.2. Recommendations

> The available methods for analyzing the lateral movement can be used only for

non-reinforced embankments. Therefore, it is necessary to develop a method to

estimate the lateral moment of GRPS embankments.

> The available methods, BS 8006, EBGEO or any other method does not provide

a way to calculate the effect of the resistance provide by the underlying soft soil

during the calculation of tension in GR layers. Therefore, more research is

required in that area.

107

> A method is needed to be developed to evaluate a multi-layer geo-reinforced

embankments.

> A method is needed to be developed for the prior estimation of maximum and

differential settlements of the embankment.

> The bending moments of the piles that are generated using the finite element

analysis needed to be verified with field data.

> Furthermore, Plaxis calculations are relatively time consuming. It is therefore

necessary to have a quick analytical design procedure, at least for the first design

calculations for a pile embankment.

> This research shows that EBGEO gives calculation results that agree best with

our Plaxis- 2D calculations. According to the Standard Deviation Tables for case

1 and case 2 show that EBGEO gives calculation results that agree best with our

Plaxis- 2D calculations.

It is therefore recommended to use this EBGEO design procedure for the first design

of a piled embankment. For detail design, Plaxis can be used to check the EBGEO

calculations and to calculate the horizontal load on the piles and to check the slope

stability of the embankments.

108