Analysis of Cutting Slope Stability on PLTM KALUKKU - Using Geoslope 2007 Software

ANALYSIS OF CUTTING SLOPE STABILITY ON PLTM KALUKKU – MAMUJU USING GEOSLOPE 2007 SOFTWARE AND FILLENIUS METHOD

Muh. Ali

ABSTRACT: Computer technologyhas been developed rapidly these days, it facilitates human in many  areas inlude the field of geotechnic. One of the example of the computer technology growth in the field of geotechnic isthe birth of a softwareprogram called geoslope whichfacilitatesits consumer to analyse the stability of a slope without requiring much time to calculate manually with Sliced Methodthat  occasionally used. Besides it this Geoslope softwere also can assist for the determination to repair the landslide of the mountain. By inputting the ground parameter and the mass of the mountainside, it has been obtained the maximal factor of the safety value. The metodological approaches are bishop of janbu, which have been conducted with manual control by using sliced method of Felleniusmethod obtained medium result, so that can be concluded that the Output of the software is critical number which can be taken as a reference in analysing a slope stability.

Keywords : Geoslope, Fillenius Method, Safety Factor ( SF), Anchor.

1.     Introduction

Nowadays the electrical problems in Indonesia particularly in central and eastern region of Indonesia becoming hot topic to discussed by the public. Especially with the frequent of outage power and the difficulty to request the addition of power due to limited power supplies. PT. PLN (Persero) as the company who has responsibility in this matter, has researchmany variety of innovations to increase the electrical supply such asbuild power plants using natural resources which available extremelly high in Indonesia, such as by using power of water.

One kind of the utilization  of  water power isusing river stream by developing Power Station Of Hydro Mini Energy ( PLTM). One of them is in Mamuju, west Sulawesi in Kalukku river  with capacities 2x700 kW formally operates on mid of April 2012 , where this time it has not beenoperated yet optimally because of some factors. One of them is because the hill residing the railrace at some natural spot station and it isblocking the water to flow tothe turbine. Therefore, the analyze of slope stability on that location was required. And then, we can find out how to strength / fix it.

To calculate the mountainside stability can be conducted manually by using slice method with various approaches. But along the growth of computer technology, the usage of geotechnic software, will very assisting in the case of the effective and accuracy of the calculation. One of them is the usage of Geo Slope  2007 version. This Software is expected to quicken the analysis process and to  get more accurate result of calculation by doing comparison of the calculation result manually with Fellenius Method approach.

This article contains analysis of mountainside stability in the side of the sliding tailrace that pursue the water irrigates to the pond by using slope geo software 2007 and compare its result through calculation  by using fillenius method approach.

In general this research is aimed to analize the montainside stability.specifically this research is aimed in:

1.       Comparingthe safety factor (SF)results before reinforcementusing Geo Slope2007 version Software and manual calculation usingFellenius method approach.

2.       Comparing the safety factor (SF)results after reinforcementusing Geo Slope 2007 version Software and manual calculation using Fellenius method approach.

2.     Slope StabilityAnalysis

2.1. Geo Slope / w 2007

 Geo Slope is an application package to model the geotechnic of geo-environmet. This Software embosom SLOPE/ W, SEEP / W, SIGMA / W, QUAKE/ W, TEMP / W, and CTRAN W. Whish has theintegrated character so it enables to use the result  from one product to other products. This unique and strong fiture is very extending the type of a problem and it will be able to be analysed and give flexibility to get the required module for different project.

SLOPE / W represents the software product to calculate the safety land factor and the inclination of the SLOPE. we can analyse the problemeither through modestly or complexly by using one of the eight balance methods of the boundary to various oblique surface. We can use limited water pore pressure element, static tension, or the dynamic pressure of the slopestability analysis. You also can analyse by SLOPE probabilystic. Slope / w Program uses Equilibrium theory in calculating security frequence of a slope though varied methods. This program enables us to analyse the complex and also simple geometry, land layers, and the external condition of the land. SLOPE Program is formolated to form the equivalence of the safety frequence that fulfills the moment balance and style balance.

 

figure 1. Geoslope appereance

2.2. Fellenius

This procedure can be used  inisotropic and non isotropic .the land mass peripatetic supposed to consist of some vertical element. The width of the element can be taken unequally and in such a way that the archedvault can be assumed as a straight line ( SKBI- 2.3.06, 1987).

Total Weight of land/rock in one particular element (Wt) includes the outside tension that is in the slope surface ( Picture 2.10 and 2.11). Wt is described in vertical and tangensial element base. In this way the influence of T style and E style which works beside the element is ignored. Safety Factor is the comparison of the resisted moment with the cause of theslide. [At] Picture 2.8 resisted moment at slide area is ( SKBI-2.3.06, 1987) :

Mresisted= R .r (2.14)

which R is the slide styleand r isslide area radius. The resisted slide in each element base is:

R = S . l = (c’ +σ tanφ’ ; σ = .......................................................... (1)

Resisted moment is in amount of:

M_resisted = r (c’l + W_t cos α tan φ’).............................................................. (2)

Tangencial component Wt works as the cause of the slide:

M_cause = (W_t sin α ) . r................................................................................... (3)

The safety factor of the slope becomes:

SF .............................................................................................. (4)

                                                                                S = c’ . ∆L_n + ∆L_n.σ tan Φ

figure 2.1. Fillenius slice method diagram                figure 2.2 diagram of fillenius momen      

                                                                                                    equilibrium        

                         

2.3. SlopeReinforcementWith Anchor System

 Land/slopeStabilization is a method which used to increase thestrength of soil’s layers support by giving ittreatment (special treatment) special for the soil’s layer. One of the stabilization land types among is mechanical stabilization by using inserted material of the land, so it can repair the characteristic mass of the soil. Mechanical stabilization is often  referred with " Land Strength (Soil Reinforcement)".Reinforced Earth is given by is certain ways, so it can form the same laboring system in shouldering tension, and ability of the system become much more big from ability earlier.

The main Princip of the application of the land strengthis to  create composite action betweenoriginal material with inserted material, that  will form corporative system to strengthen the land which have energy support much bigger from the original energy support.For example clay land, this type measures up to big comprebility, it can repair the inserted material which smaller, like applying stone  files or the sand files.

The type of the land strength can be seen from the character of the inserted material, marginally differentiated into two kinds:

1.   Land strength with flexible material : which  accept the nset material function can accept attractive force and shift style, but unable to hold the tension. The example : strip metal, geosyntetic, etc

2. Land strength with rigid material : which has broader stiff material function, because it can accept the attractive force, tension, etc. For instance : nailing, piles, and others.

One of strength application uses rigid materialis the usage of mechanical angker  which has the following excess

1. Easy  installed

2.Do not need drill process that will be installed to represent friendly environment technology

3. Do not need grouting

4. More economical.

  

figure 3. Anchor model                                   figure 4. Step of Anchor installation

Some factors that influence the behaviour and appearance of the land’s strength such as those which elaborated. The use of Material strength will influence the landslide. Aspects which need to be paid attention in order to get material strength as follows:

Ø  Form:  to have connection betweenthe material and the land, the form is having an effect on. The formsurface Influence of the material contribute on how bigor small the bond displacement

Ø  Strength ( strength) : relation of the tension-strain from the  material strength, will give criteria about permittingthe deformation. Besides that it can overcome the effect of the problem in the substace and transport.

Ø  Orientation : the location should beas long as the principal strain direction that happened.

3.     Results and Discussion

This study took place at Kalukku Mini Hidro Power Plants, which are located in Sondoang area of Kalukku Sub-District in West Sulawesi. Astronomically based on the WGS 1984 datum zone 50S, located at coordinates UTM Projection 738 600 - 738900E and 9707200 - 9706600S. With the object of research is cutting slope on the side channel of Mini HydroPower Plant (PLTM)by three observation points, namely: Sta. +0,750, Sta. +1,140 And Sta. +1,250.

3.1. Before Reinforcement (Normal Condition)

a. Software Geoslope

The results of the analysis by using geoslopecould be tabulated as follows:

Slope’s Model	Sta. Point	SF
	1 (Sta. +0.750)	1.029
	2 (Sta. +1.140)	0.646
	3 (Sta. +1.250)	0.783

Table1.Safety factor value without reinforcement using geoslope software.

b. Fillenius Method

The results of the analysis by using Fillenius methodcould be tabulated as follows:

 Table .2.Safety factor value without reinforcement using fillenius method.

3.2. Slope Reinforcement using Anchor

a. Software Geoslope

The anchor system which planned to use is mechanical anchor type skyhook (product ofMantaray) MR-68, with the following specifications:

  

figure 5. Anchor Specification

The results of the anchor reinforcement analysis using software geoslopecould be tabulated as follows :The results of 

Table 3.Safety factor value with anchor reinforcement using geoslope software.

b. Fillenius Method

The results of the anchor reinforcement analysis using Fillenius methodcould be tabulated as follows :

Table4.Safety factor value with anchor reinforcement using fillenius method.

5. Conclusion

From the results of slope stability analysis above, it can be concluded as follows:

1. The results of slope’s safety factorby using Geoslope Software obtained unstable condition (prone to landslides) for the three station points of observation view, respectively for stations 0+750, 1+140 dan 1+250 are : 1.029, 0.646 dan 0.783 so that reinforcement are required.
2. The results of slope’s safety factor by using Fillenius Method obtained unstable condition (prone to landslides) for the three station points of observation view, respectively for stations 0+750, 1+140 dan 1+250 are : 1.032, 0.711 dan 0.773 so that reinforcement are required.
3. The results ofslope reinforcement analysiswith anchor system by using Geoslope Software obtained stable value for the three station points of observation view, respectively for stations 0+750, 1+140 dan 1+250 are : 1.667, 1.496 dan 1.045.
4. The results ofslope reinforcement analysis with anchor system by using Fillenius Method obtained stable value for the three station points of observation view, respectively for stations 0+750, 1+140 dan 1+250 are : 1.708, 1.657 dan 0.843.

References

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