Analysis of Excavation Method on Inlet Tunnel of Controller Construction of Rukoh Dam Pidie District – Aceh Province

. The tunnel of controller construction is located in Panton Bunot Village, Tiro Sub District, Pidie District, Aceh Province. The tunnel construction aims to flow the water from Kr. Tiro River to Rukoh inundation for water supply to Rukoh Dam in Keumala Sub District, Pidie District. The research aimed to comprehend engineering geological condition in the study area and determine excavation method at the inlet and proper tunnel support system. The determination of proper excavation method becomes crucial and it is required in maintaining affectivity and efficiency during tunnel construction process. Than excavation method determination is carried out calculation by using empirical method based on output parameter of laboratory test to the rock samples from core drilling in the tunnel track. The outputs are rock conditions as rock mass quality (RQD), discontinuity area density of the rock and rock stress strength. The condition of tunnel track was dominated by silt stone having very poor quality. UCS value was 3 Mpa – 10 Mpa. Joins spacing was less that 60 mm. Empirical analysis of excavation method explained that tunnel opening of Rukoh Controller Construction was highly weathered (HW) and required ripping as excavation type.


Introduction
Dam is one of the constructions improving water supply reliability for various purposes, expected can accommodate water excess in the rainy season and anticipate the water shortage in the dry season.
Tiro Irrigarion Area located in Pidie District has 6,330 Ha of the total, 9.87 m 3 /sec of irrigation discharge demand taken from the main construction of Tiro Dam on Kr.Tiro River.Irrigation system and main construction of the dam was constructed in 1978.The dependable discharge of 80% on Kr.Tiro was 2.66 m 3 /sec in the dry season, the total rice field irrigated in DI Kr.Tiro was 2.643 Ha and the remaining 3.687 Ha was not irrigated.To overcome the problem, it is required to construct Tiro Dam with the total catchment area is 174.24 km 2 for the potential water in Kr.Tiro River is considerable.The landuse condition in Tiro Dam site are plantation and housing areas.
Baro Raya Irrigation Area of sub DI.Krueng Baro located in Pidie District has 11,950 Ha of total area and 18.64 m 3 /sec of irrigation discharge demand taken from the main construction located in Kr.Baro River.The irrigation system was constructed in 1995.The river discharge of Kr.Baro decreases every year and it is not sufficient for the existing area.The dependable discharge of 80% on Kr.Baro was 3.46 m 3 /sec.It was impacted that the total area irrigated in the dry season was 6,147 Ha and the remaining 5,803 Ha was not irrigated.
The problem could be overcame by constructed dam in Kr.Rukoh River as Kr.Tiro Sub River.The potential of reservoir on Krueng Rukoh is 128.65 million m 3 .The catchment area as 19.63 km 2 cannot suffice the water demand in the innundation area.The water supply from Kr. Tiro become a requirement.
The water potential of the both rivers can be optimally developed to meet water demand of Kr.Baro and Kr.Tiro Irrigation Areas, water supply demand, flow maintenance in the downstream and power plant in each Rukoh dan Tiro Dam.The two dam designs are connected by using interconnection channels.The huge water potential from Kr. Tiro can be accommodated in Rukoh Dam connected Tiro Dam.The cuurent condition, the inundation area design of Tiro Dam are housing areas in 2 villages located in Blang Rukui and Pantan Bunot Villages.These villages have not be accessible and measurement activity of LARAP for land acquisition and resettlement cannot be applied.It is required to manage other tasks in developing water resources potential to supply Rukoh Dam.
One of the project scope is tunnel construction.Tunnel is precast concrete construction by using horseshoe type.The tunnel length is ± 950 meter and dimension is 5 meter.Conduit line is 75 meter starting from STA. 6+525 to STA. 6+600 and connected to tunnel to STA. 6+800.
In the tunnel construction, water tunnel construction design on Rukoh controller construction has investigated geological condition including rock mass quality qualification by using Rock Mass Rating (RMR) method, geotechnical investigation by excavating 5 points along tunnel from inlet to outlet.The investigation output was included by laboratory investigation consisting of index and mechanical properties.From the initial investigation of excavation output, study area lithology is Silt stone.Silt stone has considerable discontinuity areas and moderate to high of weathering.The design has not investigated engineering geological characterization based on soil and rock, morphology, geological structure, groundwater, and surface and subsurface rock mass quality determinations.
From the field condition above, it is required to evaluate the classification of rock mass quality by using Geological Strength Index (GSI) method that is compatible to poor rock condition and high weathering level.It is also necessary to evaluate engineering geological condition consisting of portal slope stability analysis, tunnel excavation method analysis, and tunnel support system stability analysis used by calculating the earthquake load for the smooth and safety of the tunnel construction process.
Due to the above problem and the design not considering engineering geological condition including morphology, rocks and soil, groundwater structure, and seismic factors affecting excavation method determination, support system type, tunnel portal slope stability, this research aims to analyze excavation method and evaluate engineering geological condition of tunnel on Rukoh Dam controller construction based on engineering geology data.There are three tunnel types due to the material used in the tunnel construction according to Raharjo (2004), as mentioned below:

Cut and Cover Tunnel
The tunnel is constructed by excavating the large trench, constructing tunnel structure in the trench, and covering by the filled material when the structure completed.The material of the tunnel used is precast concrete named box culvert.This method can only be used if the tunnel is constructed on the shallow ground depth and the excavation of the ground level is feasible.

Rock Tunnel
The tunnel is constructed on the massive rock by using drilling and exploding methods.The rock tunnel construction generally is easier to be carried out compared to soft ground tunnel since rock has higher stiffness and stability affecting the reinforcement required is simpler.

Soft Ground Tunnel
The tunnel is through soft ground layer as clay, sand and soft rock.This type of material tends to collapse during the excavation process so it is required strong wall or roof as the protector.The common technique used is Shield Tunneling by using Tunnel Boring Machine (TBM).
The surface engineering geological mapping carried out in the research consist of: a. Rocky Outcrop Mapping The mapping is started by creating transverse around tunnel location constructed with 2 km x 2 km mapping area, then the mapping is continued by tracing the route map designed by using existing roads with the distance of (STA) + 100 meter per observation location.The data required in the mapping activity are as below: 1. Rock Face, consisting of rock type description, rock slope and move, joint distribution, rock structure, formation age. 2. Rock Quality, consisting of weathering level identification, joint type, mineralization, alteration, rock hardness.3. Geological Structure, consisting of folds, faults and joints.

b. Morphology
According to Ni'mah (2018), natural landscape of a location can be identified from topography or direct observation.Other landscape requires to be considered including valley shape, river flow pattern, and slope angle.Slope angle become crucial aspect and related to slope stability.

Tunnel Excavation method
The tunnel excavation can be implemented by using several methods in the site.The selected method is adapted to the surrounding natural condition and mature considered and analyzed.Based on JSCE (2007), the selection of tunnel excavation method must considered the ground condition, shape and size of excavation section, tunnel construction method, and the impact to the structure and environment around the tunnel construction site.
The excavation methods frequently used are full face, bench cut and drift advancing methods.Full face method is frequently used in small section tunnel owing to the equipment limitation used.Bench cut method is generally used in big section tunnel to ensure tunnel stability.This method is well adapted to ground condition transformation.For tunnel construction by using soft ground/rock media and small overburden, the methods suitable used are side drift advancing, bench cut, full face modified with bench cut.
Excavation method selection phase according to Minister of PUPR decree on appendix of guideline for excavation design method and strengthening systems on soil-rock mixed media (2015) can be explained as below: 1.
Evaluate the condition of rock/ground media based on field and laboratory tests.

3.
Evaluate the advantage and disadvantage of excavation method and excavation site division based on technical aspect and simplicity implementation.
The core drill is carried out in tunnel location.The output of excavation is test in the laboratory for rock and ground properties.Refer to the geological investigation along the tunnel, the result of the investigation was shown in Figure 1, (on this case only show the core box and lab result on TR 1) (a) (b) Figure 1.The Core Drill in Tunnel Area of TR.1.2 The tunnel was place on elevation 34, from the figure 1 the core box shown that the RQD on this level was very bad.Than the result of laboratorium for the rock sample was shown on table 1 until table 3 below.Table 1.Result of Laboratory Test for Rock Sample in TR. 1 Determination of rock mass quality is carried out using Rock Mass Rating (RMR) method (Bieniawski, 1989), the quality of the rock mass is controlled by five main parameters consisting of Uniaxial Compressive Strength (UCS) of intact rock material, Rock Quality Designation (RQD), discontinuity area space, discontinuity area condition, and groundwater condition (Table 4).(Bieniawski, 1989) In addition to using RMR for determining rock mass quality, it can also use another rock mass classification as Geological Strength Index (GSI).This classification is based on the correlation discontinuity area of rock and surface condition of discontinuity area (Hoek, E., Carter, T.G., Diederichs, 2013) (Figure 2) The values of RMR and GSI can be classified into five groups mass quality consisting of very good, good, fair, poor and very poor (Table 5) (Sivakugan, N. Kumar, S. Das, 2004).
Table 5.The Range of Rock Mass Quality (Sivakugan, N. Kumar, S. Das, 2004) After determination of rock type and rock mass quality measurement, it is continued by determination of rock discontinuity areas density.The rock power to the excavation method is influenced by material types especially the geotechnical properties, it also affects to work method and equipment.Discontinuity area and intact rock become the example of geotechnical properties.Others like fracture, fracture content, and strength of discontinuity area wall become other crucial factors.Three main methods of excavation are blasting, ripping and digging (Gurocak et al., 2008).

Geological Condition on Tunnel Area of Controller Construction
Engineering geological investigations on tunnel site of Rukoh Controller Construction explain that the rock in the tunnel track site is dominated by silt stone lithology and very poor rock mass quality as shown 0n Table 6a, 6b and 6c

Analysis of Excavation Method
The approach is empirically carried out to find the most suitable excavation method to the rock condition drilled in the tunnel track.It uses graph (Bieniawski, 1974).Table 6.b and 6.c explain UCS and Spacing of Discontinues, it will be reference in determining implemented excavation method.(Bieniawski, 1974) The graph plotting outputs by using data presented in the previous explanation describe that the most suitable excavation method used is ripping, the laboratory test output are 3 Mpa -10 Mpa of UCS and less than 60 mm of joint spacing as shown on Figure 7.
Tunnel is a closed passage connecting two open sides or one open side to certain object.Two open sides tunnel as water tunnel, highway tunnel, railway tunnel and other passes two open sides.

Figure 2 .
Figure 2. GSI Quantitative Analysis (Hoek, E., Carter, T.G., Diederichs, 2013) . Tabel 6a.Rock Classification Output of 5 (Five) Core Drilling Points in Tunnel Track Site Tabel 6b.Rock Classification Output of 5 (Five) Core Drilling Points in Tunnel Track Site Tabel 6c.Rock Classification Output of 5 (Five) Core Drilling Points in Tunnel Track Site Then the existing data is mathematically analyzed by using FEM (application Phase 2), the forces distribution in the tunnel due to the excavation are shown in the figure 4 and 5.

Figure 4 .
Figure 4. Deformation in the Tunnel due to Excavation near inlet

Figure 6 .
Figure 6.Classification of Mass Rock Strength and Simplicity Excavation Level

Table 2 .
Result of Laboratory Test for Rock Sample in TR. 1

Table 3 .
Result of Laboratory Test for Rock Sample in TR. 1

Table 4 .
Rate of RMR Rock Mass Quality