Hydrogeological Problems in Underground Excavation ... · Biodata Irwan Iskandar S-1: Teknik Pertambangan (Eksplorasi Tambang) ITB 1997-2002 S-2: Rekayasa Pertambangan (Hidrogeologi)

Hydrogeological Problems in Underground Excavation;

Mitigation and Modeling

Irwan Iskandar, Ph.D.

Laboratorium Hidrogeologi dan HidrogeokimiaKK Eksplorasi Sumber Daya BumiFakultas Teknik Pertambangan dan Perminyakan, ITB

Balai Diklat Tambang Bawah Tanah, ESDM, 23 April 2020

BiodataIrwan Iskandar

S-1: Teknik Pertambangan (Eksplorasi Tambang) ITB 1997-2002

S-2: Rekayasa Pertambangan (Hidrogeologi) ITB 2003 –2005

S-3 : New Frontier Science (Environmental Geology) Kumamoto Univ. Jepang, 2007-2010

Pengajar di Teknik Pertambangan dan RekayasaPertambangan (FTTM-ITB)

Pengajar di Magister Teknik Air Tanah (Hidrogeologi) (FITB-ITB)

Pengajar di Magister Teknik Panasbumi (Geothermal) FTTM-ITB

Research : Hydrogeology – Hydrogeochemistry

[email protected] dan [email protected]

mailto:[email protected]


“Water is driving force of all nature” (LdV*)

Teach what you did instead of only teach what you read

The mediocre teacher tells. The good teacher explains. The superior teacher demonstrates. The great teacher inspires.

William Arthur Ward

Materi ini dibagikan untuk kepentingan pendidikan dan pelatihan. Mohon tidak digunakan untuk kepentingan komersil ataupun hal lain yang memerlukan izin hak cipta

While in Mining Industries…..

[email protected]

http://lab.fttm.itb.ac.id/hidro/?page_id=41


Hydrogeology and Hydrogeochemistry

Sumberdaya Bumi– Sumberdaya Air Tanah

Eksplorasi-Eksploitasi SumberdayaPanas Bumi dan Migas

Masalah Lingkungan (Pencemaran, intrusi air laut, land subsidence)

Sebagai Engineering Problem

Masalah di Pertambangan

Our Laboratory…

• Fokus masalah hidrogeologi,

• Hidrogeokimia dan Isotop, e.g.

ICP-MS, Ion Chromatography, Gas

Chromatography, Isotope Ratio Mass

Spectrometry, Water Isotope), Radon

and Analisis Gas Tanah Merkuri,

Spectrometer, Radon Analysis, XRD,

XRF dan SEM)

http://lab.fttm.itb.ac.id/hidro/?page_id=41 https://www.youtube.com/watch?v=V4B82wgFc_U&t=235s

Hello are there any problems? river

Hydrogeologist

YES, there are so many!

? ?

Air, (masalah?) di dalam ekskavasidi Bawah Tanah

• Jumlah,

• Debit,

• Kualitas,

• Rekayasa,

• Pengelolaan,

• Risk

• Impact ke lingkungan?

Mitigationthe act of reducing how harmful, unpleasant, or bad something is: (Cambridge online dictionary)

Menurunkan resiko dan dampak, dan pengendalian dampak

Mitigasi; Eksplorasi Hidrogeologi

• Kondisi hidrogeologi, termasuk hidrologi (relasi airtanah dan badan air di permukaan?, resapan?)

• Kondisi geologi dan meteorologi

• Sistem dan batas sistem aliran airtanah (tracers?)

• Parameter hidrogeologi (K, S, Ø)

• Limitasi dan asumsi

EksplorasiPengujian

Data (yang valid)

https://www.hydrology.nl/iahpublications/201-groundwater-cartoons.html

• Pemetaan hidrogeologi (e.g. singkapan airtanahmata air)

• Pengujian aquifer (slug test, pumping test, packer test)

• Tracers hidrogeokimia dan isotope

• Pendekatan data geologi dan geoteknik lain (e.g. HC system, Xkuet al, 2009)

Sumber foto: dokumen pribadi

Slug Test – Pumping Test – Packer Test

Uji Intact Rock Akuifer (Laboratorium)Dari Core Sample

Constant Pressure (head) Wall Permeameter

(ASTM D5084) Keterangan:

1 = kompresor

2 = tabung air

3 = pengukur

tekanan

4 = fitting

5 = tabung sampel

6 = tabung ukur

volume

k = keran

http://lab.fttm.itb.ac.id/hidro/?page_id=41

Uji Akuifer (Lapangan)

• Slug Test

•Pumping Test

•Packer (Lugeon) Test

Pumping test preparation (kiri), pemantauan drawdown dansampling (tengah) dan Rumah pompa-genset, sensor-logger (kanan)

1. Slug tests

• Umum digunakan di lapangan untuk mengetahui harga

Konduktivitas Hidraulik (K)

• Lokasi tambang

• site investigations sipil

• Lokasi pembuangan limbah

• murah, relatif mudah, peralatan dan perlengkapan sederhana

• Limited zone of influence, tidak dapat diketahui aquifer

storativity (S), tidak digunakan pada flowing well

Beberapa metode pergitungan / analisis yang digunakan

• Cooper-Bredehoeft-Papadopulos

Method untuk confined aquifer

• Hvorslev slug-test method

• Bouwer and Rice slug-test method

Van der Kamp method (for

oscillating water level responses) Bouwer and Rice

geometry and

definitions

Bouwer, 1989

casing

2. Pumping Test

• Sumur dirancang dan dibangun untuk memungkinkan

pengambilan air secara ekonomis dari suatu aquifer

•Pembangunan sumur meliputi:

• Pemilihan metode pemboran yang sesuai

• Pemilihan material konstruksi yang sesuai

• Analisis dan interpretasi kemampuan sumur dan aquifer

Post work-Analyses

• Theis• Cooper-Jacob• Hantush• Etc..Modeling – match

https://wells.gitlab.io/unconfined.html

Karakteristik Akifer dari Pumping Test

Pumping test uji sumur dengan pemompaan debit tertentu dari akifer

memungkinkan kita mengestimasikan nilai T dan S sebagai karakteristik Akifer

• Transmissivity (T = Kb) adalah besar kecepatan aliran air melalui penampang

vertikal akifer (tebal akifer) , dengan satuan unit luas per unit waktu

• Storage Coefficient (S = Sy + Ssb) adalah perubahan air yang tersimpan per unit

volume akifer per unit perubahan head pada area tertentu

• Radius of Influence (R) jarak horisontal maksimum pengaruh dari

pengambiloan airtanah di suatu sumur dimana tidak terjadi penurunan head

akibat pemompaan di sumur tsb (head tetap setimbang seperi semula)

Pumping Test

Result

• Transmisivity (Permeability)

• Storativity

• Radius of Influence

• Qopt

Limitation and Problem

• Need construction, observation well (obs. well), Pompa, Power Supply

• Sometimes obs. well not at ‘right’ position

Permeability in Fractured Rocks


𝐾 = 𝑘𝜌𝑔

𝜇


• Dual ‘porosity’

• Secondary porosity as ‘main actor’

• Rock defects/Fracture/gouge as main porosity

• Connectivity?

• Heterogeneity?

• Isotropy / anisotropy

• K value from field/lab. test?


• Dual Porosity-100 m

-110 m

Depth

-100 m

-110 m

Laboratory

test from

core

NOT RELIABLE High K value (rock mass)

K is very low

impermeable


Fractures

• Connectivity

• heterogeneity

-100

m

-110

m

-120 m

K105 : high

DepthConnected

K115 : low

Not Connected

10 m

30 mPumping well

Observation

well 1

Observation

well 2

No drawdown

5 meter drawdown


3. PackerTest

www.PackerTest.com

http://packertest.com/files/imwa_packer_presentation_aug9.pdf

-100 m

-110 m

-120 m

K105

K115

Water enter rock

formation

‘’easily”

K >>>

Packer Test

-100 m

-110 m

-120 m

K105

K115

Very limited

number of water

can enter the

rock formation

K <<<

Packer Test

195 m

205 m

HQ Casing

NQ Rod

Injection Sub

Standart Longyear Backend

Packer Element

(can not seal rock wall): Water Flow

Surface

Rock Wall

Problem and Challenges in Packer Test

Slug Test Pumping Test Packer Test • Mudah • Sumur di konstruksi yang baik • Tidak perlu konstruksi sumur

• Murah• Lubang besar, sulit lubang bor

eksplorasi (slim hole/core)• Lubang bisa vertical-incline

bahkan hampir horisontal

• Konstruksi dan pekerjaansederhana

• Perlu konstruksi sumur, piezodan sumur pantau • Tidak ada konstruksi sumur

• Bisa digunakan padalubang bor eskplorasiukuran > core HQ • Biaya relatif mahal

• Diameter lubang bor eksplorasibervariasi dari NQ, HQ, atauPQ

• Tidak perlu sumur pantau

• Pengujian ada uji bertahap(debit desain long term) dandebit kontinu • Tidak perlu sumur pantau

• Lubang harus vertikal-idealnya

• Lubang harus vertikal-idealnya

• Rubber packer kadang rusak/tidak sealing sempurna

• •

• Perlu pressure dan pompa injeksi

Slug Test Pumping Test Packer Test

• Data nilai T atau K satuzona uji (vertikalhomogen 1 aquifer)

• Data nilai T atau K satu zona uji(vertikal homogen 1 aquifer)

• Bisa memperoleh nilai K daribeberapa zona dalam satulubang uji

• Tidak ada nilai Storativitasyg reliable

• Memperoleh nilai Storativitas ygreliable

• Tidak ada nilai Storativitas ygreliable

• Tidak ada cerminan karakter fracture • Debit optimum dewatering

• Dengan memainkan tekananinjeksi bisa diperolehkarakteristik fracture

• Cocok di aquifer homogen dan porous tetapi bukan flowing well

• Perilaku muka airtanah dinamisdan Radius of Influence diperoleh

• Cocok di aquifer heterogen-fractured aquifer, walau bisajuga di porous sediment

• Cocok di aquifer homogen, porous (confined-unconfined-leaky)


Another approach:

• In a rock mass flow can be more like a porous medium (Long et al 1982)

• Based on structure observation K can be approached by

e.g.

1) ODA method (1985, 1996) and

2)HC-System (Ku et al, 2009)

Limited number of Field Hydrogeological Test

In fractured and heterogenic rock, laboratory test is not reliable at all

A 3D Model of Hydraulic Conductivity Distribution of Fractured

Rocks Using Packer Test Result and Geotechnical Log

Irwan ISKANDAR, Ari WIBOWO, Lilik Eko WIDODO, Berry CASANOVA, Sudarto NOTOSISWOYO

EARTH RESOURCES EXPLORATION RESEARCH GROUP

FACULTY OF MINING AND PETROLEUM ENGINEERING

INSTITUT TEKNOLOGI BANDUNG, INDONESIA

37Presented in International Symposium on Earth Science and Technology – Fukuoka Japan, 2014

1. Background and Purpose of The Study

The permeability or hydraulic conductivity (K) of fractured rock is very

complex (high degree heterogeneity)

A limited number of field test of hydraulic conductivity (Ktest)

Therefore, for underground excavation, distribution of hydraulic conductivity

(K) is very important for dewatering design

Make a better 3 D distribution of Hydraulic Conductivity in a rock mass

based on limited number of field test (Packer Test /Lugeon Test)

38

2. Materials and Methods

The study area is comprised by Paleozoic rocks

that have been subjected tectonic deformation

Resulting fractured rock mass

Lithology Period Description

Siltstone Permian Fractured Siltstones,

sandstones and

argillaceous dolomite

Carbonaceous

Shale

Permian Fractured Carbonaceous

Shale

Dolomite

(Dolostone)

Carboniferous Fractured dolomite

some parts are massive

Fractures that present in the rock unit act as main

pathway for groundwater flows. 39

Core photograph shows fractured of Carbonaceous Shale


40

Field hydraulic conductivity test using straddle

packer test at 16 zones from 7 boreholes.

Schematic Figure of Straddle Packer Test

Hydraulic Conductivity (K test) is T divided by length

of Zone of Test


HC – System (Ku et al, 2009)

Empirical approaches based on

1. Rock Quality Designation (RQD)

2. Depth Index (DI)

3. Gouge Content Designation (GCD)

4. Lithology Permeability Index (LPI)

41


1) RQD (Rock Quality Designation)

From geotechnical log

‘idea’ : low RQD (poor rock)more permeable (High K)

Note:100 % RQD impermeable?

0

0 100 cm

10 cm 42

2) Depth Index (DI)

‘Idea’ :Many researchers (for example Lee & Farmer, 1993; Singhal &

Gupta, 1999) pointed out that rock mass permeability may

decrease systematically with depth.

LT is the total length of a borehole

Lc is a depth which is located at the middle of a double

packer test interval in the borehole

0 < DI < 1

0

300 m

200 m

220 m

DI =…

The greater DI, the higher permeability


43


3) Gouge Content Designation (GCD)

‘Idea’: If the fractures contain infillings such as gouges, permeability of the fractures

will reduce.

the permeability of clay-rich gouges has extremely low values (Singhal & Gupta,1999).

Rs value is defined as the cumulative length of core pieces longer than 100 mm in

a run

Rs the total length of the core run

RG is the total length of gouge content

The greater GCD will reduce the permeability of the core run.44


4) Lithology Permeability Index (LPI)

Lithology is the individual character of a rock in terms of mineral composition, grain size, texture,

color, and so forth.

45


HC-Index

HC-Index is an empirical method to estimate HC-value (HC),

HC = 1 −𝑅𝑄𝐷

100. 𝐷𝐼 . 1 − 𝐺𝐶𝐷 . (𝐿𝑃𝐼)

HC values at the same zone were plotted in scatter plot with hydraulic

conductivity from packer test at same zone (Ktest).

46

3. Result and Discussion

Hole No Interval Depth (Zone)

(m)

Lithology RQD KTest

(m/s)

02

52-62 Dolostone 15.3 3.2×10-6

63-73 Dolostone 1.9 3.1×10-6

74-84 Dolostone 6.2 2.7×10-6

86-96 Dolostone 24.1 2.6×10-6

0398-108 Carbonaceous Shale 26.1 1.5×10-7

108-118 Dolostone 25.9 1.7×10-6

146

120-130 Siltsone 5.2 3.1×10-6


189-199 Dolostone 20.8 1.2×10-6





25 30-40 Siltsone 10.0 5.2×10-8

67 212-220 Dolostone 39.0 8.2×10-8

Hole No Interval Depth (Zone)

(m)

Lithology RQD KTest

(m/s)

02

52-62 Dolostone 15.3 3.2×10-6

63-73 Dolostone 1.9 3.1×10-6

74-84 Dolostone 6.2 2.7×10-6

86-96 Dolostone 24.1 2.6×10-6


108-118 Dolostone 25.9 1.7×10-6

146

120-130 Siltsone 5.2 3.1×10-6


189-199 Dolostone 20.8 1.2×10-6





25 30-40 Siltsone 10.0 5.2×10-8

67 212-220 Dolostone 39.0 8.2×10-847


Correlation between HC-Index and Hydraulic

Conductivity from Packer Test (KTest)

Coefficient determination in this study (0.6) is

lower than coefficient determination from Ku et al

(2009) result (0.9). It may because of the

transformation of depth in DI need additional

adjustment and not only normalized the length of

total depth into vertical length.

However, the coefficient correlation between

HC values and KTest values (r = 0.774)

indicated the HC values can be used to find

the K value in other zones that there were not

field test data

48


Estimation of hydraulic conductivity based on empirical HC method was conducted for

18.915 geotechnical log zones from 127 holes

Result distribution of hydraulic conductivity estimation

from HC-system49

4. Conclusions

Based on this study it can be concluded as follows:

1. Hydraulic conductivity values in the study area were vary from 10-6 to 10-8 m/s

and not controlled by lithology only.

2. The HC index as an empirical approach to estimate hydraulic conductivity can

be used in this study, but depth index (DI) values need adjustment for incline

holes.

3. 3D spatial distribution of K values and its heterogeneity can be mapped

spatially based on HC index.

50

FUTURE WORKS

51

Applying spatial analysis method e.g. a krigging method

to make a 3D spatial distribution model of the rock

mass not only limited for K at all holes.

North

3D Spatial Distribution Konduktivitas hidraulik (K)

Next Step in Mitigation Modeling or simulation

• Permeability value in each cell / zone (done)

• Interpolation method

• Isotropy or anisotropy is assigned by honor geological structure

• Groundwater flow model

• Discretization (Finite Difference Method (FDM) or Finite Element)

• Grid cell based modeling (block model) “discretization”

• Mining use block model cell size can be adopted (FDM)

Simulating GROUNDWATER INFLOW TO UNDERGROUND MINE

Simple Analytic Solution

r

H0

Q0

Asumsi homogeny nilai K, Head tidak berubahRealistik? Atau ada Pendekatan Lain?

Simplified Groundwater Condition in UG Mine

Zeidel et al, 2010 Modified from Zeidel et al, 2010

K

K

K

K

K

K

K

K

Nilai K (parameter dari hasiluji di lapangan

Simplified Block Model (Discretization)

Modified from Zeidel et al, 2010

Tiap Cell, ada parameter (K, H(t), S)

Dengan memasukkanpersamaan aliran airtanah, dapat dihitung drain inflow(Q) di cells

North

North

3D Spatial Distribution Konduktivitas hidraulik (K)

10 x 10 x 10 meter

Vein/ore zone

Parameter Input In Groundwater Model

•water balance input = output cells

• Input : dari cell di sekitarnya recharge

•Parameter : K, S, Recharge, Lokasi-lokasi water bodies

(pond, danau, sungai, laut)

•Kondisi batas lainnya…..

Pendekatan Block (Cell)

Q (water inflow)

Q (water inflow)

Q (water inflow)

Q (water inflow)

Q (water inflow)

Q (water inflow)

Q = - K (dh/dl)t A

xK

h

x yK

h

y zK

h

zS

h

tx y z s( ) ( ) ( )

Transient (flow)

Intrinsic Geology

Mine plan

Q (water inflow)

Q (water inflow)

Q (water inflow)

Q (water inflow)

Q (water inflow)

Q (water inflow)

5 m

5 m5 m

Akan ada jutaan cells untuk perhitungan di tambang

e.g. bijih (dimensi)2000 m (strike) x 10 m (wide) x 300 m(depth) =…

dan ingat untuk perhitungan air, kita tidakhanya menghitung di cell di daerah kajian!

Pendekatan Block (Cell)

Contoh kasus (latihan sederhana)

• Single, simple vein N2700/450

• Lebar vein : 100 m, lebar shearing zone (hanging dan footwall : 100m, high permeability)

• Zona vein, permeability = 10-6 m/s, shearing zone = 10-5 m/s, host rock 10-7 m/s

• Ada sungai dengan lebar 10m, melintas di atas zona mineralisasi

• Akan diekskavasi selama 2 tahun, selanjutnya paste filling (back filing)

Host Rock

Host Rock

Sheared Zone

Sheared Zone

Vein Body

River

Host Rock

Sheared Zone

Vein Body

Sheared Zone

DRAINS OUT Time [day]

Rates [m^3/day] L/sec

0 0 0185 5045.657 58.39881365 10231.7832 118.4234730 6066.6562 70.21593

1095 0 01460 0 01825 0 0

-20

0

20

40

60

80

100

120

140

0 365 730 1,095 1,460

l/s…

0

20

40

60

80

100

120

140

0 365 730 1,095 1,460

Scenario 1, bukaan tambangselama 2 tahun langsungtanpa stage filling di mine out cells

Scenario 2, bukaan tambangselama 2 tahun dengan filling di mine out cells

Contoh Kasus

Case Study Underground Mine

Mine Plan Design

NN

N

Mining Drain Scenario (Assumption)

• Mining Development assumption finished in two period, always

open during mining activity.

• Mine Production assumption finished in seven period. Closed every

period with filling material, where filling material assumption is

impermeable.

Drain Scenario (Bukaan Ekskavasi)

File Volume (m3)Surface Area

(m2)Accumulatif Volume

Opening (m3)

Dev1 243,342.00 190,504.00 243,342.00

Dev2 215,307.00 177,459.00 458,649.00

Mine1 244,681.00 92,227.00 703,330.00

Mine2 243,566.00 88,920.00 702,215.00

Mine3 246,932.00 109,066.00 705,581.00

Mine4 251,695.00 91,688.00 710,344.00

Mine5 241,731.00 98,695.00 700,380.00

Mine6 231,848.00 91,410.00 690,497.00

Mine7 234,107.00 120,843.00 692,756.00

Mining Drain Scenario (Assumption)

Mine opening

Closed mining

Mine opening

Closed mining

Mining Development

Mine opening

Mine opening

Closed mining

Mine opening

Closed mining

Mine opening

Closed mining

Mine opening

Closed mining

Observation Head (2011) vs Calculation Head (Model) – Steady State Condition

Model Calibration (Head Calibration on Steady State)

Head contour Based On Observation Data (Field Measurements, 2011)

Head contour Based On Model Calculation(Steady State Condition)

Model Calibration (Head Calibration on Steady State)

Graphic of Groundwater Inflow (with sensitivity analysis)

0

10

20

30

40

50

60

70

80

90

100

Dev1 Dev2 Mine1 Mine2 Mine3 Mine4 Mine5 Mine6 Mine7

Q (

Lite

r/Se

con

d)

Change of Groundwater Head and Flow (Plan View)Year: 1, 2, 3, 5,7 and 9

Change of Groundwater Head and Flow (Plan View)Year: 10, 20, 30, and 40

1

3

2

4

Observation Well Location Head vs Time (Observation Well)

760

780

800

820

840

860

880

1 2 3 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26 28 30

Gro

un

dw

ate

r H

ead

(m

)

Year

OBSERVATION 1/AInterpolated OBSERVATION02/AInterpolated

OBSERVATION3/AInterpolated OBSERVATION4/AInterpolated

Resume

• Merit antara data eksplorasi hidrogeologi dan pemodelan, sangat baik untuk mitigasi

hidrogeologi di ekskavasi bawah tanah (Underground Excavation)

• Dengan kondisi geologi sama, menggunakan pemodelan block cell yang disesuaikan

dengan beberapa skenario penambangan akan menghasilkan peak discharge yang

berbeda.

• Rencana penambangan sangat berpengaruh terhadap besar debit air desain pompa

dan energi untuk pompa

• Skenario tambang bisa dikawinkan dengan pemodelan hidrogeologi dengan sistem

cell, block finite difference methods

From now on, let's build as many “scientific” bridges as possible for our better earth

Hatur nuhun

Materi ini dibagikan untuk kepentingan pendidikan dan pelatihan. Mohon tidak digunakan untuk kepentingan komersil ataupun hal lain yang memerlukan izin hak cipta

Documents

Hydrogeological Problems in Underground Excavation ... · Biodata Irwan Iskandar S-1: Teknik Pertambangan (Eksplorasi Tambang) ITB 1997-2002 S-2: Rekayasa Pertambangan (Hidrogeologi)