rehabilitation of the core zone of an earth-fill dam

Technical Note

Rehabilitation of the Core Zone of an Earth-Fill DamGeu-Guwen Yea1; Tae-Hyung Kim, M.ASCE2; Jae-Hong Kim3; and Hong-Yeon Kim4

Abstract: This paper provides a detailed study of remediation work on the core zone of a damaged earth-fill dam. The relevant materialincludes a review of the dam surface survey data, leakage monitoring data, drilling method, grouting material, and drilling and grouting pro-cedure. A compaction grouting method was selected as the remediation technique. In addition, the reduction and prevention of leakage andsettlement were assessed. Compaction grouting was successful for filling voids, closing channels, and compacting the disturbed core soils.The loose or voided zones were properly filled, and the leakagewas reduced after compaction grouting. Verification of the compaction groutingwork was performed by evaluating the grouting pressures and volumes injected internally and by monitoring the dam leakage rate and tracerexternally. All of these factors provide a good indication of changes inside the core of the dam, including reduction or closure of the leakagechannels in the dam core. DOI: 10.1061/(ASCE)CF.1943-5509.0000335. © 2013 American Society of Civil Engineers.

CE Database subject headings: Earth-fill dams; Sinkholes; Grouting; Leakage; Rehabilitation; Case studies.

Author keywords: Earth-fill dam; Core zone; Sinkhole; Compaction grouting; Leakage; Remediation work.

Introduction

Factors affecting damage to a dam vary and include external force(e.g., seismic action), problems related to design or construction,among others. Paul (2004) introduced principal causes and reha-bilitation case history for dams damaged by a devastating earth-quake. The principal causes of dam failure were severe vibration andliquefaction of the subsoil. The rehabilitation of these dams wasaccomplished in two stages. In Stage I, temporary restoration wascarried out tomake the repairable dams safe without major alterationto the earth dam section to enable them to store water during themonsoon. In Stage II, a long-term restoration schemewas carried outthat applied earthquake-resistant design and restoring and upgradingall components of the dams. The paper also presents details of therestoration and rehabilitation procedures adopted. Krinitzsky andHynes (2002) also reported that a large number of water-retainingearthen dams were affected by earthquakes because of the lique-faction of saturated alluvium soil in their foundations. Yadav et al.(2008) reported damage and rehabilitation case histories of damsseverely affected by a massive earthquake. The rehabilitation pro-cedures that were described included the use of clay core and casingmaterial, pitching on the upstream and downstream slopes of thedam embankment, and the use of riprap work to cover longitudinalcracks and graded filter. In another example of a damaged dam, Raul

et al. (2011) reported sinkholes and leakage of an earth-rock dam.From various tests, they found that the causes of these failuremodes were the large variation in the water content during thecompaction of the core, excess hydrostatic pressure, and grain sizesegregation during the placement of the filter material.

In this study, a damaged earth-fill dam is selected as an example.It is a typical modern earth-fill dam with a clay core, filter zone, andsandy gravel shell (Fig. 1). It has a crest length of 407 m and a heightof 55m.The damwas constructed between June 1992 and July 1993.The reservoir was first filled in October 1993, and was full by April1998 (Korea Water Resources Corporation 2000).

Soon after the dam was first filled (on April 22, 1998), the firstsinkhole was found, and on June 26, 1998, the second sinkhole wasdiscovered when the water level was at EL.150.3 m. The third sink-hole was found on October 15, 1998, when the water level was atEL.150.0m(Fig. 2).All three sinkholeswere excavated andbackfilledwith crushed stones, but the repair was not successful, and surfacesettlement continued at those points. The leakage through the damwaspartially monitored through a cutoff wall located downstream of thedam toe. The leakage amount is a function of the water level in thereservoir. The damwas designedwith a leakage of approximately 350m3/day, but the leakage ranged from 1,900 to 2,100 m3/day.

However, based on a review of the documents, photos of damconstruction, and visual inspection, the dam appears to be wellconstructed, which leaves the cause of the sinkholes unexplained.One possible explanation is related to settlement. The settlement ofan earth-fill dam during its initial service stage is inevitable. Becauseof the different stiffness of the core, filter, and shell, the settlementrate is different in different zones. This differential settlement cangenerate small cracks or shear zones in the core. If the core ismade oflow-plasticity soil (lacking self-healing properties) and is dispersive(water easily breaks down the core soil when water flows througha crack), erosion will expand these cracks and cause loss of soil,resulting in voids and then sinkholes. It is also possible that the coresoils may be of a type that form an optimal structure when dry andcollapse when the soil becomes saturated at some future time.

A compaction grouting method was selected as a remediationtechnique for the damaged earth-fill dam. In compaction grouting,a low-mobility grout is injected into the ground using specially sizedand modified hydraulic piston pumps. Compaction grouting has

1Senior Researcher, Construction Research Dept., Sambu ConstructionCo., Ltd., 9-1 Namchang-dong, Jung-gu, Seoul 100-804, Korea. E-mail:[email protected]

2Professor, Dept. of Civil Engineering, Korea Maritime Univ., Busan606-791, Korea (corresponding author). E-mail: [email protected]

3Senior Researcher, Korea Institute ofWater andEnvironment, Jeonmin-dong, Yuseong-gu, Daejeon 305-730, Korea. E-mail: [email protected]

4Researcher, Construction Research Dept., Sambu Construction Co.,Ltd., 9-1Namchang-dong, Jung-gu,Seoul100-804,Korea.E-mail: [email protected]

Note. This manuscript was submitted on August 7, 2011; approved onJanuary 31, 2012; published online on February 2, 2012. Discussion periodopen until January 1, 2014; separate discussions must be submitted forindividual papers. This technical note is part of the Journal of Performanceof Constructed Facilities, Vol. 27, No. 4, August 1, 2013. ©ASCE, ISSN0887-3828/2013/4-485–495/$25.00.

JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES © ASCE / JULY/AUGUST 2013 / 485

J. Perform. Constr. Facil. 2013.27:485-495.

Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

http://dx.doi.org/10.1061/(ASCE)CF.1943-5509.0000335

mailto:[email protected]





been successful in filling voids, closing channels, and compactingdisturbed core soils (Kolymbas 2005; Chun et al. 2006; U.S. ArmyCorps of Engineers 2004; Bruce 1989, 1990). In addition, groutingcan be used for seepage and settlement control and seismic miti-gation (Davidson 1990; Kemp 1974; Rodda and Pardini 1990).

This paper provides a detailed review of the project, including thedrilling method, the grouting material and procedure, a detaileddrilling record of each hole, a detailed grouting record of each hole,an as-built drawing indicating the grouting hole location (along withthe depth, grouting volume, and date), a review of the dam surfacesurvey data, and leakage monitoring data.

Investigation of Dam Core Conditions beforeRemediation Work

The design of the exploration and rehabilitation work was basedon the preliminary exploration, selected construction records, andthe dam survey and monitoring records.

Subsurface Explorations

During the subsurface exploration, five standard penetration test(SPT) holeswere drilled to the bedrock (depth of approximately 50m)

at several stations (Fig. 3). The borehole at Station 10 was washbored because a sinkhole was located. Other stations were rotarydrilled and sampled through a double casing. Because of the risk ofpossible additional damage to the dam core during drilling, the SPTswere only performed between Stations 9 and 12. Other sections ofthe dam were not investigated by drilling holes. The steel pipecasings utilized during the drilling of these exploratory holes were

Fig. 1. Plan view of the dam

Fig. 2. View of sinkhole at Station 10

Fig. 3. Layout of borehole station locations

486 / JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES © ASCE / JULY/AUGUST 2013


Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

pulled from the ground and removed as the holes were compactiongrouted.

At the borehole at Station 10, the N values were approximately0 for depths between 15 and 27m. After standard penetration testingwas completed, the hole could not befilledwith grout slurry, becausehigh grout loss indicated a risk of causing hydrofracturing of thecore. This high loss suggests a very loose zone or erosion zone. Inthis hole, the N values fell within the blow count range of 17–50 atdepths between 30 and 50 m. TheN values show that there are somerelatively loose zones from a depth of 19 to 30 m, with N values inthe range of 7–26 at Stations 9110. At Stations 10110, the N valuesrange from 12 to 33 between 13 and 33m. At Stations 11 and 10, theN value is 9 at a depth of 19 m and 18 at a depth of 14 m, but the softzone is thin. At Stations 12 and 10, the N values are between 13 and19 from 17 to 33 m (Fig. 4). The N value is dependent on the soilparticle sizes, percentage of fines, material density, and the effectiveoverburden stress. Zones where low N values or high permeabilityare encountered are indicative of internal erosion.

Uphole permeability tests were performed as listed in Table 1. Itis difficult to quantitatively evaluate the permeability based on theuphole tests, because the hydrostatic water surface is unknown inthe nonhomogenous core. However, the large differences in the rateat which the water level rises in the boreholes at different depthsindicate approximately two orders of magnitude difference in thepermeability of these zones. The zones in which erosion is suspectedare at depths between 15 and 30 m at Station 10, 20 and 35 m at

Fig. 4. Results of standard penetration tests and seismic survey

Table 1. Results of up-Hole Permeability Tests Performed at Stations 9and 10, 10 and 10, 11 and 10, and 12 and 10

Depth (m)

Stations

9110 9110 11110 12110

18.0–19.5 2:243 1026 —

19.5–21.0 — 4:593 1025 7:673 1025 5:713 1026

21.0–22.5 — — — 1:563 1025

22.5–24.0 — 4:203 1025 — 1:083 1025

24.0–25.5 — — — —

25.5–27.0 — 1:933 1025 — 2:593 1026

27.0–28.5 3:883 1026 — — 1:413 1026

28.5–30.0 — — — 9:153 1026

30.0–31.5 1:423 1026 — — 1:643 1025

31.5–33.0 — — — 2:563 1025

33.0–34.5 1:193 1026 — 2:293 1025 2:543 1025

34.5–36.0 — 3:673 1025 3:033 1025 5:493 1026

36.0–37.5 6:283 1027 — — 6:613 1026

37.5–39.0 — 1:123 1026 2:293 1026 7:333 1026

39.0–40.5 5:883 1027 — 1:013 1025 5:733 1027

40.5–42.0 — — 2:083 1026 9:783 1026

42.0–43.5 6:473 1027 7:433 1025 — 6:613 1026

45.0–46.5 2:333 1026 — — 9:913 1027

46.5–48.0 — — — —

48.0–49.5 3:933 1026 — — —



Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

Stations 10 and 10, and 31.5 and 40.5m at Stations 12 and 10, wherethe permeability is high and the SPT N values are low.

Dam Construction and Operation Records

The results of the original sieve analysis and tests during construc-tion, from June 18, 1992, to December 12, 1992, show that a total of42 tests were conducted. All of the core material was obtainedfrom residual soils in the reservoir area. In all of these tests, 100%of the core soils passed through a 38.1-mm sieve, approximately99–100% passed through a 19.05-mm sieve, 95% passed througha 4.75-mm sieve (#4), and 56–32% passed through a 0.075-mmsieve (#200), with the average sample passing approximately 50%.

Detailed laboratory tests were performed on samples obtainedfrom the borrowareas. The results presented inTable 2 show a liquidlimit in the range of 26.6–34.1%, a plastic limit in the range of 6.6–13.7%, and a plasticity index in the range of 6.6–13.7%, with ap-proximately 42.0–60.2% of the material passing the Number 200sieve. The unconsolidated undrained (UU) tests on these samplesindicated cohesion in the range of 90–135 kPa and a friction angle inthe range of 18.0–21.0�. The Unified Soil Classification Systemindicates that the samples were of the clayey sand (SC) and silty clay(CL/ML) types. Grain size tests of the core material during con-struction indicated that 25–52% of the material passed the Number200 sieve, with approximately half silt and half clay particle sizes.The permeability tests indicated a permeability in the range be-tween 9:283 1027 and 6:583 1026 cm=s.

Based on a review of the documents, photos of dam construc-tion, and visual inspection, the dam appears to be well constructed.From the outside, it has a very high quality stone facing, which is rareamong earth-filled dams. The dam crest and surface are straight andwell laid out. The pictures taken during construction show the damcorematerial being carefully placed and the use of a sheep’s foot rollerfor compaction. The core trench appears to be excavated to soundrock, dental concrete was used to smooth transitions, and consoli-dation and curtain cement grouting were performed. Higher grouttakes occurred in the bedrock below some of the sinkhole areas.

Compaction Grouting

Compaction grouting uses the injection of low-mobility grout intothe ground using specially sized and modified hydraulic pistonpumps. The grout pump needs to be capable of pumping the low-mobility grout (similar to the core material) at a consistently slowrate, during which the injection pressures vary from low to high.Slow injection is necessary to minimize the build-up of pore pres-sure in the surrounding soil, because pressure can substantially af-fect soft soils (Yang and Zou 2009). A properly designed grout mix

provides a lowmobility compaction grout with high internal frictionand cohesion. These properties can prevent hydrofracture of the damcore and the uncontrolled flow of slurry-type grouts. This stabilitycan prevent the migration of grout to undesirable areas, such as thefilter zone of the dam, or uncontrolled heave of the crest or slope ofthe dam. The surrounding soil can be densified by compressivestresses developed during the grout bulb growth. Control is critical tocompaction grouting; the right amount of low-mobility grout mustbe pumped to the right location at the right rate. Site engineersexamined the samples obtained from the sampling holes to de-termine any damaged zones. Then, they adjusted the groutingpressure, flow rate, and volume to perform the best controlledgrouting at a given hole or area.

The compaction grouting process was monitored by real-timecomputerized data acquisition systems and was displayed for useby the field team to provide the best possible control of the groutingprocess. Each system consists of a desktop computer, two NationalInstruments PCI-type data acquisition boards, a transducer powersource, a connection box, transducers, and sophisticated softwareworking in the Microsoft Windows environment. This systemrecorded the grouting depth, grout pressure, grout pumping strokeand volume, and the measurements of real-time piezometers andtiltmeters. All of the data were stored on a hard disk. All of thechannels of the data acquisition boards sampled the input signalevery three-hundredths of a second, which results in hundreds ofreadings per pump stroke. Special hardware and software wereadopted to reduce the signal noise. All of the sensors in the systemwere properly shielded and grounded.

Dam Exploration and Remediation

The main objectives of exploration and rehabilitation were theidentification and immediate backfilling of loose zones in the areasof the existing sinkholes at Stations 10 and 12. The dry drillingmethod for the installation of the grout pipe and the use of low-mobility compaction grout are the safest dam repair techniques. Ap-proximately 80 instrumentation, sampling, and compaction groutingholes were installed between Stations 9 and 13, covering a crestdistance of 80 m.

The drilling and grouting programs were performed under thefollowing parameters and conditions:• Fluid or air were not introduced into the dam, thus eliminating the

possibility of hydrofracture during drilling;• Periodic continuous or SPT samples were obtained to better

evaluate the core and to better identify erosion zones;• Loosened zoneswerefilledwith controlled compaction grouting;• Compaction grout composed of similar core soils was used to

help maintain uniform core permeability; and• The work was performed safely.

Four exploration-grouting holes were installed by the sonicmethod, and six were installed by the hollow stem auger method.This type of sampling and testing provides the most informationabout the internal condition of the core of the dam. Additionally,before the grouting work started, the dam was instrumented withpiezometers, surface tiltmeters, settlement monitor points, and sur-vey points on the dam crest and slope surfaces.

Selection of Compaction Grout Soil

The purpose of the grouting program is to return the damagedcore zones to a state that is as similar as possible to their originalstate. To do this, the compaction grout soil should have a gradat-ion similar to that of the core material. In this way, the

Table 2. Results of Laboratory Tests of Core Soils

Description D-1 area D-2 area D-3 area

Water content (percentage) 22.3 20.0 18.4Liquid limit (percentage) 34.1 26.6 26.8Plasticity index (percentage) 13.7 7.5 6.6Number 4 sieve (percentage) 82.3 93.0 73.0Number 200 sieve (percentage) 60.2 44.5 42.0Maximum dry density (kN/m3) 15.5 16.8 16.5Optimum moisture content(percentage)

20.0 16.0 17.8

Permeability coefficient (cm/s) 73 1027 3:63 1027 1:213 1026

Cohesion (kPa) 90 80 135Friction angle (degrees) 18 21 19



Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

permeability of the grout column should be similar to that of theoriginal core.

Laboratory tests were conducted on the soil samples obtainedfrom one of the original borrow areas, D-2. This area is locatedapproximately 2 km from the upstream side of the dam. Soil SamplesD2-1 and D2-2 were collected from two different locations in thearea. The soil in Sample D2-2 has a greater content of fines thanSample D2-1 (Fig. 5).

Sieve analysis, hydrometer analysis, liquid limit, plastic limit,specific gravity, and soil natural water content were tested in thelaboratory. Each soil samplewas tested twice. TheD2-1material hasan average liquid limit of 31%, an average plastic limit of 19%, anda plastic index of 12. The D2-2 material has an average liquid limitof 32%, an average plastic limit of 18%, and a plastic index of 14.The natural water contents are 18.8 and 20.6% for D2-1 and D2-2,respectively. The specific gravities are 2.66 and 2.67 for D2-1 andD2-2, respectively. The specific gravity of Sample D-2, the materialused in the original dam construction, was 2.64.

The soil samples obtained from Pit D-2 have soil characteristicssimilar to those of the core material. After reviewing the soil labo-ratory test results, these soils were used for compaction grouting.Approximately 1,000 m3 of soil were excavated from the borrowarea and transported to the soil processing facility downstream ofthe dam. In the soil processing facility, the soil was dried andscreened through a 0.5-inch sieve for moisture control and uni-formity, then stored in a warehouse.

As a routine quality control procedure, the particle-size distri-bution of the grouting material was periodically checked by sieveand hydrometer tests. The samples tested were obtained from thegrouting material on the dam. The grouting materials (denoted D2-1and D2-2 in Fig. 5) are well within the range of the core materialdesign limits, and they are similar to D-2 soil (Fig. 5). The blackcurves in Fig. 5 are the dam core soil design upper limit, lower limit,and center line.

Polymer fibers were added to the grout to further reduce thepossibility of hydrofracture. The fibers increase the internal shearstrength of the low-mobility grout, preventing the fluid type groutfrom splitting. The splitting of fluid type grout can cause the un-controlled hydrofracture propagations in soils. In addition, the fibersmove with the groutingmaterial and act as a tracer indicator, helpingto distinguish grout from the core material.

Field Findings and Volume and Pressure Criteria forCompaction Grouting

During drilling of the compaction grouting holes in the dam core, weencountered soft saturated zones below the water table that are theprobable damaged areas producing the leakage. Within these loose,soft damaged zones, the effective soil stress appeared to be verylow. Under such conditions, a large volume of grout may not gainstrength through consolidation under such low grouting pressures;thus, cement was added to gain strength close to the undamaged corematerial. To achieve the approximate strength of the grouting soilinjected into the soft loose zone (mud zone), 5% cement (by weight)was added into the grout in the 0.4m3/m zone. In the 0.02 m3/m zoneand any tighter zones, no cement was added because the groutmaterial could be consolidated and gain strength over time under therelatively high grouting pressure.

In addition, during the drilling, granular resistance was en-countered in several of the drill holes. This zone was frequentlyencountered at a depth of approximately 40.9 m. In the continuouslysampled hole numbered 12-2D, from a depth of 40.9 to 41.8 m,a sandy gravel layer was found. The gravel in this layer was as largeas 10.2 cm and appeared to be of alluvial nature, rather thanweathered rock. Additionally, in numerous solid stem auger holes,the driller felt that he penetrated through a granular zone at thisapproximate depth.

The key to effective compaction grouting work is control. Fig. 6provides a guideline for compaction grouting in the dam core,including the location, depth, grout volume limit, and grout tippressure as a function of depth. This figure gives refined criteriafor the grout volume and tip pressure.

The following parameters were monitored to effectively controlthe compaction grouting program:• Where the grout tip pressure was less than that shown in Fig. 6,

0.113 m3 of grout/0.3 m was injected;• Where the grout tip pressure was within the two lines shown in

Fig. 6, 0.057 m3 of grout/0.3 m was injected;• Where the grout tip pressurewas greater than that shown in Fig. 6,

injection was terminated at that stage and pulled to the next stage;• Grout slump was controlled to less than 5.08 cm;• Grout pumping rate was controlled to less than or equal to 0.028

m3/min;• Surface tiltmeters on the upstream and downstream slopes were

monitored;• Piezometers were monitored for significant pore-water pressure

changes;• Optical survey was monitored; and• Seepage flow was monitored.

Dam Instrumentation and Survey

In addition to the existing instrumentation inside the dam, piezom-eter sets were installed at Stations 10 and 12. At each station, thereare three piezometers at three different elevations. All of thesepiezometers are semiconductor-type pressure transducers with apressure range from vacuum to 2.07 MPa. They have 4.14 MPa ofproof pressure capacity, which is greater than any possible pore-water pressure surge as a result of compaction grouting.

A total of four tiltmeters was installed on the dam slope surfaceupstream and downstream, at Stations 10 and 12, respectively.These high sensitivity tiltmeters have a full range of 60.5� mea-surement, and a sensitivity of 0.0001�. If any rotation of the damslope occurred in the area of the tiltmeters, it would be detected bythe tiltmeters and grouting data acquisition system. During the entirecompaction grouting working period, there was no significant

Fig. 5.Comparison of soils tested (D-2-1 and D-2-2) with original damcore Soil D-2 and D-3



Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

movement of the tiltmeters. Minor movements as a result of tem-perature changes, moisture changes, and wind on the wood beamswere noted because of the high sensitivity of the tiltmeters.

To monitor the dam by optical survey methods during grouting,six original locations and 45 new locations were laid out to provideadequate coverage. They were located on both the upstream anddownstream slopes of the dam from Stations 8 to 13, near thecompaction grouting areas. A survey of these points was conductedonce a day during the 24-h/day grouting program, and every 2 daysduring the 12-h/day grouting programs.

Phase IA: Exploratory-Compaction Groutingaround Sinkholes

In Phase IA, two piezometer holes and two exploration/compactiongrouting holes were drilled at Stations 10 and 12. All of the holes inPhase IAwere drilled and continuously sampled by the sonic drivingtechnique.

Phase IA was the testing stage, in which the driving and groutingequipment were calibrated in the specific field environment. Thesonic driving penetration rate was investigated, the soil was con-tinuously sampled, and the dam core response to compactiongrouting was investigated. In Phase IA, Locations 10-2D and 12-2Dwere drilled, sampled, and grouted. These sites were located near thepiezometers and inclinometers, and therefore the soil displacementand pore-water pressure reaction could be obtained from the be-ginning of the project. All four exploratory grout holes were drilledvertically down to bedrock. The two piezometer holes and Holes10-2D and 12-2D were drilled with the Simco/RSI rig, as shown inFig. 7. Numerous difficulties were encountered when drilling tobedrock with this rig because of the high adhesion and damping ofthe unsaturated clay, unexpected rounded rock in the dam core, andmechanical problems with the drilling equipment. Although theSimco/RSI rig was able to reach the bedrock, it continually brokedown because it was pushed beyond its mechanical limits. To avoidthe use of drilling fluids, which would fracture the core, augerdrilling was successfully tested in the dam core and adopted toperform the necessary drilling. All core samples were provided forlaboratory tests and storage. These samples were reviewed andinspected to identify representative samples and samples from zonesthat could be problematic. This testing was completed to further theunderstanding of the nature of the problem within the dam core.

Initial trial drilling started at Stations 12-1-A and 10-1-A onMay18andMay 19, 2000, respectively. The objectives of the trial drillingwere to test the sonic driving system and develop an initial un-derstanding of the dam core material. Sonic drilling proved to be

Fig. 6. Pressure/volume criteria for the dam core compaction grouting

Fig. 7. Simco/RSI sonic drill penetrating through dam surface and coresoils at 12-2D



Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

very difficult because of the sticky behavior of the cohesive soils andoccasional encountering of large-diameter cobbles.

The sonic drilling resistance in the core was not uniform. Somelayers appeared to be soft, and others appeared to be very hard. Thedriller indicated that rocks were encountered, as seen in the boringlogs. The core material obtained from the sampler is basically re-sidual soil, which is composed of clayey sand (SC) with gravels.Some of the gravel is partially weathered rock that is mixed withthe residual soil. In the recovered core, river run large gravels (veryhard)5.08–7.62 cm in sizewere found. It is possible that the river rungravels encountered were mixed into the core material from the filterand/or shell layers during dam construction. The Simco/RSI rig alsoencountered drilling difficulties during work on the piezometerholes and Holes 10-2D and 12-2D because of the unexpected largegravel layer and the high adhesion and damping from the unsaturatedclay core material.

The grouting in Phase IA was performed at a conservative rate toprovide more time to customize the driving and grouting procedureand the criteria for the soil conditions encountered in the dam. Thepumping rates for compaction grout injection were maintained be-tween 0.014 and 0.028 m3/min. The slump of the grout was in therange of 2.54–5.08 cm. The first two grouting holes, 10-1-A and 12-1-A used a volume limit of 0.19 m3/m to ensure safe compactiongrouting at the start.

Extensive line loss tests were conducted in Phase IA. These testsindicated that pumping the grout material produced relatively highline loss, that is, very high adhesion or friction between the groutand the steel casing. The line loss rate is also very sensitive to thegrout material slump value (water content). The horizontal line lossrate was found to be in the range of 0.045–0.18 MPa/m, corre-sponding to grout slump values of 5.08–0.64 cm. The estimatedgrout tip pressure was calculated from the difference of the measuredgrout head pressure and the vertical downhole grout casing lengthmultiplied by the line loss and an allowance for the weight of thecolumn of grout (0.023 MPa/m of vertical height). Because there isalways some uncertainty in the line loss, estimation of the grouting tippressure is a challenging task. With two separate pressure transducers(PT1 and PT2), a real-time horizontal line loss was calculated from thepump to the head, which was then correlated to a vertical line loss.

Phase IB: Sinkhole Grouting at Stations 10 and 12

In Phase IB, approximately 18 exploration and grouting locationswere installed around the sinkhole that developed at Station 10, and22 exploration and grouting locations were installed around thesinkhole that occurred at Station 12. Two rows of holes were bat-tered (angled) 10� from the vertical to more fully cover the core. Allof the grout holes were installed to bedrock or refusal.

Fig. 8. Grouting logs of 9-3-B and 12-6-B



Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

Concrete color was used as a coding system in most of the holes.The nonsoluble color facilitated the location of the grouting materialand investigation and determination of the grout communicationbetween certain holes.

To further concentrate the efforts in the estimated sinkholezones, the grout holes were moved toward the centerline of the dam,because lower pressures developed toward the area near the center ofthe dam, rather than in the battered holes covering the downstreamportion of the core. These holes were compaction grouted from thebottom to a depth of 4.572m below the dam crest and then backfilledwith compaction grout to the surface.

All of the grouting holes in Phase IB were drilled by auger (solidand hollow stem). A comparison of the grouting logs suggests thatthere were no identifiable differences between compaction groutingthrough auger-drilled holes and sonic-driven holes.

Phase II: Exploratory-Compaction Grouting betweenStations 9 and 13

During Phase II, 18 exploration and grouting locations were in-stalled along the dam centerline, within the 80-m treatment zone. Allof the holeswere drilled vertically by a solid stem auger and a hollowstem auger. All of the hollow stem augured holes were continuously

sampled, and in some, SPT sampling and testing were performed inaddition to the continuous sampling.

At Locations 9-3-B and 12-6-B, loose zones, which have near-zero calculated grout pressure at the grout pipe tip and large grouttakes (Fig. 8), were encountered. These two holes are outside of thesinkholes at Stations 10 and 12. These data appear to indicate thatnew leakage channels and/or sinkholes were developing in theseareas. The size of the loose zones in these areas seems smaller thanthose at Stations 10 and 12, because the adjacent grout/explorationholes did not encounter loose zones. To remediate these smallerloose or voided zones, an additional secondary grout holewas placednear each. The pressure responses obtained from these holes indi-cate that the loose or voided zone had been closed.

Phase III: Final Compaction Grouting

After completion of Phases IA, IB, and II, all of the collected in-formation was reviewed to finalize the work within the 80-m sectionin Phase III.

During the review of the grouting performed in the past phases,we observed that the estimated grouting tip pressures increasedcomparedwith the values for the adjacent loose holes. An example is

Fig. 9. Comparison of grouting pressure and volume between 10-1-C and 10-2-C



Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

plotted in Fig. 9. Hole 10-1-C (grouted July 19, 2000) indicated theexistence of loose zones or possible voids in the depth ranges from21.34 to 30.48 and 36.58 to 39.6 2 m. The adjacent Hole 10-2-C,which was grouted later (July 29, 2000), exhibited an increase of thegrouting pressure and a reduction of the injected volume, in com-parison with the adjacent holes, indicating that the compactiongrouting material has already filled the void zone.

Following a review of the grout takes and pressures of the holesgrouted in Phases I and II, we determined that five secondarygrouting holes were required. The placement of the secondary holesconcentrated the efforts in the estimated sinkhole throat or chimney,where the grout takes were highest and pressures lowest.

The following grouting closure criteria were used to determinethe need for additional grout holes. These criteria are illustrated, andthe compaction grouting effects in the ground are better explained inFig. 9. The broken curve (lower solid curve to the right of the graph)represents the grouting closure pressure. If the calculated groutpressure at the tip of the injection pipe exceeds this curve (to the rightside), this signifies that the void and/or loose zones are filled. AtLocation 10-2-C, the closure pressure criterion is already satisfied.A similar method was used to determine closure of the secondarycompaction grouting locations at Station 12.

The communication of grout between holes is summarized inTable 3. This record allowed the determination of weak zones fromthe communication of color-coded grout material between groutingholes. To verify the loose zones detected by the communication ofcolored grout, an additional five compaction grouting operationswereperformed in these areas. These holes were drilled vertically to thebedrock by solid auger. The grout material and the grout pressure/volume criteria were the same as the other grouting holes in Phase III.

Verification of Compaction Grouting

Verification of the compaction grouting work completed in Phases I,II, and III can be evaluated internally by considering the grouting

pressures and volumes injected and externally in twoways. Externalverification is achieved by monitoring the dam leakage rate andobservation of the tracer. Both of these methods provide a good in-dication of changes inside the core of the dam and indicate whetherthe leakage channels in the dam core were reduced or closed.

Previously, engineers have been concerned that it is very difficultto predict the change of the seepage rate and turbidity of waterwithout knowing the conditions of the damage zones. If the leakagewas caused by channels forming in highly permeable and/or loosesoils at Stations 10 and 12, compaction grouting may have effec-tively reduced the leakage rate by densifying the surrounding soilsand reducing their permeability. If the core material was designed orconstructed improperly, the compaction grouting would not reducethe seepage rate significantly, because the grout does not permeatethe core soils, and the cross-sectional area of the grout columns issmall in proportion to the dam core cross section.

The increase of the compaction grouting tip pressure in thesecondary holes provides a good verification of the effectiveness ofgrouting for the filling of voids and compacting of loose zones. If thegrout tip pressure exceeds the closure pressure, the void or loosezone in the dam core should be properly filled.

Fig. 10 displays the estimated tip pressure and injected volume in apostprocessedmanner, with respect to the depth along the alignment ofthe 80-m treatment area. These plots also include the date grouted andtotal amount of grout placed in each hole. This plot was a useful tool indetermining the loose damaged areas of the core and the necessity andlocation of secondary grouting holes.

Fig. 10 compares the grouting tip pressure of the primary Hole10-1-C with the nearby secondary Hole 10-1-E. Hole 10-1-Cexhibits very low tip pressures, indicating a void or extremely loosecondition. Hole 10-1-E is a secondary hole in that immediate area.The pressures of 10-1-E are substantially higher, and they are wellabove those required for the closure criteria.

The leakage monitoring time histories plotted in Fig. 11 indicatethat the compaction grouting programs in Phases I, II, and III have

Table 3. Compaction Grout Communication between Holes

Item Grout from Travel to Depth (m)/color of grout Core condition Response

1 11-5A tight hole 11-5B 5.49/black Normal, near the intersection of verticaland 10� hole

None

2 12-2A loose hole 12-2B 7.62–10.67/green Normal, at the intersection of verticaland 10� hole

Use 12-1-F as second grout for closureverification

3 10-2A loose hole 10-1B 12.19–15.24/green Small amount recovery Use 10-1-F as second grout for closureverification

4 10-2A loose hole 10-2B 9.14/green Normal, at the intersection of verticaland 10� hole

Use 10-1-F for closure verification,10-3A only injected very small volume,impossible travel to 10-2B

5 9-6A loose hole 9-6B 6.10–7.62, 14.94, and24.38–30.48/red

Very loose zone at 18.29 and 30.48 m,normal at 3.05–7.62 m

Added second grouting hole (9-6F)

6 9-4 tight hole 9-3 19.81 and 21.34–24.38/red Grout travel along the dam center line,core damaged

Added second grouting hole (9-3.5B)

7 12-6 loose hole 12-7 18.29–30.48/black Grout travel along the dam center line,core damaged

Added second grouting hole (12-6.5B)

8 10-1D loose hole 10-1Cloose hole

12.19–21.34/green Very loose zone at 12.19–21.34 m, coredamaged

Use second grouting holes (9-7G,10-1E, and 10-1F), add 9-7F and9-6G to fill the loose zone

9 10-1D loose hole,unlikely from 10-3D

10-2Ctight hole

18.29–21.34/green Very loose zone at 18.29–21.34 m,core damaged

Use second grouting holes (9-7G and10-1E) to fill the loose zone

10 9-6D tight hole 9-6C 9.14/red Normal, near the intersection of verticaland 10� hole

None

11 11-4B 11-5C 13.72/ found darkmaterial, no fiber

Unlikely grout communication None



Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

Fig. 10. Pressure and volume comparison of grouting between the primary and secondary holes at Locations 10-1-C and 10-1-E

Fig. 11. Leakage reduction at the dam during the compaction grouting program



Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

reduced the leakage rate by 84%. The leakage rate on August 16,2000, was 110 m3/d (or t/day) at a reservoir level of 136.9 m. Beforethe remediation work, on February 17, the leakage rate was 672CMD at the same reservoir level.

Conclusions

Compaction grouting has been successfully applied to fill voids,close channels, and compact the disturbed core soils of a damagedearth-fill dam. From the work performed, the following conclusionscan be drawn.

The loose or voided zones have been properly filled, and theleakage has been reduced by the use of compaction grouting. Withadditional research into the nature of the problem with the core (onekey source would be the study and testing of continuous samples re-moved from the dam), a long-term plan can and should be developed.

Although the condition of the dam is partially understood and thecause of failure may never be fully determined, the authors would becapable of developing cost-effective long-term solutions for thedamaged dam.

Long-term monitoring should be performed with regard to waterflows, pore pressures, and periodic visual inspections of the dam.In addition, periodic optical survey of the points that were setupduring grouting of the dam should be performed to detect anymovement.

References

Bruce, D. A. (1989). “Contemporary practice in geotechnical drillingand grouting.” Proc., 1st Canadian Int. Grouting Seminar, USDOE,Washington, DC.

Bruce, D. A. (1990). “The practice and potential of grouting in major damrehabilitation.”ASCEAnnualCivilEng.Convention,ASCE,Reston,VA,41.

Chun, B. S., Lee, Y. J., and Chung, H. I. (2006). “Effectiveness of leakagecontrol after application of permeation grouting to earth fill dam.”KSCEJ. Civil Eng., 10(6), 405–414.

Davidson, R. R. (1990). “Rehabilitation of dam foundations.” Report,Woodward Clyde Consultants, Denver.

Kemp, E. B. (1974). “Emergency grouting of old river low sill structure.”Proc., ASCE Conf., ASCE, Reston, VA, 343–370.

Kolymbas, D. (2005). “Tunnelling and tunnel mechanics, Part I: Groutingand freezing.” Chapter 6, Grouting and freezing, Springer-Verlag,Berlin, 159–170.

Korea Water Resources Corporation. (2000). Precise safety diagnosis ofGyeongbuk Cheongdo-gun.” Report, Unmun Dam.

Krinitzsky, E. L., and Hynes, M. E. (2002). “The Bhuj, India, Earthquake:Lessons learned for earthquake safety of dams on alluvium.” Eng. Geol.,66(3–4), 163–196.

Paul, D. K. (2004). “Assessment of damage and rehabilitation of small andmedium earth dams.”Proc., 13thWorldConf. Earthq. Eng.,MiraDigitalPublishing, St. Louis.

Raul, F. B., Martin, R. R., and Emir, J. M. (2011). “Internal erosionand rehabilitation of an earth-rock dam.” J. Geotech. Geoenviron. Eng.,137(2), 150–160.

Rodda, K.V., and Pardini, R. J. (1990). “Remedial construction at Austriandam following the Loma Prieta Earthquake.” USCOLD Newsletter,July(92), 21–24.

U.S. Army Corps of Engineers. (2004). “General design and constructionconsiderations for earth and rock-fill dams.” Rep. EM1110-2-2300,Washington, DC.

Yadav, S. M., Mishra, R., and Samtani, B. K. (2008). “Rehabilitation ofearthquake affected Tapar dam, Gujarat, India.” Proc., 12th IACMAG,Curran Associates, Red Hook, NY, 4744–4747.

Yang, X.-L., and Zou, J.-F. (2009). “Estimation of compaction groutingpressure in strain softening soils.” J.Central SouthUniv. Technol., 16(4),653–657.



Dow

nloa

ded

from

asc

elib

rary

.org

by

DA

LH

OU

SIE

UN

IVE

RSI

TY

on

11/0

9/14

. Cop

yrig

ht A

SCE

. For

per

sona

l use

onl

y; a

ll ri

ghts

res

erve

d.

http://dx.doi.org/10.1007/BF02823979

http://dx.doi.org/10.1007/BF02823979

http://dx.doi.org/10.1016/S0013-7952(02)00049-2

http://dx.doi.org/10.1016/S0013-7952(02)00049-2

http://dx.doi.org/10.1007/s11771-009-0108-1

http://dx.doi.org/10.1007/s11771-009-0108-1

rehabilitation of the core zone of an earth-fill dam

Documents