Structural SurveyEmerald Article: Implications of rising groundwater level on structural integrity of underground structures - investigations and retrofit of a large building complexMuhammad Tariq Amin Chaudhary

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To cite this document: Muhammad Tariq Amin Chaudhary, (2012),"Implications of rising groundwater level on structural integrity of underground structures - investigations and retrofit of a large building complex", Structural Survey, Vol. 30 Iss: 2 pp. 111 - 129

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Implications of risinggroundwater level on structural

integrity of undergroundstructures – investigations

and retrofit of a largebuilding complex

Muhammad Tariq Amin ChaudharyProfessional Engineer, Windsor, Ontario, Canada

Abstract

Purpose – Groundwater levels (GWL) are rising in many cities in the world. The purpose of this studyis to present the multi-faceted approach adopted for examining the impact of a 3 m rise in GWL on thedurability, stability and strength of the structural components of a building complex with 40,000 m2

basement. It also reports on the retrofit measures adopted to remedy the situation.Design/methodology/approach – The overall stability of the building complex was examined forthe revised loading conditions as well as the need to strengthen the structurally deficient componentsto satisfy owner’s requirement of a dry and operational basement without the dewatering operation.Structural conditions of the basement walls and a slab of the building complex were assessed based oncode guidelines, visual observations, site investigations, analytical finite element model (FEM) studiesand sound engineering judgement.Findings – About 25 percent of the existing basement slab was found to be structrally deficient toresist the applied hydrostatic load. A number of articulation and construction details were also foundto be inadequate. Various options for retrofit for the deficient structural components and articulationdetails were examined and design details were presented for a cost-effective solution.Research limitations/implications – The presented methodology is general and can be adoptedfor similar situations. However, the presented solutions and conclusions are specific to the problempresented herein and modifications will be required for adoption to other situations.Practical implications – Practising engineers are made aware of the problem of rising GWL forunderground structures. Practical information is presented for practising engineers to solve theproblem of water leakage in a large basement.Originality/value – This paper presents an integrated approach for addressing the structuralimplications of rising groundwater level in an operational basement of a large building complex.

Keywords Rising groundwater level, Structural retrofit, Reinforced concrete, Basement,FEM analysis, Articulation details, Groundwater, Structural engineering, Finite element analysis

Paper type Technical paper

1. IntroductionRise in groundwater levels (GWL) have been reported in many countries around theglobe (Wilkinson and Brassington, 1991). GWL rise is mainly attributed to fourphenomena: first, reduced abstraction of groundwater and recovery of historical GWL.This is the case for London (Blower, 1987), Birmingham (Knipe et al., 1993), Germany(Kreibich and Thieken, 2008), Paris (Bergeron et al., 1983); second, artificial rechargeof the aquifer due to infiltration of imported water for domestic and industrialconsumption as reported for Las Vegas and San Jose (Dean and Sholley, 2006), Riyadh

The current issue and full text archive of this journal is available atwww.emeraldinsight.com/0263-080X.htm

Structural SurveyVol. 30 No. 2, 2012

pp. 111-129r Emerald Group Publishing Limited

0263-080XDOI 10.1108/02630801211228725

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(Rushton and Al-Othman, 1993), Kuwait (Al-Rashed and Sherif, 2001); third, rise inseawater level and corresponding increase in GWL as in Lagos (Oyedele et al., 2009),Osaka (Yasuhara et al., 2007), coastal areas of Bangladesh (Singh et al., 2000); andfourth, seasonal variations in GWL due to rainwater infiltration after heavy downpour/flooding. Structures that are founded in a strata, which at the time of constructionwere above the GWL but later are subjected to rising GWL, face a number of structuraland functional challenges (Wilkinson, 1985; Johnson, 1993; Yasuhara et al., 2003),in addition to financial and economical cost (Kreibich and Thieken, 2008).

Most of the time, the problem of rising groundwater and its implications forunderground structures (basements, tunnels, underground utilities, etc.) becomeapparent only after the tell tale signs of GWL rise in the form of water leakage anddeformations are visible. However, in the case of new British Library in London, theproblem was anticipated and design measures were undertaken to provide additionalcapacity in the pile foundations and the basement walls (Simpson, 1983). Examplesof structural and functional impairment due to rise in GWL after construction iscompleted can be found in the literature. Remedial measures have includedstabilization of underground subway stations with ground anchors and addition ofcounterweight in Tokyo (Kusumi, 2005), cut-off wall around the Kansai InternationalAirport (Suzuki and Okuda, 2008), pressure resin grouting behind leaking tunnels inHong Kong and Singapore and New Airport in Dubai (Pell and McDonald, 2001),installation of permanent dewatering systems for Santa Clara University Library andSan Jose City Hall buildings (Dean and Sholley, 2006), and horizontal and verticaldrains in a city district (about 1 km2 in area) in Kuwait city to lower the GWL(Al-Rashed and Sherif, 2001).

Kreibich and Thieken (2008) have pointed out that GWL rise is currently not treatedas a significant natural hazard and therefore attention to the problem has not receivedthe desired focus. However, with the ever increasing population and need to builddeeper underground structures and utilities, it is anticipated that this problem willreceive more attention in the future as the economical cost related to the correctivemeasure will escalate.

This paper presents the approach adopted for structural evaluation and retrofit ofstructural components of a 40,000 m2 basement of a building complex subjected to anunanticipated hydrostatic load due to rise in GWL. The GWL rose by more than 3 mafter the building construction was finished and a part of the building complex wasoccupied and operational for about one and a half year. The most probable reason for thisphenomenon was attributed to the completion of intensive construction activity in thevicinity of the project area that also included dewatering operations for construction ofdeeper basements in other building projects. Cessation of the dewatering operationsseemed to have resulted in a rebound of the GWL that affected the basement of thebuilding complex. The owner installed a temporary dewatering system consisting of fivewell points around the perimeter of the building to ensure functioning of the basement asparking and to safeguard the safety and integrity of the structural components, whichwere subjected to additional load from the hydrostatic water head.

Operating and maintaining the dewatering system was a large expense thatthe owner was unwilling to incur for the useful life of the building complex.This investigation was undertaken to:

(1) investigate the impact of groundwater on the quality, strength and durabilityparameters of the concrete components in contact with the groundwater;

112

SS30,2

(2) assess the structural capacity and safety of the structural componentssubjected to hydrostatic loading;

(3) ascertain the extent and location of structural components that will requirestrengthening to withstand the applied hydrostatic load;

(4) propose correctional retrofit measures for the deficient structural components;and

(5) examine existing articulation and jointing details and design remedialmeasures for the revised loading conditions.

The subsequent sections of the paper provide a description of the structural system ofthe building complex and a summary of the visual observations of the damage causedby the raised GWL as well as discussing various components of the investigationas outlined above. Conclusions and recommendations of these investigations arepresented in the last section.

2. Narrative of the structural systemThe building complex comprises of six multi-storey buildings and an iconic tower withcommon ground-level podium and an underground parking facility. Figure 1 providesthe schematic plan view of the building complex. The building complex was built intwo phases. Phase I comprised of the central iconic tower and towers 3 and 4. Whereas,Phase II consisted of four towers (1, 2, 5, 6) built symmetrically around the Phase Iconstruction. The building towers vary in height between seven and nine floors.

The building structural system was comprised of reinforced concrete floorslabs and columns with a series of shear walls providing lateral load resistance.

160

m

250 m

Icon tower

Ramp Ramp

Tow

er 4

Tow

er 3

Tow

er 6

Tow

er 5

Tow

er 1

Tow

er 2

Phase II Phase IIPhase I

Phase I

Expansion joint Elevator pit

Fig

ures

12/

13

Figure11b

VehicularRamp (type)

14b

Figures9,10

Figure4c (type)

Figure4d

Figure Figure4a

Expansion joint

Basement wall

Basement wall

Figure11a

Figure 1.Schematic layout plan of

the building complex

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Implicationsof rising

groundwater

The composition of the foundation system varied and included a 1,200-mm-thickreinforced concrete raft foundation under the footprint of the central tower and the sixbuildings, and individual spread footing for columns supporting the ground floorpodium for the area between the individual buildings and the icon tower. Thebasement floor slab, for areas excluding raft/footings, consisted of a 250-mm-thickreinforced concrete slab. The thickness of the basement floor slab varied under watertanks, stairs and elevator pits. There was a 100-mm thick screed on top of the 250-mm-thick concrete basement slab in Phase I.

The soil strata at the site consisted of medium dense to dense silty sand in the top5 m with SPT N varying between 20 and 35. This stratum was underlain by a layer ofdense sand with bands of cemented sand and weak sandstone for a depth of 6 m. SPTN value varied between 35 and 60þ in this layer. Net allowable soil bearing capacityfor individual spread footings was determined to be 345 kN/m2 with a modulus ofsubgrade reaction of 42,000 kN/m2. Modulus of subgrade reaction of strata supportingthe raft foundation was computed to be 60,000 kN/m2 with a net allowable bearingcapacity of 480 kN/m2.

3. Effect of raised GWL on the building complexFigure 2 presents the GWL information recorded at 31 borehole locations based on thesoil investigation report. It can be observed that the bottom elevation of the 1,200-mm-thick raft under the building towers is at þ 16.64 m, whereas the average groundwatertable (GWT) with capillary action is at þ 16.21 m assuming an average of 1.0 mcapillary rise in soil. This means that the difference between the raft bottom andpotential average water zone is 0.43 m. It can also be noted that the GWTwas above theaverage GWT level in about 50 per cent of the boreholes and in about 25 per cent ofthese boreholes, the GWT level with capillary rise was right at or above the bottomof the raft elevation. The bottom elevation of the 250-mm-thick basement slab was

14

14.5

15

15.5

16

16.5

17

0 5 10 15 20 25 30

Gro

undw

ater

tabl

e (G

WT

) (m

)

Borehole #

GWT elevation (m)

Average GWT

Average GWT withcapillary

Bottom of raft

Bottom of raft elevation = 16.64 m

Figure 2.Groundwater table levelper soil investigationreport

114

SS30,2

at þ 17.59 m which makes is more than 2 m above the average GWT level. Based onthese facts, the basement structure was designed as a tanked structure with one layerof torch applied styrene butadiene styrene bituminous membrane for protectionagainst moisture ingress. However, the basement structure was not designed for anyhydrostatic head.

No groundwater was encountered during the construction phase and nopiezometers were installed for monitoring groundwater variations during and afterconstruction. The groundwater started to rise after about one and a half year ofoccupancy of Phase I. It rose more than 3 m above the basement level resulting inflooding in the basement. At that time, the owner installed a temporary dewateringsystem around the building complex perimeter for structural safety as well asfunctional operation of the basement as parking. Figure 3 depicts the GWLobservations recorded in piezometers installed at the dewatering well points from thestart of the dewatering operation to the time of this investigation. It can be observedthat the dewatering operation effectively lowered the GWL to top of the basement slabelevation of þ 17.84 m. However, the owner wanted to get rid of the dewateringoperation and instead required a structural solution to the problem.

4. Field observations of water leakageFigure 4 presents some of the snapshots depicting damage to the structure due towater leakage caused by the raised GWL. During the site investigation of the 40,000 m2

basement, it was observed that most of the water ingress happened around theexpansion joints between Phase I and Phase II construction (refer to Figure 4a). Theother area of significant damage was at the construction joint between the basementslab and tower raft and both sides of the shrinkage strips (see Figure 4b). Elevators pitswere not flooded at the time of this site visit. However, areas of considerable salt depositsand damp patches were observed as depicted in Figure 4d. These observations were

14

15

16

17

18

19

20

21

22

0

GW

L (m

)

Week

P1

P2

P3

P4

P5

Bottom of raft elevation = 16.64 m

Bottom of basement slab elevation = 17.59 m

455 10 15 20 25 30 35 40

Figure 3.Groundwater level (GWL)

observations inpiezometers from the start

of dewatering operation

115

Implicationsof rising

groundwater

made when the dewatering operation was fully operational. Therefore, no cracking orwater leakage within the body of the basement slab was observed. It was discoveredduring the site investigation that some half-hearted attempts were made to stem waterleakage at the expansion joint location between Phase I and Phase II. A detaileddiscussion on this topic is presented in Section 6.2.

5. Durability and strength appraisal of structural componentsDurability of the structural components – basement slab and wall – was assessed byconducting compressive strength, pH, chloride and carbonation level tests on thesamples taken from selected locations. Whereas, a 3D finite element model (FEM)analysis was conducted to assess the capacity of the existing basement slab subjectedto the revised loading condition of about 3 m of water head. Salient findings of theexperimental testing and analytical modelling are described in the following sections.

5.1 Experimental testing for durability assessmentSix and two 98-mm-diameter cores were cut in the basement slab and the basementwall, respectively. The cores were taken from the locations identified during the visualsite examination. The core samples were visually examined for voids, colour,honeycombing and distribution of coarse aggregate. Visual examination of the cores

(a) (b)

(c) (d)

Notes: (a) Expansion joint between Phase I and Phase II; (b) at shrinkage strips; (c) at the vehicular ramp between Phase I and Phase II; (d) salt deposits in the elevator enclosure

Figure 4.Snapshots of damage dueto water leakage invarious areas as observedduring the site visit

116

SS30,2

revealed no honey combing, mostly uniform distribution of aggregates and a few smallvoids. Additionally, the cores were subjected to lab tests to determine compressivestrength, pH profile, chloride ion concentration profile and carbonation depth.

Average compressive strength of concrete samples in the basement slab andbasement wall was determined to be 43.8 and 48.5 MPa, respectively, which wasgreater than the design compressive strength of 38 MPa. The pH profile variedbetween 13.3 and 12.8 and exhibited a slight decrease near the surface. However, theminimum value was more than the minimum pH value of 12.5 required for good qualityconcrete (Neville, 2009).

Water-soluble chloride ion concentration along the depth varied from 0.05 to0.28 per cent by weight of cement in all but one sample where its value was 0.35 per centand exceeded the threshold value of 0.3 per cent as recommended by ACI (ACI 318,2005). Depth of carbonation in these samples varied between 5 and 8 mm which wasless than the thickness of the concrete cover to the rebars. Based on these test results, itwas concluded that the in situ material properties of concrete did not deteriorate belowthe design value due to exposure to groundwater. Therefore, use of the nominal designmaterial properties in analytical modelling and analysis was warranted.

5.2 Analytical studies for structural stability and strength assessmentAnalytical studies were carried out in FEM packages ETABS non-linear version 9.5.0(CSI, 2009a) and SAFE standard version 8.1.1 (CSI, 2009b) to assess strength andstability of the building complex under revised loading and boundary conditions.Gravity (dead and live), lateral (wind and earthquake) and hydrostatic loads wereapplied in the analytical models with load combinations per ASCE 7 (2005) and ACI318 (2005). Design material and geometric properties were employed in these models.Use of design material properties in these analytical models was warranted based onthe results of in situ material testing as explained in Section 5.1. Revised boundaryconditions of free boundary were introduced at the expansion joint between Phase Iand Phase II in the basement slab. This was done to accurately model the actual fieldconditions observed at these locations where no positive vertical connection withhorizontal sliding joint was provided at the interface of the basement slabs of the twoconstruction phases.

(a) Overall stability of the building complex. Results of the finite elements model builtin ETABS (CSI, 2009a) indicated that the lateral drift of the building towers was withinthe code specified limits for the controlling load cases including the actions of wind,earthquake combined with hydrostatic uplift load. Overall stability of the buildingcomplex against hydrostatic uplift was also found to be adequate with factor of safetyagainst uplift varying between 1.46 for the single storey podium columns to 4.1 forinterior columns of the nine-storey towers.

(b) Analytical results for basement slab. Existing basement slab, raft foundation andindividual spread footings were modelled in computer software package SAFE version8.1.1 (CSI, 2009b). The foundation components were modelled with four-node plateelements with appropriate thickness, concrete strength, elastic modulus and boundaryconditions. Two models were created. One for the load cases without hydrostatic loadsand the other with hydrostatic loads. Appropriate soil spring support was specified inthe first model based on the modulus of subgrade reaction of the soil and tributary areaof each node, while in the second model where hydrostatic uplift load was applied, soilsprings were removed and pin supports were introduced at the column foundationlocations.

117

Implicationsof rising

groundwater

The existing basement slab comprised of 250-mm-thick concrete slab (38 MPa) with12-mm-diameter bars spaced at 150 mm top and bottom (each way). The slab had atheoretical ultimate moment capacity of 55 kN m/m. This moment produced a theoreticalcrack width of 0.24 mm; whereas ACI 224 (2001) requires that maximum crack width isnot to exceed 0.2 mm for flexural members subjected to deicing chemicals.

Condition of the basement slab was categorized into three zones based on momentsresulting from hydrostatic load conditions and is depicted in Figure 5. Factoredmoments of less than absolute 25 kN m/m were assigned to the category of “acceptableto moderate” (shown as green). Moments values between 25 and 50 kN m/m wereassigned to the category of “moderate to critical” and shown in yellow colour(at 50 kN m/m theoretical crack width¼ 0.20 mm). Values of more than 50 kN m/m weregiven the designation of “critical to severe” and were shown in red. The last categoryzone indicated that the moment has exceeded the theoretical ultimate capacity of theslab and a structural failure has occurred while serviceability limit was exceededin the moderate to critical zone. Areas within the red and yellow zones of Figure 5required structural strengthening and retrofit measures to withstand the appliedhydrostatic load.

Based on the results of FEM analysis, about 25 per cent of the basement slab requiredstructural strengthening and retrofit. Additionally, repair to the waterproofing system in

Critical ~ severe (> 50 kN m/m)

Moderate ~ critical (25 ~ 50 kN m/m)

Acceptable ~ moderate (< 25 kN m/m)

Legend:

P–4

P–3

Phase -

II (U

/C)

Figure 5.Basement slab analyticalstrength assessment byFEM analysis in SAFEunder full groundwaterhead (partial plan)

118

SS30,2

and around the retrofit areas and to articulation details at expansion joint betweenPhase I and Phase II was also needed.

(c) Basement wall. The 300-mm-thick basement wall with vertical 16-mm-diametervertical bars at 150 mm o/c was structurally adequate for groundwater head of 3 m.However, the computed theoretical crack width in the basement wall was 0.16 mmwhich is more than the permissible crack width of 0.1 mm for water retainingstructures per ACI 224, 2001). As the basement wall is strictly not a water retainingstructure, therefore the wall design was deemed to be adequate from serviceabilitypoint of view.

6. Retrofit solutions for basement componentsIt was shown in Section 5 that the existing basement slab is structurally deficientin about 25 per cent of the basement area and required strengthening measures towithstand the applied hydrostatic load. Additionally, it was also observed during thesite visit that the other sources of water leakage and poor performance were thearticulation, expansion and construction joints in the basement. This section examinesvarious options for structurally retrofitting and strengthening the basement slab aswell as provides comments and corrective measures for the articulation details.

6.1 Options for structural retrofit/strengthening of basement slabAnalytical modelling of the basement slab in computer package SAFE demonstratedthat the 250-mm-thick basement slab is not capable of withstanding the additionaluplift load imposed by 3.0 m7 water head in about 25 per cent of the basementarea (refer to Section 5.2). Three retrofit schemes were proposed as structuralstrengthening measures against this loading condition. A brief description of eachoption is outlined below.

(a) Slab overlay. Slab overlay is a simple and straightforward way of adding weightand sectional capacity to resist hydrostatic uplift load. This option was a suitablecandidate for retrofit of those areas where headroom was not an issue and in situtesting have proved no water penetration in concrete (i.e. original waterproofing wasfunctioning as designed). Figure 6 depicts details of this option. Analysis indicated thata 250-mm-thick overlay slab was required to provide the required structural capacity.The overlay slab was to be shear dowelled at the interface with existing slab andreinforced with 20 mm rebars at 150 mm on centre. The down side of this option was

Section

Existing footing(verify condition in field)

New waterproofing formedby injectable resin as required

(by specialty waterproofing contractor)(typical)

Waterproofing resin injectiontubes by specialty

waterproofing contractor(typical)

New overlay slab(hycrete integrated waterproofing

concrete or equivalent)

Existing column/wall

Strength and thickness of overlayslab per applied loading

Existing slab(verify condition in field)

Size and spacing of reinforcementand dowels per design calculations(typical)

Surface preparation ofexisting concrete surfaceas required (typical)

DT

Figure 6.Section of slab overlay

option for strengtheningthe existing basement slab

119

Implicationsof rising

groundwater

that the overlay slab had to be provided over the entire basement area due to functionalreasons even though the overlay was not structurally required over almost 75 per centof the basement areas including the thick building tower rafts and areas with closelyspaced columns. Use of integral water proofing method was recommended for the slaboverlay to improve its long-term durability.

The big challenge in this option was to ensure effectiveness of the existingwaterproofing membrane under the original slab and proper protection of bottomrebars in the existing slab from the harmful impact of water penetration.

(b) Micro-piles. The concept of using ground anchors or micro-tension piles was toreduce the span of the basement slab in such a way that the applied forces (momentsand shears) due to groundwater head were less than the capacity of the existing slab.Details of this concept are presented in Figure 7.

Analysis of the basement slab indicated that five micro-piles with a capacity of550 kN were required in the full 9 m� 9 m bay of the basement slab area. The proposedarrangement of the micro-piles was such that one micro-pile was placed at the midpoint of the four sides of the bay and the fifth was placed in the middle. Thisarrangement of the micro-piles resulted in maximum slab moment under applied waterhead load to be less than the allowable ultimate capacity of the basement slab.Preliminary sizing indicated that 50-mm-diameter high-strength steel hollow anchorbar with a 200-mm-grout diameter will provide the required structural as well asgeotechnical capacity when drilled 8 m into the ground. Installation of the micro-pilesposed two potential problems: first, required headroom for the installation rig andsecond, installation of piles under GWL. Both issues can be tackled by an experiencedand resourceful contractor subject to the economic and financial viability.

AA

Section A-A

New waterproofing formedby injectable resin as required

(by specialty waterproofing contractor)(typical)

Micro-piles/ground anchorscapacity, size and spacing as required

(typical)

9 m±

9 m±

Plan view

Micro-piles/ground anchors(by specialty contractor)spacing and layout of micro-piles/ground anchors to be designedfor applied load (typical)

See detail B

Bulkhead as required

Existing footing(verify condition in field)

Waterproofing resin injection tubeby specialty waterproofingcontractor (typical)

Figure 7.Schematic details ofmicro-pile option forretrofit of basement slab

120

SS30,2

Micro-piles/ground anchors were not required for the building tower rafts and areas ofbasement slab in the “green” zone as depicted in Figure 5. Ensuring or enhancing theeffectiveness of existing waterproofing membrane and providing waterproofingaround the locations of micro-piles was another issue that was to be handled by thewaterproofing specialist. Installation of micro-piles/ground anchors was to be carriedout under operational dewatering to avoid flooding in the basement.

(c) Break and re-build. This option required demolition of basement slab at thelocations identified by the FEM analysis and rebuilding of a new slab of therequired design thickness to withstand the applied loads. Figure 8 shows detailsfor this option and how the new slab was to be integrated with the existing slab thatwill stay.

This option may seem to be quite radical when adopted for the whole basementslab. However, it could be the only option in certain portions of the basement areawhere headroom was limited and/or access for micro-pile rig was difficult. Thissolution was to be implemented anyway for slab areas that were close to the heavywater leakage zones near the expansion joint and were exposed to harmful salts andsalt deposition.

Analysis indicated that in the full 9 m� 9 m bay, 450-mm-thick slab was requiredwith 20-mm-diameter bars placed at 150 mm on centres. Adoption of this option hadthe advantage that no specialty contractor was required and waterproofing under thenew slab could be implemented with more confidence.

(d) Adopted solution for basement slab retrofit. Decision to adopt a particular retrofitand strengthening scheme was based on the considerations of economic feasibility,ease of construction with minimum disruption to the operational use of the facility,required completion time for the work and available contracting resources. All retrofitoptions were to be carried out under continuous dewatering operation.

Schemes (a) and (c) did not require specialty contracting services. However, cost ofscheme (c) was less than both schemes (a) and (b). Although the time required forexecution of option (c) was estimated to be more than option (a) but option (c) providedthe flexibility of carrying out retrofitting and strengthening operation at therequired locations only and also offered the opportunity to inspect and replace thewaterproofing membrane under the severely affected portions of the basement slab.Option (b) required mobilization of a specialty micro-piling contractor besides beingmore costly as well as more time consuming.

Based on the above considerations, it was decided to adopt the break and rebuildoption (i.e. option c) for retrofit of the basement slab.

Section

Figure 8.Details of break and

rebuild option forbasement slabstrengthening

121

Implicationsof rising

groundwater

6.2 Review and retrofit of construction detailsThe current problem of leakage and structural deterioration in the basement of thebuilding complex was due to a combination of non-standard structural details andsub-standard workmanship that made the matter worse when the GWT rose due tounknown circumstances.

A thorough review of the existing design documents in conjunction with fieldobservations revealed some critical deficiencies in expansion and construction jointdetails in the basement slab and basement wall. It seemed that these articulation jointswere not designed and detailed for the high-water table conditions. Some attempts toprovide a fix for this deficiency were carried out after water started leaking from theseareas. However, these measures did not provide any durable solution to the problem asthese were executed without any sound engineering judgement. A summary of thesalient observations related to these issues is provided in the following.

(a) Details for basement slab expansion joint at interface with Phase I wall. Severeleakage was observed at the base of the wall located at the expansion joint locationbetween Phase I and Phase II as presented in the schematic plan view in Figure 1.A picture of the situation is shown in Figure 4a while Figure 9 graphically depicts theas built detail at this location. It can be observed that no positive connection wasprovided between basement slab of Phase II and wall of Phase I. The solid rubber stripwater stop provided between the two elements was not sufficient to withstand theapplied hydrostatic pressure and resulted in severe water leakage at this location.

There were attempts to control water leakage through the joint by providing a200 mm� 1,000 mm concrete step on top of the Phase II slab and injecting waterproofing

200 mm x 1,000 mm step

Section

Phase II Phase I

Hydrophilic solid rubber strip water stop

See plan

2

–5.00

Joint filler board

255

Existing structure

1. Slab end is free. No positive connection is provided with existing structure.2. Field–modified waterproofing details are missing.3. Not recommended detail for tanked structure with high water table.

Figure 9.Existing basement slabdetail at interface ofPhase I and Phase II

122

SS30,2

resin under the slab at the joint location. This measure may have provided a temporaryfix but during the site visit, severe leakage and pooled up water was observed aroundthis area. The main reason for the failure of the original detail as well as the fix was thelack of positive connection between Phase II slab and Phase I wall.

Figure 10 provides a detail for repair at this location. This detail calls not only for apositive connection between Phase II slab and Phase I wall, but also considers designmoment at the interface and calls for providing adequate reinforcing to withstand theapplied loads.

(b) Ramp locations between Phase I and Phase II. About 5 m wide openings were cutin the Phase I wall at four locations to provide access between the two phases asdepicted in the schematic plan view shown in Figure 1. Concrete ramps were builtacross these openings for providing movement of vehicles between the two phases.Figure 11 depicts the situation graphically while Figure 4c provides a pictorial view. Itcan be observed from Figure 11 that there was no positive connection between Phase IIslab and Phase I wall. The only connection between the two elements was provided bythe 200-mm-thick ramp slab, which was just sitting on top of the two slabs without anypositive (doweled) connection.

Phase II Phase I

Basement wall

Existing slabto remain

Remove existing basement slabas required and replace

Dowels andreinforcement to be

designed by specialtyconsultant (typical)

Thickness to be determined

Waterproofing detailby specialty contractor

Waterstop as requiredby specialty contractor

New concrete slab systemto provide continuity between

Phase I and Phase II(to be design by concrete

repair specialist)

Existing waterproofing membrane(verify condition in field)

Waterstop as requiredby specialty contractor

New waterproofing membrane(by waterproofing specialist)

Section

Figure 10.Sectional detail of

basement slab repair atexpansion joint

123

Implicationsof rising

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Water seepage under these ramps was observed because the rubber waterstop betweenPhase II slab and Phase I wall was not adequate to withstand the applied hydrostaticload. The provided detail, with no positive connection between Phase II slab and PhaseI foundation, was also not acceptable at ramp locations even when no groundwater waspresent due to the fact that constant vehicular movement was likely to cause crackingand deterioration of the free end of the slab in a short period of time. A doweled

Phase I wall demolished

at ramp locations

Phase IIPhase I

Ramp8 mm diameter at 25 cm each way

Phase I slab and wall foundation

Phase II slab

Solid rubber waterstop

Phase I wall demolished at ramp location

Phase I

Phase II Phase I wall to remain

outside the ramp

Ramp

Ramp

B

B

Figure4c

Notes: (a) Plan view; (b) section B-B

(b)

(a)

Figure 11.Existing detail of rampbetween Phase I andPhase II

124

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connection with horizontal movement capacity at one end was required for proper loadtransfer and satisfactory performance.

A detail similar to the one previously discussed for the situation described in(a) (i.e. Figure 10) was required as well at these locations providing the requiredpositive connection between the two elements with resin waterproofing under the slabat the interface location.

(c) Detail at interface of basement wall between Phase I and Phase II. Figure 12depicts this detail as presented in the construction documents. This detail was not arecommended detail at an expansion joint as water can find its way across the rubberstrip waterstop at the expansion joint and cause leakage in the basement anddeterioration of the concrete and reinforcement in the wall. A more positive way ofwaterproofing the expansion joint between Phase I and Phase II should have beenrecommended as depicted in Figure 13.

(d) Failure of the waterstop in shrinkage strips and construction joints. Figures 14aand b depict waterstop details and waterproofing information at shrinkage stripsand at the interface between basement slab and tower raft, respectively. These werethe locations where leakage and damp spots were observed during the site visit.A review of the design documents indicated no apparent problem with the designdetails. However, water leakage at these locations is indicative of failure of waterstopand/or improper installation. Repair details at these locations are presented inFigures 14a and b.

7. ConclusionsThe GWL at the building complex rose by more than 3 m and caused excessivewater leakage in the basement along with structural damage at certain locations.A temporary dewatering system was installed to limit further structural damage aswell as to ensure functioning of the basement. However, the owner wanted a permanent

Plan view

Phase I Phase II

Hydrophilic solid rubber strip water stop

Water proofing

Outside

Basement wall

Joint filler board

2

Existing structure

Inside

30

(Expansion joint detail)

1. Clarify waterproofing detail adopted in field.2. Not recommended detail for high water table.

30

Figure 12.Existing plan detail of

the basement wall atthe interface of Phase I

and Phase II

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groundwater

structural solution without the dewatering system. This study examined the existingdesign documents and drawings, conducted site visits and performed analyticalstudies to determine the extent of the damage and required structural strengthening ofthe various components of the building complex due to the raised GWL. Conclusionsof the study are summarized as follows:

(1) GWL are rising in many urban areas around the world which can have seriousimplications for in-service underground structures.

(2) Results of 3D FEM modelling and analysis of the building complex inETABS indicated that the structure was globally stable for the code specifiedload combinations of gravity, lateral (wind and seismic) and hydrostaticloads.

(3) 250 mm basement slab as detailed in the construction documents was notcapable of withstanding the additional applied hydrostatic load and needed tobe strengthened in about 25 per cent of the basement area.

(4) 300 mm basement wall as designed and detailed in the construction documentshad sufficient strength to withstand the applied hydrostatic head. However,theoretical crack width was more than the code limit for water retainingstructures.

(5) Three options for strengthening of the basement slab were examined anddetails were prepared. Break and rebuild option was adopted as the retrofitmeasure for the structurally deficient areas based on financial considerationsand ease of construction.

Phase IIPhase I

Waterproofing as required byspecialty contractor

Outside

Inside

Waterproofing details andinstallation by specialty

contractor

Expandable waterstopas per waterproofing

specialist

Stainless steel anglesto be designed

Horizontal slotted hole

Plan view

Existing rubber strip waterstop(verify condition in field)

Waterproofing resin injectiontubes by waterproofingspecialist

Figure 13.Plan view of expansionjoint repair in basementwall at the interface ofPhase I and Phase II

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(6) As-built articulation details like expansion joints, construction joints andshrinkage strips were also examined for the condition of revised GWL andconstruction deficiencies. Proper remedial measures for rectification weredesigned and detailed.

References

ACI 224 (2001), Control of Cracking in Concrete Structures, American Concrete Institute, Detroit, MI.

ACI 318 (2005), Building Code Requirements for Concrete Structures, American ConcreteInstitute, Detroit, MI.

Repair to waterproofing bywaterproofing specialist

Construction joint

(a)

(b)

1. Carefully hand chip and remove deteriorated concrete

2. Examine condition of rebars3. Repair with specialty mix

Existing basementslab

Section

Section

Existing tower raft

Existing basementslab

Construction joint

Waterproofing resininjection tube by

waterproofingspecialist 1. Verify condition in field

2. Waterproofing repair by waterproofing specialist

Figure 14.(a) Repair detail at

shrinkage strip;(b) sectional detail of

repair at interfaceof basement slab

and tower raft

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Al-Rashed, M.F. and Sherif, M.M. (2001), “Hydrogeological aspects of groundwater drainage ofthe urban areas in Kuwait city”, Hydrological Processes, Vol. 15 No. 5, pp. 777-95.

ASCE 7 (2005), Minimum Design Loads for Buildings and Other Structures, American Society ofCivil Engineers, Reston, VA.

Bergeron, G., Dehays, H. and Pointet, T. (1983), Remontees des nappesd’eau souterraine: causeet effets, Bureau de Recherches, Geologiques et Minieres, Paris (in French).

Blower, T. (1987), “The potential consequences for surface structures of rising groundwaterlevels beneath London”, The Structural Engineer, Vol. 65A No. 6, pp. 234-5.

CSI (2009a), ETABS v 9.5.0 – Integrated Analysis, Design and Drafting of Building Systems,CSI, Berkeley, CA.

CSI (2009b), SAFE v 8.1.1 – Design of Slabs, Beams and Foundations, CSI, Berkeley, CA.

Dean, J.L. and Sholley, M.G. (2006), “Groundwater basin recovery in urban areas and implicationsfor engineering projects”, in Culshaw, M., Reeves, H., Spink, T. and Jefferson, I. (Eds),Engineering Geology for Tomorrow’s Cities, Theme 2, The Geological Society of London,Nottingham, CD-ROM.

Johnson, S.T. (1993), “Rising groundwater levels: engineering and environmental implications”,in Wilkinson, W.B. (Ed.), Groundwater Problems in Urban Areas, Thomas Telford ServicesLtd, London, pp. 285-98.

Knipe, C.V., Lloyd, J.W., Lerner, D.N. and Greswell, R. (1993), Rising Groundwater Levels inBirmingham and the Engineering Implications, Special Publication 92, CIRIA, London.

Kreibich, H. and Thieken, A.H. (2008), Assessment of Damage Caused by High GroundwaterInundation, Water Resources Research (AGU), GFZ, Potsdam.

Kusumi, K. (2005), “Protection of subway station against recovery of groundwater table”,Tunnels and Underground, Vol. 36 No. 8, pp. 33-40 (in Japanese).

Neville, A.M. (2009), Properties of Concrete, Pearson, New York, NY.

Oyedele, K.F., Ayolabi, E.A., Adeoti, L. and Adegbola, R.B. (2009), “Geophysicaland hydrogeological evaluation of rising groundwater level in the coastal areas ofLagos, Nigeria”, Bulletin of Engineering Geology and the Environment, Vol. 68 No. 1,pp. 137-43.

Pell, A. and McDonald, Y. (2001), “Tunnel waterproofing today”, available at: www.allbusiness.com/manufacturing/nonmetallic-mineral-product-manufacturing/906174-1.html (accessed 20 December 2011).

Rushton, K.R. and Al-Othman, A.A.R. (1993), “Control of rising groundwater levels in Riyadh,Saudi Arabia”, in Wilkinson, W.B. (Ed.), Groundwater Problems in Urban Areas, ThomasTelford Services Ltd, London, pp. 299-309.

Simpson, R. (1983), “Verbal contribution to an informal discussion on rising groundwaterlevels and geotechnical consequences at the Institution of Civil Engineers”, Reportedin the Proceedings of the Institution of Civil Engineers, London. Part I, Vol. 76,pp. 791-3.

Singh, O.P., Khan, T.M.A. and Rahman, M.S. (2000), “The vulnerability assessment of the SAARCcoastal region due to sea level rise: Bangladesh case”, Report No. 3, SAARC MeteorologicalResearch Centre, Dhaka.

Suzuki, S. and Okuda, Y. (2008), “Building a safe airport that resists natural disasters: thecompletion of three major safety projects at Kansai International Airport”, CivilEngineering – JSCE, Vol. 92 No. 12, pp. 1-8.

Wilkinson, B. (1985), “Rising groundwater levels in London and possible effects on engineeringstructures, hydrogeology in the service of man”, Memoires of the 18th Congress of theInternational Association of Hydrogeologists, Cambridge, pp. 145-57.

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Wilkinson, W.B. and Brassington, F.C. (1991), “Rising groundwater levels – an internationalproblem”, in Downing, R.A. and Wilkinson, W.B. (Eds), Applied Groundwater Hydrology,Oxford Science Publication, Oxford, pp. 35-53.

Yasuhara, K., Murakami, S., Mimura, N., Komine, H. and Recio, J. (2007), “Influence ofglobal warming on coastal infrastructural instability”, Sustainability Science, Vol. 2 No. 1,pp. 13-25.

Yasuhara, K., Murakami, S. and Mitsuyama, S. (2003), “Instability of foundations undergoing risein groundwater level”, in Komatsu, M., Nishigaki, M. and Kono, I. (Eds), GroundwaterEngineering – Recent Advances, Proceedings of the International Symposium onGroundwater Problems Related to Geo-environment, Taylor & Francis, Okayama, London,pp. 205-10.

About the author

Muhammad Tariq Amin Chaudhary is a registered Professional Engineer in the USA andCanada and is certified in the practice of Structural Engineering by the Structural EngineeringCertification Board (SECB) in the USA. He graduated with an Honors Degree in CivilEngineering from the University of Engineering and Technology, Lahore, Pakistan in 1990 andearned his Master’s degree in Structural Engineering from University at Buffalo, New York, USAin 1992 and doctoral degree from University of Tokyo, Japan in 1999. He has more than 16 yearsexperience of working as a consulting structural engineer in the USA, Japan, UAE and Pakistan.He has been involved in dozens of design, repair, rehabilitation, strengthening and seismicupgradation projects in his career. Muhammad Tariq Amin Chaudhary can be contacted at:mtariqch@hotmail.com

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