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IntroductionThis publication is one of nine that has been translated from Norwegian. They are taken from a series of publica-tions produced by the Norwegian Building Research Institute (NBI) series, Byggdetaljer, which literally translatedmeans building details. It is hoped that Alaskan builders will be able to glean useful ideas from these publications.The translations were done by Dr. Nils Johanson and Richard D. Seifert of the University of Alaska Fairbanks withthe cooperation and permission of NBI, Oslo, Norway. The nancial support for the translations and printing camethrough the Alaska Department of Community and Regional Affairs, from USDOE Grant DE-FG06-80CS6908. Thepublications use the original index code of the Norwegian Byggdetaljer series so that specic translations can bedirectly cited. All questions on these translations should be directed to Richard D. Seifert, Alaska Cooperative Exten-sion, P.O. Box 756180, University of Alaska Fairbanks, Fairbanks, Alaska 99775-6180. Phone: 907-474-7201.

0 GENERAL01 This bulletin gives an overview of the various meth-

ods that can be utilized to improve older buildingfoundations and to retrot building foundations. Italso gives information about common damage tofoundations and basement walls.

02 The condition of the foundation can be a determin-ing factor as to whether a building can or shouldbe improved. Extensive repair or retrotting arequite expensive to carry out and must be carefully

evaluated ahead of time. A certain amount of tiltand some cracks in old buildings is acceptable ifsettlement has stopped. All large scale retrot workdemands professional assistance in evaluating thegeotechnical and structural conditions.

03 A technical survey combined with a historical surveyof the foundation and foundation walls should becarried out in connection with improvements. Theextent of the analysis depends on the size of thebuilding, its age, foundation conditions, changesin use, and so on. The analysis may include the fol-lowing:

Investigation of construction records and govern-ment archives to map the soil conditions

Survey of foundations and foundation walls Report of damage Visual survey and ground excavations Crack survey Foundation survey including drilling, testing etc. Report of settlements and time dependent settle-

ments (precision leveling, precision settlementmeasurements)

Calculation of the foundation load (static sys-tem)

Measurements of groundwater level and pore waterpressure

Leveling and straightening of foundation and otherwalls

Stress measurements in existing tension ribbons Vibration measurements Control of material quality

04 Changes and improvements in the building founda-tion can lead to great problems with adjacent struc-

tures. For instance, buildings that are still settlingmay hang up on the area that has been improved.Strengthening or retrotting must, therefore, takeneighboring structures into account.

05 Rehabilitating the foundation may also require cor-recting already existing differential settlement. Suchcorrection is often possible by jacking wooden framehouses. Masonry construction is often sensitive tomovement and should not be jacked or leveled.

1 TYPES OF FOUNDATION DAMAGE

11 Erosion

111 Natural rockThe durability and strength of rock is determinedby the amount and distribution of the smallest andweakest mineral. As these minerals are worn awayeverything breaks down or dissolves, and thereare no connections left between the other strongermineral groups. The original stone then consists ofa conglomeration of loose particles. If the founda-tion surface has been damaged by frost action, salt

ALASKA BUILDING RESEARCH SERIES HCM-01555

FoundationRetrot &

Rehabilitation NBI: A541.702

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14 Moisture damageWalls where lime and clay are used as a mortaroften absorb moisture. This usually does not leadto signicant problems as long as the wall has beenuntreated or has been covered with lime mortar. Lo-cal repairs with cement mortar on an original limemortared foundation wall does not work very well.The cement mortar, which is relatively tight, disturbs

the moisture balance in the wall, and the mortar doesnot breath enough, nor does air escape. Moisture canthus penetrate farther up into the wall before it ndsan exit (see Figures 14a to c). Old buildings are oftensurrounded by terrain which, because of occasionallling, asphalt work, and so on, lies higher than theoriginal terrain. Mortar, masonry work, and possiblewood construction, which were never designed tobe in contact with the soil, can in this way sufferfrom signicant moisture damage.

Figure 14Moisture damage on foundation wallsa. Moisture penetrates up through the wall

b. The old mortar covering deterioratesc. By repairing of old imperfections the evaporation zone is

moved higher up on the wall.

141 Frost wedgingWater that penetrates up or out through the wallcan freeze and break it in pieces; the mortar mate-rial crumbles and loses its binding ability. In boxwalls the core can be torn to pieces, leaving the shellstanding without any signicant mortar.

142 Salt bloomMoisture that travels in foundation walls can carrywith it easily soluble salts that occur in mortar andstone material. These materials are carried to theouter surface where the water evaporates and the

salt crystallizes. This "salt bloom" can damage thesurface. Crystallization may also occur inside the rockor the cover and lead to of salt build-up, which canthen ake off the covering mortar or rock material(see Figure 142).

washing or the like, the deterioration accelerates. Itusually takes a long time before natural rock starts toerode, but limestone, sandstone, and shale are morelikely to be exposed to problem-causing erosion.

112 BrickBrick is the most porous foundation material and willabsorb moisture. The moisture leads to frost damage

which materializes by exfoliation or splitting of thesurface parallel to the outside. Large continuouscracks can totally destroy the bricks. The bricks frostresistance depends on material properties such aspore distribution, water absorption, and strength.Other factors such as moisture, climate, number offreeze-thaw cycles, and the freezing speed are alsoimportant.

12 RotFungus rot is the most common reason for dam-age to wood. Fungus thrives on nutrients that arefound in wood. However, the temperature must

be between 0 and 40C and the wood must haveat least 20% water with respect to its dry weight inorder for the fungus to grow. Another importantelement in fungus rot in wood foundations is theavailability of oxygen.

Raft and pile foundations are subjected to attackby fungus rot when the water table sinks belowthe top of the foundations (see Figure 12; see alsoPoint 151.)

Figure 12Groundwater lowering leads to raft and wooden piles beingexposed to air and thereby rotting.

13 Insects

Insects can attack wooden foundations above groundlevel. Boring beetles and carpenter ants are the woodboring insects that do the most damage. Certain partsof the country are more exposed to attacks than otherparts. Most wood-boring insects are active between 0and plus 30C (32F and 85F). Wood that has alreadybeen damaged by rot is especially vulnerable to at-tack by wood boring insects. The same conditionsare true for caissons and poles at beaches.

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213 Drainage and irrigationIn some circumstances drainage and irrigation ofthe foundation can yield good results by reducingthe moisture availability.

Draining and securing from moisture damage onthe outside of basement wall is carried out afterexcavation.

Figure 213Draining and airing of foundation

214 Sealing joints with lime mortarThis does not prevent air from entering the masonrywork but it can reduce the extent of damage whenthe wrong kind of mortar has been used for improve-ments. Pure lime mortar is porous, and moisturewhich has been added can evaporate. Loose orpoor-quality mortar should be chipped away andthe cracks cleaned of dust and leftover mortar pieces.The cracks should then be moistened and lled witha lime mortar as similar as possible to the originalmortar. The foundation wall should not be exposedto sun or rain during the curing time.

215 Injecting mortarThis method may be used in the middle room of abox foundation. Mortar injection strengthens thewall and reduces damaging moisture penetration.The loose mass inside the wall should be removedto the greatest extent possible by excavation orushing with water. The cement mortar is injectedthrough openings in the outer wall. Numerousopenings will give the best distribution of the water(see Figure 215).

Figure 215Injection of mortar in box foundations

stability can occur. In some cases, movement can alsobe caused by frost action, temperature variations ormoisture variations.

17 Frost heave/adfreezingSmall older houses are usually not founded tofrost-free depth if they do not have a basement. Onfrost-susceptible soil the damage to small house

foundations can be extensive because of the adfreez-ing or the lateral grip of the frozen soil. The damageis normally more signicant on walls where there ismortar between the blocks. Surface damage can alsooccur where there are connections with log houses(see Figure 17).

Figure 17The lled in area between point foundations on log housesoften settle without this causing a problem for the stability ofthe building.

18 Alum ShaleAlum shale contains pyrite, which when exposedto oxygen (for instance by a lowered groundwatertable) will be converted to sulfuric acid. This acidattacks concrete and metal. Sulfuric acid and limeform plaster of gypsum. When this process takes

place there is a volume expansion which, in the worsecase, can lift the foundation. Foundation damagein connection with alum shale is rst and foremostrelated to the Oslo area. (Editors note: There is noknown alum shale in Alaskan communities.)

2 IMPROVEMENT METHODS

21 Preventing Moisture Damage

211 Coating of the foundation wall. This method, whichis little used in Norway, consists of establishing acapillary barrier in the foundation by drilling and

injecting a mixture of polyester and rock our.

212 Electro-osmosisElectro-osmosis can also be used to prevent capillaryabsorption of water in masonry work. Electrodes areplaced in the incision zone between the foundationwall and the soil. By changing the electrostatic condi-tions, the capillary rise can be reduced.

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22 Preventing frost damageMovement in the foundation/foundation wall asa result of frost action can often be prevented orreduced by ground insulation laid out along thebuilding. A problem with this is that old constructionwill act as a cold bridge where the frost can penetratedown regardless of insulation (Figure 22).

Figure 22Frost protection of foundation with ground insulation

23 Raising the groundwater tableRaising the groundwater table can protect theexisting support system of wood from damage inareas where the water table is shrinking. The woodmust be healthy at the start, however, otherwise themethod has little going for it. In areas where settlingis occurring, it may be desirable to stop this by in-creasing the poor pressure in the soil. This methodrequires inltration through permeable soils sincea local increase in water table will normally not besufcient to raise the groundwater table in densesoil masses.

231 Controlled wateringIn this method the upper groundwater storage aqui-fer is lled to prevent exposure of the wood in raftsabove the water surface. A well is dug next to the wall,down to the upper part of the raft. The well must besupplied with water so that the water table alwayscovers the wood. This can be maintained by installingan automatic leveling regulator. Several observation

pipes must be installed along the circumference ofthe building to control the water level. Controlledwatering requires a permanent survey system.

232 Removing large treesIf large deciduous trees are next to the foundationwall, the roots can absorb so much water that thelocal groundwater table is drawn down.

233 InltrationSurface inltration is done by connecting shallowwells or pipes to the water bearing layer (see Figure233).

Deep inltration is done through shafts in rock orthrough pipes that extend down to the actual depthof the water table. The water must normally be sup-plied under signicant overpressure with respect tothe existing pore water pressure.

Figure 233Inltration of building soil

Inltration must be monitored by installing porepressure meters (Piezometers) in the ground. Shafts

and pipes must be constructed so that they can becleaned on a regular basis.

A permanent inltration system is difcult to main-tain and must be planned by specialists. Practicalexperience from Norway is limited.

24 Constructing a dry wallSmall walls are, as a rule, easy to repair, but theymust rst be secured against further damage, forexample, by placing ground insulation under them.See Point 22.

Rocks that have fallen out and rock that has beendisplaced must be removed. With larger walls, onemust determine what kind of construction shouldbe used before the wall work commences.

25 Reinforcing drywall with concrete and reinforcing steelDrywall foundations were originally thought to con-duct vertical loads only from the walls to the groundor raft. Local settling, rot in raft foundations, andso on can make it desirable to strengthen the wall

Figure 231Example of controlled watering

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2 m. The point on the pile should be hardened, axlesteel. The piles can be spliced at each pile segmentin the upper end and welded on a box of angle steelwith a length of about 500 mm of which 250 mmshould protrude above the top of the pile segment.There should be a clearing between the rolled steelsegment and the sleeve of angle iron of about 1 to2 mm. The sleeve can be centered in the length of

the pile by wedging it with steel pieces. See Figure282a. The sleeve is then lled with a small amountof epoxy and the next pile is mounted so that theepoxy ows out into the hollow space betweenthe rolled steel piece and the sleeve of angle steel.The overlying pile segment is centered with steelwedges, and the sleeve is warmed up to about 40Cto get a rapid hardening of the epoxy. This type ofpile is quite suitable for use with homogeneous soilconditions. The joint is not, however, particularlymovement resistant, and because of the small surfacearea, the pile is not very sensitive to corrosion. Thepile has, however, a relatively large load capacity.For piling work, the roof height in the basementshould be at least 2.5 m; however, with short pilesegments the room height can be as low as 2 m. Thesmallest distance from the wall to center of a pileshould be 150 mm.

Figure 282aExample on pile of rolled steel

There are numerous light hollow pile types on the

market. An example is the steel plastic pile whichhas a diameter of 76.1 mm and a wall thickness of4 mm. The steel quality is ST52. Externally the pileis rust protected with a 1.8 nicron thick layer ofpolyethylene. (Figure 282b). The pile comes withan epoxy treated pile edge. The top plate consistsof a steel plate with a pipe welded on and tted tothe inner diameter of the pile. The joint consists ofan concentric sleeve with a wall thickness of 3.65mm. The sleeve is threaded in place by a layer ofpolyethylene on the joint. The polyethylene is fused

light air hammer. Another method is to install pilesin drilled sleeves. Both pushing piles and ramming

piles with a light air hammer requires that the soil ishomogeneous. It is very important to look for solidmineral soil and rocks in the ground, to map the rocktypes, and to be aware of inclined rock surfaces. It isalso very important to recognize alum shales and toknow where erosive groundwater exists. Installingpiles requires thorough technical evaluation andplanning. For example, placing piles next to foun-dation wall, establishing a foothold, evaluating ofrock bearing strength and straightness of the pilecan all affect the success of the foundation. It is alsonecessary to take into account possible damage tothe structure by excavation and reestablishment of

loads. There are examples given of several pile typesthat can be used. Figure 282a to 282b.

282 Driven or rammed steel pilesThere are several types of driven or rammed steelpiles, including rolled steel piles, light, hollow steelpiles, steel proles, and steel pipe piles.

Use rolled steel with steel quality ST37 with variablecross section (i.e. 40 mm x 40 mm to 120 mm x 120mm). The pile length should vary between 1.5 m and

Figure 27Repairing existing piles.

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at the adjoining pile ends by heating it up. The sleeveis heat-shrunk to 80 microns in thickness. After thepile is installed, the inside volume is lled with con-crete. The pile is quite easy to handle. It can be drivenwith an air hammer and is easy to use under tightconditions. The hollow space inside the pile makesit possible to control its straightness. The joint mustbe set to be movement stiff. The steel cross-section

is, however, only 950 mm2, and the load capacity is,therefore, limited. The necessary height for the rigis about 2.1 m. The center pile should be placed 150mm from the edge of the wall.

Figure 282bSteelplastic Pile

There are many steel proles in use. Streetcar andrailroad tracks have been used with good results. Aspecial prole is the so-called SW-steel pile whichhas a cross-shaped cross-section, which gives the pilea relatively large bending resistance with respect to

the area. It is available in three sizes with cross-sec-tions of 2,600, 6,100 or 8,100 mm2. The steel qualityis ST37 (see Figure 282c). The pile is provided witha pile point and a top plate of steel. The top plate isxed, either with guide ribs or by welding, to thecenter portion of the pile. The pile is joined at eachpile end, being welded to a steel plate so that theconnection can be established with four bolts. Thejoint is relatively shear resistant. The smallest pilecan be driven down with a light air hammer. Thelarger types demand a greater ram capacity. Thepiles are normally delivered untreated, and they

Figure 282dMegasteel pilea. rammed down to solid groundb. with poured concrete foot

will, because of their large surface area, be somewhatsubject to corrosion.

The megasteel pile is a square steel pipe pile whichis pushed down into the soil with a hydraulic jackwhile the soil mass is being ushed away from theedge of the pile. If the soil is difcult to hose awaywith water it can be drilled down through the pipe.

The joints are made by welding. The piles can bepushed down and supported on solid rock or asmall man-made concrete lump in the soil. In thelatter case, the pipe is rammed to a desired level andconcrete is pumped into the soil to create a massivebearing surface under the pile. This method can beused only in friction soils which can be penetratedeasily enough for concrete to be injected. When theconcrete has hardened and has full bearing capac-ity, the rest of the pile is lled with concrete. Thepile can be dimensioned as if it consisted only ofsteel. The concrete protects against corrosion andshould prevent bending. When calculating capacity,take into consideration the external corrosion andthe danger of concrete breaking in loose soils (seeFigure 282d).

283 Pressed or driven concrete pilesThere are two types of pressed or driven concretepiles: normal, joinable, prefabricated piles, andspecial piles.

Normal, joinable, prefabricated piles can be adjustedfor refoundation work. They are useful when thereis room to ram piles down on the outer perimeterof the building. Such piles can also be rammed orpressed down inside buildings. Because they havejoints, the length of the pile element and the stresscapacity of each pile must be calculated in eachindividual case.

An example of a special pile is the megapile which isrammed into place by hydraulic jacks. The buildingitself can be used as a counter balance. This method

Figure 282cSW-steelpile

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is often used on large buildings built on easilypenetrable soil masses. The pile is usually squarewith a cross-section of about 300 mm. The lengthis about 1 m, but many lengths are available. Thepile has a sentry hole, which makes it possible tocontrol its direction during the placement process(see Figure 283).

Figure 283Megapile

Splicing can be carried out in several ways. A singlesleeve around the joint will prevent twisting andeccentricity between the piles; a threaded steel pipealong the center of the piles with the joint will giveadequate bending capacity; and rigidly mountedsteel plates that can be welded together at the endsof the piles will give a joint that is resistant to move-ments, but they are quite expensive.

In silt or sandy soil the center hole can be ushed

through with water or air pressure to aid in thedriving process. There is also equipment availablefor predrilling in areas where there are large rocksand other obstacles in the ground. Downshaftingunderneath the foundation of the building normallyprovides resistance for pushing down of the piles.Normal excavation depth under the foundation isabout 1.5 m.

284 Board pilesTwo types of board piles are used, steel core piles andinjected concrete piles. Steelcore piles are used insolid rock. The Lindo pile is an example. Because of its

high price, it should be used only where large rocksand other obstacles in the ground make it difcultto press down piles without predrilling. The pileconsists of a round steel core which is surroundedby concrete and covered by a sleeve (see Figure284). The diameter of the steel core varies between50 and 100 mm with a steel cross-section betweenabout 19.60 and 78.50 mm square. The steel qualityis ST50 enabling the load capacity to cover a widearea. An eccentric drill bit is used to drill the steelpile down to solid ground. The pipe is drilled down

into bedrock a small distance so it will have a goodseat. Pipe length can be 1 to 3 m, depending on howmuch height one has to work with. Different pipelengths can be screwed or welded together.

Figure 284Lindo pile

After the pipe is in place is lled with concretemortar. The concrete will corrosion-proof the bear-

ing element in the pile. The core consists of massivesteel rods in suitable length which are being splicedtogether with welds or threaded sleeves. The rodsare placed immediately after pouring of the concrete.There are special machines for boring in narrowand low rooms.

Injected concrete piles are used as friction piles incircumstances where the load is carried down tobearing soil layers. An example of such a pile is theso-called root pile, which is used in Sweden andelsewhere in Europe. This pile uses an aggregatewith a 1.8 m work height and is drilled down 1

m using spliceable steel piles. The bottom pipe isconnected with a large powerful shear ring. Loosematerial is transported upwards while the pipe isbeing bored by a spray of bentonite or water underhigh pressure. When the desired pile depth has beenreached, prefabricated reinforcing baskets are sunkand welded as they come down into the tube. Anaerated concrete is then poured down into the pipethrough a hose, as with conventional underwaterpouring. A closed lid is mounted on the top of thepile and the concrete is pressurized. Finally, the pipeis pulled up in sections as the tube pile is lockedand the concrete is pressurized. This assures that

the pile will adhere well with the surrounding soiland provide a high carrying capacity.

285 Other piles. Wooden piles and wing piles are alsouseful with refoundation workUnfortunately, wooden piles must be completelysubmerged to keep from rotting. If wood is exposedto variable humidity above the groundwater table,it will rot very quickly. However, for certain kindsof buildings such as piers and houses that are nextto the sea, wooden piles are still the best type of

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foundation. Wooden piles are inexpensive, but theyshould be straight and they must be prepared well.The bark must be removed and branches cut off closeto the trunk. The top diameter must not be less than150 mm. The pile is driven with the top down. It isimportant to use piles impregnated with preserva-tive, such as creosote. (See Figure 285a).

In Sweden, a cohesion pile has been developedwhich consists of a relatively thin steel pipe withlong longitudinal ribs. The length of the piles joinedwith the sleeve can vary according to building condi-tions. Figure 285b. The advantage of a cohesion pilelies in its great bending resistance and its cohesivesurface qualities with respect to the displaced soilmaterial. Driving is done with a light air hammer orvibration hammers. There is, however, little experi-ence with this system.

Figure 285a Figure 285bExample of wooden pile Wingpile

286 Load transmissionLoad transmission from pile to structure can be ar-ranged in several ways. One method is to dig underthe foundation wall and place the pile directly underthe foundation wall. The forces from the structureto the pile will then be transmitted directly or via aboard cap on top of the pile. (Figure 286a). Anothermethod of load transmission is through slits in thefoundation wall and/or the foundation. The pile isplaced inside the slit and concrete poured around it.The forces from the building are transmitted to thepile by cohesion forces. The same principle can beused with piles installed in bored holes using heavy

construction foundation plates. (Figure 286b).

Figure 286aDirect load transmission under foundation wall

Figure 286bLoad transfer by slit in foundation

Load transmission can also be accomplished by apile, or piles, placed on either side of the foundationwall. A beam (i.e. a steel beam with concrete) placedover the piles and in direct contact with the lowerportion of the foundation establish a beam whichwill transmit the load to the pile (Figure 286c).

Piles can be driven on either side of the foundationwall for load transmission. A beam is poured oneither side of the foundation wall over the piles. The

load from the foundation wall to the concrete beamis transferred by cross beams (i.e. poured steel beamsor ties). The force in the ties should be checked to besure that the friction is sufcient (Figure 286d).

Figure 286c Figure 286dLoad transmission Load transfer viavia cross beam longitudinal beams

29 Replacement of material

Around buildings where there is consolidation set-tling, it is possible to replace existing lls with lighterlls such as lightweight concrete or sawdust.

3 REFERENCES31 This bulletin has been developed by Knut I. Ed-

vardsen, Norwegian Building Research Institute.Svein Bjorberg, Multiconsult A/S and Arne Nesje,Mur-sentret. Rolf Hauan, Engineers Bonde & Co. and

Bjorn Finborud, NOTEBY have been consultants.

The editing was completed September 1981.32 Literature

321 Translated into English by Nils Johanson and RichardD. Seifert, University of Alaska Fairbanks, 1989.

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Published by the University of Alaska Fairbanks Cooperative Extension Service in cooperation with the United States Department of

Agriculture. The University of Alaska Fairbanks is an afrmative action/equal opportunity employer and educational institution.

2013 University of Alaska Fairbanks.

8-91/RS/10-13 Reviewed April 2012

www.uaf.edu/ces or 1-877-520-5211

Art Nash, Extension Energy Specialist.