building performance and retrofit

7/27/2019 Building Performance and Retrofit

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Evaluation and Retrofitting of Building Foundations

1. Survey on the Integrity of Building Foundations1.1 Introduction1.2 Survey on the ground surface1.3 Survey on the underground foundations1.4 Survey on Bearing Capacity1.5 Evaluation of degree of damage

2. Restoration and reinforcement of building foundations2.1 Outline

2.2 Repair, reinforce, settlement restoration2.3 Restoring the settled, detached houses

Annexes

Annex 1 Integrity Investigation TechniquesAnnex 2 The Techniques of Restoration, Reinforcement and Settlement RestorationAnnex 3 Countermeasure Techniques Against Differential Sedimentation


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1. Survey on the integrity of foundations

1.1 Introduction

Generally, in the case where any of such damages as differential sedimentation,inclination, cracks, and defects has been caused to foundations by an earthquake or consolidationsettlement, a survey on the integrity of foundations is required. Great attentions should be paidto the sites, which may involve the risk of liquefaction or a settlement disaster, even if nodifferential settlement has been actually occurred. Nevertheless, for existing buildings, theactually-occurring phenomena such as differential settlement and inclination of the buildings andcracks in the foundation members tend to attract greater attention than the results of evaluations

based on design calculation. In contrast, recently, precast piles and improved soil materials have been increasingly used in housing renewal and therefore, the supporting performance of precast piles needs to be confirmed.

The evaluation items of foundation integrity may be largely classified as shown below:1) Location of a foundation2) Dimensions and geometry of the foundation3) Quality of the foundation (strength/rigidity)4) Bearing performance of the foundation

Data on the location of the foundation in 1) and the dimensions and geometry of thefoundation in 2) are useful at the stage of survey if design documents and construction executionreports are available. In many cases, no detailed record has been stored. The design documentsused for building construction authorization may be kept by the owner but the constructionexecution reports have not kept anywhere in many cases except for special cases. In the surveyon the earthquake damages, the foundation might have to be digging out for visual check. Onthe other hand, in some cases, the dimensions and geometries of foundation slabs and footingsare different from those described in the design drawing in some cases and thereby, it is veryimportant that the detail of the foundation referring not only to the design document but also tothe construction execution report. The length of the pile may be roughly estimated by the IT test(PI test). For a bearing pile, its length may be different from the measured length depending onthe depth of the bearing stratum and therefore, it is necessary to confirm it referring to theconstruction execution report.

To determine the quality of the foundation, the strength test and the neutralization test areconducted using coarse samples for concrete, and the strength test as well as the check test for any corrosion are require for reinforcement. With an exception of the case where:

1) reuse of the existing foundation is required,2) differential settlement and inclination has occurred, or 3) cracks or defects is found in the rising part of the foundation on the surface of theground which may be visually checked,

almost no survey on the quality of the foundation is conducted (Photo 1.1.1). The bearing performance of the foundation is generally evaluated based on the differential settlement or inclination if any. Thereby, the integrity is not considered in reusing the existing piles with theexception when the bearing force needs to be verify by the loading test.


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Photo 1.1.1 Method of conducting a survey on concrete integrity (general survey on concretestructures)1) core recovery2) core strength test3) reinforced concrete gauge4) reinforced concrete gauge5) carbonation test (peeled off)6) carbonation test (drilled out)7) carbonation test (sampled core)8) impact strength measurementSupplied by: Hitoshi HAMAZAKI (Building Research Institute) (excluding 2) and 4))

1 2

3 4

5 6

7 8


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In conducting the survey on the integrity of the existing foundation, the sampling test or the nondestructive test is compelling to be carried out in many cases because it is difficult toconduct in-depth survey on the entire foundation under the ground, which cannot be visuallychecked. In making an attempt to improve the reliability of this type of test, analysis usingexecution management data is useful and it is important to get deep inside into variations anddifferences in executed construction based on the result of execution management. At the

present time, however, almost no construction execution report is prepared for evaluatingvariations and differences in executed construction and therefore, there is an urgent need todevelop any technique for solving this problem.

Building Research Institute is making efforts in developing a quality control system (3-DQC) for visualizing information on construction execution in cooperation with Koda/SatohsLaboratory. This system provides correlated information on parameters such as excavationresistance per unit depth and material input relative to any of vertical and horizontal crosssections in the area under construction for easy identification (for example, M. Tamura, H. Satoet al, A 3-Dimensional Quality Control System in Foundation Construction, ISOPE, Toulon,France, 2004). Fig. 1.1.1 shows an example of the results from the management process of thedeep mixing method of soil stabilization. Any of methods, which can automatically acquire andmanage data on construction execution, may give similar views to the view shown aboveincluding the deep mixing method of soil stabilization and the penetration method of rotating

piles using stirring blades. This management method provides such a function that a group of piles are managed together rather than individuals, allowing the constructor to grasp anyvariations in the geological stratum and any differences in construction during or immediatelyafter construction and therefore, is expected to be useful in evaluating the integrity of the existingfoundations.


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Besides, it is also effective to use any method for easy survey on the integrity of thefoundations when new piles are constructed. Photo 1.1.2 shows a marker for measuring anydifferential settlement installed on the rising part of the house foundation at the completion of construction. It is strongly recommended that this type of marker to be used to verify thehorizontal plane prior to construction.

10 11 12 13 14 15 16 17 18

0.2

0.4 190.0

0.6 160.0 160.0 175.0 165.0 170.0 170.0 160.0 175.0 190.0

0.8 155.0 165.0 160.0 150.0 175.0 170.0 160.0 180.0 185.0

1.0 160.0 155.0 150.0 160.0 170.0 170.0 160.0 175.0 180.0

1.2 165.0 160.0 155.0 170.0 175.0 165.0 160.0 165.0 180.0

1.4 155.0 160.0 165.0 165.0 170.0 170.0 160.0 165.0 175.0

1.6 145.0 145.0 150.0 145.0 155.0 165.0 165.0 150.0 175.0

1.8 135.0 135.0 130.0 140.0 145.0 140.0 160.0 150.0 155.0

2.0 115.0 125.0 125.0 125.0 125.0 130.0 155.0 160.0 160.0

2.2 105.0 110.0 115.0 110.0 135.0 120.0 150.0 160.0 155.0

2.4 110.0 95.0 120.0 115.0 130.0 120.0 145.0 155.0 160.0

2.6 120.0 105.0 120.0 115.0 155.0 145.0 155.0 150.0 160.0

2.8 120.0 115.0 135.0 130.0 165.0 145.0 150.0 155.0 160.0

3.0 115.0 140.0 130.0 145.0 180.0 155.0 145.0 150.0 155.0

3.2 135.0 140.0 145.0 155.0 170.0 155.0 150.0 160.0 155.0

3.4 145.0 150.0 155.0 155.0 175.0 160.0 155.0 155.0 165.0

3.6 150.0 150.0 155.0 160.0 175.0 160.0 150.0 160.0 155.0

3.8 160.0 160.0 165.0 150.0 170.0 165.0 150.0 150.0 165.0

4.0 155.0 150.0 155.0 160.0 160.0 155.0 150.0 160.0 155.04.2 150.0 165.0 155.0 160.0 165.0 150.0 145.0 160.0 160.0

4.4 160.0 160.0 155.0 155.0 160.0 170.0 155.0 155.0 160.0

4.6 150.0 150.0 155.0 155.0 160.0 150.0 155.0 165.0 165.0

4.8 150.0 160.0 155.0 160.0 175.0 155.0 155.0 150.0 155.0

5.0 250.0 233.3 250.0 248.3 340.0 396.4 245.0 261.7 261.7

Column Number

D e p

t h ( m )

Fig. 11 Number of mixing per 1 meter advance at X-3

10 11 12 13 14 15 16 17 18

0.2

0.4 190.0

0.6 160.0 160.0 175.0 165.0 170.0 170.0 160.0 175.0 190.0

0.8 155.0 165.0 160.0 150.0 175.0 170.0 160.0 180.0 185.0

1.0 160.0 155.0 150.0 160.0 170.0 170.0 160.0 175.0 180.0

1.2 165.0 160.0 155.0 170.0 175.0 165.0 160.0 165.0 180.0

1.4 155.0 160.0 165.0 165.0 170.0 170.0 160.0 165.0 175.0

1.6 145.0 145.0 150.0 145.0 155.0 165.0 165.0 150.0 175.0

1.8 135.0 135.0 130.0 140.0 145.0 140.0 160.0 150.0 155.0

2.0 115.0 125.0 125.0 125.0 125.0 130.0 155.0 160.0 160.0

2.2 105.0 110.0 115.0 110.0 135.0 120.0 150.0 160.0 155.0

2.4 110.0 95.0 120.0 115.0 130.0 120.0 145.0 155.0 160.0

2.6 120.0 105.0 120.0 115.0 155.0 145.0 155.0 150.0 160.0

2.8 120.0 115.0 135.0 130.0 165.0 145.0 150.0 155.0 160.0

3.0 115.0 140.0 130.0 145.0 180.0 155.0 145.0 150.0 155.0

3.2 135.0 140.0 145.0 155.0 170.0 155.0 150.0 160.0 155.0

3.4 145.0 150.0 155.0 155.0 175.0 160.0 155.0 155.0 165.0

3.6 150.0 150.0 155.0 160.0 175.0 160.0 150.0 160.0 155.0

3.8 160.0 160.0 165.0 150.0 170.0 165.0 150.0 150.0 165.0

4.0 155.0 150.0 155.0 160.0 160.0 155.0 150.0 160.0 155.04.2 150.0 165.0 155.0 160.0 165.0 150.0 145.0 160.0 160.0

4.4 160.0 160.0 155.0 155.0 160.0 170.0 155.0 155.0 160.0

4.6 150.0 150.0 155.0 155.0 160.0 150.0 155.0 165.0 165.0

4.8 150.0 160.0 155.0 160.0 175.0 155.0 155.0 150.0 155.0

5.0 250.0 233.3 250.0 248.3 340.0 396.4 245.0 261.7 261.7

Column Number

D e p

t h ( m )

Fig. 11 Number of mixing per 1 meter advance at X-3

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

0.2 1. 6 1. 8 1.3 1.2 1. 5 2. 3 1.1 1.8 1.6 2.2 2.2 7.8 2.2 1. 3 2. 1 2.3 1.4 2.8 1.9 1.4 1.2 2. 2 1. 6 1.5 8.2 2. 2

0.4 7. 1 7. 4 3.5 3.9 7. 1 8. 9 3.7 7.1 7.0 4.3 3.6 9.2 7.4 3. 7 8. 6 7.1 3.5 7.3 6.9 1.9 4.3 8. 9 3. 4 1.8 8.2 3. 7

0.6 9. 3 9. 3 8.9 8.7 9. 0 9. 4 8.6 9.3 9.5 9.0 6.6 9.2 8.7 7. 2 9. 0 8.9 6.9 9.3 9.0 3.9 9.5 9. 1 9. 3 3.9 8.7 6. 7

0.8 9. 5 9. 4 9.3 8.7 9. 3 8. 9 9.2 9.2 9.1 8.8 8.7 9.0 8.8 9. 1 9. 2 8.7 9.2 9.4 8.8 9.1 9.2 9. 1 9. 3 9.0 9.6 8. 8

1.0 9. 6 9. 2 9.1 8.9 9. 2 8. 6 9.1 9.2 8.9 8.6 8.8 8.8 8.7 9. 3 8. 9 8.8 7.4 9.0 7.2 8.8 9.1 9. 1 9. 5 9.3 9.7 9. 3

1.2 9.5 9.1 9.1 9.3 8.9 8.9 7.4 9.8 9.0 8.7 8.3 7.5 8.5 9.2 8.5 8.4 3.9 9.0 4.1 8.9 9.4 8.7 10.0 10.4 9.5 8.9

1.4 9. 4 8. 9 8.5 9.1 8. 9 8. 8 3.9 9.4 9.1 8.5 8.3 3.8 8.4 9. 0 8. 7 6.9 3.9 9.3 2.6 9.1 9.2 8. 9 8. 9 9.5 8.9 7. 2

1.6 9. 4 9. 1 8.9 9.0 8. 6 8. 4 2.3 8.9 9.0 8.6 7.1 4.0 8.0 9. 2 8. 6 4.2 8.3 9.2 4.2 8.9 9.0 8. 9 8. 4 8.7 8.7 2. 6

1.8 9. 3 9. 3 9.0 8.8 8. 4 8. 7 3.9 8.9 9.0 8.5 8.6 7.2 8.4 9. 2 8. 4 7.2 8.8 9.2 7.3 8.8 9.1 8. 9 8. 6 8.9 8.4 4. 4

2.0 9. 4 9. 1 9.0 9.4 8. 6 9. 1 8.5 8.9 9.2 9.1 9.0 8.9 8.7 9. 1 9. 0 8.6 9.4 9.2 9.0 8.9 9.2 9. 0 9. 2 9.2 9.3 9. 0

2.2 9. 2 9. 0 9.2 9.5 9. 0 9. 4 9.0 8.9 9.1 9.0 9.2 8.8 8.8 9. 5 9. 0 8.7 7.6 9.4 9.0 9.0 9.3 9. 0 7. 6 9.2 8.7 8. 9

2.4 9. 1 9. 3 9.4 9.2 8. 9 9. 1 9.0 9.2 9.1 9.4 9.2 8.8 9.1 9. 2 9. 1 9.0 9.1 9.1 9.2 9.2 9.4 8. 9 9. 1 9.2 8.8 9. 1

2.6 9.5 9.1 9.4 9.8 9.3 9.1 9.1 9.2 8.9 10.3 8.8 9.1 8.9 9.3 8.9 8.9 9.7 8.8 9.6 9.3 9.4 9.0 10.2 9.1 9.6 8.9

2.8 9.6 9.4 9.6 9.7 9.1 9.1 8.9 9.3 5.8 9.1 8.8 9.0 8.7 9.3 9.0 8.6 9.3 9.2 9.2 9.4 9.1 8.8 10.8 8.9 10.5 9.3

3.0 10.0 8. 8 9.7 9.5 9. 3 9. 1 8.7 9.5 9.1 8.7 9.1 9.0 9.0 9. 2 9. 1 9.0 9.3 9.1 9.3 9.2 9.2 9. 2 8. 8 9.1 9.2 9. 1

3.2 9.8 8.9 9.5 9.6 9.0 9.1 9.0 9.6 8.9 9.4 8.9 9.1 9.3 9.1 8.9 9.3 9.6 9.1 10.0 8.6 9.9 10.0 9.7 9.4 8.8 8.6

3.4 10.7 9.5 9.0 9.6 8.9 8.8 9.1 9.9 9.2 10.4 9.2 8.9 9.5 9.3 10.4 9.1 9.8 9.8 9.6 10.1 11.5 12.2 9.7 9.7 8.6 8.5

3.6 11.6 11.8 9.5 9.3 9.5 9.0 10.0 9.8 9.4 9.5 6.8 9.1 9.0 10.9 7.2 9.3 11.6 10.8 11.4 11.1 13.9 11.0 10.0 10.1 10.2

3.8 11.2 14.6 10.4 11. 8 12.6 11.7 10. 3 10.5 12.8 9.2 9.0 8.8 10.3 16.6 10.1 9.8 13. 4 8.6 14.2 13.8

4.0 18.5 13.3 14.1 17.7 9.9 8.6 9.1 9.6 8.4 9.5 11.4 12.4 9.2

4.2 10.9 10.9 8.4 9.1 9.8 10.5 14.1 9.3

4.4 11.8 10.1 8.9 8.4 12.0 8.4

4.5 14.0 10.8 10.6 10.1

Column Number

D e p

t h ( m )

Fig. 1.1.1 Example of the result of quality control for visualizing any change or variation inconstruction (3-DQC) (Example of correspondence between the number of rotations/the state of

running and column numbers/depth torque or in the deep mixing method of soil stabilization)


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Alternatively, to sense damages in addition to differential settlement and inclination,sensors and inspection windows may be prepared on the foundation members such as piles prior to construction. Several methods have been proposed for attaching optical fibers or carbon fibersto the pile bodies or winding them around the piles. Photo 1.1.3 is an example of PHC piles withoptical fibers buried inside, method still under development. It has been verified that the opticalfibers can endure centrifugal fabrication. Fig. 1.1.2 shows a schematic drawing explaining thistype of damage detection technique.

Difficulties may arise not only in the evaluation of where responsibility for repair of damages lies or how severe of damages, but also in the determination of whether the repair work is required and in the repair work itself. Accordingly, if the damage detection system for thestructures such as foundations as shown in the figure is required, this type of piles are expectedto be put into practical use in future considering their importance/use and users expectation toreusability. Unfortunately, such piles are not commonly used. In the case where any of construction methods, where piles and other members are built on site, such as the cast in-placeconcrete pile methods the procedure may be the following: two or more inspection windows

Photo 1.1.2 Marker put the periphery of the house foundation for settlement monitoring

Photo 1.1.3 Example of PHC piles damage device survey methodusing optical fibers. Any cracks are checked by the bending test on

piles with optical fibers attached

Fig. 1.1.2 Example of pilefoundation damage detection system

Marker


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In most of standard buildings, the rising element of the foundation can not be visuallychecked. On the other hand, for small-sized houses such as detached houses, cracks or flaws of the external portion of the foundation are used as an indicator of possible defects. Accordingly,it is important that the survey on the element of the foundation, which may be visually checked,to be conducted. To check to see if defects have occurred for confirmation of the integrity of theconcrete foundations on the ground surface, simple instruments such as an insert clearance gauge,as well as magnifying mirrors for check the widths of cracks, repulsive strength measuringdevices, and reinforced concrete exploration devices may be used.

In recent years, any soft coating material has been applied to the external elements of thefoundations in some cases and therefore, it is required that the widths of cracks and other flawsto be measured fully considering the kind and properties of a finishing material.

1.3 Survey on the underground foundations

One of the direct foundations structure representative damage is inclination of rigidmembers witch is usually evaluated to be minor, even if the building differentially settles. Thistype of damage is not representative for pile foundations. For direct type, the underground part of the foundation is buried near the surface and can the ground can be excavated to check theintegrity of them visually.

It may be difficult to visually check the foundation integrity for the old buildings becausethe survey require dig-out the piles and loading test. Recently for direct and piles foundationsmuch frequently are used soil improvements technique. Accordingly it is more important thanever to evaluate the integrity of the improved soil if differential settlement or any other damageoccurs.

During the Miyagi Prefecture Earthquake (1978) and Southern Hyougo Earthquake(1995) many piles have been damaged. The damages were found not only at the heads but alsoin the middle portions of the piles. To estimate or visually checked for any damage in the middle

portions and heads of piles, surveys and tests are conducted from the heads of the piles or through the hollow portions or bore holes, which have been opened in the piles.

The terms of survey are classified largely into 1) those on the foundations directly beneath the building and 2) those on the underground foundations. For the direct type, thesurvey on the directly beneath the building is generally conducted, while any other inspection isrequired depending on the pile type if soil improvement or reinforcement such as the deepmixing method of soil stabilization have been employed to protect the piles.

Table 1.3.1 summarizes the individual surveys. In conducting the survey, it is alwaysrequired to allow for determining whether the damages to the foundation have been caused dueto insufficient bearing capacity of the foundation or due to the defect in the pile, as well aschecking to see if the precast piles may be reused for selecting appropriate restoration method.To determine whether the precast piles may be reused, the survey on the integrity of the pile

bodies as foundation members by the non-destructive test and the bearing capacity of thefoundation by the loading test must be conducted in some cases.

One of the methods for roughly examining the states and positions of the damages of theunderground piles is the non-destructive test. The non-destructive methods use low-strain elasticundulation, or earthquake generating equipment installed at the top of the pile produce vibrationor an impact given on the top of the pile to measure the force exerted and vibrations. Another


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method, where various types of sensors are inserted into a bore holes formed in the hollow portions of the piles or in the piles themselves, or inspection windows previously formed duringconstruction, may be included in the non-destructive test.

Table 1.3.1 Underground survey method (mainly pile foundations, see Annex 1)

Method Description

Drilling survey Visually checks the states of foundations.Leveling survey Measures inclination or differential settlement of

underground foundations and others.IT test (PI test) Surveys the integrity of the pile bodies by carefully

hitting the heads of piles.Borehole camera Observes piles through their hollow portions, boreholes,

and gaps/cavities and others.Borehole radar Surveys the positions of damages in the piles, if any,

through boreholes and others.Borehole sonar Surveys the integrity of pile bodies through the boreholes

and the hollow portions of the piles.Ultrasonic measurement Surveys the integrity of pile bodies through the hollows

of the pile bodies.Caliper logging Measures any variation in diameter of minute holes of the

hollow portion at the cracks or cross sections of pile bodies. Used in conducting the surveys ondamages/integrity through the hollow portions of piles.

Gamma-ray density logging Identifies gaps, if any, in the concrete elements using thedependency of the result of measuring the gamma-raydose density. It is difficult to detect such a variation indensity that may be caused by a crack.

AE measurement(acoustic emission)

Detects damages to pile bodies, if any, through an elasticwave induced by a crack.

Inclinometer Used in estimating the positions of the damages to pile bodies based on L-discontinuous points for inclination.

Loading test Estimates bearing capacity (static, quick, impact, etc.)

Others Estimates the positions and sizes of the damages throughsurface wave measurement.

(1) Survey from the heads of piles IT test.This method uses elastic undulation in a low-strain region to estimate the lengths and

damaged portions of piles based on the profile of its reflected wave. If a survey can beconducted on the piles after being removed from the footing, the result may be easily obtained.In contrast, even if the piles remain attached to the footing, this method enables the test to beconducted.

With the footing attached to the tops of the piles, an impact is generally applied on thefooting or the anchors installed on pile heads. With the pile heads being not open, a signalreflected from the lower portion of the pile, as well as a signal reflected from the footing or


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column in the upper part is mixed into the resulting signal. Alternatively, another method (stereomeasurement method) may be used. This method involves the following steps: 1) installingsensors at two test points on the piles, 2) separating a falling wave and arriving wave based onthe phase contrast between elastic undulations measured at these points, and 3) evaluating theintegrity of the piles based on information from the arriving wave.

(2) Survey through the hollow portions of pilesThe non-destructive tests conducted from the heads of piles, such as the IT test, is

effective as a primary method for estimating actual states of the damages to pile bodies. In somecases, however, any more direct method for grasping the damaged positions and the actual statesof damages is required.

Various types of measurements may be conducted through the hollow portions for precast piles and core holes formed in the pile bodies for cast-in-place piles, respectively, which givesdeeper insight into the actual states of the piles. These survey methods, however, are generallyeffective only when the heads of piles are open. If a footing or any other member has beenconstructed, boreholes need to be drilled in it. In this type of measurement method, sensors (or cameras) and others are inserted into the hollow portions of piles, where measurements areconducted.

In this method, 1) borehole cameras, 2) inclinometers, 3) gamma-ray densiometer, 4)caliper (hole or diameter) gauges, 5) ultrasound (acoustic intensity) measuring devices, 6)

borehole sonars, etc., may be used. When the devices listed in 2), 3), and 4) are used, the sensorsshould be brought into contact with the sides of the holes and then slid on them for measurement(Photo 1.3.1, Annex 1).

One, which allows for most direct measurements and give distinctive results, isobservation of hole walls using 1) the borehole cameras. The borehole camera is a kind of videocamera and several types have been developed including those integrating a fiber scope. Someenables measurements at an angle of 360 all at once. If the boring step is required in makingmeasurement on the cast-in-place piles and others, the states of the concrete elements may bedetermined to some degree by observing core samples collected. Cracks, however, may occur in

Fig. 1.3.1 Example of a survey on the underground foundation (borehole camera, IT test, and bore sonar)


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boring and thereby, it is difficult to correctly distinguish between the cracks caused by theearthquake and those occurring later by boring in some cases.

If there is no information about the construction of pile or foot foundation, methods likethe borehole radar and surface wave exploration should be used and after a rough inspection withthese method, the integrity of the piles need to be checked by another method.

Some of the individual survey methods are described in Annex 1. See Damage toBuilding Foundations and Their Restoration (Kenchikugijyutsu, 1995, Special Issue, 1) andother literatures as the need arises.

1.4 Survey on Bearing Capacity

Possible causes for differential settlement of buildings and the damages to the pile bodies,is insufficient bearing capacity. Once differential settlement has occurred, the loading test may

be used to ensure the direct understanding of the bearing capacity of existing piles.In some cases, before the loading test on the existing piles, the load supported by the piles

must have been temporarily up borne by some way. In the commonly used method (the steel pier technique), steel pipe piles are pressed into the bearing stratum using jacks by means of reactive force from the footing to support the load applied on the footing. The reactive force will

be supported by the load on the footing and the piles in the vicinity of it in the loading test.Photo 1.4.1 shows an example of the static loading test, which is most commonly used.

The loading test includes the static loading test (the reactive pile method), as well as the rapidloading test and the impact loading test. Among them, the test, which recently has attractedattention, is the rapid loading test. Photo 1.4.2 shows an example of the rapid loading test, wherealmost all the load displacement relations may be obtained.

Photo 3.4.3 is referred only for reference instead of exemplification. In this figure, a kindof pile construction method commonly used in China, by which piles are pressed in by applyingstatic force. In the case where the pile diameter is small, it may be possible to conduct the testunder press-in force for complementing the loading test. The steel pier technique commonlyused in restoring the settled pile foundations is similar to this static steel pier technique, by whichthe bearing capacity is estimated, confirmed, and managed based on the relation between the

press-in force and the amount of settlement and other parameters, if applicable.

(5000kN ) (50000kN )

Fig. 1.4.1 Vertical loading test on repulsive force piles (see Annex 2-1)

Loading equipment (5000kN class) Loading equipment (50000kN class)


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1.5 Evaluation of degrees of damages

1.5.1 Outline

The integrity of the building foundations is basically evaluated by checking for anydifferential settlement or inclination of buildings and for any crack or defect in their foundations.The parameters including an angle of inclination and a crack width may be used.

The criteria for determining whether any defect has occurred are applicable only to themembers, on which visual check may be easily done, such as the raising portions of thecontinuous footing foundation of a detached house. For underground piles, it is important toevaluate their integrity and the degree of damages to them depending on the type of piles.Similarly, for pile caps and foundation slabs, may need to be evaluated considering the type of

piles, the location of piles, and the effects of the technique used for attaching the pile heads.As an institutional method for evaluating the degree of damages and severity of disaster

damages to foundations, an evaluation method using the parameters such as the state and angleof deformation of foundation and the state of settlement in surrounding ground as indexes has

been proposed for determining rapidly the risk level and severity of disaster damages of buildings after an attack of earthquake.

Only a few studies have been conducted on the degree of damages to the undergroundslabs and piles of buildings and thereby, definitive data is almost not available.

H

GL

OD-SYSTEM

AD

AD

500tf

Fig. 1.4.2 Example of the quick loading test method (see Annex 2-3)

Monogen

Pile strain gauge

Accelertor

Load cell

Cussionmaterial

Bridge box

Dynamicstrain amp

AD converter

Opticaldisplacementgauge target

AD converter

OpticaldisplacementgaugeCD system

Test pile

Cellasto buffer

Load cell(1000tf)

Opticaldisplacement gauge

Pile stress

Exampleof 500tf

Fig. 1.4.3 Static steel pier technique (Push piles, Shanghai, China)


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It should be noted that it is possible to evaluate the degree of damages to buildingfoundations and the integrity of them based on the state of piles and the result of structuralcalculation in a certain way, while unlike the foundations of structures constructed by publicworks, the necessity of restoration and recovery and the intent and degree of restoration may bedependent on a case-by-case basis in determining the severity of disaster damages to buildingsand handling the result of determination. In the case where not only an earthquake but alsosettlement damages due to consolidation settlement have occurred, if the damages to the upper structures are not severe, inclination, if any, is perhaps restored only by replacing the floor materials with new ones to flatten in many cases because restoration of the settled foundationsrequires a large amount of money. Also, it should be noted that the pile heads are seldom dugout to make closer inspection unless serious building settlement or inclination occurs.

The guideline 2) mentioned above assumes that the conditions (condition A) described below may be applicable to the buildings, of which foundations was damaged. For the buildingsincluding those which satisfy the condition A, those for which settlement or inclination wasdetected in the rapid determination the dig-out survey it is require to be conducted.

Conditions which implicitly indicate damages to foundations 2) 1. Buildings situated in the area where a geotechnical flow due to the land slide or

liquefaction was observed.2. Buildings without being damaged, which are situated in the area where a

earthquake with a magnitude of VI+ or larger attacked and their surrounding buildings were seriously damaged.

3. Buildings with an aspect ratio of 2.5 or higher, which are situated in the area wherean earthquake of a magnitude of V+ or larger attacked.

1.5.2 Evaluation of degree of damages to foundation slabs

Table 1.5.2.1 and Figure 1.5.2.1 show the degrees of damages to foundation slabs. Anycrack width was evaluated by ranking in four levels: 0.2 mm or less, 0.2 to 1 mm, 1 to 2 mm, and2 mm or more. On the other hand, the severity of damages was evaluated by roughly ranking infive levels: rank I (mild), rank II (minor), rank III (moderate), rank IV (serious) and rank V(destructed).


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Table 1.5.2.1 Scheme of degree of damages to foundation slabs 2)

Degree of damage

Symptoms

I 0.2 mm or less of fine crack occurred. No concrete material fallen off.

II Approx. 0.2 to 1 mm of crack occurred. No concrete material fallen down.Concrete material slightly fallen off with reinforcing steels not visible.

III Approx. 1 to 2 mm of crack occurred.Concrete material very slightly fallen off.Reinforcing steels may be slightly visible.

IV2 mm or more of crack occurred.Concrete material significantly fallen off.Reinforcing steels seriously exposed.

V Reinforcing steels have bent and internal concrete structure collapsed.Foundation slabs deformed in the direction of its height.Settlement and/or inclination detected.In some cases, reinforcing steels broken.


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1.5.3 Evaluation of degree of damages to pile foundations

Fig. 1.5.2.1 Example of degrees of damages to foundation slabs 2)

Degree Symptom

0.2 mm or less

Approx. 0.2 1 mmMinor peeled surface

No reinforcing steel observed

Approx. 1 2 mm

Minor peeledconcrete

No reinforcing steel

2 mm or more of reinforcing steelobserved

reinforcing steel not bent2 mm or more

Reinforcing steel observed

Deformation in height Settlement/inclination

Brokenreinforcingsteel

Internal concretecompletely broken

Reinforcing steel bent and internal concretecompletely separated

Brokenreinforcingsteel


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Table 1.5.3.1 and Figure 1.5.3.1 show the scheme for evaluating the degree of damages

to cast-in-place concrete piles and examples of evaluation. As in the case of foundation slabs,crack widths were ranked at four levels: 0.2 mm or less, 0.2 to 1 mm, 1 to 2 mm, and 2 mm or more. Precast concrete piles (e.g., PHC piles), as shown in Table 1.5.3.2, were ranked at threelevels: 0.1 mm or less, 0.5 mm or less, and 1 mm or less. Smaller crack widths were used inevaluating the degree of damages when the degree of damages were at the same levelconsidering that the effects might exert on a prestressed, high-strength concrete material.

Table 1.5.3.1 Scheme for evaluating the degree of damages to cast-in-place concrete piles 2)

Damages due to axial tensionor bending

(in the case where a crack hasoccurred at an angle of 45 to

almost the horizontal line)

Damages due to axialtension or shearing stress(in the case where a crack has occurred at an angle of 45 to almost the vertical

line)

Damages due to axial tension

(in the case where only ahorizontal crack occurred)

I 0.2 mm or less of fine bending crack (horizontalcrack) occurred.

0.2 mm or less of fine bending shearing crack (atan angle of 45) occurred.

One to three cracks occurredwithin 1.5 D on one side. No concrete material fallen

off.

0.2 mm or less of finecrack occurred.

One or more cracksoccurred within 1 to 3 D. No concrete material

fallen off.

0.2 mm or less of finehorizontal cracksoccurred.

Cracks occurred at aninterval of approx. 1 D or more.

No concrete material fallenoff.

II 1 mm of horizontal crack occurred.Approx. 1 mm of crack

occurred at an angle of 45.One to three cracks occurred

within 1.5 D on one side. No concrete material fallen

off, or only the surfacematerial fallen off.

Reinforcing steels notvisible.

Approx. 1 mm of finecrack occurred.One or more cracks

within 1 to 3 D occurred. No concrete material

fallen off.

1 mm or less of finehorizontal crack occurred.Cracks occurred at an

interval of 0.5 to 1 D or less. No concrete material fallen

off.

III Approx. 1 to 2 mm of horizontal crack occurred.

1 to 2 mm of crack occurredat an angle of 45.

Three or more cracksoccurred within 1.5 D or cracks occurred at aninterval of approx. 20 to 30cm.

Surface concrete materiallocally fallen off (approx. 10 cm in height,or within 0.2 D)

Reinforcing steels may beslightly visible.

Approx. 1 to 2 mm of crack occurred.

One or two cracksoccurred within 1 to 3 D.

Oblique crack occurredwith concrete materialfallen off from its top.

Horizontal reinforcingsteel not visible.

Approx. 2 mm of horizontalcrack occurred.

Cracks occurred at aninterval of 0.5 to 1 D or less.

Only 10 cm-width of concrete material fallenoff along crack.

Reinforcing steels areslightly visible through agap left after concretematerial was fallen off.


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IV 2 mm or more of horizontalcrack occurred.

2 mm or more crack

occurred at a angle of 45.Five or more cracksoccurred within 1.5 D.

Cracks occurred at aninterval of approx. 20 to 30cm.

Surface concrete materialfallen off.

Approx. 20 to 30 cm of crack occurred or crack occurred within approx.0.5 D.

Concrete material remainsinside reinforcing steel

members.Local buckling found inreinforcing steels.

Vertical crack occurred.

2 m or more crack occurred.

Two or three cracks

occurred within 1 to 3 D.Concrete material fallenoff along oblique crack.

Reinforcing steels arevisible along obliquecrack.

Buckling not found inreinforcing steels.

Concrete material fallen off along crack (approx. 10 cmin width).

Reinforcing steels exposedalong gap left after concretematerial was fallen off.

Clearance left between pilehead and footing, throughwhich fixed concretematerial is visible.

V Pile axially compressed.Concrete material broken

down and buckling found inall the reinforcing steels.

Reinforcing steels brokendown.

Buckling found inreinforcing steels alongoblique crack.

Vertically compressed.Reinforcing steels broken

down.

Buckling found inreinforcing steels.

Axially compressed.Pile clinched.Reinforcing steels broken

down. Note) D indicates the diameter of a pile in the table.


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Fig 1.5.3.1 Example of evaluation of degrees of damages to cast in place concrete piles

Degree

Foundation slab Foundation slab Foundation slab Foundation slab

A


1-3 crackswithin 1.5 D

0.2 mm or less

1-3crackswithin1.5 D

App. 1mm

Peeled surface, No

reinforcing steel observed

3 crackswithin1.5 D

Approx. 10cm or 0.2 D

Approx.1-2 mm

Local peeled

concrete,reinforcingsteel partiallyobserved

Peeled sconcrete

Vertical c

Reinforcing ste partially bucked

B

P i l e f

o un

d a t i on

C

0.2mm1mm or less

Peeled concrete, Noreinforcing steelobserved

Approx. 1-2mm

Peco

Reinforcing steel observed, buckled


Peeled concrete

Exposedreinforcing stee

Separfrom fixedreinfsteel

Approx 2mm

Peeled concreteApprox. 10 mm(minor)

Reinforcingsteel slightlyobserved

0.5-1 D or less

1 mm or less

0.5-1 D or less

0.2 mm or lessApprox.1D

2 mm or more

A=Damages due to axial force and bending force CB=Damages due to axial force and shear force


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Table 1.5.3.2 Scheme for evaluating the degree of damages to precast concrete piles (PC, PHC,PRC) 2)

Degreeof

damageType of damage

Damages due to axialtension or bending stress.(in the case where crack occurred at an angle of

horizontal line to almost45)

Damages due toaxial\tension or shearing

stress.(in the case where crack

occurred at an angle of 45to almost vertical line)

Damages due to axialtension.

(in the case where onlyhorizontal cracks

occurred)

I

0.1 mm or less of fine bending crack (horizontalcrack) occurred.

0.1 mm or less of fine bending shearing crack occurred (at an angle of 45).

Two or three cracksoccurred within 1.5 D onone side. No concrete material

fallen off.

0.1 mm of fine crack occurred.

One or more cracksoccurred within 3 D on oneside. No concrete material

fallen off.

0.1 mm of fine horizontalcrack occurred.

Cracks occurred at aninterval of approx.0.5 D or more.

No concrete materialfallen off.

III

Approx. 1 mm or less of horizontal crack occurred.

Approx. 1 mm or less of crack occurred at an angleof 45.

Three or more cracksoccurred within 1.5 D onone side. Or, cracksoccurred at an angle of approx. 20 to 30 cm or less.

Local surface concretematerial may be fallenoff (10 cm in height or within 0.2 D).

Steel material may beslightly visible.

0.5 mm or less of finecrack occurred.

Three or less cracksoccurred within 3 D on oneside. No concrete material

fallen off.

Approx. 1 mm of horizontal crack occurred.Cracks occurred at aninterval of 0.5 D or less.Concrete material

slightly fallen off alongcrack (10 cm in width).

V

1 mm or more of horizontal crack occurred.

1 mm or more of crack occurred at an angle of 45.

0.5 mm or more crack occurred.

Three or more cracksoccurred within 3 D on oneside.

Concrete material fallenoff along crack (10 cm inwidth).

Steel material exposedalong gap left after


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Five or more cracksoccurred within 1.5 D onone side.

Cracks occurred at aninterval of 20 to 30 cm or less.

Local buckling or breakage found in copper material.

Vertical crack occurred.Pile axially compressed.Concrete material broken

down.

Concrete material fallenoff along oblique crack.

Buckling or breakagefound in steel materialalong oblique crack.

Pile axially compressed.

concrete material wasfallen off.

Clearance formed between pile and footing,through which fixedreinforcing steels arevisible.

Buckling or breakagefound in steel material.

Pile axially compressed.Pile clinched.

2. Restoration and reinforcement of building foundations

2.1 Outline

To restore and reinforce foundations, first of all it is necessary to determine whether thedamaged elements will be restored for reusing, whether they are replaced with new ones, andwhether the damaged elements will be left with no restoration for retrofitting using additional

piles. If differential sedimentation occurred, needs to be corrected. For the foundations, therestoration of damages are usually done in parallel with the correction of differentialsedimentation without an exception of repairing works on the raising elements of foundationsand cracks and defects on foundation slabs because the differential sedimentation occurs in mostcases.

Generally, the foundation members (composed mainly of concrete) are repaired in thesame way commonly used as that for the structural members on the ground. On the other hand,at deep points under the ground, usually, repair works are not easily done and thereby, the use of additional piles may be basically useful in repairing when the members have been apparentlydamaged. If no other methods are available, such a method may be used that the surroundingarea around the damages member is compacted by improving the ground (e.g., the groutingtechnique). This method is difficult to apply to structural computation and usually, is consideredto be a quick fix or reserve-capacity one. Resin injection (the automatic low-pressure groutingtechnique) may be essentially used in repairing cracks in concrete materials and cross-sectionrepairing with high-strength mortar or concrete in repairing defects. In some cases, however,steel pipes are attached to the damaged piles to restore or reinforce depending on the degree of damages and the type of piles.

The methods for restoring settlements may be classified mainly into two: jack up andgrouting. Herein, the outline and basics of settlement restoring methods will be described. The


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individual rearing, reinforcing, and settlement restoring methods are introduced in Annex 3. Inaddition, they are also described in References 1 and 2.

2.2 Repair, retrofitting, settlement restoration

To restore damaged foundations, various types of methods are used depending on thefactors, such as the foundation form, building size, and desired restoration level, especiallymainly on the foundation form (pile foundation/direct foundation).

It is unlikely that broken direct foundations lead to functionality deterioration even if thefoundation members themselves incline to the same extent as in the case of pile foundations. Inmany cases, insufficient bearing capacity tends to incline the entire building together with itsfoundation and therefore, differential sedimentation needs to be restored from the standpoint of the functionality and dwelling performance. Expectation on restoration considerably varies on acase by case basis. To restore the settled buildings, the most commonly used methods are

jacking-up or grouting and the level is adjusted to use the existing bearing layer with nomodification. In some cases new piles may be used, depending on the state of the ground.

In the case where the buildings incline with minor damage, a simple method, by whichthe upper part above the foundation of its settled portion is jacked up and mortar is filled inclearances, or a method, by which differential sedimentation is restored using the groutingtechnique. On the other hand, in the case where settlement or differential sedimentation is severewith many cracks in the foundation, the upper side of the foundation may be jacked up constructa new foundation. If it is difficult to jack up the foundation due to the site condition or any other factor, it may be jacked down to adjust the level. Note that methods for restoring settlementcommonly used in foreign countries are introduced in Section 2.5. Among them, one of themethods used in China involves digging out soil under the foundation on the raised side (on thenot-settled side) by boring to restore to the horizontal level. To prevent middle size of detachedhouses and RC buildings from settling in the future, new piles are pressed into the ground tomodify the form of the foundation. To press piles into the ground for stabling the entire groundunder the foundation by means of improvement, various methods are used; for example, 1) actual

piles are used, 2) mortar is injected into the ground to form pile-like cement bodies, small-diameter of steel pipes are pressed into the ground, or 3) post ground improvement (in themethods 1) to 3), virtual piles are used). The jack-up and grouting techniques are described

below.

4.2.1 Jack-up technique

The jack-up technique, by which buildings are lifted, is the most used method for restoring the settled buildings and may be classified into several groups depending on the size of a building, site conditions, actual damages, and actual factors. The jack-up technique involveslifting up the settled portion of a building or the entire building using jacks literally. Hydraulic

jacks are commonly used. The jacks with capacity two to three times the building load should becorrectly inserted so that the same level of post load is applied on each of jacks. The jacks areusually inserted beneath the foundation footing supporting the posts. In some cases, however,they may be inserted beneath the underground beams. A special important factor is the capacityand arrangement of jacks to be used.


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For jacking-up the building, reaction force is requiring. The reaction force can beobtained in three ways described below depending on the size of a building and the ground statearound it:

1) The existing foundation is used as reaction force as it is.2) A mechanical jacking is used to ensure reaction force.3) New piles are pressed into the ground to ensure reaction force.The method 1) is used to easily and speedy restore settlement in the relatively small-sized

buildings (detached houses, steel-structured warehouses, etc.) with minor damages. Thistechnique does not restore substantially the settled building and thereby, the building may settleagain depending on the cause of the initial settlement. The method 2) is useful in the case wherethe ground around the settled building is relatively stable and the possibility of resettlement islow. The method 3) is used when reaction force can not be ensured on the existing foundation or ground, or when future settlement needs to be prevented in any way possible.

The most commonly used method for restoring differential sedimentation of buildingsusing jacks is the steel pier technique. This technique involves a process, in which steel pipeswith 200 to 400 mm in diameter, 1 m in length, are pressed into the ground one after another,up to the bearing layer using the building load as reaction force. It may be assumed that 1/2 to1/3 times the maximum press-in force is set for long-term permissible bearing capacity. Whenthe piles are pressed into the ground, the pressing-in force can be read using a manometer. Thismeans that the technique has an advantage in that most of bearing force may be verified as in theload test (note that it is not complete unlike the standard load test). Moreover, construction ismade only under the foundation and thereby, the building can be used as usual. The workingspace under the foundation is about 1.5 m.

Photos 2.2.1.1 and 2.2.1.2 show the states of the steel pier technique and the buildingrestored by this technique in Niigata Earthquake in 1964. Photo 2.2.1.3 shows the buildingrestored by the mechanical jacking technique.

In addition to the steel pier technique, typical jack-up techniques include the techniquesof mechanical jacking, saddle technique, shed restoration technique, and nekagami technique, of which outlines are described in Fig. 2.2.1.1. For more information, refer to Annex 3 if necessary.

Photo 2.2.1.1 Example of construction by steel pipe press-in technique


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Photo 2.2.1.3 Example of settlement restoration by pressure board techniqueThe ground in the vicinity of the periphery of the building was dug out and concrete was cast on a suitable natural

ground. Then, jacks were inserted between the concrete board and the bracket attached to the side wall of the periphery of the foundation to lift the foundation.

Photo 2.2.1.2 Examples of settlement restoration by steel pier techniqueand lifting technique Examples of settlement restoration of direct foundation type buildings settled by an

attack of Niigata Earthquake by steel pier technique while being used. As a part of constructionmanagement in settlement restoration, any vertical and horizontal displacement was automatically

measured using a slide meter and a seismometer.


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Fig. 2.2.1.1 Outline of jack-up technique(Supplied by: Mase Construction)

Steel pier Pressure board Sandle

Shed restoration Negarami

Support jack Hydraulic jack Hydraulic jack

Pressure board

Steel pipe piles are cast toreinforce the foundation anduse as a repulsive force inrestoration. Prevents re-settlement from occurring.

Concrete board (pressure board) is cast under thefoundation to use as arepulsive force in restoration.

In many cases, used for prefabricated and reinforcedconcrete houses. Uses theground as a repulsive force inrestoration.

Base

Bracket

Reinforcingsteel post

Negarami steel

Hydraulic jack

Often used for buildings constructed by conventional methods such astimbered axis. Note that it is

prerequisite that the ground is stable.

Often used for large-scale reinforcedconcrete buildings (factories andwarehouses). It is also prerequisitethat the ground is stable.


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2.2.2 Grouting technique

Most of restoring techniques basically involves a mechanical process for lifting thefoundation up using jacks, ensuring high certainty. In some cases, the grouting technique, bywhich grout is injected into the ground for raising it, lifting the building, is also used for directfoundation buildings. This technique has a reduce reliability and certainty; however, it may beuseful when easy and speedy restoration is required. The grouting technique is largely classifiedinto two types: in one type, the grout is permeated into the ground and in the other type it issolidified by itself without permeating. To improve safety of the entire foundation ground, theformer may be used under the foundation or around piles. To restore differential settlement, thelatter is suitable. Cement grout is used as grout because of its excellent durability (Photo 2.2.2.1).The chemical grouting technique involves a process for injecting a chemical (for jacking up,cement flash-set chemical), which requires a given time for curing when injected, to compact theground (the chemical can not permeate into the viscous soil layer and thereby, it enters into theground in the form of nervation). Recently, a new grouting technique has been put into practicaluse by which highly illiquid grout with a slump of almost zero is pushed into the ground under high pressure (Photo 2.2.2.2).

To restore differential settlement by grouting, it is required that the impermeable grout be pressed into the ground on the depressed side to increase the volume of the ground causing theground to rise. This results in the raising ground. In the chemical grouting technique, severalgrouting works are used. To restore settlement, the simple rod technique or the double packer technique, which allows for close construction management, is used. The chemical is in a liquidstate and has high fluidity, when injected, even if an impermeable one is used and therefore, ittends to travel in the form of nervation or layer. Accordingly, it is difficult to artificially control

the degree to which the ground is raised. Depending on the ground condition, no effect of grouting is observed.

On the other hand, unlike chemical grouting, in compaction grouting, illiquid (slump being almost zero) cement mortar is pushed into the ground under high pressure (approx. 100kgf/cm2 of max. discharge pressure) and so, it is unlikely that the grout travels in the form of nervation or layer and a mass (bulb-like) of cemented bodies are usually formed. Note that if theground, into which the grout is injected, is heterogeneous, the injected grout deforms. Since for the grout is hard to travel out from a given area, the degree to which the ground is raised can beeasily controlled. Accordingly, the settled building may be restored if construction is carefullymade while the lifting condition and effects of lifting on the periphery of the building are beingmonitored. Determining from the past results, the foundation form, to which compaction

grouting is applicable, is the direct foundation (especially, raft foundation). For a larger size of building, the vertical load under the foundation is also large. This means that the ground tends toexpand laterally when the foundation is raised. In this case, simply the ground around the

building may be raised without the building itself being lifted. This technique is only applicableto a moderate size of buildings.

It should be sufficiently noted that compared with the jacking up technique, the groutingtechnique has an advantage in time for completion and construction cost, while depending on theground condition/foundation form/size of building, no effect of grouting is expected. It isrequired to consider the ground environment because: 1) the grout may enter the neighboringsites across the boundary; 2) a water survey is conducted when a grouting work is made in the


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civil engineering field, and 3) it is difficult to conduct the ground survey or evaluate the grounditself when the site is reused for housing rehabilitation.

Photo 2.2.2.1 Example of settlement restoration using cement groutThe direct foundation-type of building is being restored from settlement by injecting a cement

grout.

Photo 2.2.2.2 Example of compaction groutingThe direct foundation type of building include due to liquefaction caused by an earthquake is being

restored by compaction grouting. Some of Slamps 2, 3, and 4 is used for the grout. This is an example pf applying compaction grouting to a Japanese house. This technique has not been usually used insettlement restoration in Japan.


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2.3 Restoring the settled detached houses

For the detached houses, basically, the steel pier technique is used to restore settlement(Photos 2.3.1 and 2.3.2). In the case where the continuous footing foundation has been used, theworking space can be ensured by digging a fox hole. For the raft foundation or the foundationwith piles jointed, construction is difficult and careful attention must be paid because of workingspace and steel pipe arrangement. The form of the foundation after the steel pile was pressed inresembles a pile foundation (since rolling compaction under the ground is difficult, almost noground bearing capacity can be expected). Depending on the interval between steel piles, thefoundation needs to be reinforced.

The grouting technique (Photo 2.3.3) is also used in some other cases. Since no designand construction methods for grouting have been established, its effects may vary on a basis of case-by-case and improvement of design and construction methods and accumulation of data isrequired. Compared with the continuous footing foundation, the raft foundation is easily lifted.If the periphery of the building is surrounded to limit grouting to the inner area, this technique isuseful. On the other hand, it is also important to discuss the effects on the surroundingenvironment (the grout may travel the neighboring sites and enter the discharge layer of the

backside of the retailing wall) and the ground environment.Furthermore, it is also important that the cost of settlement restoration varies depending

on the conditions such as design/construction techniques and the assurance system to be used.


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(f) Inclination measurement instrument (g) Joint (h) Vertical precision management (i) Loading testFig. 2.3.1 Steel pipe press-in technique for detached houses

(d) Joint welding (e) Pressed-in steel pipes

(a) Panorama view of test site

(b) Used steel pipes (1 m in length)

(c) Pressure management


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Photo 2.3.2 Steel pier technique for detached houses

(b) Steel pipes used by steel pipe press-in technique

(c) Steel pipe head treated

(a) Steel pipe pressed into the groundunder the foundation

Photo 2.3.3 Example of settlement restoration by steel pier technique for detached housesBy injecting flash-set type cement grout, a detached timbered house is lifted. The construction management is

performed using an auto level in settlement restoration.


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References1 Foundation and Method of Restoration of Damaged Building, Masahito TAMURA, Kenchiku Gijutsu,vol.9, 1995.2 Damage Grade Classification Manual of Building Foundations and Some Examples of Repair Techniques

by Mikio Futaki, Takashi KAMINOSONO and Shinsuke NAKATA, Kenchiku Kenkyu Shiryo vol.90,Building Research Institute, 1997.8

building performance and retrofit

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