- 15 - http://www.ivypub.org/AE Architect ural Engineering February 2014, Volume 2, Issue 1, PP.15-19 Case History Based on Jacked Steel Pipe Piles to Rectify Inclined Buildings H aile i Kou # , Mi ngyi Zhang Institute of Geotechnical Engineering, Qingdao Technological University, Qingdao 266033, China # Email: [email protected] Abstract Steel pipe piles are often used as an effective technique for improving the performance of inclined buildings, which derive their load-carrying capacity due to lateral confinement from the surrounding soil and toe resistance. The traditional steel pipe piles may lead to uncontrollable settlement and instability after rectification. In this paper, an alternative method of enhancing the performa nce of steel pipe piles with screw devices driven vertically is suggested. The method is developed in a practical engineering and verified feasible. The investigation is carried out by monitoring the cracks on the wall with Electronic Levels during and after rectification. It is indicated that the steel pipe piles with screw devices have much higher stability with a significant reduction in settlement comparing with other methods. Keywords: I nclined Buildings ; Stee l Pipe Pil e s ; Rectif icati on; Sc rew Device I. INTRODUCTION Among various techniques for improving the performance of inclined buildings, jacked steel pipe piles are considered as one of the most versatile and cost-effective improvement techniques (Guo Tong et al., 2002). Steel pipe piles,which the end locates on bearing stratum, act as strong and stiff elements that can carry higher bearing capacity (NICOLA,1999).It is well established that jacked steel pipe piles can supply load-carrying capacity in building rectification (Thorburn,1985).Afte r installation, the steel pipe piles may not derive significant load carrying capacity owing to uncontrollable settlement. In order to enhance the performance of steel pipe piles when treating weak deposits, it is imperative that the tendency of uncontrollable settlement during rectification should be restricted effectively. Hence, there is a need to identify effective and alternative methods which should be practically feasible to enhance the performance of steel pipe piles in building rectification. In this paper, an alternative method to enhance the performance of steel pipe piles in building rectification by special screw device on top of steel pipe piles is suggested. Through the rectification case history in Shanxi province of China, the design and technological process of the screw device are introduced in detail. II. DESIGN PROGRAMME As steel pipe piles are generally used beneath uniformly loaded areas such as buildings, the common method of restraining further settlement fails adequately. A special adjustable screw device is designed to reduce the subsequent settlement after rectification and enhance the stability of buildings, as shown in Figure1.The screw device, which locates on the steel pipe piles, can be adjusted according to engineering needs. As the most important part of the method, the screw devices need have good self-lock property in order to prevent subsequent settlement. Therefore, triangle screw thread is taken and number 45 carbons steel is chosen as the material. The parameters of the screw device should be chosen according to the largest force of the inclined building and, the strength needs be checked before used. In order to prevent further sink during rectification process, pre-compression screw devices with two single screws are adopted in the side with larger settlement, as shown in Figure 2. After rectification, the jack would be pulled out and only one pair of screw device will be used.
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8/12/2019 Case History Based on Jacked Steel Pipe Piles to Rectify Inclined Buildings.pdf
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Architectural Engineering
February 2014, Volume 2, Issue 1, PP.15-19
Case History Based on Jacked Steel Pipe Piles to
Rectify Inclined BuildingsHailei Kou
# , Mingyi Zhang
Institute of Geotechnical Engineering, Qingdao Technological University, Qingdao 266033, China
#Email: [email protected]
Abstract
Steel pipe piles are often used as an effective technique for improving the performance of inclined buildings, which derive their
load-carrying capacity due to lateral confinement from the surrounding soil and toe resistance. The traditional steel pipe piles
may lead to uncontrollable settlement and instability after rectification. In this paper, an alternative method of enhancing the
performance of steel pipe piles with screw devices driven vertically is suggested. The method is developed in a practical
engineering and verified feasible. The investigation is carried out by monitoring the cracks on the wall with Electronic Levels
during and after rectification. It is indicated that the steel pipe piles with screw devices have much higher stability with a
significant reduction in settlement comparing with other methods.
Keywords: I nclined Buildings; Steel Pipe Pil e s; Rectif icati on; Screw Device
I. INTRODUCTION Among various techniques for improving the performance of inclined buildings, jacked steel pipe piles are
considered as one of the most versatile and cost-effective improvement techniques (Guo Tong et al., 2002). Steel
pipe piles,which the end locates on bearing stratum, act as strong and stiff elements that can carry higher bearing
capacity (NICOLA,1999).It is well established that jacked steel pipe piles can supply load-carrying capacity in building rectification (Thorburn,1985).After installation, the steel pipe piles may not derive significant load carrying
capacity owing to uncontrollable settlement. In order to enhance the performance of steel pipe piles when treating
weak deposits, it is imperative that the tendency of uncontrollable settlement during rectification should be restricted
effectively. Hence, there is a need to identify effective and alternative methods which should be practically feasible
to enhance the performance of steel pipe piles in building rectification.
In this paper, an alternative method to enhance the performance of steel pipe piles in building rectification by special
screw device on top of steel pipe piles is suggested. Through the rectification case history in Shanxi province of
China, the design and technological process of the screw device are introduced in detail.
II.
DESIGN PROGRAMME As steel pipe piles are generally used beneath uniformly loaded areas such as buildings, the common method of
restraining further settlement fails adequately. A special adjustable screw device is designed to reduce the
subsequent settlement after rectification and enhance the stability of buildings, as shown in Figure1.The screw
device, which locates on the steel pipe piles, can be adjusted according to engineering needs. As the most important
part of the method, the screw devices need have good self-lock property in order to prevent subsequent settlement.
Therefore, triangle screw thread is taken and number 45 carbons steel is chosen as the material. The parameters of
the screw device should be chosen according to the largest force of the inclined building and, the strength needs be
checked before used.
In order to prevent further sink during rectification process, pre-compression screw devices with two single screws
are adopted in the side with larger settlement, as shown in Figure 2. After rectification, the jack would be pulled outand only one pair of screw device will be used.
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screw bolt
screw cap
(hexagan)
soleplate
foundation ring beam
H-steel
transmission bar
pile
foudation ring beam
precompression screw
device (as tool) jack
the reserved pisition
of screw
pile FIG. 1 SCREW DEVICE AND INSTALLATION FIG. 2 PRE-COMPRESSION SCREW DEVICE
Before start to rectify, the accurately accommodation amplitude must be calculated to make sure that the building is
safe enough during the process. The calculated principle is shown in Figure 3,where△stands for inclination
magnitude and H is the total height of the building. The theoretical fulcrum should be in the middle of bottom
surface. However, in practical engineering, there may be no pile at that point, the pile nearest to the point is taken as
the fulcrum. s1, s2, s3 and s4 in the Figure 4 stand for the demanded rectification magnitude of piles respectively,
which can be calculated by graphic method or simple proportional relation. The rectification should be done for
several times, and about 1/10 of the total regulation magnitude for each time.
fulcrum
the rectified plane
incline plane
H
FIG.3 CALCULATION PRINCIPLE OF RECTIFICATION MAGNITUDE
In order to avoid further cracks, it is more effective that lifting-up and forcing-down are carried out simultaneously.
Forcing-down measures, including moving away the excessive remained foundation under the foundation ring beam,
soaking the soil under remained foundation, and loading heavy objects on the floor ， are necessary in the method.
The up or down extent of screw device can be controlled precisely, that is, corresponding up or down value occurs
when the device turns some angle. Because of good self-lock property of screw device, there is no need to measure
the angle one by one. The magnitude of each rectification should be controlled strictly in order to avoid temporary
twist of building caused by lifting-up. It is generally about 1-3mm or 1/10 of the total magnitude mentioned above.
The upper structure can afford such small deformation through inner force redistribution, and the further cracks can
be avoided. After every lifting-up, the space on another side will shrink in several hours and repeat that until the
building is ok. When the rectification is finished, the screw device has to be welded and wrapped with protective
concrete.
III. ENGINEERING APPLICATION
A. Example situation
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The inclined building is a brick -concrete structure with 48.0m of length, 7.8 m in width, and 15.0m in height, which
is located in Yi xing, Shanxi Province, China. It is divided into 4 units, and the total floor area is 2031 m2. Two years
after construction, the building has been inclined because of non-uniform settlement and has big space between
building and ground (see Figure.4 and Figure.5). At northeast corner, the largest settlement is 17.5 cm, about 1.13 %
of the total height, and the ratio is over 0.7 %. According to Chinese code ‘The identification standard of dangerous
building’ (CJ13-86), it is termed as dangerous building and there are several cracks through the building. Through
field investigation before rectification, the main reason is that within 10m under the building ,there exists
non-uniform miscellaneous fill and silty clay which is not treated sufficiently .The ring beams with section of 0.4
m×0.3 m in each floor are integrity and the foundation is made of rubble.
A. FULL-LENGTH CRACK UNDER THE BUILDING B. SOME CRACK UNDER THE BUILDING
C. CRACKS THROUGH THE BUILDING
FIG.4 SITUATION OF INCLINED BUILDING
FIG.5 SKETCH MAP OF INCLINED BUILDING
B. Rectif ying constructionIn this engineering, the designed dead load of each unit is 12500KN, and 58 piles are used, which the standard
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bearing capacity of each pile Rk is 220 kN.The final installation pressure should not be lower than 330 kN (1.5×220
kN).Hence, the biggest load of each screw device is confirmed as 350KN, and M36×3 is chosen according to
mechanics code. The detailed parameters are shown in Figure 6. In addition, the shear stress, bending stress and
bearing capacity of screw device should be calibrated in laboratory before used.
Before rectification, some remained foundation must be moved away, and then pilot holes with 60cm in width
should be excavated immediately, as shown in Figure7.Steel pipe piles are pressed into the holes sectionally byhydraulic jack, which the section is about 2 meters and joined with sulphide mastic. The total pile with 10.5m in
length can reach the stratum of dense sand through the stratum of silty clay and miscellaneous fill. But in practice
several piles may not follow the procedure exactly because it is mainly controlled by the pressure. Static loading
testing is later carried out to substantiate the piles’ bearing capacity.
3 0
1 4 5
1 2
0
1 0
5
¦ µ50
hexagonals=55,e=66
M36×3
M60
1 2 5 1
3 5 ~
1 8 5
FIG.6 STRUCTURE OF SCREW DEVICE
FIG.7 PILOT HOLE IN BUILDING RECTIFICATION FIG.8 SCREW DEVICE IN BUILDING RECTIFICATION
A. I NTEGRAL DECLINE OF THE BUILDING B. SITUATION AFTER RECTIFICATION FIG.9 COMPARISON BEFORE AND AFTER RECTIFICATION
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