Complications Caused by Neighboring and Building Construction in Urban Areas- Three Case Studies
Abolfazl Eslami* and Hasan Moghaddasi
Deptartment of Civil and Environmental Engineering, Amirkabir University of Technology, Iran
Submission: May 8, 2018;Published: June 25, 2018
*Corresponding Author: Abolfazl Eslami, Professor, Department of Civil and Environmental Engineering, Amirkabir University of Technology, AUT, (Tehran Polytechnic), Tehran, Iran, Tel: +98-2164543057; Email: email@example.com
How to cite this article: Abolfazl E, Hasan M. Complications Caused by Neighboring and Building Construction in Urban Areas- Three Case Studies.
Civil Eng Res J. 2018; 5(4): 555668. DOI:10.19080/CERJ.2018.05.555668
One of the major considerations for design and serviceability criteria in urban areas is the effect of stress induced on the subsoil from adjacent constructions. If adequate prevention is not provided in design, the overstress causes general or punching bearing capacity failure, or differential settlement, and subsequently, causing damages to existing structures. In this paper, three case studies of construction activities adjacent to existing structures were reviewed, in which serious damages have occurred. The buildings are 4 and 6-story buildings in Iran with shallow foundations located on problematic deposits. The reasons are investigated and discussed. In addition, for the third case, further analyses are performed in order to present an improvement design for the foundation system. According to the case studies, the damages were mainly observed as cracking, tilt and serviceability difficulties. The main causes of these instabilities were stress variations, by either loading or unloading, non-uniform forces, locating partly on non-engineered fills or weak and compressible deposits, poor construction, incorrect design as well as non-conservative design. In case of such instabilities, modification measures such as subsoil improvement, employment of complementary deep or semi-deep elements combined with current foundation system accompanied by jacking have been applied and worked.
A major concern for construction in urban areas is the impact of construction-related ground movements and induced stresses on adjacent buildings and utilities. In many cases, strict deformation control is required to minimize damages to adjacent structures .
The stress distribution with depth varies as bulb shape
stress lines as depicted in Figure 1a. When a new building is
constructed adjacent to an existing building, the stress bulbs
overlap, which imposes additional stress on the foundation of
the existing building. Figure 1b shows how the foundations of
two buildings interact as the distance between two foundations
decreases and are close. The additional stress or induced stress
can be problematic from two aspects :
a) Stress due: in this condition the sum of the existing
stress and additional stress exceeds the soil bearing capacity.
b) Non-uniform settlement: the changes in the soil
surcharge and stress imposed additional stress on one side
of the existing building, causing differential settlement and
rotation of the foundation of the existing building.
Apart from new construction, other changes and
inconsistencies in the environment may impose unwanted
stresses or displacements on the existing buildings and
structures. For instance, considerable fluctuation in groundwater
level, construction on fills, adjacent excavation and underground
excavation can cause significant differential settlement in a
The first case is a 4-story building located in Tehran, Iran
. As depicted in Figure 2 the building experienced instability
in form of rotation. The damages appeared as internal and
external cracks as shown in Figure 3. Observations have shown
cracking was more considerable in upper floors, which indicates
there have been other factors influencing the rotation apart
from land sliding. Therefore, a comprehensive investigation has
been carried out to find out the causes of this instability. Overall,
three factors were considered to be as the main causes. Firstly,
the building was built partly on a fill, which has led to nonuniform
settlement and consequently rotation of the building. In
addition, in the structural design, the bracing system designed
for this building was asymmetric which has caused an additional
torsion in the building. Furthermore, the building was adjacent
to an excavation, which has caused lateral displacement, and
subsequently, rotation of the building.
This case was a 6-story building located in Mazandaran
Province, Iran . The instability in this building has occurred
during final construction stages. Initial visits from the site
showed that the columns in six parts of the mat foundation has
experienced punching shear failure, with the settlement values
varying between 5 and 20cm. This differential settlement has
caused turning in the building, and subsequently, appearing
damages in the appearance Figure 3.
The investigation operations included boring of four test
pits (TP1 to TP4) using an auger, depth of which is presented
in Table 1 site soil consisted of a non-engineered fill layer with
1m thickness, underlain by a layer of fine clay with low plasticity
in brown, which was classified as CL according to the Unified
soil classification. Also, an intermittent layer of fine sand was
observed in the depth of 10 to 11m. The SPT number values in the
mentioned layer varied between 8 to 11 per 30cm penetration
and the groundwater level was at the depth of 2m. Therefore, the
site soil did not suffice the applied loads, which could bear the
approximate load of a three-story building Figure 4.
Several factors have caused this instability all of which were related to construction stage:
a) The thickness of the mat foundation was 70cm
according to the design, while the thickness of the constructed
foundation was 60cm.
b) Eliminating the foundation heel for about 110cm in the
northern and southern side, and 20cm in the western side.
c) The compressive strength of the concrete was not
sufficient either (89 to 167kg/cm2 according to the coring
samples instead of 210kg/cm2).
d) Another external cause was considered to be the
accumulation of the materials in the west side of the building
on various floors which has led to the non-uniform settlement of
the building Figure 5&6.
In order to cease the problem, in the first step, the
substructure was improved by semi-deep foundations.
This measure provided an appropriate support for jacks,
and increased the foundation bearing capacity along with
preventing the differential settlements and punching failure. It
also improved the uplift capacity of the foundation. Then, the
building was brought back to its initial condition by jacking.
The final step was strengthening the substructure which was
performed by improving the geotechnical properties of soil by
means of semi-deep foundations. Furthermore, the punched
columns were retrofitted and improved by additional bar
cages and high-strength concrete. Finally, a supplementary
mat foundation was constructed with the thickness of 40cm
over the existing foundation. The graphical presentation of the
modification measures is depicted in Figure 7.
The third case study is about the settlement induced on a
building due to the adjacent construction of a new building as
shown in Figure 8 . It was located in Mazandaran Province
near the Caspian Sea shoreline, Iran, and the site soil profile
consisted of a watery clay down to the depth of 4m, underlain
by a sand layer in depth 4 to 6m. Following this layer, there was
a layer of clay over the depth of 6 to 10m followed by a dense
The structure is a residential three-story building, with
allocated dead and live loads equal to 700kg/m2 and 200kg/m2,
respectively. The initial foundation system was a strip foundation
with the total area of 48m2 and contact stress of approximately
6t/m2. The foundation system sufficed the geotechnical criteria
against applied loads. However, the construction of the four-story
building in the west side of the current building has imposed
stress of about 8t/m2. Considering the overlap of the stress
bulbs, the stress below the existing structure has increased up to
14t/m2, which exceeds the allowable bearing capacity of 7t/m2.
Because of the clay layer in superficial surfaces, more
differential settlement is anticipated as the consolidation occurs
To solve this issue, it was required to improve the subsoil
property. In this regard, employing bored piles or micropiles
have been proposed in combination with the existing footing
so that in addition to increasing the bearing capacity, tensile
capacity against seismic loads and decreasing the stresses
caused by neighboring, it provides more promising serviceability
performance and restricts the settlements.
In order to design and assess the sufficiency of the new
foundation system against new conditions, i.e. the loads from the
structure itself and the imposed load from adjacent construction,
a numerical analysis has been carried out.
PLAXIS 3D FOUNDATION was used for numerical modeling.
The soil characteristics used in the model are presented in Table
The foundation was simulated in three conditions:
a) Initial geometry and design loads
b) Initial geometry and design loads plus load imposed by
c) Improved foundation and design loads plus load
imposed by adjacent construction.
Figure 9 demonstrates the soil layers as well as foundation
geometry before and after modifications. As presented, for the
enhanced foundation, eight bored piles were added in different
parts of the existing foundation.
The results of settlement analyses are shown in Figure 10.
Figure 10(a-c) are the settlement contours for above-mentioned
models 1 to 3, respectively. It can be inferred by the results that the
minimum and maximum settlement of the initial foundation was
54mm in center and 49mm in the peripheral area, respectively.
The differential settlement is therefore 5mm which is within
the allowable range. However, according to Figure 10b, when
applying additional load in the west side of the foundation, the maximum settlement occurs in the west part of the foundation,
which equals 140mm. Also, the minimum settlement pertains to
the east side of the foundation which is 76mm. Consequently, the
differential settlement is 64mm .
For improving the performance of the foundations, eight
bored piles were considered with the embedment length and
diameter of 11m and 1000mm, respectively. According to Figure
10c, employing additional piles results in significant decrease
in the values of settlement, subsequently, providing safe
It should be mentioned that employing these piles, in
addition to increasing the bearing capacity and reducing
settlement, provides higher capacity against lateral loads and
instability of soil at shallower depths [11,12].
One of the major considerations for construction in urban
areas is the effect of induced stresses due to adjacent structures.
If adequate preventions are not provided in construction, it may
have adverse effects on existing structures, in terms of imposed
stress or differential displacement, subsequently causing
serviceability problems and damages to existing structures
including differential settlement, punching bearing capacity
failure, and building rotation.
Three building case studies have been reviewed, in which
the construction adjacent to a building caused significant
damages to existing structures. The buildings were 4 to 6 stories
built on shallow footings. The damages mainly occurred as
serviceability issues, building rotation and cracks which were
more significant in upper floors. The investigations showed
that the main reason was stress variations, either loading or
unloading, which imposed extra underground stress, leading to
punching failure and differential settlement. In addition, other
factors such as non-uniform loading, locating building partly on
non-engineered fills as well as non-conservative design and poor
construction have intensified the damages.
Numerical modeling analyses indicate that employing
additional short bored piles in conjunction with the existing
piled-strip footing significantly reduced the differential
settlement values. In addition, using short bored piles would
increase tensile capacity of foundation as well as the bearing
capacity against lateral loads. The new retrofitted foundation
was capable of bearing any other changes in environmental
conditions such as groundwater level changes, passing heavy
traffic on the adjacent street, probable earthquakes and
For projects encountering neighboring construction, a few
modification measures can be employed to cease the progressive
a) Enhancing subsoil properties within the influence zone
by soil improvement techniques feasible for the project.
b) Increasing foundation bearing capacity by employing
supplementary foundation elements, preferably semi-deep
or deep. In this regard, bored piles as well as micropiles are
considered to be an appropriate options depending on the
feasibility for a specific project.
c) Jacking so as to reduce the undesirable settlement, and
bring the building back to initial condition.
d) Providing safe and sufficient connection between the
old foundation and added elements, in order for long-term