laboratory investigation on construction materials from kubwa extension building collapse site,...

7/28/2019 LABORATORY INVESTIGATION ON CONSTRUCTION MATERIALS FROM KUBWA EXTENSION BUILDING COLLAPSE SITE,

1/15

LABORATORY INVESTIGATION ON CONSTRUCTION MATERIALS FROM KUBWA EXTENSION BUILDING COLLAPSE

SITE, ABUJA

1 | P a g e

LABORATORY INVESTIGATION ON CONSTRUCTION

MATERIALS FROM KUBWA EXTENSION BUILDING COLLAPSE

SITE, ABUJA


2/15


SITE, ABUJA

2 | P a g e

CONTENTS

1.0 INTRODUCTION

2.0 BACKGROUND

3.0 GEOTECHNICAL INVESTIGATIONS

4.0 ANALYSIS OF TEST RESULTS

5.0 DISCUSSIONS AND RECOMMENDATIONS


3/15


SITE, ABUJA

3 | P a g e

TABLES AND FIGURES

List of Tables

Table 1 Allowable Bearing Capacity Values

Table 2 Summary of Laboratory Test Results

Appendices

Appendix A Particle Size Distribution Graphs

Appendix B Atterberg Limit Test

Appendix C Direct Shear Test

Appendix D Consolidation Test


4/15


SITE, ABUJA

4 | P a g e

1.0 INTRODUCTION

Construction materials comprises of any item consumed or used in a construction project and

incorporated into the constructed building or structure. It covers a wide variety of materials

ranging from aggregates (fine and coarse), reinforcement, cement, bricks, blocks e.t.c. To ensure

the durability and stability of any structure, it is pertinent that a detailed engineering design is

carried out to ensure that the proper construction material is recommended for the proposed

work. Hence, construction material testing is a critical component in the design and construction

of any civil engineering structure. Unfortunately, this is not the case as the use of poor

construction materials has been attributed to be the major cause of building collapse in Nigeria

(NBRRI Technical Reports No. 22 & 23). As a result, to ascertain the cause of any building collapse,

the first step would be to conduct a thorough laboratory investigation of the construction

materials used on the site.

The report for the laboratory investigation conducted on the construction materials at the

building collapsite site at Kubwa Extension is presented herein.

1.1 Project Objectives and Scope of WorkThe purpose of the laboratory investigation was to determine the physical and engineering

parameters of the construction materials used on the building collapse site. This will determine if

the cause of the building collapse in question was as a result of poor quality of construction

materials and identify which of the construction materials. To achieve this, the investigation

comprised of the following:


5/15


SITE, ABUJA

5 | P a g e

Laboratory testing of soil samples collected from the site to determine index andengineering properties of the subsoils. Tests conducted include:

Particle size distribution Atterberg limits Direct shear test Consolidation test

Compressive strength test on concrete rubbles and blocks collected from the site. Tensile strength test on reinforcement collected from the site Engineering analysis to determine suitability of materials used. Preparation of report including conclusions and findings.


6/15


SITE, ABUJA

6 | P a g e

2.0 BACKGROUND

The building collapse site was located at No 3 Ademola Awosika Road, close to the Living Faith

Church, Kubwa Extension III, FCT. The collapsed Buildingwas an L-shaped framed structure

and collapse occurred in the early hours of Wednesday 8th of August, 2012.

The foundation of the building was completed and abandoned for over ten years. The structure

was under construction with the second floor and its columns completed; while the roof beams

were being formed when it collapsed. The framed structure collapsed and came down

completely with the structural elements reduced to a heap of rubble; and concrete dissociating

from element reinforcement. The mode of failure was not as expected for a framed structure

still under construction. This is indicative of weak foundation and failure of structural

elements.


7/15


SITE, ABUJA

7 | P a g e

3.0GEOTECHNICAL INVESTIGATIONS3.1Collection of Samples

Samples were collected from the building collapse site on the 27 th of September, 2012. Soil

samples were collected at a depth of 1m below ground level from three different locations on the

site. Two intact block samples (9 and 6)were collected from the site as well concrete debris.

Reinforcement of diameters 12mm, 16mm and 20mm were also collected to test their tensile

strength.

3.2Laboratory Testing of Soil SamplesThe following tests were conducted on the samples collected from the site:

Particle size distribution Atterberg limits Specific Gravity test Direct shear test Consolidation Test

Particle Size Distribution:This test is performed to determine the percentage of different grain sizes contained within

a soil. The mechanical or sieve analysis is performed to determine the distribution of the

coarser, larger-sized particles, and the hydrometer method is used to determine the

distribution of the finer particles. This test is performed in accordance with BS 1377: Part

2: 1990. The distribution of different grain sizes affects the engineering properties of soil.


8/15


SITE, ABUJA

8 | P a g e

Grain size analysis provides the grain size distribution, and it is required in classifying the

soil.

Atterberg LimitsThe Atterberg limits are based on the moisture content of the soil. This test is performed to

determine the plastic and liquid limits of a fine grained soil. The liquid limit (LL) is

arbitrarily defined as the water content, in percent, at which the soil changes from a plastic

to a viscous fluid state The plastic limit is the moisture content that defines where the soil

changes from a semi-solid to a plastic (flexible) state. The shrinkage limit is the moisture

content that defines where the soil volume will not reduce further if the moisture content is

reduced. A wide variety of soil engineering properties have been correlated to the liquid

and plastic limits, and these Atterberg limits are also used to classify a fine-grained soil

according to the Unified Soil Classification system or AASHTO system.

This test was performed in accordance with BS 1377: Part 2: 1990.

Direct Shear TestThe direct shear test is used for carrying out drained shear tests for the determination of

effective shear strength parameters in cohesionless soils. The test was carried out using the

small shearbox apparatus on undisturbed specimens obtained from the trial pit. This test

was carried out in accordance with clause 4 of BS 1377: Part 7: 1990.

Condolidation TestThe consolidation/oedometer test is performed to determine the rate of one-dimensional

consolidation in clayey soil samples. This test is performed to determine the magnitude and


9/15


SITE, ABUJA

9 | P a g e

rate of volume decrease that a laterally confined soil specimen undergoes when subjected

to different vertical pressures. This test was carried out in accordance with clause 2 of BS

1377: Part 5: 1990.

3.3Laboratory Testing of Concrete and ReinforcementIn the laboratory, the compressive strength test is carried out on concrete to determine the

maximum strength at failure. A normal force is applied on the concrete element until it fails and

this force is divided by the surface area to ascertain the compressive strength of the element. To

obtain a represenative compressive strength, ten samples are usually crushed and the average is

calculated as the compressive strenght. Unfortunately, an adequate number of samples from the

salbs, beams or columns could not be obtained from the collapse site as most of the concrete

elements had been broken up. Hence, the compressive strength test could not be performed.

Similarly, the reinforcement obtained was deformed and rusted, hence could not be tested.


10/15


SITE, ABUJA

10 | P a g e

4.0ANALYSIS OF TEST RESULTSThe purpose of the laboratory investigation was to determine the physical and engineering

parameters of the construction materials used on the building collapse site. This will determine if

the cause of the building collapse in question was as a result of poor quality of construction

materials and identify which of the construction materials.

4.1 Bearing Capacity Analysis

The ultimate bearing capacity for foundations can be evaluated using shear strength parameters

obtained from in situ or laboratory tests with suitable theoretical analysis. The Terzaghi equations

which are applicable to foundations where the depth of foundation is less than the minimum

width can be used as follows:

For strip foundation,

Qu = cNc + Z(Nq-1) + 0.5BN

For square footing,

Qu = 1.3cNc + Z(Nq-1) + 0.4BN

For circular footing,

Qu =1.3 cNc + Z(Nq-1) + 0.3BN

Where: Qu Ultimate bearing capacity (kN/m2)

c Cohesion (kN/m2)

Unit weight (kN/m2)

Z Depth of footing (m)

B Width of footing (m)

Nc, Nq, and Nare bearing capacity factors dependent on the angle of internal friction ()


11/15


SITE, ABUJA

11 | P a g e

The allowable bearing capacity Qa, is the ultimate bearing capacity divided by a suitable factor of

safety to limit settlements to 25mm and is usually in the range of 2 4. For foundations, a factor of

safety of 3 is recommended.

The table below presents the allowable bearing capacity for a square footing assuming a width of

2m.

Table 1: Allowable Bearing Capacity Values

Allowable Bearing Pressure kN/m2

Sample A Sample B Sample C

DEPTH m

1 126 133 154


12/15


SITE, ABUJA

12 | P a g e

5.0DISCUSSION AND RECOMMENDATIONS5.1 Discussion

a. SubsoilThe subsoil investigation at the collapsed site show that the subsoil consists basically of reddish to

brwonish clayey sand. The grain size distribution of the soil showed more than 50% of the soils

were retained on sieve No 200, indicating the soils are coarse grained. Since, 50% of these soils

passed through sieve No 4, the soils are generally sandy soils. Also, the atterberg limits of two of

the samples plotted below the line while the third plotted above the A-line on the Cassagrande

plasticity chart. Based on the USCS soil classification system, these soils fall into the silty sands and

clayey sands groups respectively. These soils generally have slight to medium expansion and

compressibility with poor drainage characteristics.

The results from the direct shear test further revealed the soil to be cohesive soils with an average

internal friction of 180. Allowable bearing pressures ranged from 126 154 kN/m2. These values

indicate that the soils bearing capacity was not exceeded. Hence, it can be deduced that the failure

was not as a result of poor bearing capacity of the soil.

b. ConcreteAs discussed in the previous section, compressive strength test could not be conducted due to

insufficient number of samples. However, the following deductions were made based on visual

observation of the concrete rubbles collected:

Percentage of fine aggregates was more than the coarse aggregate Poor mix(voids observed in sample)


13/15


SITE, ABUJA

13 | P a g e

Single sized aggregate(1 inch)was used Low cement content Aggregate Crushing Value(ACV) is over 37 Fine aggregate used did not pass the required envelope

c. ReinforcementSimilarly, the tensile strength test could not be conducted due to insufficient number of

samples. Also samples collected were bent and rusted which would reduce the tensile strength

of the members.

d. BlocksFrom visual observation, the blocks collected from the site appeared to be okay. As mentioned

above, ten blocks are required to give a representative value of the blocks used on the site.

5.2 Recommendation

Details of laboratory investigation of construction materials collected from a building collapse site

at Kubwa Extension are presented in this report. Building was an L-shaped framed structure still

under construction. Laboratory investigation of the subsoil shows that the bearing capacity of the

soil was satisfactory. However, the soils exhibited medium expansion and compressibility

characteristics. Laboratory tests could not be performed on the other construction materials

(concrete elements, blocks and reinforcement) due to the insufficient number of samples collected

from the collapse site. It is recommended that ten samples of each material to be tested should be

collected from building collapse sites to ensure that a representative value is obtained. However,


14/15


SITE, ABUJA

14 | P a g e

visual observation of the concrete elements indicates a poor structural design was conducted

prior to construction.


15/15


SITE, ABUJA

15 | P a g e

REFERENCE

NBRRI Technical Report No. 22: Collapse of Buildings in Nigeria (Technical Report on the Collapse

of a 2-Storey Building at Mararaba. October 2011

NBBRI Technical Report No. 23: Collapse of Buildings in Nigeria (Technical Report on the Collapse

at Adenubi Close, Ikeja Lagos State. October 2011

laboratory investigation on construction materials from kubwa extension building collapse site,...

Documents