Zonal Mapping of Risk Information Model of Construction in Laterite Soil

International Journal of Advanced Science and Technology Vol. 29, No. 6, (2020), pp. 8548-8556 Zonal Mapping of Risk Information Model of Construction in Laterite Soil

Bhagyashree1 *, Kavyashree2

1Assistant Professor, Dept. of Civil Engineering,

Manipal Institute of Technology, Manipal Academy of Higher Education, Manipal, India

2Research Scholar, Manipal School of Architecture and Planning,

Manipal Academy of Higher Education, Manipal, India

[email protected], [email protected]

Abstract

The present study is an experimental investigation on the geotechnical properties of soil samples relevant to construction industry. The main point of view of the study is to understand the characteristics of soil samples before carrying out of any construction on it which is essential too. These papers summarize the characteristics of laterite and its suitability for the construction of high-rise buildings on it.For this the samples were collected from nine different places which are nearby to each other in the coastal belt of Dakshina Kannada district. Geotechnical tests were performed that includes all the preliminary tests to be conducted on the soil. Construction Risk Management is considered to be the integral part of any construction project and it is achieved by forming risk matrix. Five Point Likert scale is used to categorise the risks from very high to very low. Safe Bearing Capacity of soil is considered for the above calculations.

Key words: Laterite soil, Safe Bearing Capacity, zonal map, Likert scale

1. Introduction

Soil is an organic compound which has been evolved from centuries together due to decomposition of bigger rock particles. It is essential for all the civil engineering works as it is the underlying material for any kind of structure. All the physical properties along with mineralogical properties play an important role in the stability of the soil structure. Its load bearing capacity is very crucial in deciding the type of buildings to be constructed on a particular type of soil. Bearing capacity may be calculated in many ways. Soil type, foundation width, its weight in the zone of shear etc. are the factors influencing safe bearing capacity of the soil. While calculating safe bearing capacity of soil it is assumed that a there is uniform contact pressure in between the underlying soil and foundation. If all other factors are kept uniform, there are still few more factors affecting the safe bearing capacity of soil like failure type of soil, foundation depth and water table.

International Journal of Advanced Science and Technology Vol. 29, No. 6, (2020), pp. 8548-8556

1.1 Laterite soil

Among all the significant sets of the tropical and subtropical soils in the globe, laterite soils conquer a distinctive place, with respect to both their widespread existence and irregular characteristics. Laterite is highly weathered type of soil and is most abundantly available in coastal Karnataka region.it contains heavy but varying extents of iron and aluminium oxides as well as quartz and other minerals. Most laterites are red in colour due to the existence of iron oxides. They grow by concentrated and ongoing weathering of the fundamental parental rock.These type of rocks are readily available at lower rates, eco-friendly and their availability is also ample. Therefore it is used as a building material in the tropical region. In developed and under developed countries these stones are used as building materials especially in rural areas.Construction of high storeys on these soil is highly depended on the SBC of the soil in that place. Usually laterite soil has a higher SBC but sometimes it may not be sufficient to withstand the load from high storey building.

1.2 Risk

Construction industry has to manage lots of risk. This includes financial risk, design risk, safety risk, settlement risks etc. Risk management in construction industry involves understanding, evaluating and countering towards the risk. There is different methodology which has been adopted to analyse the risk. It includes the wide-ranging of Optimistic and destructive influences on the upcoming result of a mission. It is thinkable to guess the probability and the harm that could occur. The risk investigation is observed as the examination of opposing events even at the phase of planning and proceeding of any construction project

Risk Assessment is the first stage of risk management. Presently, a huge number of risk management approaches are present, but none of them relate to a condition where numerous factors are required to work on one plan. By creating risk assessment matrix it is possible to understand the probability of risk and in the present study the safe bearing capacity of soil is considered as one factor to understand the risk present in the respective regions.Bearing capacity plays a vital role when it comes to construction industry as the structure is going to stand on the particular soil carrying its entire load by putting the pressure on the soil on which it is established. The sub soil study is something essential to be understood before carrying out any work on it as repeated study of sub soil is impossible once any work begins on the particular soil. It can lead to major changes that are required to be done to reduce risk. Risk may occur with respect to cost, time, and resources anything which may effect on the project hugely.

2. LITERATURE REVIEW

2.1 Soil in Construction Engineering

The appropriateness of soil for its better usage should be known depending on its geotechnical characteristics, not just by seeing it or its noticeable resemblance with similar soils. Description regarding the top, middle and sub-surface characteristics is necessary for designing and for development of any structures [1]. As per several articles the evaluation of engineering characteristics of soil insitu is needed before the construction phase as it helps in getting appropriate information for the design foundations for the planned structures[2].The nature of soil varies worldwide. Soil type, colour, nature etc. varies from one place to another depending on the type of rock, minerals present in it and also on the environment of the respective places. Settlement of soil can lead to several savoir problems which can cause critical effect if they are left unanswered. Subsurface geological conditions therefore can be understood by complete geological investigations prior to the design and the construction work .The introductory

International Journal of Advanced Science and Technology Vol. 29, No. 6, (2020), pp. 8548-8556 investigations are intended towards the character and formation of the rocks at the site, and to get exact information about the soil [3]. Thus careful sampling and documentation of collected soil samples has to be prepared. Arranged document must be a source for site environment, earth science, rock science, seismicity and hydrology. And based on information collected the variation of ground should be done accordingly.

2.2 Safe Bearing Capacity of Soil

Laterite soil is considered as one of the cost effective and carrying more energy efficiency than other type of soil [4]. In foundation engineering, the footing bearing capacity with eccentric load is taken into consideration by two researches. They are effective area and reduction factor methods [5]. Wherein it gives information about contact pressure distribution below the footing as well as reduction in the size of the footing in order to impose the pressure on the reduced area. Several civil services in different nations provide the allowable bearing capacity that can be used for different types of footing in their building codes.

2.3 Risks in construction due to soil

Construction projects can be managed with the help of diverse risk management tools and techniques. The eventual objective of risk management is to boost the probability of activities involved in project to be succeeded by having focussed concentration on complex areas in the beginning itself and thus to reduce the quantity of expensive modification in the future [7]. The unfavourable happenings should be analysed in planning phase itself for any construction projects, which terms to be risk analysis [8]. Risk can occur in various terms when it comes to construction engineering. Many researchers’ have worked on finding out the probability of risk with respect to different random constraints. There are several ways to proceed with for risk analysis which includes either qualitative or subjective assessment of the project risk. Risk Assessment Matrix is one of the effective methods to analyse risk which includes two major constraints that is risk factors and risk ranking guidelines [9]. Risk factors are the one which influence the project majorly. The risk ranking guidelines are the one which helps in quantifying the risks as low, medium, and high-risk profiles. They are used to establish the impact of risk considering each of the risk factors to the project baseline.

2.4 Communicating & Managing Risk in Geotechnical Engineering Practice

Studies have shown inspections regarding six areas of geotechnical risk commonly come across have been discussed. The six areas comprises of sites with unrestrained fill, sites with extremely malleable soils, the existence of rock, cover collapsing sinkholes, deep foundations and mechanically modified earth retentive walls. Geotechnical risks may arise in all phases of a project life that is in designing phase, construction phase, and during operation. Also it is not restricted to the spatial dissimilarities of engineering properties.

2.5 Bearing Capacity of soil and foundations of buildings Foundation structures go through soil-structure interface. So, the performance of footing rely on the properties of soil. Determining the characteristics of soil itself is a specified subject in geotechnical engineering. Accepting the interfacing activities are also hard. Hence, several assumptions were made and adopted for the design and analysis. In reality, for the design of foundations of any structures the difficult soil conditions must be well known by the geotechnical professional who includes the type of foundation to be adopted for different type of soil depending on the type of structure [6].Failure by shear

International Journal of Advanced Science and Technology Vol. 29, No. 6, (2020), pp. 8548-8556 itself is considered to be bearing capacity failure. So understanding of this concept for any soil prior to the construction phase is very much important to get an effective result.

3. METHODOLOGY

Undisturbedsoil samples are collected from the selected strategic points. Geotechnical tests i.e Specific gravity, Water content, Liquid limit, Plastic limit, Dry density by core cutter method and Unconfined compression test are conducted as per IS codes.

Dry density Test by Core cutter method: Core Cutter will be conducted to determine the dry density of Natural or Compacted Soil in-situ, as per IS: 2720 (Part XXIX) 1975.

Water content determination: Water content can be determined using 3 methods – 1) Oven Drying Method 2) Infra-Red Heat Method (Torsion Balance Method 3) Pycnometer. Here Oven drying method was used to determine the Water Content of the Soil Sample, as per IS: 2720 (Part-2)1973.

Determination of Specific Gravity: Specific gravity of the soil particles will be determined, as per IS: 2720 (Part- III) 1975. The Specific Gravity of most of the soil lies between 2.65 to 2.85, high specific gravities as 3.00 or more can be attributed due to the presence of specific minerals like Iron etc. The Specific gravity of minerals are generally higher for Quartz (2.65) and clay with specific gravity 2.9 are not uncommon. For fine grained soil, a 50cc specific gravity bottle is used whereas for coarse soil 1000cc Pycnometer bottles are used. Pycnometer method will not give accurate results for fine grained soils, as it is difficult to remove the air-voids from the fine grained soils.

Liquid Limit test and Plastic Limit test: Geotechnical properties of the coarse and fine grained soils, usually for clayey soilsfluctuatemore at altered water contents. Clayey soils act as liquids,sometimes plastic or sometimes will be firmbased on the water content.Another important property is plasticity that can be described as the capability to go throughvariations in naturedevoid offalling-out.

Plasticity Index is defined as the numerical difference between liquid limit and the plastic limit. The slope of the flow curve (water content versus number of blows on semi log sheet) is called flow index.  Liquid Limit of the soil is carried out using the Casagrande Liquid Limit Apparatus, as per IS: 2720(Part V) – 1970.  Plastic limit test is carried tout to calculate the plasticity index, as per IS: 2720(Part V) – 1970. Unconfined compression tests: The UCC test is one of the simplest and the quickest tests used for the determination of the shear strength of cohesive soils. In undrained tests on saturated or nearly saturated cohesive soils, the contribution of friction is negligible and the strength is almost entirely due to cohesionIS: 2720(Part X) – 1970. The results are tabulated in table 1.

International Journal of Advanced Science and Technology Vol. 29, No. 6, (2020), pp. 8548-8556

Table 1.Results of Geotechnical Engineering Tests

Specific Liquid Limit Plastic Limit Core Cutter UCC Results Gravity

Dry Specific Avg. Liquid Avg. Plastic SBC Density(g/cm3) Place Gravity Limit (%) Limit (%) (kN/m2)

Mundkoor 2.28 38.2 18.7 1.625 477.149 Mulki 2.15 52.6 32.4 1.753 338.344 Aikala 2.10 48.8 34.5 1.501 229.813 Niddodi 2.07 47.4 27.1 1.540 261.212 Bajpe 1.93 21.5 35.0 1.107 163.019 BenjanaPadavu 2.00 47.8 31.9 1.089 285.818 Thokkottu 2.31 57.7 37.5 1.175 151.235 Deralakatte 2.06 41.1 28.4 1.220 273.097 Mudipu 2.25 39.4 19.3 1.111 204.981

3.1 Soil Classification based on SBC

As the safe bearing capacity of any soil is the extreme mean of contact pressure amongst the footing and the soil which should not create shear failure in the soil SBC is considered as one of the major affecting factor for risk in subsoil and risk factors are calculated using SBC.Safe bearing capacity values were calculated using unconfined compression tests (UCC). The dial gauge readings were noted down as the load gets applied on the allowed soil samples. Deformation of the specimens prepared is observed and the proving ring readings were noted down. By the obtained readings stress, strain and axial loads were calculated and with these readings along with the consideration of failure angle suitable formulae were applied to get safe bearing capacity values of soil samples of the regions.SBC of each place are tabulated and based on the SBC, grading is done listing the soil profiles from very weak, weak, vulnerable, good and very good. The Average/Mean (M) and Standard Deviation (SD) of the SBC of all the places are calculated and the grading is done according to the below Table 2.

Table 2. Assignment of risk

M+2SD Very Good

M+SD Good

M Vulnerable

M-SD Weak

M-2SD Very Weak

International Journal of Advanced Science and Technology Vol. 29, No. 6, (2020), pp. 8548-8556

3.2 Preparation of Risk Model & Zonal Map

Zone Map is prepared containing the Soil profile details, based on this the area is classified into low, medium, high, very high and extreme risk zones. According to the SBC of the soil the type of foundation suitable to that area is selected. Risk factor index is prepared considering Soil Profile Risk and Cost of Construction in High Risk and Medium Risk Zones.

3.3 Procedure Implemented To Form Risk Matrix

Principle used to form the risk matrix is by the application of Likert scales, which is a tool used to understand the Level of Acceptability, Level of Support/Opposition, Level of Appropriateness, Level of Probability, Level of Appropriateness Level of Agreement, Priority, Level of Probability, Level of Agreement Level of Desirability, Level of Participation etc. Likert scale is usually form for either seven points scale or five points scale .Here for the simplicity of arrangement we are forming a five point Likert scales wherein the risk is classified as Low, High, Very High, Very Low, Normal, Very Low and Very Low. With the help of the formed matrix cost risk with respect safe bearing capacity in all the opted places. The key factors used for creating the risk matrix are three. And they are mean value of SBC, Standard Deviation and probability risk ratio.

The mean and standard deviations are calculated and tabulated with certain notations used for cost risk and SBC risk which starts from one(very low) to five (very high) that is based on Likert scale. The assignment made is tabulated and shown in Table 3. The SBC values are in kN/m2.

Table 3. Value Assignments for Cost Risk and SBC Risk

SBC COST M+2SD 453.663 VERY HIGH 1 1 M+SD 342.407 HIGH 2 2 M 231.15 NORMAL 3 3 M-SD 119.893 LOW 4 4 M-2SD 8.636 VERY LOW 5 5

Choosing these colours shown in table 5 to indicate risks is purely based on assumptions. The risk is denoted according to the scale from green to red representing low risk to high risk.

With the help of above formed table level of risk is drawn. The probability of risk is considered by multiplying SBC risk and cost risk and thus the peak of risk is calculated. Table 4.3 shows the margin of risk.

International Journal of Advanced Science and Technology Vol. 29, No. 6, (2020), pp. 8548-8556

Table 4.Assignment of Risk from Low to High

Cost risk

1 2 3 4 5 Very High - 5 Medium - 05 High - 10 15 Extreme - 20 Extreme - 25 4 Medium - 04 Medium - 08 High - 12 Very High - 16 Extreme - 20 Very High - SBC 3 Low - 03 Medium - 06 Medium - 09 High - 12 15 2 Very Low - 02 Medium - 04 Medium - 06 Medium - 08 High - 10 1 Very Low -01 Very Low - 02 Low - 03 Medium - 04 Medium - 5

Table 5. Colour Denotation for Risk

Very Low 01-02

Low 03

Medium 04-09

High 10-14

Very High 15-19

Extreme 20-25

Risk information Model is prepared from which risk index of any place coming under the zone map can be measured.

4. Results and Discussion

The values for SBC were found to be wide-ranging from place to place and the dissimilarity in SBC values are noted. 477.149, 338.344, 229.813, 261.212, 163.019, 285.818, 151.235, 273.097, 204.981(in kN/m2)are the SBC values obtained for the places Mundkoor, Mulki, Aikala, Niddodi, Bajpe, Benjana Padavu, Thokottu, Deralakatte and Mudipu respectively. The value of SBC obtained in mundkoor which was first place among nine, is seems to be having higher value of SBC and lowest SBC is value was found in Thokottu compared to other places.

The values of SBC is as shown in the risk matrix formed table (6).As the risk matrix is used to rank the uncertainties, the formed matrix is showing the most expected risk zone to least expected risk zone which is done on the basis of the values of SBC obtained from the selected nine places.

International Journal of Advanced Science and Technology Vol. 29, No. 6, (2020), pp. 8548-8556

Table 6. The Level of Risk based on SBC

Risk SBC Risk SBC Cost SBC Matrix Risk Probability Risk Risk Value Mundkoor 477.149 Very High 1 1 1 Very Low Mulki 338.344 Normal 3 3 9 Medium Aikala 229.813 Low 4 4 16 Very High Niddodi 261.212 Low 4 4 16 Very High Bajpe 163.019 Very Low 5 5 25 Extreme BenjanaPadavu 285.818 Normal 3 3 9 Medium Thokottu 151.235 Very Low 5 5 25 Extreme Deralakatte 273.097 Normal 3 3 9 Medium Mudipu 204.981 Low 4 4 16 Very High

5. Conclusion

From the study conducted, following points can be concluded: . As the objective was set to classify the risk free and risky zones the risk matrix is formed according to the Likert scale, the colour codes were given based on the safe bearing capacity obtained from the soil samples amongst the nine places selected. . As per the risk matrix formed the risk with respect to cost as well as safe bearing capacity was found to be very low in mundkoor and extremely high in Bajpe and Benjana Padavu which had the bearing capacity values below point of reference. . Aikala, Niddodi and Mudipu were the places having bearing capacity values quite more than the benchmark and hence according to the matrix the place comes into very high risk zone. . Mulki, Thokottu and Deralakatte were found to be falling in medium risk zones with SBC values nearest to the highest SBC obtained.

6. Future Scope of Study

Cost risk assessment can be done in the form of cost risk matrix

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