Bearing capacity mapping of Morang district for shallow foundation

. Foundation is the part of all structure, which helps transmit the all the loads from above structure to the ground. The bearing capacity value mainly affected by two major factors, they are type of soil and also the location where the stratum. Due to various reasons such as; Economy, miser, unconsciousness etc, people don’t conduct soil test in many cases and starts to build high rise buildings in different locations. From the prevention of collapse and settlement of building bearing capacity of soil should be checked. Zonation mapping of bearing capacity is inevitable in many cases of newer and expansion storey construction. In many countries, zoning mapping of bearing capacity has been available for crowd or urbanized cities. In case of Nepal, there are absences of such zoning maps. The thesis report tries to fill such gap present in Nepal. Different bearing capacity has been found using different tests; SPT Value, Terzaghi, and among them least of the resulted value of bearing capacity is used for Zonation mapping of Morang district of Nepal. These targets are achieved by various data and tests conducted in the soil investigation with boring logs and SPT N value from 239 different locations and terrain around Morang District of Nepal. The methods initially adopted are collecting, selecting, grouping and plotting the data Location in Morang District map using GIS. Various analytical, experimental and theoretical approaches also used for the estimating and analyzing bearing capacity of soil. The research shows that the bearing capacity of soil of Morang ranges from 50kPa to 628kPa.


Introduction
Geotechnical engineering is a science which deals with the soil properties.Foundation is not only one of the components of structure.Foundation is vital structures without which any kind of structure cannot be imagined.For better performance, foundations are integral parts.Foundation provides connections between superstructure and sub-structure.
The capacity of soil supporting the loads from above of the ground applied to the ground is known as bearing capacity.Structures have to satisfy two conditions to satisfy the performance [1][2][3][4].The conditions are;safe against overall shear failure in the soil that supports them and must not undergo excessive settlement.For preliminary design the zonation mapping will facilitate designer for preliminary design, feasibility study, planning of detail investigation of complex formations, estimate of future risks and disasters related to soil failure [5][6][7].For the new construction or to increase the number of storey, zonation mapping is needed.Thick alluvium deposits are found in Terai plain of Morang district, Nepal.Gravel, sand and clay sequence in alternate manner turn into multi aquifer system.The geotechnical investigation works comprise the exploratory drilling, in-situ field testing of SPT test, borehole logging, collection of samples to perform necessary tests on soil samples for detail information on subsurface conditions of the soil strata [8][9].The researchwork finally developsresult ofsafe bearing capacity of the foundation.For cohesion less soils,Standard penetration value (SPT) is most commonly used in-situ test.Cohesion less soils like clay and silt cannot be easily sampled.For cohesion less soils,relative density of the soil and the angle of shearing resistance SPT test are very useful.The main objective focuses on to provide the zonation map of bearing capacity.It will hence reduce varioustimes and cost of project that lapsed during investigations.To predict the bearing capacity of soil and also the settlement based on test reports [10][11][12][13][14][15].To examine and analyze standard penetration test (SPT) N-values.To Presents results of the subsurface investigation works carried out for the proposed site at different parts of Morang District.

Literature Review
Ultimate bearing capacity: Gross pressure or stress at the base atwhich soil fails is known as the ultimate bearing capacity.The foundation fails in shear.Allowable bearing capacity: The Allowable bearing capacityof soil is defined as net load intensity up to which no failure of the soil occurs.For Calculation of gross allowable load, the bearing capacity of soil for foundation factor of safety (FOS) to the gross ultimate bearing capacity of soil.

Q allowable= Qultimate/ Factor of Safety (FOS)
Net ultimate bearing capacity: The ultimate pressure per unit area that can be supported by the soil is commonly known as Net ultimate bearing capacity.The difference between unit weight and the concrete is negligible, then q Net (u)= q (u)-q Here, q = unit weight x Depth of foundation So, qAllowable (net)= (q(ultimate)-q) / FOS Safe bearing capacity: The safe bearing capacity is defined as the maximum stress or Pressure the soil can bear without failure in shear.It is recommended that the factor of safety,Factor of safety, FOS should be taken between 2 and 4 according to project or surrounding need.The table may be used as guide for structure in reasonable homogeneous condition.Jay Ram Panthee & Indra Prasad Acharya: Accoring to Jay Ram Panthee & Indra Prasad Acharya, For any kind of structures foundation is the vital part.Foundation is a part of structure, which transmits the load from above to the ground.Bearing capacity value affected by various reason.Soil type and location of soil, where the structure might be hold by the foundation affects the bearing capacity value.Every city or place is nowadays converted into concrete village or town each and every day.Without conducting soil test, the constructing of building are takes place rapidly.To safeguard from collapse and settlement, Bearing capacity of soil should be checked at required location and number before construction.Newer construction and extending number of storey can be easy preliminary with the help of zonation mapping.Internationally bearing capacity zone of different urbanized cities has been done previously.In Nepal, no proper maps for the bearing capacity are prepared.This study aims to map the bearing capacity of the soil.For construction of map, the researcher uses data of various boreholes locations around Kathmandu, Nepal.There are different performed methods.Among them main are: collecting, selecting, grouping and plotting of all data location in Morang district map.For estimating bearing capacity, different analytical and theoretical approach has been followed.Terzaghi, Meyerhofetc are used for finding bearing capacity of the soil.And among them least value of bearing capacity is used in mapping.Study of the researcher shows that the bearing capacity of Kathmandu valley ranges from 49 kPa to 307 kPa M. P. Koirala & G. Ojha, According to paper, it deals mainly with foundation or soil characteristics of different parts at Nepal.Multiple approaches are adopted to explore soil or foundation characteristics in the paper.14 different sites from different parts of the country were selected.There were 2 sites from hilly areas, 2 sites from inner terai areas and mostly 10 sites from terai areas.Two test sites were selected in each site.In each test site simplified penetration Apparatus (SPA) tests were carried out and were accompanied by the auger tests.Samples from different depth were collected in each site.Soil classification, direct shear test, LL-PL test, and density tests etctests are carried out to the samples collected in laboratory.The output value of bearing capacity of soil from laboratory was compared to soil types of certain depth and also NC value at certain depths.According to paper, the value of NCfound to be depends upon type of soil and the compactness of the soil.From the paper, it is also known that NCvalue can be converted to ultimate bearing capacity.For this the value obtained from NCshould be multiplied by value of factor of 35 percent within 80 percent confidence.For the explore of the suitability of soil of sites and also for the purposed of construction of the substations in terms of earthing, resistivity measurements were carried out.Resistivity measurement helps for the sites to select suitable or not for the construction of purposed sites of substations.
Residential area land is a land whose used in housing predominates, and also as opposed to industrial as well as commercial area.Housing varies significantly between and through, residential areas.These may include various housing.They are; single-family housing, or mobile homes or multi-family residential.Residential zoning may completely exclude industries and commercial areas.They also may permit some kind of service and work opportunities.According to different criteria considering, it may permit low density area as well as high density areas.Smaller floor area ratio (FAR) included for After careful study of both the data collected during the field investigation and the results hence obtained from the laboratory tests, soil properties, strength, etc were determined for the design of the foundation.Furthermore, the paper gives the soil properties of the each layer of subsurface deposits.
From the field data and the laboratory results, the safe bearing capacity in general for the isolated 1.5 mx 1.5 m, Raft 15 mx 15 m for all the sites are calculated and are documented in the chapter "bearing capacity of the soil''.
Boreholes: Location of the bore holes are given in the GIS map of each substation.A total of 2 bore holes for the each site were drilled at the maximum depth of 6 m where ever possible and necessary.Each bore hole was drilled by using the auger or rotatory and using soil sample thus collected, litholog for each site were prepared.These litholog are incorporated with N value verses depth curves.Water table and major types of soil horizons are described in the litholog.
Standard Penetration (SPT) test: The field investigation was mainly consisted of three boreholes at proposed BH1, BH2 and BH3 at the proposed building site.The bore holes BH1, BH2, BH3, drilled to depth of 10.5mThe drilling work was performed with percussion drilling machine.Casings of 6 inch diameter were used for purpose of protecting hole from collapsing by side fall or caving.The standard penetration tests (SPT) consist of driving a split-spoon sampler with an outside diameter of 50mm into the soil at the base of borehole.Driving was accomplished by a trip hammer weighing 63.5kg falling freely through a height of 75cm onto the drive head which was fitted at the top of rods.First of all the split spoon was driven 15cm into the soil at the bottom of the borehole.It was then driven a further 30cm and then the number of blows needed to drive for each 15cm distance was recorded.The blow count for driving last 30cm penetration was referred to SPT 'N' value.The equipment with attached SPT hammer was according to ASTM D 1586.The results of the SPT test are shown in the respective bore hole logs; Annex-I.
Soil sampling: Two types of the sampling were done; disturbed sampling and undisturbed sampling.The laboratory test includes the following: sieve analysis, LL-PL test, natural moisture content, specific gravity, and direct shear test.Disturbed samples were collected for laboratory tests such as sieve analysis, LL-PL test, moisture content, and specific gravity.Undisturbed samples were collected for direct shear test.The undisturbed samples were collected in the tube by hammering the tube on the material in the boreholes.The sample lifted from the depth is sealed with the wax at the both ends of the tube to prevent the moisture loss and taken to the laboratory for the testing Foundation characteristics of the soils of different parts of Nepal Ground water table: For each site the ground water table in each bore hole is carefully recorded and is shown in the litholog presented.The ground water table in most of the places is due to unconfined shallow aquifers except at region between Mahendra Highway and Biratnagar-Rangeli Road the ground water table is generally below 3 m from the surface and should be considered while designing the foundation.
Sieve analysis: The initial measure for classification of soil is particle size analysis.Mechanical or grading method results are the particle size distribution curve.The size of particles in a soil in terms of percentages by weight of boulder, cobbles, gravel, sand, silt, and clay can be expressed by the particle size distribution.Sieving and Sedimentation are two methods used for the determination of particle size distribution of soil.
From visual inspection basis, the fineness and coarseness of the soil are separated.Sand and gravel (Coarser particle) is visible by naked eyes.Silt and clay (finer particles) cannot be distinguished by naked eyes.Boulder cannot be held in paw.Cobbles can be easily grasped within a hand.Pebbles can be held between fingers.The grains can be picked up from the mass of sediment having size smaller the pebble is considered as granules.Sands are considered as smaller grain size than granules.The finer particles are difficult to judge by naked eyes, So easiest method is chewing.During chewing process if the particles feels smooth then they are clay otherwise silt.
According to the distribution of particle size, the soil can be classified as following: Uniformly graded, the proportion of particle size concentrating within a narrow range is described as uniformly or poorly graded.
Well graded: Coarse-grained soil without excess of particles in any size range and without any lack of their intermediate size-range is regarded as well-graded soil A well graded soil possess a wide range of particle size ranging.
Gap or skip graded: A gap-graded soil lacks some or at least one intermediate size particles.
Sieve analyses of all the samples collected during the field work are presented in Table 2.The results of the sieve analysis show that the soil types found in the different sites are of medium to low compressibility i.e. excellent for the foundations.Liquid limit and plastic limit test: The deformation behavior of the soil is controlled by amount of water content in a cohesive soil.Degree of firmness of a cohesive soil is defined as consistency of soil.Water content increases or decreases, the properties of soil change.Liquid state, Plastic state, Semi solid state and solid state are states of cohesive soil.The change of properties are called as Alterberg limits.The Alterberg limits are; Liquid limit (LL), Plastic limit (PL) and Shrinkage limit (SL).The three limits are derived on the basis of the presence of water content in the cohesive soil.When presence of water content decreases from soil particle, continuously the state of soil changes from liquid state to plastic state, Plastic state to semi-solid state and semi-solid state to solid state and vice versa.
Liquid limit (LL): Water content from which a cohesive soil (clay) changes from viscous to plastic state and vice versa is regarded as the liquid limit.At liquid limit stage soil starts to gain or possess small shear strength.

Plastic limit (PL):
The water content at the transition or between of a plastic soil into a semi-solid soil is regarded as plastic limit.When soil rolled into threads of about 3mm in diameter just crumbles, the plastic limit arrives.Between plastic limit and liquid limit, the soil behave as a plastic material.Plasticity index(PI) is the term used for the distinguish the range of plastic stage.P.I. = L.L.-P.L. Shrinkage limit (SL): When the water content decreases from the plastic limit, the soil approaches a point where no volume of the soil change on further drying up.Beyond this point discoloration of soil may occur.This limit is called as shrinkage limit.The semisolid stage is present in between plastic limit (PL) and shrinkage limit (SL) Results of the liquid limit (LL) and plastic limit (PL) of results are presented in below table.The results presented in tables are used to find out Plasticity Index (PI).A Line Ip, Flow Index and Toughness index.They also can be used for the liquefaction potential of the soil.Most of the sites are safe from liquefaction from the vertical loading except Biratchowk.Due to very shallow ground water table at Biratchowk sand boiling may occur and should be considered during detail design stage.The liquid limit (LL) and plastic limit (PL) data are mainly used for the classification of the cohesive soil.These data are also used to cross check the strength parameters such as c (cohesion), o (friction angle) and for determining the compressibility of the soil.

Moisture content (MC):
The research results of the moisture content are presented in Table .Moisture content is determined taking some portion of the undisturbed sample collected for the direct shear at the time of sample preparation for direct shear test and also from the disturbed sample.Both of these samples were waxed and sealed to prevent moisture loss.Generally the granular soil has less moisture content than the fine soil.The unit weight of the soil can be considered from dry unit weight which helps in calculation of reliable safe bearing capacity of soil.The test can be performed either on undisturbed sample or remolded sample.Disturbed samples are not suitable.Remolding purpose can be fascinated when soil sample may be compacted at optimum moisture content (OMC) in a mold used for the compaction.Specimen for direct shear test might be obtained by using the correct cutter provided for the test.

Location
Specimens are introduced to normal load and the specimen is sheared across predetermined horizontal plane in between the two halves of shear box.Measurements are recorded as; Shear load, Shear displacement and Normal displacement.The test is repeated two or more times (as per recorded result analysis) under different normal loads.Shear strength parameters can be determined by the test conducted.
We use direct shear test to calculate the cohesion (C), friction angle (o) and unit weight (7) of the soil.The entire test is carried out in undisturbed soil samples.These result values of the test are tabulated in Table 6.Bearing capacity of the soil: Direct shear test data are used to calculate mainly bearing capacity of the sampled soil.Allowable bearing capacity means the maximum allowable net loading intensity on the soil allowing for both shear and settlement effects.Shear parameters in the plain strain measured in the laboratory by the direct shear test are used for the calculations.Ultimate bearing capacity for strip foundation is calculated by using the "Terzagh Equation (Terzaghi and Peck, 1967) as given.
Nc. Nq and Ny are the Terzaghi bearing capacity coefficients, B is width, Z is depth For the isolated 1.5m x 1.5m, Raft 15m x 15m, the safe bearing capacity in general for all the sites are calculated.The results are presented in Table .The inclination factor and the pore water pressure are not considered while calculating the bearing capacity of the soil.Similarly the bearing capacity by SPT and Terzaghi methods depends on the friction angle and cohesion onlyand slight variation in the friction angle has greater effect on bearing capacity of the soil.Therefore, the factor of safety (FOS) in the calculation of the bearing capacity of soil is taken between 3 and 5 as per needed.In a case; the excavated depth is left for a long time without filing the safe bearing capacity of those soil particles is determined by the formula-Safe bearing capacity of the soil =q/ES.Net safe bearing capacity of the soil =q/ES.-yZ   Boreholes were drilled using drilling auger so if boulder were encountered, the boreholes were stopped at that depth.The test is done as according to standard method of Standard penetration test.The bearing capacities obtained by the Terzaghi methods are recommended for the design as it is calculated by considering both cohesion and the friction angle of the soil.The length and breadth of the footings also control the bearing capacity.So it is recommended that if the design not similar as given above it is recommended that bearing capacity should be recalculated after the detail design of the foundation.For the calculation of the bearing capacity, inclined loading and horizontal loading like earthquake shaking is not considered.The SPT test should be performed twice to prevent any biases from the sampling location.

Conclusion
Map of allowable bearing capacity had been prepared using the results obtained from the 87 bore holes soil investigation at different locations of Morang district, Nepal.The other applications such as Google earth, Excel and mainly GIS (Geographical Information system) application helps to cook geotechnical maps which now provides or gives a helpful way to predict the non-spatial data areas.
The map considered as powerful database and also as the visual display of the tests, and collected data.It also helps to save time, money and effort of many people for preliminary design.The suitability of construction of the infrastructure can be judged preliminary with the help of the map.And stakeholders, engineers can take reference from the map to proceed further or not.It also provides ideas about what kind and extent of treatment needed for the soil to support the load.
It has been found that allowable bearing capacity of the researched area i.e.Morang district, Nepal ranges from 50 KPa to 628 KPa.There are some areas like Budhiganga, Biratnagar, Jahada and near rangeli road havecomparatively low bearing capacities.So attentionat the soil must be given during design of structures.For development of smart cities and extension of number of storey also the map can be used.since value of both allowable bearing capacity andmodulus of elasticity is not uniform with respect to depth.Therearelittle noticeable contrasts in values with their depth.It is henceindicates some presence of the thin strata of various differentmaterial.It is not necessary in every situation that after increase in depth of foundationsubstructure makes the foundation better.The main factor is recognizing of thebearable soil layer.The thickness is necessary for the efficient andsafe foundation design.The bearing capacity evaluated highly depends upon the method used and codes.The most sensitive parameter of soil for calculation of bearing capacity are cohesion for cohesive soil and friction angle for cohesion less soil.

Fig.
Fig. Comparison of Bearing Capacity of Soil for shallow foundation By SPT and Terzaghi Method.
Fig. Chart of Bearing Capacity of Soil for depth By SPT Method.
/doi.org/10.1051/e3sconf/202343001295295 430 Neeru K. C. et.al., Investigation of Soil at different location of the Kathmandu Valley, explains main parameters which are commonly associated with the determination of liquefaction potential are the saturated sand and silty soils.This study was focused on the investigation of soil bearing capacity at different locations of Kathmandu valley of Nepal.The study was conducted during the period of 2019.A laboratory test of the soil is the major tool of the investigation.

Table 2 :
Result of Sieve Analysis

Table 6 :
Results of Direct shear Tests

Table 7 :
Results of the bearing Capacity by Terzaghi Method(Isolated Footing)The soil investigations are held at 29 different locations of Morang districts of Nepal.In 29 different locations total of 87 boreholes are conducted.For each borehole bearing capacity of the soil are calculated using SPT N value and Terzaghi approach.For this, we considered depth of 1.5m, 3m, 4.5m & 6m.And the least value among from above tests is considered as the bearing capacity of the soil of that location where bore holes are conducted.The maximum bearing capacity of 883.19 KPa has been found out at Miklajung and lowest value of 27.29KPa has been found out at katahari.Maps are then prepared using various calculations and applications such as excel, Google earth, GIS etc.And in map control building locations are situated according to orientation.