How to calculate bearing capacity of soil from n value

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By ckwMay 12, in Civil Engineering. Is there any way of determining the bearing capacity of soil based just on the n-values from a spt test? Or do I need more tests done? A really big question is whether or not we are discussing a shallow foundation or a deep foundation.

Then there are some deviations depending on the heterogeneity of the underlying strata and contemplation of the material - mostly sands, clays, or silts? So, what I am getting at - it takes more information and some judgement based on the end result of the data e. If you have a more specific question, please feel free to post or PM me. I am not a bearing capacity guru but I can certainly pass along to others who are more informed than myself.

This is for a road that will have minimal traffic for 32, lbs truck. It is mostly limerock. We need to determine if the subbase has the capacity to hold that type of vehicle. Right now there is 6' of subbase. Based on the test results we got, it seems fine, but of course the company needs numbers and formulas and such What if you have a stiff clay cohesive material with a shallow mat foundation and water table below the influence line? From there you should be able to calculate if the existing pavement composition is sufficient to handle the traffic.

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Posted July 1, Could someone elaborate on this? How do you apply the n-value when estimating bearing pressure? Posted October 17, Posted October 28, Thanks for answering. Posted July 9, Join the conversation You can post now and register later.All Rights Reserved.

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Hottest Questions. Previously Viewed. Unanswered Questions. Civil Engineering. How Bearing capacity of soil can be calculated from spt n values? Wiki User SPT n Values can help to calculate the Bearing Capacity of any soil specimen as they will combine to change the density of the soil by extracting various chemicals such as helium and hydrogen. Asked in Soil Bearing capacity of soil? It is the power of the soil to bear the load coming on to it is known as bearing capacity.

Asked in Civil Engineering, Soil What do you mean by soil bearing capacity? Asked in Civil Engineering, Soil What is the soil bearing capacity?

Asked in Soil What is a soil compaction test? Bearing capacity of soil. The the bearing capacity of silt soil can be improved by: Compacting the soil to increase it's density. Asked in Civil Engineering, Soil What are bearing capacity factors? Bearing capacity is the ability of the underlying soil to support the foundation loads without shear failure. Bearing capacity factors are empirically derived factors used in a bearing capacity equation that usually correlates with the angle of internal friction of the soil.

While you design a footingit is the main factor to consider. The link between CBR and bearing capacity if you get figures in CBR how can you link them to the bearing capacity in kPa, this is the link in soil testing. Asked in Civil Engineering What is the difference between bearing capacity and bearing pressure?

Asked in Soil How do you improve the bearing capacity of slit soil? Asked in Philippines What is the range of soil bearing capacity at Pasay City? As ofthe range of soil bearing capacity at Pasay City is Pasay City makes up the Metro Manila in the Philippines and in the population wasAsked in Civil Engineering What are the factors to consider when selecting a building foundation?

Load bearing capacity of the soil. Asked in Machinery and Tools What is gross safe bearing capacity? Gross SBC means, adding additional soil bearing capacity with net bearing capacity. This additional bearing capacity density of filling material above the footing. SL Suthar.Plate load test is a field test which is commonly adopted to determine the bearing capacity and settlement of soil under a given condition of loading.

In this test a square or circular rigid plate of standard dimension generally mm2 for square or mm dia for circular is placed at foundation level and load is applied in increments. Then settlement of the plate corresponding to each load increment is recorded for calculating bearing capacity of soil.

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How to perform Plate Load Test On site? The whole process of calculating bearing capacity of soil using plate load test data consists of the following 4 primary steps. Depending on the type of soil below the test plate, the load settlement curve can be of 4 different types as shown below. Curve A: This type curve is obtained in case of loose to medium cohesion less soil i. This type of curve shows no clear point of failure.

Curve B: This type curve is obtained in case of cohesive soil. As the load increases the curve leans toward settlement curve. Curve C: This type curve is obtained in case of partially cohesive soil i. C-phi soil.

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This type of curve also does not show a clear point of failure. Curve D: This type curve is obtained in case of dense cohesionless soil i. This type of curve is common in case of dense sand or gravel deposits. After drawing the load settlement curve, the next step is to identify the failure point on the load settlement curve.

Or draw two tangent lines from the beginning straight portion of the curve and end straight portion of the curve. The point where these two tangents cross each other is called the point of failure. The pressure corresponding to this point is called ultimate bearing capacity of the soil. To overcome this problem scientist Abbet introduced another method of drawing load settlement curve. According to his method, a log-log chart is plotted with settlement are plotted as abscissa against corresponding pressure intensities as ordinate.

Such a plotting will give two straight lines, the intersection of which will be considered as the failure point.

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Find the corresponding value of pressure to the failure point. This is considered as the ultimate bearing capacity of soil. In order to calculate safe bearing capacity of the soil, divide the ultimate bearing capacity of soil by a suitable factor of safety.

The values of factor of safety normally used are 22. The following formula as suggested by Terzaghi and Peck is used to calculate the settlement of footing for granular soil. For calculating settlement of a given size of foundation subjecting to a given loadfirst calculate the corresponding intensity of loading by dividing the area of footing by the load, i.

Then from the load settlement curve drawn using PLT data, find out the plate settlement corresponding to the calculated intensity of loading and use this value of settlement in the formula to calculate the settlement of footing. A plate load test was conducted using a plate of 0. Calculation of Safe Bearing Capacity.

HOW TO CALCULATE SAFE BEARING CAPACITY OF SOIL ON SITE?

Geotechnical-Material Engineer. To know more about me just visit AboutMe.One of most commonly method for determining allowable soil bearing capacity is from standard penetration test SPT numbers.

It is simply because SPT numbers are readily available from soil boring. The equations that are commonly used were proposed by Meryerhof based on one inches of foundation settlement.

For footing width, 4 feet or less:. For footing width, greater than 4 ft:. N: SPT numbers below the footing. B: Footing width, in feet. D: Depth from ground level to the bottom of footing, in feet.

Soil SPT number: Footing type: 3 feet wide strip footing, bottom of footing at 2 ft below ground surface. Meryerhof's equation. Footing type: 8 feet wide square footing, bottom of footing at 4 ft below ground surface. The editor made reasonable effort of editing. Nevertheless, the editor does not warrant, and assume no liability for accuracy and completeness of its content. Webmaster: www. Related topics Pressure under footing Foundation settlement Spread footing design Combined footing design Strap footing design RC retaining wall design.

Bearing capacity online calculator

All Rights Reserved.The ultimate bearing capacity Q u is the theoretical limit of the bearing capacity. Much like how the Leaning Tower of Pisa leans due to the deformation of soil, engineers use these calculations when determining the weight of buildings and houses.

As engineers and researchers lay down foundation, they need to make sure their projects are ideal for the ground that supports it.

Mod-01 Lec-11 Shallow Foundation - Settlement Calculation - I

Bearing capacity is one method of measuring this strength. Researchers can calculate the bearing capacity of soil by determining the limit of contact pressure between the soil and the material placed on it. These calculations and measurements are performed on projects involving bridge foundations, retaining walls, dams and pipelines that run underground. They rely on the physics of soil by studying the nature of the differences caused by pore water pressure of the material underlying the foundation and the inter-granular effective stress between the soil particles themselves.

They also depend upon fluid mechanics of the spaces between soil particles.

How to Calculate the Bearing Capacity of Soils

This accounts for cracking, seepage and the shear strength of the soil itself. Shallow foundations include strip footings, square footings and circular footings. The depth is usually 3 meters and allow for cheaper, more feasible and more easily transferable results.

The other variables depend upon other calculations. K pg is obtained from graphing the quantities and determining which value of K pg accounts for the trends observed. There can be situations in which the soil shows signs of local shear failure.

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This means the soil strength cannot show enough strength for the foundation because the resistance between the particles in the material isn't great enough.

Deep foundations include pier foundations and caissons. This gives you another formula for bearing capacity of soil. D c is the critical depth for piles in loose silts or sands in m or ft. This should be 10B for loose silts and sands, 15B for moderate density silts and sands and 20B for very dense silts and sands. For the skin shaft friction capacity of pile foundation, the theoretical bearing capacity Q f is A f q f for a single homogeneous soil layer and pSq f L for more than one layer of soil.

S is the summation of differing soil layers i. It is equal to c, the cohesion of soil for rough concrete, rusty steel and corrugated metal. For smooth concrete, the value is. L is the effective length of the pile in m or ft. The safety factor ranges from 1 to 5 for various uses. This factor can account for magnitude of damages, relative change in the chances a project may fail, the soil data itself, tolerance construction and accuracy of design methods of analysis.

For instances of shear failure, the safety factor varies from 1. For dams and fills, the safety factor ranges from 1.

HOW TO CALCULATE BEARING CAPACITY OF SOIL FROM PLATE LOAD TEST?

For retaining walls, it's 1.Geotechnical Info Search. Geotechnical Forum Ask for technical help or discuss geotechnical issues with other engineers. Geotechnical Publications Free publications and resources for geotechnical engineers. Geotechnical Software Download free software and links to geotechnical software. Technical Guidance Valuable technical information for geotechnical engineers. Your questions may be answered here.

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Market yourself. Bearing capacity of soil is the value of the average contact pressure between the foundation and the soil which will produce shear failure in the soil. Ultimate bearing capacity is the theoretical maximum pressure which can be supported without failure.

Allowable bearing capacity is what is used in geotechnical design, and is the ultimate bearing capacity divided by a factor of safety.

how to calculate bearing capacity of soil from n value

Theoretical Ultimate and allowable bearing capacity can be assessed for the following: Shallow Foundations strip footings square footings circular footings Deep foundations end bearing skin friction For comprehensive examples of bearing capacity problems see:. Notes: Effective unit weight, gis the unit weight of the soil for soils above the water table and capillary rise. For saturated soils, the effective unit weight is the unit weight of water, g w9. Find more information in the foundations section.

The first equation is for ultimate bearing capacity, while the second two are factored within the equation in order to provide an allowable bearing capacity. Linear interpolation can be performed for footing widths between 1. Notes: Determining effective length requires engineering judgment. The effective length may also be the length of a pile segment within a single soil layer of a multi layered soil.Dynamic cone penetration test or DCPT is a quick, simple and low cost test which is extensively used by many agencies around the globe to measure the strength of compacted material of unbound granular and sub grade layers with reasonable accuracy.

The basic principle involved in the operation of this apparatus is the measuring of the resistance offered by the pavement layers to the penetration of a standard cone with a diameter of 20 mm with 60 0 apex angle driven by an 8 kg hammer freely falling through a height of mm.

To get a clear understanding of the calculation, an example is also given at the end of the procedure. To down load the excel sheet for the above calculation click here. Geotechnical-Material Engineer. To know more about me just visit AboutMe.

how to calculate bearing capacity of soil from n value

Thanks very much because you have helped me with how to deal with dcpt results to come out with cbr values but now another thing is to get the total bearing capacity of the soil.

Please help me because i have a task to design a foundation. Thank you. Good day Sir, hope everything is fine. I would like to request if you can give me some exemples. I have 5 blows to a depth of 74mm then 10 blows to a depth of mm. I would like to know how to fill in the design data summary table. Penetration rate column, Material class and estimated CBR. I need fomulars to fill in these columns I have just mentioned please. End how the boss. Your email address will not be published.

Notify me of follow-up comments via e-mail address. Save my name, email, and website in this browser for the next time I comment. Notify me of follow-up comments by email. Notify me of new posts by email. DCPT Dynamic Cone Penetration Test Dynamic cone penetration test or DCPT is a quick, simple and low cost test which is extensively used by many agencies around the globe to measure the strength of compacted material of unbound granular and sub grade layers with reasonable accuracy.

Now a days DCPT is commonly used during construction for the following purposes. To control quality of construction To determine in situ CBR value To evaluate quality of flexible pavement Principle of DCPT The basic principle involved in the operation of this apparatus is the measuring of the resistance offered by the pavement layers to the penetration of a standard cone with a diameter of 20 mm with 60 0 apex angle driven by an 8 kg hammer freely falling through a height of mm.

Procedure Record the initial reading on the dynamic cone penetrometer scale.

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Calculate the value of penetration in mm for each blow by subtracting the previous recorded reading i. Calculate the cumulative depth of penetration in mm for each blow by adding all the previous individual depth of penetrations.

how to calculate bearing capacity of soil from n value

Draw a chart using the data of cumulative depth of penetration and number of blows. See Fig-1 This step is about identifying the depth of each layer. Identify the slope change of the penetration curve. Every change in slope represents a change in layer type.


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