Settlement, S1 v M z˜ Where vis the change in vertical stress due to the loading and is generally calculated according to Boussinesq and Mis the 1- D constrained modulus that can be estimated from the CPT. The settlement calculation is therefore a summation over the depth range where z is the interval between CPT readings.
Full Answer
Can the CPT be used to calculate vertical settlement?
Robertson’s Remarks - Settlement Calculations using the CPT- Traditionally the CPT has not been used extensively for the calculation of vertical settlements due to foundations loads. Partly this has been due to the somewhat poor correlation between CPT results and soil modulus.
How to estimate soil modulus from CPT results?
It is now possible to make good estimates of soil modulus from CPT results over a wide range of uncemented soils, from soft clay to dense sands. It is common practice in many parts of the world to estimate vertical settlement under footings using the simple one-dimensional formula: Settlement, S1 v M z˜
Can We estimate liquefaction-induced ground settlements using CPT data?
Abstract: An integrated approach to estimate liquefaction-induced ground settlements using CPT data for sites with level ground is presented.
How are the calculated settlements different from the actual settlements?
The calculated settlements are quite similar to the measured/estimated settlements with the calculated set- tlements slightly larger than the actual values. O’Rourke et al. (1991) used the SPT-based method of Tokimatsu and Seed (1987) to estimate the liquefaction- induced settlement at the Marina District.
How do you calculate total settlement?
5:489:18Consolidation Settlement Equations - YouTubeYouTubeStart of suggested clipEnd of suggested clipTimes the log of our final stress which is Sigma prime Z naught plus Delta Sigma minus the log ofMoreTimes the log of our final stress which is Sigma prime Z naught plus Delta Sigma minus the log of the initial vertical effective stress. That's the change in void ratio.
How do you calculate immediate settlement?
Determine the point where the settlement is to be computed and divide the base so the point is at the corner or common corner of one or up to 4 contributing rectangles. The zone of influence is either of the following: Depth z = 5B where B is the least total lateral dimension of base.
What is the difference between settlement and consolidation in soil?
Different from immediate settlement, consolidation settlement occurs as the result of volumetric com- pression within the soil. For granular soils, the consolidation process is sufficiently rapid that consolida- tion settlement is generally included with immediate settlement.
What is the total settlement?
Total settlement refers to the overall change in vertical distance. Differential settlement involves an expected amount that the total settlement will vary between points over a horizontal distance, which can be caused by variations in the foundation soil profile and wall height over a certain distance.
What is allowable settlement?
The allowable settlement is defined as the acceptable amount of settlement of the structure and it usually includes a factor of safety.
How do I calculate my soil settlement?
H = Thickness of the field consolidating stratum at the end of primary consolidation. Commonly initial thickness is used unless the primary consolidation is very large. Say more than 10% of initial thickness. t2 = t100 (f) + Δt = time for which secondary settlement is to be calculated.
How is consolidation settlement calculated?
The primary consolidation settlement can be calculated from the coefficient of volume compressibility mv, which can further lead to the Young's modulus E′ = (1 + v′)(1 − 2v′)/[mv(1 − v′)], with an assumed Poisson's ratio v′.
How do you solve soil settlement?
Install drainage ditches or drain pipes to prevent soil settlement in areas. If water has a path to follow, it is less likely to erode land areas. Create small mounds of soil in between plant rows to keep soil from shifting or settling due to a slope in the field.
What is immediate settlement of soil?
Immediate settlement occurs in the soil upon load application and involves reduction in void space and rearrangements of the soil particles in response to that load. The consolidation settlement is induced due to volumetric change.
How is pro rata insurance settlement calculated?
A formula used to determine the amount of coverage each insurer pays when more than one source of insurance is available to handle a given loss. Take the coverage written by Company A, divide that amount by the total coverage written by all sources and multiply the resulting percentage by the actual loss amount.
How do settlements work?
A settlement agreement works by the parties coming to terms on a resolution of the case. The parties agree on exactly what the outcome is going to be. They put the agreement in writing, and both parties sign it. Then, the settlement agreement has the same effect as though the jury decided the case with that outcome.
What is settlement analysis?
Soils consolidate under the application of loads from buildings. All foundations settle as the soil around and beneath the foundation adjust to the loading. Buildings with light loads or built on rock may experience negligible settlement.
What do we need to know
To make a calculation of settlement, we must characterize three fundamental things:
Estimating stiffness
There are many tools in the toolbox for the engineer to estimate stiffness based on the results of laboratory or in-situ tests. Alternatively, published tabulated ranges of values and local experience are available for preliminary estimates. A list of possible methods is described below:
Applied loads and their dimensions
In practice at the stage a geotechnical report is written, detailed information on the dimension and magnitude of applied loads is unlikely to be available. We may at best have some preliminary information on the type of building (warehouse, apartment building).
Variation of stress with depth
To calculate the compression of the soil, we will need to determine how the stress applied at the surface translates into stress at depth. If the loaded area is very large relative to the thickness of the compressible layer, we can simply assume that the change in stress at depth is the same as at the surface.
Example calculation
In this section I will present an example calculation that demonstrates the method. Consider the case of a 3.0 m square footing, with a service load of 100 kPa. The ground profile consists of a firm clay and we have assessed a modulus of 8 MPa based on the results of a site investigation program comprising CPTs.
Spreadsheet
The method described in the article has been implemented in the spreadsheet below. You can enter in the load, dimensions of the load, and modulus parameters and output a quick estimate of settlement.
Improvements and disclaimers
I wouldn’t be a geotechnical engineer if I didn’t write some disclaimers into my article. There are of course many ways to improve upon (or complicate), and they all center around the three fundamental ‘need to knows’. I have of course greatly simplified things for presentation in this article. Some examples are listed below:
What is the CPT instruction in Rung 2?
In Rung 2 a CPT instruction is used to compute an average of three registers: System_DINT [6] , System_DINT [1] and System_DINT [2] .
What is CPT in ladder logic?
The CPT, also known as the compute, is an instruction which has extensive capabilities when it comes to mathematical and logic functions in ladder logic. This instruction allows the user to input a complex string of instructions composed of computational, operational and comparison functions and computes the result which is stored in ...
What is CPT used for?
The CPT can be used to compare two values of identical types or mismatching types such as float and integer. You may also specify a boolean register which is frequently used for logical evaluations.
What are the drawbacks of using multiple operands?
Multiple operands interact with each other which leads to a confusing execution and inability to troubleshoot or tweak when needed.
Does CPT work with operands?
The instruction will work with operands used in the based instructions as well as many others. The CPT instruction has many advantages as well as drawbacks. Based on personal experience, you should only use this instruction if absolutely necessary and the same could not be achieved with several basic instructions.
Where is the result of a computation stored?
The result of the computation is set to be stored in the “Dest” register which is specified to be System_REAL [2].
Does the function break down the operands?
The function does not break down the different operands and requires one to go into controller scoped tags in order to see what the values are set to. The general rule of thumb I’d recommend when using this instruction is that you should only use it if you can’t accomplish the same operation through 3 basic instructions.
How deep is the OCR of soil?
I plotted the soil OCR versus depth and it indicated about 8 meters of high OCR crust. The OCR eventually reached a OCR of close to 1 at a depth of about 25 meters.
Which is better, CPT or soil OCR?
The CPT showed the soil OCR better, but most importantly the OCR from the vane was only about 20% higher than the OCR from the CPT. This little research project gave me a lot greater faith in John Schmertman's procedure.
Is the undrained strength of a soil higher than predicted?
For overconsolidated soils the undrained strength is higher than that predicted by Skempton's equation. The amount of increase in strength is related to the overconsolidation ratio (OCR) by an emperical relationship presented by Schmertmann. The ratio of (Su/p')overconsolidated to (su/p')normally consolidated (Sr)is used to calculate the OCR.
Can you estimate cohesive soil parameter using SPT data?
I should say that BigH is quite right. But beyond that I think it should not be the way to estimate any cohesive soil parameter using SPT data. Because SPT test gives very erroneous results especially if we are going to think that the soil is saturated (since BigH considered consolidation settlement). I can only suggest an experimental solution before you're going to make assumptions; if you have split sampling tube samples from SPT test you can easily find out the unit weights at each depth, and if you've disturbed samples at that depths you can easily prepare remolded samples at known unit weights. Then the only thing you need to do is to conduct a number of oedometer and shear strength tests to figure out the engineering properties of the stratum.
Can you use SPT data for cohesive material?
I would not use SPT data for any cohesive material. A piezocone or a flat dialatometer would be useful in determining the OCR.
Is Webb's equation semi-emperical?
Webb does stress that the equation is semi-emperical and that it provides only a crude approach to settlement prediction because of the uncertainties relating to stress distribution, stress history and overburden pressure. On the basis of experience Webb believes that the above equation allows settlement (of shallow foundations) to be estimated within 30 to 35%. Webb also states that calculation of settlement using SPT N values usually provides an over estimate of settlement.
Can you use DCP to calculate footing settlement?
It is just not very practical to perform DCP to a relatively deep depth. No matter for sandy or clayey type of material, it is not appropriate to use DCP blow count to estimate the footing settlement (especially for large footings). Locally, CPT and DMT have been widely used to calculate the settlement.
