Introduction Cone Penetration Testing (CPT) is an in-situ testing method used to determine geotechnical engineering properties of soils and precisely describing soil layers and it is currently one of the most widely used methods. The CPT begins on the ground surface and determines the tip resistance during penetration. The mechanics of the test begins with the cone tip penetrating the soil at a constant rate of 20 mm/s. Readings are continuously obtained and usually recorded every 20 mm and as the cone penetrates through the soil, the cone has a sleeve load cell that measures sleeve friction and a tip load cell that measures the tip stress (Gouda-Geo). All the data and measurements are recorded on the computer that is connected to the rig. Cone Penetration Testing has different methods and variations based on the CPT rig. Rigs can vary in size from portable sizes to large truck-mounted ones and the large truck-mounted rig was used to conduct the experiment of this lab. Each rig has its own purpose and many factors contribute to the size chosen to carry out the test. The most important factor is the surface conditions as the type of condition in a particular location will determine the size of the rig. CPT is not only effective for delineating soil stratigraphy but is also used to determine the liquefaction-triggering resistance of each soil layer. This helps to determine if layers are predicted to liquefy for different levels of earthquake shaking (VertekCPT). Moreover, the Standard Penetration Test (SPT) is an alternative method for determining the mechanical properties of soil. SPT differs to CPT such that, the tool used for the SPT is hammered into the soil and not pushed like that of the CPT rig. Additionally, according to Lewis, SPT uses manual data collection, whilst CPT uses electronic data collection. In-situ tests and lab tests are different such that in-situ tests are done at the existing location of the soil to be tested whilst for a lab test, a soil sample is taken and tested away from the source. One advantage of in-situ testing is that it is done without any disturbance caused by sampling. Disturbances caused by sampling can potentially alter the particle arrangement and stresses or strains. In comparison to lab testing, in-situ testing generates more practical results as larger volumes are tested. Also, in-situ tests are fast and cost effective. One disadvantage of in-situ testing is that the behavior and drainage conditions of the soil being tested will not be known. One big advantage the CPT as an in-situ test is that you don't have to wait for your sample results to get back from a lab. This is very beneficial when you are pressed for time. The disadvantage of this test method would be that a disturbance caused will lead to the sample having a boundary layer between two soil types and become mixed, making the soils more difficult to identify. Geotechnical Boring and CPT provide great options for obtaining useful information, therefore there are more benefits to using CPT over drilling. CPT is not only a cost-effective option but it 1 also provides immediate data review. On the other hand, SPT tests are simpler to conduct but is a harsh method, causing samples to be disturbed. The results obtained are usually variable and uncertain. Background The CPT test by itself has roots that date back to the 1930’s, Records indicate on a roadway in close proximity to Gouda in the Netherlands, A civil servant by the name of Pieter Barentsen perform the first test on record by pushing a 10 cm3 cone manually, by only using his own body weight to do so. This method invented a way to accurately measure the soil resistance on a conical tip. By using this CPT test he could measure the “hydraulic pressure gauge.” However, the CPT test today is no longer done manually but is digitally recorded. Testing Method The Cone Penetration Test was done at the University of South Florida’s Geo park. Data from the CPT investigation was gathered using the College of Engineering’s CPT testing rig. As the cone advanced through the soil, tip stress and sleeve stress were relayed to an excel file through a MegaDaq data acquisition system. The test ended when the force of the soil pushing against the cone was enough to overcome the weight of the truck to which the CPT rig was attached. Although hand augers was not used for this experiment, it is a manual procedure and approach to obtain soil sample. Hand augers method differs from the CPT procedure since the hand augers are filled with soil during the drilling process and must be periodically lifted to the surface and emptied. Figure 1: CPT Apparatus (left) & Penetrating Cone (right) 2 Data Analysis and Results Tip Stress vs. Depth Sleeve Stress vs. Depth Tip Stress (ksf) 50 100 150 200 250 Tip Stress (ksf) 300 350 400 0 6600 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 Depth (ft) Depth (ft) 0 6800 6900 7000 7100 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 Figure 1 - Tip Stress v Depth 6700 Figure 2- Sleeve Stress v Depth 3 Friction Ratio vs. Depth Equivalent SPT-N vs. Depth Friction Ratio (%) 1 2 3 4 SPT-N 5 6 7 0 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 Depth (ft) Depth (ft) 0 12 20 30 40 50 60 70 80 90 100 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 Figure 3 - Friction Ratio v Depth 10 Figure 4 - SPT - N v Depth 4 Soil Profile Depth (ft) 0.000 0.683 0.701 0.755 0.768 0.825 0.843 Legend Sandy Silt Silty Sand Very Stiff Fine Grained 8.717 8.737 9.176 9.190 10.541 10.559 11.535 11.553 18.027 18.042 18.511 18.526 21.733 21.749 21.785 21.800 21.928 Figure 5 - Soil Profile 5 Table 1. Showing the onsite testing Sand Type,Soil description and Average phi (deg) Depth (ft) Soil Type Soil Description Average Φ (deg) 0-0.22 Sand Silty Sand 29.6 0.24 Clay Sandy Silty 0.00 0.25-0.68 Sand Silty Sand 29.76 0.69-0.75 Sand Very Stiff Fine Grained 34.0 0.76-0.83 Sand Sandy Silt 0.00 0.84-3.00 Sand Silty Sand 31.2 3.02-6.87 Sand Silty Sand 30.7 6.88-6.90 Clay Sandy Silty 0.00 6.92-6.96 Sand Silty Sand 32.0 6.97 Clay Sandy Silt 0.0 6.99 Sand Silty Sand 32.0 7.00 Clay Sandy Silt 0.00 7.02-8.70 Sand Silty Sand 32.0 8.74-9.17 Clay Sandy Silt 0.00 9.18-10.54 Sand Silty Sand 31.6 10.55-11.54 Clay Sandy Silt 0.00 11.55-13.32 Clay Silty Sand 30.8 13.34-13.35 Clay Sandy Silt 0.00 13.37-17.25 Sand Silty Sand 30.5 17.26-17.33 Clay Sandy Silt 0.00 17.40-18.02 Sand Silty Sand 31.7 6 18.03-18.48 Clay Sandy Silt 0.00 18.498 Sand Silty Sand 32.0 18.511 Clay Sandy Silt 0.00 18.52-21.73 Sand Silty Sand 31.2 21.74-21.78 Clay Sandy Silt 0.00 21.8-21.928 Sand Very Stiff Fine Grained 34.0 Table 2. Showing the laboratory testing soil description and soil type at depth 1-3ft Depth (ft) Soil Type Soil Description 1.00-3.00 Sand Poorly Graded Sand with Clay Conclusion Based on the soil samples taken from USF’S GeoTech Park, it was concluded that soil taken mostly consisted of sand. Silty sand dominates the soil profile with some occasional smaller layers of sandy silt. The largest layer of silty sand stretched from .84’ to 8.7’ and another large layer was between 11.5’ to 18’. Layers of sandy silt tended to be about 1 to 1.5’ thick between the layers of silty sand. Very stiff fine grained soils were encountered at the end of test about 22 below ground level which the cone only penetrated about 1.5”. Therefore, when looking at the total depth , the soil was classified as sand with miniscule layers of silt/clay. This information is presented graphically in the soil profile above (Figure 5). The results for the onsite testing data and the Soil Classification laboratory experiment data at depths 1-3 ft were very similar and both classified the majority of soil as Sand. However, the onsite testing data had a majority soil description of Silty Sand while the laboratory testing data had a soil description of Poorly Graded Sand . As for the friction angle, the comparison between the onsite data and Direct Shear laboratory experiment data can not be done since the soil sample tested for Direct Shear experiment was not the same soil sample that was collected from the CPT site. It can be concluded that the soil consisted mostly of sand since both the CPT data and laboratory tested samples resulted in a soil classification of Sand. The friction angle would be based only on 7 the CPT data since the Direct Shear laboratory experiment sample used was different. The friction angle of the sample resulted in an average friction angle of 0 ° for Clay and an average friction angle range of 29.6 ° - 34 ° for Sand as shown on table 1 above. On any site, an engineer should always know what they are working with or on before committing to any site before getting started. Knowing the soil samples are detrimental in understanding the scope of the project, in order to carefully plan for future project mishaps. There is a significant amount of information available from different methods that can be performed prior to drilling, to assist in boring the soil sample locations. Every site will vary and every soil bore site location depth can change. Hence, different soil testing methods may vary for each site test location based on topography, moisture content, and even usage of the site. 8 References Applied Research Associates, I. (2018). ​The Advantages and Disadvantages of Geotechnical Boring; Why CPT May be Your Better Option​. [online] Vertekcpt.com. Available at: http://www.vertekcpt.com/blog/advantages-disadvantages-geotechincal-boring#.W7pVymhKhP Y [Accessed 7 Oct. 2018]. Gouda-Geo. “History of Cone Penetration Testing (CPT).” ​History of Cone Penetration Testing (CPT) - Gouda Geo-Equipment BV​, www.gouda-geo.com/products/cpt-equipment/background-information/history-of-cone-penetrati on-testing-cpt “History of Cone Penetration Testing (CPT).” ​History of Cone Penetration Testing (CPT) Gouda Geo-Equipment BV,​ www.gouda-geo.com/products/cpt-equipment/background-information/history-of-cone-penetrati on-testing-cpt. Ruwhenua, Komihana. “​What Is a Cone Penetration Test (CPT)?” ​EQC Earthquake Commission, www.eqc.govt.nz/sites/public_files/images/What%20is%20a%20cone%20penetration%20test.pd f VertekCPT. “Why Are There So Many Kinds of CPT Rigs?” In-Situ Soil Testing 101: The Different Types of Tests, Applied Research Associates, Inc., 25 Feb. 2014, www.vertekcpt.com/blog/cpt-rigs-variations 9 Cover page ❖ Introduction: ❖ Background: ❖ Testing and Analysis Method: ❖ Data Analysis: Tip Stress vs. Depth Tip Stress (Ksf) 0 50 100 150 200 0 1 2 Depth (ft) 3 4 5 6 7 8 9 Figure 1: Tip Stress verse Depth graph 250 Sleeve Stress vs. Depth Sleeve (bar) 0 1 2 3 4 0 1 2 Depth (ft) 3 4 5 6 7 8 9 Figure 2: Sleeve Stress verse Depth graph 5 6 Friction Ratio vs. Depth Friction Ratio (%) 0 1 2 3 4 5 0 1 2 Depth (ft) 3 4 5 6 7 8 9 Figure 3: Friction Ratio verse Depth graph 6 7 SPT-N vs. Depth SPT-N 0 10 20 30 0 1 2 Depth (ft) 3 4 5 6 7 8 9 Figure 4: SPT-N verse Depth graph 40 50 Depth (ft) Clay Silty Clay Clayey Slit Sandy Silt Silty Sand Sandy Silt Sand Gravelly Sand Clayey Sand Very Stiff Fine Grained 0 Organic Soil Type Sensitive Fine Soil Type vs. Depth 0 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 Figure 5: Soil Type verse Depth graph Depth (ft) Soil Type Soil Description Friction Angle (average) Cohesion (average) 0 - 0.04 Sand Silty Sand 30 0 0.06 – 0.39 Clay Sandy Silt 0 2.46 0.41 Sand Silty Sand 30 0 0.43-0.80 Clay Sandy Silt 0 2.78 0.82-1.14 Clay Clayey Slit 0 2.46 1.16-1.37 Clay Sandy Silt 0 2.24 1.39 Clay Clayey Slit 0 2.72 1.41-1.44 Clay Sandy Silt 0 2.16 1.46-1.78 Clay Clayey Slit 0 2.35 1.80-1.93 Clay Silty Clay 0 2.57 1.95-2.73 Clay Clay 0 2.72 2.75-2.77 Clay Silty Clay 0 2.08 2.80 Clay Clay 0 3.19 2.82-2.96 Clay Silty Clay 0 2.34 2.99-3.06 Clay Clayey Slit 0 1.98 3.09 Clay Silty Clay 0 2.59 3.12-4.01 Clay Clay 0 3.21 4.03-4.08 Clay Silty Clay 0 2.29 4.10-4.58 Clay Clay 0 3.10 4.61-4.72 Clay Silty Clay 0 2.35 4.75-5.53 Clay Clayey Slit 0 2.28 5.56-5.58 Clay Silty Clay 0 2.95 5.61-6.04 Clay Clayey Slit 0 2.39 6.07-6.22 Clay Silty Clay 0 3.35 6.24-6.43 Clay Clayey Slit 0 2.77 6.45-6.48 Clay Sandy Slit 0 2.52 6.50-6.53 Clay Clayey Slit 0 3.51 6.56-6.92 Clay Sandy Silt 0 3.07 6.95-7.00 Sand Silty Sand 32 0 7.02-7.19 Clay Sandy Slit 0 3.34 7.21-7.36 Sand Silty Sand 32 0 7.38 Clay Sandy Silt 0 4.15 7.41-8.12 Sand Silty Sand 32.83 0 8.15-8.24 Clay Sandy Slit 0 4.04 8.26-8.29 Clay Clayey Silt 0 3.69 8.30 Clay Silty Clay 0 4.0 8.30-8.31 Clay Clay 0 4.80 Table 1: Soil type, Friction angle and cohesion ❖ Discussion: ❖ Reference: FORMAL REPORT CHECKLIST: EVERYTHING MUST BE COMPUTER GENERATED! o Introduction (15 pts) • What is CPT? • How does it work? • What are some different methods/variations of CPT? • How does it differ from SPT? • Advantages/disadvantages of in-situ testing vs. laboratory testing • Advantages/disadvantages of CPT vs. SPT o Background (10 pts) • Provide a brief history of CPT and how it is used today o Testing and Analysis Method (10 pts) • Describe the methods and procedures used during a CPT investigation and our analysis method o Data & Analysis (35 pts) • You are given depth, tip stress, and sleeve stress as your raw data • Calculate friction ratio for all depths • Provide plots for: 1) Tip Stress vs. Depth 2) Sleeve Stress vs. Depth 3) Friction Ratio vs. Depth • Use Excel to determine soil classifications for the entire subsurface (every point on the data set) according to the CPT-Classification Diagram. Also determine equivalent SPT N-values according to the diagram. • Provide plots for: 1) Equivalent SPT N-Values vs. Depth 2) Soil Type vs. Depth • After determining SPT N-values, use Excel to determine friction angle and cohesion for the entire data set. Use the correlations from Table 2.3 (from PowerPoint). o Discussion (20 pts) • Comment on the soil profile. What kinds of soil layers are present? Where (depth) and how big are they? • Comment on the field data correlations. Which laboratory experiments would need to be performed to obtain similar data? Which is more accurate? • As an engineer, it is important to be aware of the benefits and shortcomings of insitu and laboratory testing as they pertain each individual application or project. There is no ‘one size fits all’ in geotechnical investigation. Discuss the factors of a project (i.e. size, type, importance, location, etc.) and how they would influence your choice of testing. When would one be preferred over the other? When should a combination be used? o References (10 pts) • Cite your sources! Use a consistent format (e.g. MLA, APA, etc.)
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