CVEEN 6340 Assignment 2 CPT and SPT Data and Correlations

(80 points) 1. One of the major issues involved in site characterization is the horizontal variability of the

soil deposits across a given site. The CPT is a good way to explore horizontal variability. To do this, develop a stratigraphic correlation chart similar to Figure 1 using the following CPT soundings and use CPT soundings: 06-SC-125, 06-SC-128, 06-SC-131, 06-RC-12, 06-SC-33. Label each stratigraphic unit. (The data for the CPT sounds is found in cptdata.xls. Note that the units and elevations for these soundings are found on the notes worksheet within the file cptdata.xls. The locations of the CPT soundings are found on Plates A-7 and A-8.) (10 points)

2. Use the CPT soil classification system developed by Robertson (1989) to develop a soil

profile versus elevation for 06-SC-128. For the profile you develop include the following plots versus elevation (m): qt, Rf, Qt, FR, u, Ic and SBT. SBT is the soil behavior type obtained from the Robertson (1989) (Figure 3a). Make a composite plot with each of these CPT parameters versus elevation the same page, similar to what is done in Figure 2. In addition, show how the CPT data plot by layer on the SBT chart. Use a different data symbol for each layer. Note also that the formula for Ic is found in Note 4 of Gregg Inc. Assume that the water table is at a depth of 2 m. (20 points)

3. On another page, use the CPT data from 06-SC-126 and 06-SC-128 and the appropriate

correlations to make a plot of the following:

a. drained friction angle for triaxial compression versus elevation (cohesionless soils) using eq. 4-12 of the EPRI manual. (10 points)

b. undrained shear strength for triaxial compression versus elevation (cohesive soils) using eq. 4-61 and fig. 4-53 of the EPRI manual. (10 points)

Before estimating the drained friction angle or undrained shear strength, screen the data first using the Soil Behavior Type Index, Ic (see Gregg, Inc.). Treat soils with an Ic number less than 2.6 as cohesionless soils and soils with an Ic number greater than or equal to 2.6 as cohesive soils. Drained friction angles should be calculated for all cohesionless soils. Undrained shear strength should be calculated for all undrained soils. Plot all of the drained friction angles from both CPT sounding versus elevation on a single page using a different symbol for each CPT sounding. Plot all of the undrained shear strength values from both CPT versus elevation on a separate, single page using a different symbol for each CPT sounding. For 3b, assume that the Nk factor is 14 and that the failure mode is direct simple shear.

4. Use SPT N values from boreholes 06-SB-125 and 06-SB-128 to develop a plot of the drained friction angle versus elevation for all granular soils. Put the estimated friction angles for

both boreholes on one page. (Note that in developing the drained friction angle from SPT data, that Equation 4-11 (see handout) uses SPT N60 and not SPT (N1)60. Thus, before using this equation you must convert the data back to SPT N60 values by dividing by CN. Use the unit weights shown in Figure 3 to calculate CN.). (10 points)

5. Make a comparison plot of the drained friction angles made in 3a and 4. Put all data on the

same plot using different symbols for each method. Discuss how similar or dissimilar the phi estimates are for both SPT and CPT methods and any reasons for possible differences. Note that we will compare 06-SB-125 with 06-SC-126 instead of 06-SC-125, because 06-SC-125 has some data errors in the file.) (5 points)

6. Use the preconsolidation stress versus depth (Figure 4) and SHANSEP to estimate the

undrained shear strength (Su) for this area. Use the SHANSEP parameters for the direct simple shear (DSS) mode of failure. Make a plot of Su versus elevation using the SHANSEP parameters given in Design and Performance of the Foundation Stabilization Treatments, I-15 Reconstruction (pp. 11 -12) for the direct simple shear mode of failure. (10 points)

7. Make a comparison plot of the undrained shear strength calculated in 3b and in 5. Put all

data on the same plot using different symbols for each method. Discuss how similar or dissimilar the estimates of Su are for the CPT and SHANSEP methods and any reasons for possible differences. (5 points)

Figure 1. Example stratigraphic correlation using CPT soundings from I-15 Reconstruction Project.

Figure 2. Example CPT log with soil classification system.

Figure 3. Wet (Saturated) Unit Weight versus Depth for South and North Temple Area, I-15 Reconstruction.

Figure 4. Preconsolidation stress (kPa) versus depth for the North and South Temple, I-15 Reconstruction.