ML20206L064
| ML20206L064 | |
| Person / Time | |
|---|---|
| Site: | PROJ0734 |
| Issue date: | 04/18/2012 |
| From: | Robert Williams Division of Decommissioning, Uranium Recovery and Waste Programs |
| To: | |
| Desotell L | |
| Shared Package | |
| ML20206K862 | List: |
| References | |
| SDU6 K-CLC-Z-00026 | |
| Download: ML20206L064 (15) | |
Text
K-CLC-Z-00026, Rev. 0 Sheet 2 TABLE OF CONTENTS
- 1. INTRODUCTION ...........................................................................................................................3
- 2. INPUT .........................................................................................................................................3 2.1 SOFT ZONE INPUT ....................................................................................................................3
- 3. COMPUTATION ...........................................................................................................................4 3.1 SOFT ZONE SETTLEMENT .........................................................................................................4 3.2 METHODOLOGY FOR COMPUTING SURFACE SETTLEMENT .......................................................5
- 4. RESULTS.....................................................................................................................................5 4.1 SURFACE SETTLEMENT DUE TO THE COMPRESSION OF A NARROW SOFT ZONE .......................6 4.2 SURFACE SETTLEMENT ............................................................................................................6
- 5. CONCLUSIONS ............................................................................................................................7
- 6. REFERENCES ..............................................................................................................................7 FIGURES ............................................................................................................................................8
K-CLC-Z-00026, Rev. 0 Sheet 3
- 1. Introduction The purpose of this calculation is to provide an estimate of the settlement resulting from the compression of soft zones for Saltstone Disposal Unit 6.
- 2. Input 2.1 Soft Zone Input Twenty-three (23) CPTs and SCPTs were pushed for the Saltstone Disposal Unit 6, see Figure 1.
Stratigraphic interpretations of the CPT and SCPTs are summarized below (Ref. 1). These 23 CPTs and SCPTs were evaluated for the presence of soft zones.
Elevation Top Pick (ft, msl)
CPT SRS SRS Elevation C2 S3 S4 ID Congaree Type Northing Easting ft, msl Layer Layer Layer Z-SDU6-C01 CPT 77413.3 66270.1 281.9 233 226 190 Z-SDU6-C02 SCPT 77448.1 66350.4 281.4 233 227 190 Z-SDU6-C03 CPT 77478.3 66494.3 281.6 233 225 190 Z-SDU6-C04 CPT 77503.3 66578.8 281.8 236 229 190 Z-SDU6-C05 SCPT 77624.5 66594.9 278.1 235 226 187 Z-SDU6-C06 CPT 77587.6 66472.8 278.6 234 227 189 Z-SDU6-C07 CPT 77546.9 66357.1 279.4 237 230 191 Z-SDU6-C08 CPT 77511.4 66258.9 279.7 236 230 186 Z-SDU6-C09 CPT 77621.8 66210.4 278.3 237 230 194 Z-SDU6-C10 CPT 77644.2 66285.6 278.0 237 230 190 Z-SDU6-C11 CPT 77663.3 66354.1 277.6 238 233 186 Z-SDU6-C12 SCPT 77682.6 66452.6 277.7 239 234 188 Z-SDU6-C13 CPT 77722.6 66523.4 276.3 234 228 188 Z-SDU6-C14 CPT 77720.6 66180.9 277.3 234 222 181 Z-SDU6-C15 CPT 77748.2 66249.8 276.8 232 217 192 Z-SDU6-C16 SCPT 77772.2 66312.2 276.7 234 216 184 Z-SDU6-C17 CPT 77796.3 66393.3 276.0 235 219 187 Z-SDU6-C18 SCPT 77819.4 66471.7 275.6 235 217 186 Z-SDU6-C19 SCPT 77869.3 66155.6 276.4 235 227 183 Z-SDU6-C20 CPT 77895.0 66236.9 276.0 226 219 176 Z-SDU6-C21 CPT 77920.9 66321.6 276.3 233 225 182 Z-SDU6-C22 CPT 77947.5 66415.1 276.5 237 230 187 Z-SDU6-C23 CPT 77967.7 66482.5 275.5 238 233 190 Five (5) borings were also performed for this investigation. Stratigraphic interpretations for the borings are listed in the table below. Borings Z-SDU6-B01 and Z-SDU6-B03 are adjacent to each other.
K-CLC-Z-00026, Rev. 0 Sheet 4 Elevation Top Pick (ft, msl)
SRS SRS Elevation C2 S3 S4 ID Congaree Northing Easting ft, msl Layer Layer Layer Z-SDU6-B01 77771.3 66309.1 276.6 Z-SDU6-B02A 77625.3 66594.8 278.0 Z-SDU6-B02B 77629.2 66588.9 278.1 234 227 191 Z-SDU6-B03 77769.6 66304.5 276.5 232 217 188 146 Z-SDU6-B04 77663.9 66351.1 277.9 236 232 191 145
- 3. Computation Soft zones are layers of underconsolidated soils within the Santee Formation (S4 layer) which are identified by a corrected tip stress value less than or equal to 15 tsf. Layers of soft zone soils (corrected tip stress less than or equal to 15 tsf) are considered to behave as a single soft zone if the interval of harder material (corrected tip stress greater than 15 tsf) between the soft zone soils is less than or equal to 2 feet in thickness. The thickness of the soft zone is the summation of the less than 15 tsf material. The top elevation of the soft zone is the top of the first layer of soil with a corrected tip stress less than 15 tsf within the Santee Formation Santee Formation (S4 layer).
If the interval of harder soil (corrected tip stress greater than 15 tsf) between soft zone soils is greater than 2 feet, the layers of soft zones soils are considered to behave as two separate soft zones (See Figure 3).
Soft zones may also be identified by N value less than or equal to 5 blows per foot (including weight of rod and weight of hammer events) within the Santee Formation (S4 layer). Loss of circulation is also an indication of the presence of soft zones.
3.1 Soft Zone Settlement No soft zone samples were obtained during the geotechnical investigation for Saltstone Disposal Unit 6. The properties from Saltstone Vault 2, used for analysis in this calculation, are summarized below (Ref. 2).
Compression Index, Cc 0.196 Initial Void Ratio, e0 0.72 Overconsolidation Ratio, OCR 0.9 Compression Ratio, Cc/(1+e0) 0.114 The bottom of the excavation will be 265 ft, msl at Saltstone Disposal Unit 6. The average top of the S4 layer (Santee Formation) at the site is 187 ft, msl. For conservatism, it will be assumed that the top of the soft zone is located at the top of the S4 layer.
The compression of the soft zone sS at depth is estimated assuming full overburden pressure:
sS = H {Cc/(1 + eo)} log {(Po + P)/Po}
Where sS is the compression of the soft zone and H is the thickness of the soft zone. Cc and e0 were described in the previous section. When the arch above the soft zone is weakened, the Po +
P term is equal to the overburden pressure and the Po term in the denominator is the soft zone preconsolidation pressure. In this instance the equation becomes:
K-CLC-Z-00026, Rev. 0 Sheet 5 sS = H {Cc/(1 + eo)} log (1/OCR) where OCR is the overconsolidation ratio of the soft zone.
3.2 Methodology for Computing Surface Settlement A vertical slice of subsurface with unit thickness or perpendicular to the longitudinal direction of the soft zone was considered. Ground settlement, which is propagated from the subsurface deformation, was computed considering the surface settlement profile resembles the shape of an inverted normal distribution curve (Ref. 3). The surface settlement s(x) at any point x is:
s(x) = s(0) Exp.{-x2/(2i2)} (Eq. 1)
Where i is the distance from the center of the normal probability curve to the point of inflection:
i = W/(2)1/2 (Eq. 2) and W is the half width of the normal probability curve and may be estimated as (Ref. 3):
W = z tan + WSZ/2. (Eq. 3) where:
z is the soft zone depth and is based on soil type The volume lost at-depth due to compression of soft zone can be computed as:
VL = sS WSZ. (Eq. 4)
Where sS is the compression of the soft zone computed in the previous section and WSZ is the width of the soft zone.
As the soft zone collapses, the volume of the soil above the soft zone will be increased as a result of dilation and loosening as the soil stresses redistribute. For granular soils, appreciable volume changes can occur in the soil as a result of disturbances and displacement (Ref. 3).
The volume of the surface settlement is:
VS = RS/LVL (Eq. 5) where RS/L is the ratio of the volume of the surface settlement to the volume lost at-depth due to compression of the soft zone. Substituting Equation (4) into Equation (5):
VS = RS/L sS WSZ. (Eq. 6)
Surface settlement at the center of the normal probably curve is:
s(0) = VS/W (Eq. 7)
Substituting Equation (6) into Equation (7) s(0) = RS/L sS WSZ /W (Eq. 8)
Substituting Equation (8) into Equation (1), settlement at any point x can then be expressed as s(x) = RS/L sS WSZ /W Exp[-x2/(2i2)] (Eq. 9)
Figure 3 illustrates the properties of a normal probability curve settlement trough.
- 4. Results Soft zones were identified in 3 CPTs: Z-SDU6-C01, Z-SDU6-C10, and Z-SDU6-C15. The soft
K-CLC-Z-00026, Rev. 0 Sheet 6 zones in C01 and C15 are 1.25 feet and 1.38 feet thick, respectively. The CPT Z-SDU6-C10 contained 5.8 feet of soft zone material. This soft zone was used for settlement computations.
4.1 Surface Settlement due to the Compression of a Narrow Soft Zone The assumption of normal probability is for underground disturbance over a short width.
Assume the width of the soft zone is:
WSZ = 5 feet For the project site, at elevation of the foundation, 265 feet, MSL, the distance to the average depth of the soft zone is:
z = 265 - 187 = 78 feet For SRS soil conditions falls between 33 and 50 degrees. For sands below groundwater level, is generally greater than 50 degrees. A smaller will provide conservative values of maximum slope and maximum change of slope (Ref. 3) at the project site, consider = 33 degrees:
W = z tan + WSZ/2 = 78 tan(33o) + 5/2 = 53.154 feet i = W/(2)1/2 = 53.154 / (2)1/2 = 21.205 feet The volume of the surface settlement is generally one third to two thirds less than the volume of lost ground (Ref. 1). In this calculation, RS/L is conservatively taken as 1.0, ie surface volume settlement is the same as the volume of lost ground at depth.
Using the soft zone properties from Vault 2, the compression of the soft zone is:
sS = H {Cc/(1 + eo)} log (1/OCR) = 5.8 x 0.196/(1 + 0.72) x log (1/0.9) = 0.030 feet or sS = 0.3629 inches.
Equation 8 becomes:
s(0) = RS/L sS WSZ /W = 1.0 x 0.3629 x 5/53.154 = 0.0341 inches Equation 1 becomes:
s(x) = 0.0341 Exp {-x2/(2 x 21.2052)} inches or s(x) = 0.0341 Exp(-x2/899.304) inches 4.2 Surface Settlement Wide soft zones maybe represented as a series of adjacent narrower soft zones. Surface settlements due to the wide soft zone are computed by superimposing the settlement troughs for each of the narrow soft zones. For this calculation, a series of 5 foot wide soft zones were utilized to represent soft zones ranging in width from 25 feet to 150 feet.
Maximum differential settlement is assumed to be equal to the total soft zone induced settlement.
Maximum slope is the rate of change of settlement along the settlement trough, while curvature is the rate of change of the slope along the settlement trough.
Figure 4 presents the surface settlement profiles for each of the soft zone widths considered.
Figures 5 - 7 illustrate the maximum surface settlement, maximum slope, and maximum curvature as functions of soft zone width. The values for these parameters are summarized in the
K-CLC-Z-00026, Rev. 0 Sheet 7 table below. The maximum curvature summarized in the maximum absolute value of the concave up and concave down curves. The ratio of the surface settlement to the compression of the soft zone at depth is also given in the table below.
Maximum Ratio of Maximum Maximum Maximum Soft Zone Differential Maximum Settlement (S0) to Soft Settlement Curvature Width (ft) Settlement Slope (ft/ft) Zone Compression at (in) (ft/ft per ft)
(in) Depth 25 -0.162 0.162 0.00036 0.00003 45%
50 -0.276 0.276 0.00053 0.00003 76%
75 -0.335 0.335 0.00057 0.00002 92%
100 -0.356 0.356 0.00057 0.00002 98%
125 -0.362 0.362 0.00057 0.00002 100%
150 -0.363 0.363 0.00057 0.00002 100%
Maximum -0.363 0.584 0.00057 0.00003 100%
- 5. Conclusions Considering the maximum values presented in Section 4.2, the following values are recommended for design of soft zone induced settlements.
Parameter Recommended Value Maximum soft zone settlement 1/2 inch Maximum soft zone differential settlement 1/2 inch Maximum Slope 0.0006 ft/ft Maximum Curvature 0.00003
- 6. References
- 1. K-CLC-Z-00022, Rev. 0, Stratigraphy for Saltstone Disposal Unit 6 (SDU6), March 2012.
- 2. K-CLC-Z-00009, Rev. 0, Settlement due to Compression of Soft Zone, March 2006.
- 3. Cording, E.J., et al., Displacements Around Tunnels in Soils, Report No. 76T-22, U.S.
Department of Transportation, Washington D.C.
K-CLC-Z-00026, Rev. 0 Sheet 8 Figures
K-CLC-Z-00026, Rev. 0 Sheet 9 Z-SDU6-C23 274 Z-SDU6-C22 276 Z-SDU6-C18 Z-SDU6-C21 #
278 Z-SDU6-C13 Z-SDU6-C17 )
Z-SDU6-C20 #
- Z-221
- Z-SDU6-C05
)#
)
Z-SDU6-B02B Z-SDU6-B02A 280 Z-SDU6-C12 Z-SDU6-C16 #
Z-SDU6-C19 #
)
" Z-SDU6-B01
)
- Z-SDU6-B03 282 Z-SDU6-C15 Z-SDU6-C06 Z-SDU6-C04
- Z-SDU6-C11 #
)
Z-SDU6-B04 284 Z-SDU6-C14 Z-SDU6-C10
T NO AN PL RTH NO Z-SDU6-C01 0 50 100 200 300 Feet Figure 1: Location of Geotechnical Investigations
K-CLC-Z-00026, Rev. 0 Sheet 10 Thickness Depth 100.0 ft One Soft Zone 1.5 feet thick qt = 15 tsf - 2.5 feet thick 101.5 ft Top depth - 100 feet 0.5 feet thick qt > 15 tsf 102.0 ft 1.0 feet thick qt = 15 tsf 103.0 ft 100.0 ft Two Soft Zones 1.5 feet thick qt = 15 tsf - 1.5 feet thick 101.5 ft Top depth - 100 feet
- 1.0 foot thick 2.5 feet thick qt > 15 tsf Top depth - 104 feet 104.0 ft 1.0 feet thick qt = 15 tsf 105.0 ft Figure 2: Graphical Depiction of Soft Zone Determination
K-CLC-Z-00026, Rev. 0 Sheet 11 Figure 3: Geometry of Surface Settlement Trough
K-CLC-Z-00026, Rev. 0 Sheet 12 Figure 4: Surface Settlement Profile for Soft Zones of Various Widths
K-CLC-Z-00026, Rev. 0 Sheet 13 Figure 5: Maximum Surface Settlement for Soft Zones of Various Widths
K-CLC-Z-00026, Rev. 0 Sheet 14 Figure 6: Maximum Surface Slope for Soft Zones of Various Widths
K-CLC-Z-00026, Rev. 0 Sheet 15 Figure 7: Maximum Surface Settlement Curvature for Soft Zones of Various Widths