ML20032C539
| ML20032C539 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 11/06/1981 |
| From: | Jackie Cook CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 14843, NUDOCS 8111100553 | |
| Download: ML20032C539 (24) | |
Text
-_
e Const!mers Power James W Cook Vice President - Projects, Engineering and Construction oeneral Offkes: 1945 West Parnell Road, Jackson, MI 49201 e (517) 7880453 November 6, 1981 f
,gn siitdj N d
^
s C NOVO 9198pe.
a Harold R Denton, Director
" g g* A W 7 Office of Nuclear Reactor Regulation 9
4f7 US Nuclear Regulatory Commission Washington, DC 20555 Co i/
N MIDLAND PROJECT MIDLAND DOCKET NOS 50-329, 50-330 RESPONSE TO NRC STAFF REQUEST FOR ADDITIONAL INFORMATION PERTAINING TO THE PROPOSED UNDERPINNING OF THE SERVICE WATER PUMP STRUCTURE FILE 0485.16, B3.0.8 SERIAL 14843 ENCLOSURE: RESPONSES TO THE NRC STAFF REQUEST FOR ADDITIONAL INFORMATION PERTAINING TO THE PROPOSED UNDERPINNING OF THE SERVICE WATER PUMP STRUCTURE On September 17, 1981, a request for additional information relating to the service water pump structure was made by the Staff in a meeting at the NRC's offices in Bethesda, Maryland. We are responding to this request by forwarding the above enclosure. The enclosure addresses each of the individual Staff concerns transmitted to us in the September 17, 1981 meeting.
We believe the enclosed information adequately responds to the request and individual concerns identified for us by the Staff. The discussion and data contained in the enclosure tc this correspondence leni further support to our conclusion that the design of the service water pump structure combined with the remedial actions are adequate and appropriate for this structure.
/
G r-W f
~
gOf JWC/RLT/dsb
.s iI, 81'1'1100553 811106
~
PDR ADOCK 05000329 A
o 2
CC Atomic Safety and Licensing Appeal Board, w/o CBechhoefer, ASLB, w/o MMCherry, Esq, w/o FPCowan, ASLB, w/o RJCook, Midland Resident Inspector, w/o RSDecket, ASLB, wio l
JHarbour, ASLB, w/o DSHood, NRC, w/a (2)
DFJudd, B&W, w/o JDKane, VRC, w/a FJKelley, Esq, w/o RBLandsman, NRC Region III, w/a WHMarshall, Esq, w/o JPMatra, Naval Surface Weapons Center, w/a W0tto, Army Corps of Engineers, w/a WDPaton, Esq, w/o FRinaldi, NRC, w/a HSingh, Army Corps of Engineers, w/a BStamiris, w/o oc1181-0473a100
RESPONSE TO THE NRC STAFF REQUEST FOR ADDITIONAL INFORMATION PERTAINING TO THE PROPOSED UNDERPINNING OF THE SERVICE WATER PUMP STRUCTURE CONSUMERS POWER COMPANY MIDLAND PLANT UNITS 1 AND 2
MIDLAND PLANT UNITS 1 AND 2 RESPONSE TO THE NRC STAFF REQUEST FOR ADDITIONAL INFORMATION PERTAINING TO THE PROPOSED UNDERPINNING'OF THE SERVICE WATER PUMP STRUCTURE 1
CONTENTS Page
1.0 INTRODUCTION
1 2.0 REQUESTS FOR ADDITIONAL INFORMATION 1
3.0 DESCRIPTION
OF PROTECTION FOR THE EXISTING 7
STRUCTURE DURING CONSTRUCTION 4.0 DISCUSS THE BEARING CAPACITY OF THE UNDISTURBED 9
NATURAL SOIL SUPPORTING THE UNDERPINNING 5.0 EVALUATE THE DIFFERENTIAL SETTLEMENT BETWEEN 9
THE MAIN PART OF THE STRUCTURE AND THE UNDER-PINNED PORTION
6.0 DESCRIPTION
OF PROCEDURE FOR TIMING OF FINAL 10 JACKING LOCK OFF 7.0 DISCUSSION OF THE VALIDITY AND USE OF THE 11 PENETROMETER
8.0 DESCRIPTION
OF THE CRITERIA FOR FAILURE OF THE 12 SOIL RESULTING FROM JACKING LOADS 9.0 DESCRIBE THE PROCEDURE FOR MONITORING GROUND-12
^
WATER LEVELS DURING CONSTRUCTION OF THE UNDERPINNING WALL 10.0 COMMENT ON BORING CE-2 S'HOWING FILL MATERIAL 12 BELOW EL 587.0 11.0 EVALUATIuN OF SOIL SPRINGS VALUES - STATIC 13 AND DYNAMIC LOADING CONDITIONS REFERENCES 14 il 3
l
Midland Plant Units 1 and 2 NRC Request for Additional Information:
Service Water Pump Structure Underpinning Table of Contents (continued)
, FIGURES 1
Service Water Pump Structure Settlement Marker Locations 2
-Service Water-Pump Structure Estincted Top of Pier Deflection Due to Creep of Concrete Versus Time 3
Service Water Pump Structure Estimated Top of Pier Deflection'Due to Shrinkage of Concrete Versus Time 4
Service Water Pump Structure Estimated Top of Pier Deflection Due to Total Deformation Versus Time i
5 Service Water Pump Structure Estimated Top of Pier Deflection Due to Consolidation of Soil Versus Time i
1 l
1 i
l l
iii l
,4 m,
+.,,,. _,..,,
..,.-,y
.r,yr_m....__.m..
.y,
MIDLAND PLANT UNITS 1 AND 2 RESPONSE TO THE NRC STAFF REQUEST FOR ADDITIONAL INFORMATION PERTAINING TO THE PROPOSED UNDERPINNING OF THE SERVICE WATER PUMP STRUCTURE
1.0 INTRODUCTION
On September 17, 1981, representatives of Consumers Power
- Company, Bechtel Power Corporation, and the NRC met in Bethesda, Maryland, for a presentation of the proposed remedial action for the Midland plant service water pump structure (SWPS).
The discussion of the proposed underpinning construction resulted in several requests for additional information.
This report responds to these requests and supplements the Technical Report on the Service Water Pump Structure Underpinning (Reference 1).
2.0 REQUESTS FOR ADDITIONAL INFORMATION 2.1 ASSUMPTIONS AND CONCLUSIONS FOR THE PRELIMINARY ANALYSIS OF
)
THE UNDERPINNED STRUCTURE 2.1.1 Stability Analysis 2.1.1.1 Discussion The underpinned structure was analyzed for sliding, overturning, and resistance to buoyancy for the design flood condition in conformance with Final Safety Analysis Report (FSAR) Subsection 3.8.6.3.4.
Sliding in the north-south direction was critical and overturning was critical in the east-west direction.
The critical load combination for sliding and overturning is:
D + H + E' where i
D = dead load of :tructure and equipment H= lateral earth pressure E'
= safe shutdown earthquake load' 2.1.1.2 Assumptions a.
The normal groundwater was assumed at the level of the pond (el 627').
f 1
.~
Midlcnd Plant Units 1 cnd 2 NRC R3 guest for Additional Information:
Service Water Pump Structure Underpinning b.
The long-term shear strength parameters are C' = 36*
and C' = 0.73 ksf, based on Woodward Clyde Consultants' test data at the SWPS location.
c.
The lateral earth pressure dynamic increment was obtained by using FSAR Figure 2.5-45.
d.
The forces from the safe shutdown earthquake (SSE) were increased by 50% to provide for a possible increase in this requirement.
e.
Because of the flexibility of the underpinning wall, only the side walls and approximately 25% of the north underpinning wall are considered effective in resisting the force that attempts to cause sliding.
The validity of this assumption will be verified in the final analysis.
2.1.1.3 Conclusions f
The minimum factor of safety against sliding is 1.17 and is based on a sliding force of 16,500 kips and a total resistance of 19,200 kips.
This figure is calculated for sliding in the north-south direction and exceeds the allowable factor of safety of 1.1.
The minimum factor of safety against overturning is 1.45 versus an allowable factor of safety of 1.1.
This value is based on an overturning moment of 1.9 x 108 ft-kips compared to a stabilizing moment of 2.75 x 10s ft-kips.
The east-west direction is the critical direction for overturning.
The building has a factor of safety of 2.1 versus the required 1.1 against the buoyancy force for a flood level of el 631.
The building has a total dead weight of 42,000 kips and a buoyancy force of 20,000 kips.
2.1.2 Lower Foundation Slab 2.1.2.1 Discussion The lower foundation slat > is 90 feet long, 74 feet wide, and 5 feet thick and forms the base for the SWPS sump.
Interior walls divide the foundation into three slabs:
two small slabs 45 feet by 30 feet with effective span lengths of 38 feet, 9 inches by 25 feet, 9 inches and a large slab 90 feet by 44 feet with effective span lengths of 79 feet, 6 inches by 30 feet, 6 inches.
The large slab was judged most critical and was analyzed for the following load combinations:
2
\\*
Midland Plant Units 1 and 2 NRC Request for Additional Information:
Service Water Pump Structure Underpin.'ing U = 1.4D + 1.7L + Pg U = 1.4D + 1.7L + 1.4Pg U=D+L+P
+ E' t
U = 1.25 (D + L + P
+ E) g where U = required strength to resist design loads or their related internal moments and forces I
D = dead load of the structure and equipment L = conventional floor and roof live loads (includes movable equipment loads or ott.tr loads which vary in intensity)
P
= load (ni structure due to jacking t
E'
= SSE load E = operating basis earthquake 2.1.2.2 Assumptions a.
The groundwater was assumed at the level.of the pond (el 627').
b.
The plant fill under the upper-foundation slab offers no vertical support for the upper slab.
b c.
The effects of dead load, live load, and jacking load are carried only by the lower foundation slab.
All other loads are transferred to the foundation composed of the lower slab and the underpinning wall.
2.1.2.3 Conclusions i
The maximum imposed out-of-plane moment of 180 ft-kips was exceeded by the moment capacity of the slab, which amounts to 200 ft-kips.
The maximum soil pressure was 11.3 ksf.
2.1.3 Effect of Construction Dewatering on the Lower Foundation Slab 2.1.3.1 Discussion Fluctuations of the water table will affect the values of the soil pressures under the foundation slab.
The drawdown of the 2
~~
Midland Plant Units 1 and 2
-NRC Request for Additional Information:
Service Water Pump Structure Underpinning groundwater for constructing the underpinning wall will decrease the. buoyancy of the structure, causing an increase in bearing pressure.
4 2.1.3.2 Assumptions a.
The original groundwater is assumed at the level of.the pond (el 627').
b.
The groundwater. will be drawn down to el 58'/ ' at the north underpinning wall, c.
The shape of the drawdown curve is narabolic.
d.
The drawdown is nniform for the full width of the structure.
2.1.3.3 Conclusions Considering dead load, 3ise load, and buoyancy, and the assumed groundwater at el 627'-0." the bearing pressure under the slab varies with a maximum value of 5.35 ksf at the north edge.
For the construction condition, dewatering to el 587'-0", this pressure increases to 8.12 ksf, which is well below the allowable pressure of 16.7 ksf.
This pressure, 8.12 ksf, will be reduced as the construction of the underpinning wall proceeds because the addition of jacking forces reduces the weight of the structure supported by the lower base slab.
The pressures from the enderpinning construction condition are less than the values usad in Subsection 2.1.2 of this report and are not considered critical'in analyzing the slab.
2.1.4 Upper Foundation Slab 2.1.4.1 Discussion The slab is 86 feet long, 38 feet wide, and 3 feet thick.
An interior wall divides the slab into two slabs of unequal size.
The smaller slabs are 38 feet by 35 feet and 51 feet by 38 feet.
The larger slab, with effective span dimensions of 48 feet, 3 inches by 25 feet, 4 inches, was analyzed for the following load combination, which included the effects of compartment flooding to a depth of 12.5 feet.
U = 1.0D + 1.0L + 1.0E' + 1. OT, + 1.25H. + 1.0R + Pt 4
~
Midland Plant Units 1 and 2 NRC Request for Additional Information:
Service Water Pump Structure Underpinning 2.1.4.2 Assunptions a.
The fill under the upper foundation slab offers no vertical support.
The slab is simply supported on four sides but is continuous over the interior wall.
b.
The seismic effects and the containment of water to a depth of 12.5 feet does not occur simultaneously.
2.1.4.3 Conclusions The maximum imposed moment of 109 ft-kips (from the analysis) is less than the slab capacity of 150 ft-kips.
Therefore, the slab is considered to be adequate.
2.1.5 Sidewalls of the Overhang 2.1.5.1 Discussion The exterior walls at the face of the overhang were analyzed for shear and bending stress for the load combination of:
U = D + L + E'
+P t
2.1.5.2 Assumptions a.
The groundwater was assumed at the level of the pond (el 627').
b.
The fill under the upper foundation slab offers no support.
c.
The resisting section at the face of the overhang consists of a box section and the attached underpinning walls.
The box section is composed of the exterior walls of the overharg, the roof slab, and the foundation slab.
The support offered by the interior walls was ignored.
The resisting section was modified for the effects of shear lag.
2.1.5.3 Conclusions The maximum computed compressive stress in the walls was 0.32 ksi and the maximum shear stress is 0.103 ksi.
The largest tensile stress in the reinforcemen* is 2.2 ksi.
All values are below the American Concrete Institute (ACI) 318-71 allowable values.
5
Midland' Plant Units 1 and 2.
~
NRC Request for Additional Information:
Service Water Pump Structure Underpinning 2.1.6 Interface Connectors 2.1.6.1. Discussion t
The underpinning walls are designed to act as integtal parts of
- the structure.
Apolication of jacking loads and the use of anchor bolts will ensure that loads are adequately transferred between the structure and the underpinning walls.
Rock bolts and 3
anchor bolt assemblies will be used to ensure that the walls and structure do not separate.
Because the construction procedure.
requires that the anchor bolts and rock anchors be installed after the application of the jacking loads, the connectors are i
not affected by the jacking operation or the dead load of the structure.
i 2.1.6.2 Assumptions a.
The connectors will be designed to carry all loads'on-I the structure, except the jacking loads, e
b.
The behavior of the connection is governed by shear 7
friction requirements.
c.
The connectors were designed for the following load j
combinations:
U = 1.4D + 1.7L + P t U = D + L + E'
+ P t 7
2.1.6.3 Conclusions The maximum-shear load to be transferred at each vertical interface is 1,300 kips.
Nine 2-inch diameter, hollow core rock anchors at a maximum spacing of 3 feet, 9 inches are required to fulfill the shear friction requirements.
A maximum shear of 1,700 kips will be transferred at the horizontal interface by 2-3/4-inch diameter anchor bolts at a maximum spacing of 3 feet, 9 inches.
2.1.7 Underpinning Wall 2.1.7.1 Discussion
)
The underpinning wall extends from the underside of the upper foundation to firm bearing or undisturbed soil.
The wall is 4 feet thick and 30 feet higa.
The base of the north wall is i
a 6
s
..... -. -., - _, ~., ~ -. -.. ~... _ _.......
..mm.
-..._.,_....m _ _. _ _.. _,. _. _,,,.
Midland Plant Units 1 and 2 NRC Request for Additional In fo rma tion :
Service Water Pump Structure Underpinning widened to 6 feet.
The wall is connected to the existing structure with rock and anchor bolts.
The wall was analyzed for the following load combination:
U = D + L + l' '
+P t
2.1.7.2 Assumptions a.
The "all was analyzed as a shear wall for in,. te forces.
b.
Because the north wall has a horizontel span length of approximately 86 feet, the wall at midlength was analyzed as a vertical simply supported beam and was j
also analyzed with partial restraint at the base for i
out-of-plane forces.
2.1.7.3 Conclusions For in-plane forces, each side wall carries a moment of 50,000 ft-kips and a shear of 400 kips.
The capacity of the wall is 75,000 ft-kips for moment and 1,000 kips for shear.
Because the aspect ratio of the north wall is much more favorable, it was considered not critical in the preliminary analysis.
The analysis of the north wall for out-of-plane forces showed the maximum moment to be 150 ft-kips per foot of wall, which is less than the 190 ft-kip moment capacity.
Shear was not critical.
3.0 DESCRIPTION
OF PROTECTION FOR THE EXISTING STRUCTURE DURING CONSTRUCTION 3.1 CONSTRUCTION PROCECURE (Refer to Figure 4 of Reference 1)
Protecting the existing structure while constructing the underpinning wall is a major concern.
This concern is reflected in the procedure that was established for constructing the underpinning.
This procedure was developed with the purpose of providing the maximum degree of safety to the structure.
As a precautionary measure, the upper portion of the north-south exterior walls will be post-tensioned before the permanent dewatering begins.
The dewateting will reduce the buoyancy force acting on the overhang and will increase bending stresses in the walls.
Post-tensioning the upper portion of the exterior walls will induce compression in the walls and will minimize the effects of the tensile forces caused by dewatering.
The first three piers, which are located at the northwest and northeast corners of the structure, will be constructed from tunnels proceeding simultaneously from the access shafts at the 7
Midland Plant Units 1 cnd 2 NRC Requ2st for Additional Information:
Servica Wster Pump Structure Underpinning east and west sides of the building.
In this way, the jacking force will be symmetrically applied to the structure.
The construction procedures prevent advancing either tunnel to the area where the next pier is to be constructed until the jacking load is placed on the completed nier.
Thus, the decrease in soil support of the upper foundation slab is kept to a minimum.
After the corner piers are in place, the construction procedures call for th_ installation of the center piers under the north wall.
This requires advancing the tunnel approximately 25 feet to the next pier.
To prevent excessive loss of support, the following provisions will be made.
3.1.1 Only one tunnel will be extended from the pier 3 to pier 4 location at one time.
When the first pier 4 and pier 5 are load bearing, the other tunnel will be extended to the remaining pier 4.
3.1.2 Measurement devices will be provided at piers 1, 2, and 3 to monitor variations in applied loads to the piers.
If a sudden increase in pier loading of the magnitude of approximately one-third is indicated while the tunnel is being advanced from pier 3 to pier 4, tunnel construction will be stopped.
Pier 8 will then be constructed as a series of piers instead of as a large monolithic pier.
This procedure will provide a gradual increase in the jacking support to the overhang as the tunnel is advanced to pier 4.
3.1.3 When the tunneling operation toward the center begins, the three piers on each end will have a total jacked load of 465 kips.
This results in an average bearing pressure of 5.8 ksf in the till.
The till is considered adequate for an allowable bearing intensity of 19.2 ksf at a safety factor of 2.5 against bearing failure.
These figures indicate that a total allowable bearing load of 1,600 kips for eacn pier group is available to adequately support the overhang portion of the structure.
The north wall is adequate at ACI-acceptable stresses to span betwten the end pier groups if necessary.
Analysis of the north wall for this condition, considering the wall as a deep concrete beam and assuming no vertical soil support to the overhang, shows that the compressive stress amounts to 0.250 ksi and tension in the concrete amounts to 0.300 ksi which is less than the modulus of rupture, 0.475 ksi.
3.2 CRACK MONITORING In anticipation of the underpinning wall construction, a crack mapping program has been started.
Existing crack locations and widths have been accurately measured.
Future mappings, to monitor the existing cracks and the appearance of new cracks, are scheduled to take place before and after major underpinning 8
Midland Plant Units 1 and 2 NRC Request for Additional Information:
Service Water Pump Structure Underpinning construction procedures, such as post-tensioning, dewatering, and jacking.
Because of the sequence of construction procedures, it is not anticipated that existing cracks will significantly widen or that significant new cracks will appear.
However, any new structural cracks or changes in existing structural cracks exceeding 0.01 inch will be evaluated and if any. crack widths reach C.03 inch, construction in the affected' area will be modified or suspended until the reasons for excessive cracking are established and appropriate remedial measures are implemented.
3.3 SETTLEMENT MONITORING In addition to the crack monitoring program, a program to closely monitor structure settlement has been planned.
Besides the four existing eettlement markers at each corner of the building, five additional markers will be installed on the building (Refer to Figure 1) and a settlement dial indicator will be installed at each of the two building corners where the underpinning will be constructed.
The dial indicators will be attached to the building with their probes connected to permanent bench marks founded in undisturbed soil approximately 50 feet below the bottom of the underpinning wall.
The depth at which the tip of the bench mark is located ensures that the bench mark movement will be negligible.
The settlement markers will be monitored before and af ter major construction procedures as discussed in Section 3.2.
Building movement and crack data will enable the project engineer to evaluate the effects of the underpinning construction on the existing structure.
4.0 DISCUSS THE BEARING CAPACITY OF THE UNDISTURBED NATURAL SOIL SUPPORTING THE UNDERPINNING The estimated, ultimate bearing capacity is based on the many borings taken in the area by Dames and Moore and others including the recent borings taken by Woodward-Clyde Consultants.
The soil samples and laboratory analysis of the most recent borings indicate the soil has shear strength conservatively estimated at 8 ksf and an ultimate hearing capacity of q8_ksf.
5.0 EVALUATE THE DIFFERENTIAL SETTLEMENT BETWEEN THE MAIN PART OF THE STRUCTURE AND THE UNDERPINNED PORTION The construction procedure requires that jacking loads be applied to the piers soon after the pier is constructed.
This load is sustained for sufficient time to dissipate the major portion of the long-term settlement of the underpinning.
The underpinning is not attached to the structure until after the settlement has taken place.
9 1
.w
,-me
-my-----,---,.,..e
--m-
.=
Midland-Plant Units 1 and 2 NRC Request for Additional Information:
Service Water Pump Structure Underpinning j
Variations in deformations over the entire foundation, assuming a flexible structure, are predicted to be on the order of 0.2 inch.
l Soil-- springs are being _ developed to reflect total deformations including variations.
The structure will be modeled and analyzed j
with the'resulting supporting springs.
In the soil-structure j
system modeling, the ' rigidity of the structure is considered.
The interaction of the flexible springs and rigid structure reflects the true behavior of the structure.
1 1
6.0 DESCRIPTION
OF PROCEDURE FOR TIMING OF FINAL JACKING LOCK OFF 6.1 METHODOLOGY The final jacking loads will not be locked off until-it is determined that the major portion of the pier settlement has occurred.
By comparing predicted concrete and soil behavior.
curves and instrumented observations of the pier deflections the optimum time for locking off the jacking load will be determined.
Vertical deflections at the top of the underpinning piers will result from the summation of several time-related properties of 6
the pier concrete and the underlying soil.
During the j
underpinning work, the soil deflection will be monitored at the top of each pier by connecting a settlement indicator to the' top i
of a rod that extends to a plate at the-base of the pier (refer 4
to Section D-D of Figure 5, Reference 1).
The rod is greased and placed within a tube to separate it from the concrete.
The total top of pier deflections will be measured by another settlement indicator on top of the pier.
The difference between these two deflection readings will represent the behavior of the concrete in the pier and the supporting soil.
The monitored pier deflections will be compared to predicted values.
The expected concrete behavior is based on observations 1
l reported in recognized engineering standards.
Four deflection curves for the pier concrete and glacial till are shown in l
Figures 2 through 5.
The curves are plotted as displacement versus the logarithim of time.
Figure 2 depicts a plot of the predicted top of pier deflection due to the creep of concrete j
under compressive load.
As indicated, the total. deflection will amount to approximately 0.03 inch.
Figure 3 plots the to of pier deflection due to concrete shrinkage as the concrete dries and cures.
The 10,000-day line is equal to about 27 years of elapsed time after pier construction.
As shown in Figure 3, the total shrinkage-caused pier deflection is estimated at about 0.2 inch with the deflection leveling off after approximately 90 days.
Figure 4 is a plot of the anticipated top of pier deflection due to soil consolidation.
This graph indicates the settlement within a minimum and maximum range of values.
The i
10 4
e
-ew,,---3---y.y w..
vg-.+.-..r--y-..----
-r----
---wg 4
,e-
.-,wy-,,
-c,>---y y-
,c
,,,-.9.---,e
-.9.--,---
-,.,,---.,.-9
--,-m
Midland Plant Units 1 and 2 NRC Raquest for Additional Information:
Service Water Pump Structure Underpinning indicated total settlemant due to soil consolidation is expected to be between 0.4 and 0.5 inch.-
By combining the curves of predicted' pier deflection due to concrete behavior as show7 in Figures 2 and 3,'and the soil deflection curve shcwn in Figure 4, a composite top-of-pier-deflection-versus-log-time curve can be drawn.
This is shown in Figure 5 using the maximum predicted soil 'a**1ement.
The Figure 4 of initial-jacking of Stage 1 load (as shown Reference'l) into the pier severa?. days after concrete placement vill result in early rapid deflection, as shown.
After about 90 days of Stage 1 loading, the jacking load will be increased to the final level which will result in another, but smaller, dip in-the deflection curve.
This increase in jacking load will combine with the shrinkage effect, which is greatest between 10 and 90 days' tims.
At about 110 days, the curve will flatten so it will appear as a straight line on this semi-log plotting.
On a linear
-time scale, the deflection rate would appear much flatter.
This.
semi-log straight line prediction is a typical observation for soil reaction after an initial elastic reaction period and is based on numerous test observations in the laboratory, as well as long-term field observations on in-place structures and buildings.
The key factor in the process of final jacking and locking-off is determining when this more predictable phase has begun.
This will be donc at the site by plotting deflection curves, both at the top and bottom of the piers, while maintaining the final jacked loadings.
This phase of the settlement curve is anticipated to occur soon after the final load level is applied assuming that all pier concrete is more than 90 days old.
6.2 ACCEPTANCE CRITERIA The final jacking load will total 4,400 nips and will be inposed on underpinning piers 1 through 10.
At that time, all piers will be at least 90 days old.
This load level will be maintained for a period of about 2 weeks or until the settlement rate is'within acceptable limits.
The previous plottings of pier deflections under load will form a performance record which will greatly influence the determination of final acceptance and locking off.
7.0 DISCUSSION OF THE VALIDITY AND USE OF THE PENETROMETER To aid the geotechnical engineer in assessing the adequacy of bearing capacity of the soil under the aase of each underpinning pier, the construction procedures specify the use of the Waterway Experimental Station cone penetrometer, Model CN-973.
The penetrometer consists of a 30
- cone with a 1/2-square inch base, an 18-inch extension rod, a proving ring, a dial indicator, and a handle.
A force applied through the handle deforms the proving ring and forces the cone to genetrate the soil.
The proving ring 11
~
Midland Plant Units 1 and 2 NRC Request for Additional Information:
Service Water Pump Structure Underpinning deformation is proportional to the force applied, and the value of the applied force is indicated on the dial.
The force is an index of the shearing resistance of the soil.
To evaluate the allowable bearing capacity of the soil, a family of curves relating allowable bearing capacity to applied force and cone penetration is utilized.
These curves are based on the work of G.G. Meyerhof (Reference 2).
8.0 DESCRIPTION
OF THE CRITERIA FOR FAILURE OF THE SOIL RESULTING FROM JACKING LOADS Deflection at the bottom of an underpinning pier which approaches 2 inches is at about 90% of the point at which soil indicates plastic behavior.
Other time-versus-rate-of-deflection criteria which are useful are that soil deflection should slow to about i
0.01 inch in 3 hourc after 3 days of constant load, and 0.02 inch for the interval between 10 and 20 days under constant load.
9.0 DESCRIBE THE PROCEDURE FOR MONITORING GROUNDWATER LEVELS DURING CONSTRUCTION OF THE UNDERPINNING WALL As part of the temporary. dewatering procedure, piezometers will be installed to monitor the groundwater level.
Before the access shafts are excavated, a piezometer will be installed adjacent to each shaft.
While constructing the tunnel under the north wall of the structure, three piezometers will be installed: one at each end and one at mid-length.
When the tunnel is completed, a monitoring system of five piezameters will have been installed.
If required, additional piezometers will be installed as the tunnels under the side walls are advanced.
10.0 COMMENT ON BORING CH-2 SHOWING FILL MATERIAL BELOW EL 587.0
(
The log for Boring CH-2 indicates silty sand to el 583'-8".
From the results of other nearby borings and the general excavation plan for the site, it is believed that the predominant soil type is sandy clay till.
If this is borne out during pit excavation and the till is compact and well bound, it will be acceptable for bearing at el 587.
This acceptance would be based on the judgement of the geotechnical engineer using qualitative criteria, such as taking soil samples for strength analysis.
On the other hand, if the till is not compact and well bound, or if it is silty sand, the material will be excavated to adequate till and replaced to el 587' with lean concrete on a pit-by-pit basis.
12
_,-v,
,---,e
,_w.
n
-,n
i Midland Plant Units 1 and 2 NRC Request for Additional Information:
Service Water Pump Structure Underpinning 11.0 EVALUATION OF SOIL SPRINGS VALUES - STATIC AND DYNAMIC LOADING CONDITIONS The soil springs are presently being evaluated as part of the final analysis of the structure.
When this evaluation is completed, the requested information will be submitted.
13
t Midland Plant ~ Units 1 and 2 NRC Request for Additional Information:
Service Water Pump Structure Underpinning REFERENCES 1.
Consumers Power Company, Technical Report on the Service Water Pump Structure Underpinning, August 26, 1981 2.
G.G. Meyerhof, The Ultimate Capacity of Wedge-Shaped Foundations," Proceedings of the 5th International Conference on Soil Mechanics and Foundations, Paris, 1961 t
j I
f i
14
--r----
,-.w--e-..--c..m.,-y.
-y 4,
c,.
,ve,-,.w,.
,w-.--
..,m-.-w..,
3-.-..-..-.m.-
~,
E SERVICE WATER PUMP STRUCTURE SETTLEMENT MARKER LOCATIONS SETTLEMENT MARKER SW N
-1 SWg03 SW-2 (Typical)
O O
v O SW-104 SW-102 G CIRCULATING SERVICE l
WATER WATER STRUCTURE PUMP STRUCTURE SW-101 O O SW-105 S
4 S
-3 COOLING POND G-1584 100
l 1
l SERVICE WATER PUMP STRUCTURE l
2STIMAYED YOP OF PIER l
DEFLECTION DU2 YO CREEP OF i
CONCREYd VS YIME i
i l
0 i
ELASTIC DEFLECTION l'
Y
, IN CONCRETE 7
0.01 l
2 N
.E 0.02 z2 o
0.03
~
Lu a
d 0.04 5
0.05 1
10 100 1,000 10,000 TlME (days)
- o.,,,,., 3 FIGURE 2
4
)
1 l
SERVICE WATER PUMP STRUCTURE ESYllWAYED YOP OF PIER I
DdFLECYION DUE TO SHRINKAG2 OF CONCRETE VS TIME 1
i 0.1 ii l
5 0.2 w
l O<
x 0.3 l
Z TEMP
= 72 F 3
REL HUM = 50%
o i
l M
0.4 m
us
(
.0.5 i
1 10 100 1,000 10,000 I
TIME (days)
FIGURE 3 c.i ss4.i i
l SERVICE WATER PUMP STRUCTURE ESYIMAYED TOP OF PIER l
l DEFLECTION DUE TO l
CONSOLIDAYIOW OF SOIL VS TIME (Time is Measured from Start of Jacking)
I 0
0.1 i
ii
)
s I
z 0.2 ESTIMATED POSSIBLE RANGE OF DELAYED 3
i B
o.3 SETTLEMENT l
MlNIM_ UM
^
x x
g l
1 0.5 J
1 10 100 1,000 10,000 TIME (days)
{
FIGURE 4 a.i sa4.i 4
(
SERVICE WATER PUMP STRUCTURE aSYIkUMYED YOP OF PIER DEFL2CYl6M DUE TO YOYAL l
DEF6MMYION VS Ylh012 STAGE I l
JACKED LOAD
?
l f
0.2 1
=
l z
FINAL 9
0.4 JACKED LOAD H
i f LOCK-OFF 0.6 Q
l o
a a
o 0.8 o
)>
F as in 1.0 1
10 100 1,000 10,000 TIME (days)
FIGURE 5 ca ss i-u i