ML18192A404

Rebound, Settlement and Subsidence Instrumentation

ML18192A404
Person / Time
Site:	Palo Verde
Issue date:	12/24/1976
From:	Fugro Inc
To:	Arizona Nuclear Power Project, Office of Nuclear Reactor Regulation, NUS Corp
References
Download: ML18192A404 (54)

Text

REBOUND, SETTLEi~lENT AND SUBS XDENCE INSTRUi4ENTATXON FOR TEE PALO VERDE NUCLEAR

'ENERATING STATXON For:

NUS Corporation Arizona Nuclear Power Project By:

Fugro, Xnc.

P. O. Box 68 Goodyear, Arizona Decem& r 24, 1976

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TABLE OF CONTENTS Page XNTRODUCTXON XNSTRUMENTATXON PROGRAM ~ ~ ~ 0 0 ~ ~ ~ ~ Ã l FREQUENCY OF MONXTORING ~ ~ ~ ~ q ~ 0 ~ ~ 3 ANALYSIS OF DATA PROGRAM ~ ~

FIGURES l Settlement Monitoring Locations (Unit 1) 2,:. Settlement'.Monitorirlg Locations (Unit 2) 3 Settlement. Monitoring Locations (Unit 3) 4 Settlement Monitor Point Locations 5 Permanent Benchmark Locations APPENDICES APPENDIX A BORXNG LOGS APPENDIX B .- MULTXPLE POSITXON EXTENSOMETER INSTALLTION TECHNIQUES AND DETAXLS APPENDIX C MECHANXCAL REBOUND STATXON CONSTRUCTION TECHNIQUES. AND DETAXLS

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INTRODUCTION In order to provide a means by which the actual set'tlements experienced, by plant structures could be. determined, an instru-mentation system was. established.. The following rebound-settle-ment and subsidence monitoring program for'the. ANPP Palo Verde'uclear Generating. Station is intended to monitor foundation and ground movements during and after plant construction. In addition to. monitoring. settlements as they occurred, the instru-mentation progr'am was designed to determine the soil rebound occurring during excavation. By establishing the rebound which I

occurs, the accuracy of the settlement analysis can be assessed.

This gives the opportunity to reevaluate the 'settlement analysis from a safety standpoint. as well as provides an opportunity to

..revise structural designs in order to reflect the actual settle-

. ments likely.- .The-instrumentation installed to monitor settle-'ent.

will also be used to monitor .ground subsidence. In l

addition to the dual use that the settlement instrumentation will serve, specific instrumentation is intended to monitor possible =ground subsidence.=

This monitoring program being implemented at the site is designed to meet..the objectives outlined in the ANPP Palo Verde Nuclear Station PSAR, Section 2T.'7 of Appendix 2T. 'enerating INSTRUMENTATION PROGMi4!

The basic =rebound, settlement, and subsidence monitoring 'system is composed of three basic components; The first is a system

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of multiple position extensometers which provides rebound, settlement, and subsidence"data from three depths -'at each installation. These instruments possess remote readout.

capability so they can be left, in place beneath structures and will continue to provide settlement data for an extended period of ti'me. Figures lp 2I and 3 show the location of each instru-

.ment station. Each multiple position extensometer is anchored in rock at a. depth in excess of 300 feet below tne ground surface. Anchors with displacement sensors (Strain. Meter, SXNCO Model No. 51703) are located at. three levels above the rock anchor. For the location of the individual displacement sensors and the basal rock anchor, refer to the boring logs, Appendix A.

-A description of multiple position extensometer installation techniques is provided in Appendix" B..

The, second component. of the instrumentation program is a system of eighteen (18) mechanical rebound stations. These instru-ments are designed to yield information on the rebound system which occurs as a result of the site excavations.. Xn addition to,providing rebound data, the mechanical rebound-system pro-vides an .independent check on the data gathered from the multiple position borehole extensometers. Details of the installation techniques are presented in Appendix C. The mechanical rebound station-locations are shown on Figures 1, 2, and 3.'he third major component of the settlement-rebound monitoring program is a system of survey monuments and control points set fUBRD

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within the structures. In a typical power. block there will be '

thirty-eight (38) points at which settlements will,-be. monitored

.. Figure 4. These stations will be installed as soon after *the construction'sequence allows as possible. An integral component of the survey monitoring program is"the-.establishment of two-benchmarks on rock outcrops.-'our additional'enchmaxks are located in the vicinity of the three power blocks, Figure 5.

These benchmarks are designed to monitor potential ground sub-sidence associated with groundwater withdrawal. Figure 5 shows the location of the benchmarks which, as installed, on a basalt flow, will provide site elevation control, FREQUENCY OF MONITORING The monitoring schedule is as follows:

Benchmarks o Monthly for first 3 months of monitoring.

o Annually to end of construction.

o Annually for first year of operation.

o 5-year intervals during operation.

Extensometers and Mechanica'l'ebound'nch'ors o Until failure or abandoned, or o Weekly to completion of overlying mat foundation.

o Monthly for l8 months after first concrete.

'I o 3-month intervals to end of construction.'I o Annually for first year of operation..'

. 5-year intervals during rest, of operation.

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4 Control Points'.on Structures o - Monthly for. 18 months after first. concrete (all points).

o 3-month intervals to end of construction (all points) .

o Annually for first year of. operation (one point each unit) .

o 5-year intervals during'est of operation (one point each unit) .

Groundwater levels will be. measured with the same frequency as the benchmarks during the operating period. The gxoundkvater data will be compared to the subsidence monitoring'data. Any anticipated movement of the monitoring benchmarks will occur from groundwater withdrawal.

The weekly readings in the pre-excavation stage are intended to provide a check on the repeatability of the in-place system.

The monitoring program is intended to be flexible enough so that if the frequency of readings needs to be increased at any particular stage of construction the increased frequency will be implemented.

ANALYSIS'OF DATA PROGRAM The analysis of data gathered during the excavation-construction phases will be evaluated with the following objectives:

1) Establishing the degree of conformance of actual rebound-settlement data to the original estimated values. Since the original settlement analysis incorporated very conser-vative assumptions, the comparison of actual to calculated values will enable a final assessment of the degree of conservatism which exists in the settlement analysis.

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2) Assessing the compatability of the actual rebound-settlement patterns with those calculated. .This would include evalu-ating differential .rebound-settlement values as overburden'elease or structure loading rates vary between the struc-tures.

3) 'Assessing the adequacy of the time dependent rebound-settlement assumptions based on actual data.

4) Review of assumed soil parameters to insure that. assumed 'L soil-groundwater conditions were conservative with respect to actual soil behavior. If the measured, data indicates the assumed soil parameters are not conservative, the soil

.parameters will be revised to conform to observed rebound-settlement data using known unloading-load conditions.

5) Compari'son of mechanical rebound data'ith data generated by the multiple position extensometers. In this manner a constant check between the two types of instrumentation will enable the reliability of data gathered by each instrument to be assessed.

By the time. the excavations are complete, the rebound. data should allow an assessment of. the adequacy of the settlement-rebound analysis to be made. If the soil-groundwater conditions used in the analysis are not conservative the magnitudes of rebound would exceed the calculated values. Should the actual values of rebound exceed the calculated values, then the settle-ment analysis will be modified by using soil parameters which are compatable with the observed magnitudes of settlement.

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MR 12 N869,000 LOCATION OF SETTLEMENT REBOUND. OBSERVATION POINTS N869,710.03 7 N869/706.60 MR 10 N869,996 11 Z210,660.51 Z210, 653.71 E210,833.08 4'MPE-MULTIPLE POSXTXON MR 8 N869/802.36 Z21 0/ 709 37 ll N869/522.58 E21 0/ 651 71

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APPENDIX A BORING . LOGS.

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APPENDIX B MULTIPLE POSITION EXTENSO&TER INSTALLATION TECHNIQUES AND DETAILS

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INSTALLATION PROCEDURE Strain Meter, Model 51703 The following procedures were followed for the 15 Stain Meters

'nstalled at five locations (3 Strain Meters were placed per bo"ing location at three different depths) at the Palo Verde Nuclear Generating Station Units lI 2I and 3 in Arizonan The borings were drilled with a Failing 1500, rotary drill rig, truck mounted. The first three'oles were initially about 8

'aches in diameter, the last two borings reduced to 6.5 inches in diameter. To install the Strain Meters, the following pre-pa"ations vere made for preassembly of components and installa-tion of the instrumentation equipment. Refer to figures B-l, B-2, and B-3 for visual explanation of component terminology.

PR:-KSSHABLY

1) One PVC component Schedule 40 PVC slip coupling was con-.

nected and cemented to one end. of each 10-ft. length of 3/4" PVC Schedule 80 pipe.

Since there vere to be three sensors in the borehole, each end of each length of 3/4" PVC pipe was painted using a. can of spray paint. Also, the electrical cable was painted at intervals along its length. The same color was used for one instrument .(sensor, riser pipe, and cable) . The fol-lowing color code was used throughout the project: bottom sensor cor ponent materials red; middle, sensor component g

materials green; top sensor component materials white.

2) Tne preassem>led 10-ft. lengths of 1/4" OD stainless steel rod were slipped inside 10-ft. lengths of 1/2" OD Polyethylene

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tubing. A 3/8" OD stainless backup ring was inserted inside each end of 1/2" OD tubing.

A 1/4" galvanized pipe coupling was then attached to the end of each 1/2" Polyethylene tube and the pipe coupling color coded, as in 1), above.

3) The hydraulic anchor anQ bottom adapter (figure B-3) were shop assembled together and" shipped-as "a..single unit. The hydrau3.ic pressure tubing.'as.attached:..to the..ancho'r,, pre-

-fitted with oil, and color coded, as'n 1'), above.

4) The bottom adapter and anchor were connected to the drill rod (N-size) by means of the special coupler which had left hand threads. This coupler was welded to a sub furnished by the driller to match the drill rod. The first two in-stallations were made with this drill rod; which had 3-inch diameter couplings. ='The remaining three installations were attached to 2-inch diameter galvanized water pipe.

5)'The lifting line" foi. the drill rod with swivel was

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attached and 'su'spended over the borehole from the'ry.'ll rig..

6) While the drill rod anQ bottom anchor and adapter were suspended from the drill rig, a 2-ft. length of 1/4" stain-less steel rod was attached to the bottom adapter.

INSTALLAT'ION The following steps were repeated with each of the three in-struments in the borehole during installation.

1) A 10-ft. length of preassembleQ 1/4" OD stainless steel guano

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rod and 1/2" OD Polyethylene tubing was raised vertically over the 2-ft. length, attached to the bottom adapter, and the two 1/4" rods were tightened.

2) The 1/2" OD Polyethylene tube (with 1/4" coupling at the top) was slid down and threaded into the bottom adapter.

3) The bottom anchor and. adapter were then lowered into the hole, pulling down the 1/2" tubing and 1/4" rod in 10-ft.

lengths. As these lengths were added, the joints in the 1/2" tubing were made with the 1/4" galvanized pipe coup-lings.

, 4). Measurements of the stickup of the 1/4" rod out of the 1/2" tubing were taken periodically as lengths were added and as the instruments were lowered into the hole. Plotation of the tubing caused this stickup to decrease from upward pressure due to the density of the drilling fluid.

To obtain the desired distance between bottom anchor:.and sensor, the last section of 1/4" rod was a selected length, depending on the total length required, and the depth at which the sensor was to be installed.

5) The distance between the top of the last 1/2" OD tubing and the top of the last 1/4" rod. was measured and a piece of 1/2" tubing cut to a length 6 inches 1ess than that measured.

The blank end was threaded with a 1/4" pipe thread die. This short length was slipped over the top .of the last rod and threaded into the last 1/4" pipe coupling on the 1/2" tubing.

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6) After the correct length of 1/4" stainless steel rod and 1/2" OD Polyethylene tubing was added, it was threaded to the 1/4" rod of the sensor which, in turn, was attached to the hydraulic anchor by means of four tubing clamps.

7) With the sensor attached to the 1/4" rod and attached to the anchor, the 1/2" OD Polyethylene tubing was tensioned, thus keeping the sensor reading at zero (sensor rod in retracted position inside the sensor) . The length of the top piece of l/2" OD Polyethylene tubing was adjusted, as necessary, to obtain sufficient tension to maintain zero reading.

8) A length of 3/4" PVC pipe was then threaded over the 3-wire SJO electrical cable and cemented to the sensor.

9) The instruments were lowered into the hole'dding l0-ft.

lengths of 3/4" PVC pipe after threading over the 3-wire SJO cable from the first sensor, and 10-ft. assemblies .of 1/4" rod and 1/2" tubing connected for the additional two sensors.

10) The sensors were tested with.SXNCO's 51811 Portable Indicator in the field against, the calibration sheets provided for each sensor by SINCO prior to their use and assembly.

'll) The completed sensor was connected to the indicator and readings taken periodically as the in'struments were lowered into the hole. The 3/4" PVC riser pipe was also pulled up to obtain a change in reading on the sensor. 'ension in the 1/2" tubing would return the sensor reading to zero.

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12) .Buoyancy of the-3/4" PVC pipe changed the sensor -reading.

To overcome this, a 2-1/2-foot length of 1-3/8" steel tubing was slipped over each 10-ft.. length of 3/4" PVC pipe.

This weight was to balance the flotation of the 3/4" pipe.

The number of weights depended upon the density of the drilling fluid. Only the second boring required this'pro'-

cedure. The. remaining borings did not require any metal tubing to overcome flotation.

13) When the bottom hydraulic anchor and adapter was in position at the required depth, the 51811 Portable Indicator was connected and the sensor reading checked. By pulling up .on the 3/4" PVC pipe, the proper reading was- obtained. The 3/4" PVC pipe'was fastened in to 'the drill rig to maintain the proper reading.

'14) The. bottom. anchor pressure tubing was then attached to.the hydraulic pump and the bottom hydraulic anchor prongs ex-panded by operating the pump. The amount of oil.pumpeQ was

me'asured in'he reservoir gauge attached to the pump. The extension of the prongs were determined =by means .of the.

calibration curve; all prongs- were extended about, 12 inches diameter using, as much as 2500 to 3000 psi oil pressure.

When the anchor was set in the rock, the drill roQ was rotated clockwise one or more turns. to,make. sure the threads were detacheQ and the rod separated.

15) The hole'as'filled up with high-"density drilling fluid dur-ing the time of installation to increase the uplift of the

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drilling fluid which, in turn, supported the equipment in the center of the boring. One batch of grout, approximately 300 gallons, was mixed and pumped through the drill rod (or 2" diamet'er pipe in the later installations see drawing of anchor) discharging it out the bottom anchor adapter.'rout mixtures used were,determineQ by the Fugro personnel who obtained batch samples during each installation. For the bottom portion, 14, bags of cement anQ 150 gallons of water were used. The top portion was grouted by using 5 bags cement,,5 bags of bentonite, and 325 gallons of water.

All installations were made in two stages except for the .

first installation which was completed by continuous grout placement in one day. All,other installations, however, were'installeQ iwo stages. The first stage grouted the bottom anchor with a heavy cement batch and the bottom sensor was grouted with,cement anQ bentonite. The second stage was completed the following day, whereby the midQle anQ upper sensors were grout.eQ using mixtures of cement anQ bentonite.

After the first. hatch .of grout haQ been placeQ in the hole, the drill rod was disconnected from the bottom anchor by rotating clockwise. The drill rod was xaised to just below the top of the first batch .placed in the hole and the grout-ing continued until .its level was at least 10 feet above the sensor.

3.6) The drill rod was withdrawn until the bottom was approxi-mately five feet above the lowest sensor.

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17) The sensor, reading,was,.continuously checked. on the Portable Indicator making certain that. the sensor reading was at the setting desired by raising or lowering the sensor with the

.3/4" PVC pipe before'he prongs of the anchors were jacked

- out As described before, the sensor, anchor prongs were expanded by operating the pump. The sensor reading on the Portable Indicator was checked for any changes while expanding the anchor prongs.

18) Additional grout was pumpeQ into the hole until a level drill rod

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above the next sensor was reached. The was then raised to a position above the next sensor.

19) The second, sensor. anchor was expanded as described before,

-and repeated for the third sensor.

20) The hole was then filled to the top with grout and all drill rods were removed.

21) The PVC pipes were firmly attached to the drill rig and the grout allowed to set before the drill rig was demobilized anQ moved to the next location.

22) The sensors 'were monitored with the Portable Indicator and recordeQ as initial readings. The results of the readings obtaineQ during the time of installation are attached.

23) The PVC pipes were cut above the grounQ and the readout cable rolled up and secured in a 6" diameter casing.

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I V APPENDIX C MECHANICAL REBOUND STATION CONSTRUCTION TECHNIQUES AND DETAILS

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INSTALLATION PROCEDURES FOR THE MECHANXCAL REBOUND STATIONS Refer to figure C'1 for description of component terminology.

1) Drill borings with 8" hollow stem auger (3-3/8" XD) to 4 feet below depth of excavation.

2) Assemble 2" PVC casing (2.975" OD coupling) with cap on bottom. The bottom cap will be drilled with a l-l/2" hole in the bottom to allow the anchor pin to pass through.

3) Measure length of PVC accurately.

4) Clean out. auger with 3" diameter drive sampler (go about.

3" below the bottom of the auger) ..

5) Install the PVC casing into the borehole and'push down into loose soil. The casing should go a few inches below the bottom of the auger.

6) Using a shear pin, attach the "A" rod to the monitor pin.

Lower the monitor pin to the bottom through the PVC and drive it until the tip of the pin is 24" below the tip of the PVC. Record the number of blows of a 140-pound hammer dropping 30 inches.

7) Withdraw "A" rods and hollow stem auger'.

8) Backfill the area between the PVC and soil with white sand.

9) Put. on removable PVC cap.

A readout rod was also included as a part of the system. Xt consisted of 3 and 4-Zoot long .surveying range rods calibrated for length. A l-l/2" diameter piece of steel was used on the guano

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bottom contact piece. The assembly of rods would be lowered to rest on the monitor pin and the top elevation of, the rod-would be monitored usi;ng normal surveying"-techniques.

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