Section 1812 — California Building Code (Title 24, Part 2)

EARTH RETAINING SHORING [OSHPD 1R, 2 & 5]

1812.1 General.¶

The requirements of this section shall apply to temporary and permanent earth-retaining shoring using soldier piles and lagging with or without tie-back anchors in soil or rock, only when existing or new facilities are affected. Shoring used as construction means and methods only, which does not affect existing or new facilities, is not regulated by this section and shall satisfy the requirements of the authori- ties having jurisdiction.

Design, construction, testing, and inspection shall satisfy the requirements of this code except as modified in Sections 1812.2 through 1812.8.

1812.2 Duration.¶

Shoring shall be considered temporary when elements of the shoring will be exposed to site condi- tions for a period of less than or equal to 2 years, and shall be considered permanent otherwise. Permanent shoring shall account for the increase in lateral soil pressure due to earth- quake. At the end of the construction period, the existing and new structures shall not rely on the temporary shoring for support in anyway. Wood components shall not be used for permanent shoring lasting more than 2 years. Wood compo- nents of the temporary shoring that may affect the perfor- mance of permanent structure shall be removed after the shoring is no longer required.

All components of the shoring shall have corrosion protec- tion or preservative treatment for their expected duration. Wood components of the temporary shoring that will not be removed shall be treated in accordance with AWPA U1 (Commodity Specification A, Use Category 4B and Section 5.2), and shall be identified in accordance with Section 2303.1.9.

1812.3 Surcharge.¶

Surcharge pressure due to footings, traf- fic, or other sources shall be considered in the design. If the footing surcharge is located within the semicircular distribu- tion or bulb of earth pressure (when shoring is located close to a footing), lagging shall be designed for lateral earth pres- sure due to footing surcharge. Soil arching effects may be

174 2019 CALIFORNIA BUILDING CODE

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considered in the design of lagging. Underpinning of the foot- ing may be used in lieu of designing the shoring and lagging for surcharge pressure. Alternatively, continuously contact- ing drilled pier shafts near the footings shall be permitted. The lateral surcharge design pressure shall be derived using Boussinesq equations modified for the distribution of stresses in an elastic medium due to a uniform, concentrated or line surface load as appropriate and soil arching effects.

1812.4 Design and testing.¶

Except for the modifications as set forth in Sections 1812.4.1 through 1812.4.3, all Pre- stressed Rock and Soil Tie-back Anchors shall comply with PTI Recommendations for Prestressed Rock and Soil Anchors.

1812.4.1 Geotechnical requirements. The geotechnical report for the earth retaining shoring shall address the following:

1. Minimum diameter and minimum spacing for the

anchors including consideration of group effects.

2. Maximum unbonded length and minimum bonded

length of the tie-back anchors.

3. Maximum recommended anchor tension capacity

based upon the soil or rock strength/grout bond and anchor depth/spacing.

4. Allowable bond stress at the ground/grout interface

and applicable factor of safety for ultimate bond stress for the anchor. For permanent anchors, a mini- mum factor of safety of 2.0 shall be applied to the ground soil interface as required by PTI Recommen- dations for Prestressed Rock and Soil Anchors Sec- tion 6.6.

5. Minimum grout pressure for installation and post-

grout pressure for the anchor. The presumptive post- grout pressure of 300 psi may be used for all soil types.

6. Class I Corrosion Protection is required for all per-

manent anchors. A minimum of Class II Corrosion Protection is required for temporary anchors in ser- vice less than or equal to 2 years.

7. Performance test for the anchors shall be at a mini-

mum of two times the design loads and shall not exceed 80 percent of the specified minimum tensile strength of the anchor rod. A creep test is required for all prestressed anchors that are performance tested. All production anchors shall be tested at 150 percent of design loads and shall not be greater than 70 per- cent of the specified minimum tensile strength of the anchor rod.

8. Earth pressure, surcharge pressure, and the seismic

increment of earth pressure loading, when applicable.

9. Maximum recommended lateral deformation at the

top of the soldier pile, at the tie-back anchor loca- tions, and the drilled pier concrete shafts at the lowest grade level.

10. Allowable vertical soil bearing pressure, friction resistance, and lateral passive soil resistance for the

SOILS AND FOUNDATIONS

drilled pier concrete shafts and associated factors of safety for these allowable capacities.

11. Soil-pier shaft/pile interaction assumptions and lat- eral soil stiffness to be used in design for drilled pier concrete shaft or pile lateral loads.

12. Acceptable drilling methods.

13. Geotechnical observation and monitoring recommen- dations.

1812.4.2 Structural requirements :

1. Tendons shall be thread-bar anchors conforming to ASTM A722.

2. Anchor design loads shall be based upon the load combinations in Section 1605.3.1 and shall not exceed 60 percent of the specified minimum tensile strength of the tendons.

3. The anchor shall be designed to fail in grout bond to the soil or rock before pullout of the soil wedge.

4. Design of shoring system shall account for as-built locations of soil anchors considering all specified construction tolerances in Section 1812.8

5. Design of shoring system shall account for both short- and long-term deformation.

1812.4.3 Testing of tie-back anchors :

1. The geotechnical engineer shall keep a record at the job site of all test loads and total anchor movement, and report their accuracy.

2. If a tie-back anchor initially fails the testing require- ments, the anchor shall be permitted to be re- grouted and retested. If the anchor continues to fail, the followings steps shall be taken:

a. The contractor shall determine the cause of

failure: (variations of the soil conditions, installation methods, materials, etc.).

b. The contractor shall propose a solution to

remedy the problem. The proposed solution will need to be reviewed and approved by geo- technical engineer, shoring design engineer, and the building official.

3. After a satisfactory test, each anchor shall be locked off in accordance with PTI Recommendations for Prestressed Rock and Soil Anchors Section 8.4.

4. The shoring design engineer shall specify design loads for each anchor.

1812.5 Construction:¶

The construction procedure shall address the following:

1. Holes drilled for piles/tie-back anchors shall be done

without detrimental loss of ground, sloughing or cav- ing of materials and without endangering previously installed shoring members or existing foundations.

2. Drilling of earth anchor shafts for tie-backs shall

occur when the drill bench reaches 2 to 3 feet below the level of the tie-back pockets.

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SOILS AND FOUNDATIONS

3. Casing or other methods shall be used where neces-

sary to prevent loss of ground and collapse of the hole.

4. Drill cuttings from the earth anchor shaft shall be

removed prior to anchor installation.

5. Unless tremie methods are used, all water and loose

materials shall be removed from the holes prior to installing piles/tie-backs.

6. Tie-back anchor rods with attached centralizing

devices shall be installed into the shaft or through the drill casing. Centralizing devices shall not restrict movement of the grout.

7. After lagging installation, voids between lagging and

soil shall be backfilled immediately to the full height of lagging.

8. The soldier piles shall be placed within specified tol-

erances in the drilled hole and braced against dis- placement during grouting. Fill shafts with concrete up to top of footing elevation, rest of the shaft can generally be filled with lean concrete. Excavation for lagging shall not be started until concrete has achieved sufficient strength for all anticipated loads as determined by the shoring design engineer.

9. Where boulders and/or cobbles have been identified

in the geotechnical reports, the contractor shall be prepared to address boulders and/or cobbles that may be encountered during the drilling of soldier piles and tie-back anchors.

10. The grouting equipment shall produce grout free of lumps and indispensed cement. The grouting equip- ment shall be sized to enable the grout to be pumped in continuous operation. The mixer shall be capable of continuously agitating the grout.

11. The quantity of grout and grout pressure shall be recorded. The grout pressure shall be controlled to prevent excessive heave in soils or fracturing rock formations.

12. If post-grouting is required, post-grouting operation shall be performed after initial grout has set for 24 hours in the bond length only. Tie-backs shall be grouted over a sufficient length (anchor bond length) to transfer the maximum anchor force to the anchor grout.

13. Testing of anchors may be performed after post- grouting operations, provided that grout has reached a strength of 3,000 psi as required by PTI Recommen- dations for Prestressed Rock and Soil Anchors Sec- tion 6.11.

14. Anchor rods shall be tensioned straight and true. Excavation directly below the anchors shall not con- tinue before those anchors are tested.

1812.6 Inspection, survey monitoring, and observation.¶

1. The shoring design engineer or his designee shall

make periodic inspections of the job site for the pur- pose of observing the installation of the shoring sys-

tem, testing of tie-back anchors, and monitoring of the survey.

2. Testing, inspection, and observation shall be in

accordance with testing, inspection and observation requirements approved by the building official. The following activities and materials shall be tested, inspected, or observed by the special inspector and geotechnical engineer:

a. Sampling and testing of concrete in soldier pile

and tie-back anchor shafts.

b. Fabrication of tie-back anchor pockets on soldier

beams

c. Installation and testing of tie-back anchors.

d. Survey monitoring of soldier pile and tie-back

load cells.

e. Survey monitoring of existing buildings.

3. A complete and accurate record of all soldier pile

locations, depths, concrete strengths, tie-back loca- tions and lengths, tie-back grout strength, quantity of concrete per pile, quantity of grout per tie-back and applied tie-back loads shall be maintained by the spe- cial inspector and geotechnical engineer. The shoring design engineer shall be notified of any unusual con- ditions encountered during installation.

4. Calibration data for each test jack, pressure gauge,

and master pressure gauge shall be verified by the special inspector and geotechnical engineer. The cali- bration tests shall be performed by an independent testing laboratory and within 120 calendar days of the data submitted.

5. Monitoring points shall be established at the top and

at the anchor heads of selected soldier piles and at intermediate intervals as considered appropriate by the geotechnical engineer.

6. Control points shall be established outside the area of

influence of the shoring system to ensure the accuracy of the monitoring readings.

7. The periodic basis of shoring monitoring, at a minu-

mum, shall be as follows:

a. Intitial monitoring shall be performed prior to

any excavation.

b. Once excavation has begun, the periodic read-

ings shall be taken weekly until excavation reaches the estimated subgrade elevation and the permanent foundation is complete.

c. If performance of the shoring is within estab-

lished guidelines, shoring design engineer may permit the periodic readings to be biweekly. Once initiated, biweekly readings shall continue until the building slab at ground floor level is completed and capable of transmitting lateral loads to the permanent structure. Thereafter, readings can be monthly.

d. Where the building has been designed to resist

lateral earth pressures, the periodic monitoring of the soldier piles and adjacent structure can be

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discontinued once the ground floor diaphragm and subterranean portion of the structure is capable of resisting lateral soil loads and approved by the shoring design engineer, geo- technical engineer, and the building official.

e. Additional readings shall be taken when

requested by special inspector, shoring design engineer, geotechnical engineer, or the building official.

8. Monitoring readings shall be submitted to shoring

design engineer, engineer in responsible charge, and the building official within 3 working days after they are conducted. Monitoring readings shall be accurate to within 0.01 feet. Results are to be submitted in tab- ular form showing at least the intial date of monitor- ing and reading, current monitoring date and reading and difference between the two readings.

9. If the total cummulative horizontal or vertical move-

ment (from start of construction) of the existing build- ings reaches ¹ /2 inch or soldier piles movement reaches 1 inch all excavation activities shall be sus- pended. The geotechnical and shoring design engi- neers shall determine the cause of movement, if any, and recommend corrective measures, if necessary, before excavation continues.

10. If the total cummulative horizontal or vertical move- ment (from start of construction) of the existing build- ings reaches ³ /4 inch or soldier piles movement reaches 1 ¹ /2 inches all excavation activities shall be suspended until the causes, if any, can be determined. Supplemental shoring shall be devised to eliminate further movement and the building official shall review and approve the supplemental shoring before excavation continues.

11. Monitoring of tie-back anchor loads:

a. Load cells shall be installed at the tie-back heads

adjacent to buildings at maximum interval of 50 feet, with a minimum of one load cell per wall.

b. Load cell readings shall be taken once a day

during excavation and once a week during the remainder of construction.

c. Load cell readings shall be submitted to the geo-

technical engineer, shoring design engineer, engineer in responsible charge, and the building official.

d. Load cell readings can be terminated once the

temporary shoring no longer provides support for the buildings.

1812.7 Monitoring of existing OSHPD 1, 1R, 2, 4 and 5 structures.¶

structures.

1. The contractor shall complete a written and photo- graphic log of all existing OSHPD 1, 1R, 2, 4 & 5 structures within 100 feet or three times depth of shor- ing, prior to construction. A licensed surveyor shall document all existing substantial cracks in adjacent existing structures.

SOILS AND FOUNDATIONS

2. The contractor shall document the existing condition of wall cracks adjacent to shoring walls prior to start of construction.

3. The contractor shall monitor existing walls for move- ment or cracking that may result from adjacent shor- ing.

4. If excessive movement or visible cracking occurs, the contractor shall stop work and shore/reinforce excava- tion and contact the shoring design engineer and the building official.

5. Monitoring of the existing structure shall be at reason- able intervals as required by the registered design pro- fessional, subject to approval of the building official. Monitoring shall be performed by a licensed surveyor and shall consist of vertical and lateral movement of the existing structures. Prior to starting shoring instal- lation a preconstruction meeting shall take place between the contractor, shoring design engineer, sur- veyor, geotechnical engineer, and the building official to identify monitoring locations on existing buildings.

6. If in the opinion of the building official or shoring design engineer, monitoring data indicate excessive movement or other distress, all excavation shall cease until the geotechnical engineer and shoring design engineer investigate the situation and make recommen- dations for remediation or continuing.

7. All reading and measurements shall be submitted to the building official and shoring design engineer.

1812.8 Tolerances.¶

The following tolerances shall be speci- fied on the construction documents.

1. Soldier piles:

i. Horizontal and vertical construction tolerances

for the soldier pile locations.

ii. Soldier pile plumbness requirements (angle with

vertical line).

2. Tie-back anchors:

i. Allowable deviation of anchor projected angle

from specified vertical and horizontal design pro- jected angle.

ii. Anchor clearance to the existing/new utilities and

structures.