Section 1813A

VIBRO STONE COLUMNS FOR GROUND IMPROVEMENT

This section shall apply to vibro stone col- umns (VSCs) for ground improvement using unbounded aggregate materials. Vibro stone column provisions in this section are intended to increase bearing capacity, reduce set- tlements and mitigate liquefaction for shallow foundations. These requirements shall not be used for grouted or bonded stone columns, ground improvement for deep foundation ele- ments, or changing site class. VSCs shall not be considered a deep foundation element. Ground improvement shall be installed under the entire building/structure footprint and not under isolated foundation elements only. Design, construc- tion, testing and inspection shall satisfy the requirements of this code except as modified in Sections 1813A.2 through 1813A.5.

The geotechnical report shall specify vibro stone column requirements to ensure uniformity in total and differential immediate settlement, long term set- tlement and earthquake induced settlement.

1. Soil compaction shall be in accordance with California Geological Survey (CGS) Special Publication 117A (SP-117A): Guidelines for Evaluating and Mitigating Seismic Hazard in California.

2. Area replacement ratio for the compaction elements and the basis of its determination shall be explained. Minimum factor of safety for soil compaction shall be in accordance with SP-117A.

3. Depth of soil compaction elements and extent beyond the footprint of structures/foundation shall be defined. Extent beyond the foundation shall be half the depth of the VSCs with a minimum of 10 ft or an approved alternative.

4. Minimum diameter and maximum spacing of soil com- paction elements shall be specified. VSCs shall not be

Copyright © 2019 ICC. ALL RIGHTS RESERVED. Accessed by Kevin Day (kevin.day@dgs.ca.gov), (California Building Standards Commission) Order Number #100735044 on Jul 24, 2019 03:54 PM (PDT) pursuant to License Agreement with ICC. No further reproduction or distribution authorized. Single user only, copying and networking prohibited. ANY UNAUTHORIZED REPRODUCTION OR DISTRIBUTION IS A VIOLATION OF THE FEDERAL COPYRIGHT ACT AND THE LICENSE AGREEMENT, AND SUBJECT TO CIVIL AND CRIMINAL PENALTIES THEREUNDER.

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SOILS AND FOUNDATIONS

less than 2 feet in diameter, and center to center spac- ing shall not exceed 8 feet.

5. The modulus of subgrade reactions for shallow founda- tions shall account for the presence of compaction ele- ments.

6. The modulus of subgrade reactions, long-term settle- ment and post-earthquake settlement shall be specified along with expected total and differential settlements for design.

7. The acceptance criteria for Friction Cone and Piezo- cone Penetration Testing in accordance with ASTM D5778 complemented by the standard penetration test (SPT) in accordance with ASTM D1586, if necessary, to verify soil improvement shall be specified.

8. The requirements for special inspection and observa- tion by the geotechnical engineer shall be specified.

9. A final verified report (FVR) documenting the installa- tion of the ground improvement system and confirming that the ground improvement acceptance criteria have been met shall be prepared by the geotechnical engi- neer and submitted to the enforcement agency for review and approval.

VSCs under the shallow foun- dation shall be located symmetrically around the centroid of the footing or load.

1. There shall be a minimum of four stone columns under each isolated or continuous/combined footing or approved equivalent.

2. The VSCs or deep foundation elements shall not be used to resist tension or overturning uplift from the shallow foundations.

3. The foundation design for the shallow foundation shall consider the increased vertical stiffness of the VSCs as point supports for analysis, unless it is substantiated that the installation of the VSCs result in improvement of the surrounding soils such that the modulus of sub- grade reaction, long term settlement, and post-earth- quake settlement can be considered uniform throughout.

VSCs shall be installed with vibratory probes. Vertical columns of compacted unbounded aggregate shall be formed through the soils to be improved by adding gravel near the tip of the vibrator and progressively raising and repenetrating the vibrator which will results in the gravel being pushed into the surrounding soil. Gravel aggregate for VSCs shall be well graded with a maximum size of 6 inches and not more than 10 percent smaller than ³ /8 inch after com- paction.

Construction documents for VSCs, as a minimum, shall include the following:

1. Size, depth and location of VSCs.

2. Extent of soil improvements along with building/struc- ture foundation outlines.

3. Field verification requirements and acceptance criteria using CPT/SPT.

4. The locations where CPT/SPT shall be performed.

5. The testing, inspection and observation (TIO) program shall indicate the inspection and observation required for the VSCs.

210 2019 CALIFORNIA BUILDING CODE

Copyright © 2019 ICC. ALL RIGHTS RESERVED. Accessed by Kevin Day (kevin.day@dgs.ca.gov), (California Building Standards Commission) Order Number #100735044 on Jul 24, 2019 03:54 PM (PDT) pursuant to License Agreement with ICC. No further reproduction or distribution authorized. Single user only, copying and networking prohibited. ANY UNAUTHORIZED REPRODUCTION OR DISTRIBUTION IS A VIOLATION OF THE FEDERAL COPYRIGHT ACT AND THE LICENSE AGREEMENT, AND SUBJECT TO CIVIL AND CRIMINAL PENALTIES THEREUNDER.

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CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE