Section 1813 — California Building Code (Title 24, Part 2)

VIBRO STONE COLUMNS FOR GROUND

IMPROVEMENT [OSHPD 1R, 2 & 5]

1813.1 General.¶

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 as a deep foundation element.

Ground improvement shall be installed under the entire building/structure footprint and not under isolated founda- tion elements only.

Design, construction, testing and inspection shall satisfy the requirements of this code except as modified in Sections 1813.2 through 1813.5.

1813.2 Geotechnical report.¶

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. The report shall address the following:

1. Soil compaction shall be sufficient to mitigate potential for liquefaction as described in California Geological Survey (CGS) Special Publication 117A (SP-117A): Guidelines for Evaluating and Mitigating Seismic Haz- ard in California.

2. The area replacement ratio for the compaction ele- ments and the basis of its determination shall be explained. Minimum factor of safety for soil compac- tion shall be in accordance with SP-117A.

3. The 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’ or an approved alternative.

4. The minimum diameter and maximum spacing of soil compaction elements shall be specified. VSCs shall not be less than 2 feet in diameter and center to center spacing 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 piezocone penetration testing in accordance with ASTM D5778 complemented by a standard penetration test (SPT) in accordance with ASTM D1586, if necessary, to verify soil improvement shall be specified

SOILS AND FOUNDATIONS

8. The requirements for special inspection and observa- tion by the geotechnical engineer shall be specified. 9. A Final Verified Report (FVR) documenting the instal- lation of the ground improvement system and confirm- ing that the ground improvement acceptance criteria have been met shall be prepared by the geotechnical engineer and submitted to the enforcement agency for review and approval.

1813.3 Shallow Foundations.¶

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

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

1813.4 Installation.¶

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 re-penetrating 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 compaction.

1813.5 Construction Documents.¶

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

1. Size, depth and location of VSCs. 2. The extent of soil improvements along with build- ing/structure foundation outlines. 3. Field verification requirements and acceptance criteria using CPT/SPT. 4. The locations where CPT/SPT shall be performed. 5. A Testing, Inspection and Observation (TIO) program indicating the inspection and observation required for the VSCs.

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18-38 2022 CALIFORNIA BUILDING CODE

CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE

CHAPTER 18 A – SOILS AND FOUNDATIONS

(Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user.

See Chapter 1 for state agency authority and building applications.)

Adopting agency	BSC	BSC- CG	SFM	HCD			DSA			OSHPD						BSCC	DPH	AGR	DWR	CEC	CA	SL	SLC
Adopting agency	BSC	BSC- CG	SFM	1	2	1/AC	AC	SS	SS/CC	1	1R	2	3	4	5	5	5	5	5	5	5	5	5
Adopt entire chapter								X	X	X				X
Adopt entire chapter as amended (amended sections listed below)
Adopt only those sections that are listed below
Chapter / Section

The state agency does not adopt sections identified with the following symbol: The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.

18A-2 2022 CALIFORNIA BUILDING CODE

CHAPTER 18 A

SOILS AND FOUNDATIONS