October 18, 2026

Drainage gravel, geotextile fabric and a perforated pipe are the three parts that keep water pressure from pushing a retaining wall over. How manufacturer installation guides specify each one, why Bay Area clay makes skipping them riskier, and what a pre-backfill check should cover.

Using the City of Concord’s published grading standards as a worked example: the October 1-April 15 rainy season, the September 1 erosion control plan deadline, the October 15 slope-stabilization deadline, and why wet Bay Area clay makes bad timing costly.