Geotechnical-expansive soil

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When using shallow spread footings on soil has Expansive Index (EI) more than 20, is there a relation between soil’s EI and footing’s depth (or thickness)?

Some soil reports suggest deepen shallow spread footings to 30 or 36 inches below grade (that is 30-in or 36-in thick footings) along with rigid slab-on-grade. This is to make the foundation system into gradebeam from the structural’s point of view and the foundation system becomes somehow rigid to overcome differential settlement of high EI soil beneath. Please correct me if your understanding is different.

Some soil reports might allow the new placing soil up to EI less than 50 without extra deepen footings (that is 12 or 18 inches below the finish grade). I cannot find a reference for this suggestion. If you know where I can look it up or what theory it is please kindly share with me. Additonally, I am practicing in CA.

Personal experience handling expansive soils is performing grading to mitigate impact on shallow spread footings. Replacing expansive soil with new soil that has EI less than 20, tested by ASTM 4829. After performing grading, shallow spread footing is then putting on compacted fill. I do not deal with expansive soils in day to day basis and have less knowledge about it. I believe others here have much more experience in this area than me. I would like your opinions. Thanks

請問土壤的的EI常基礎的深度（厚度）之間的關係？

有些土壤的報告，當土壤的的EI>50, 淺基礎要30英寸或36英寸厚。從結構的角度來看，基礎的系統變得剛性, 故克服的高EI土壤的不均勻沉降。

另外一些的土壤報告, 可能讓新土壤EI低於50 and 沒有額外的加深淺地基（即12或18英寸以下）的。我無法找到這個建議的參考。如果你知道我在哪裡可以看，什麼理論，請與我分享。

個人經驗using 淺基礎上膨脹土，要更換膨脹土，新土膨脹指數（EI）要小於20 (ASTM4829),以減輕影響。

我不常處理膨脹土常基礎，並沒有多少關於它的知識。我相信在座的其他人有更多的經驗，在這方面比我強。我想你的意見。謝謝