The effect of on-site-cast C-RHA micropiles on slope stability by centrifuge modeling

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Title:	The effect of on-site-cast C-RHA micropiles on slope stability by centrifuge modeling
Authors:	彭萬;Abiyoga, Nurza Purwa
Contributors:	土木工程學系
Keywords:	離心模型試驗;微型樁;稻殼灰;邊坡穩定;Centrifuge modeling;Micropile;Rice husk ash;Slope stability
Date:	2022-08-24
Issue Date:	2022-10-04 10:47:58 (UTC+8)
Publisher:	國立中央大學
Abstract:	稻殼灰 (Rice Husk Ash, RHA) 常用來替代水泥作為卜作嵐材料，以降低水泥需求量且減少製程中溫室氣體排放量。稻殼灰混凝土 (Concrete-Rice Husk Ash, C-RHA) 微型樁為一種具環保與高經濟效益之邊坡加勁工法，其增加邊坡穩定性原理與土釘相似。本研究以中央大學地工離心機進行七組靜態試驗，透過增加人造離心力場直至邊坡破壞，探討場鑄C-RHA微型樁的早期強度與樁身完整性對邊坡穩定適用性與影響。邊坡以石英砂與高嶺土混合並採濕搗法製作，模型高度為200 mm，坡度為70 度，黏土質砂單位重為17.81 kN/m3，含水量為13.3%。 C-RHA微型樁由50% 石英砂、30% 稻殼灰與20% 水泥均勻拌合製成，含水量為90%。C-RHA微型樁直徑為5% H，長度為50% H，其中H為邊坡高度。離心模型試驗結果顯示: (1) 在C-RHA微型樁加勁區域面積與總坡面面積比為 2.95×10-2 條件下，場鑄C-RHA微型樁加勁工法可以有效提高邊坡穩定性，其中，下排微型樁距離坡趾高度為23.5% H； (2) 場鑄微型樁的早期強度較預鑄微型樁低，因此早期需架設臨時性側向支撐。然而，場鑄微型樁經過28天養護後，其加勁之邊坡穩定性較佳； (3) 場鑄微型樁身之蜂窩現象與澆置造成之土壤擾動會影響其邊坡穩定性，而場鑄微型樁之長度對邊坡穩定性影響不顯著。 ;Rice Husk Ash (RHA) is a pozzolanic material commonly used for cement substitution. RHA utilization could reduce cement consumption and greenhouse gas emissions. Concrete-Rice Husk Ash (C-RHA) micropile is proposed as an eco-friendlier and cost-efficient slope reinforcement by utilizing RHA and working similarly with soil nails. Seven centrifuge models simulated slopes reinforced with on-site-cast C-RHA micropiles subjected to increased gravitational acceleration. This study investigates the serviceability of on-site-cast C-RHA micropiles in stabilizing slopes by considering the early strength and imperfection of micropiles. The compacted slopes are made from clayey sand with 17.81 kN/m3 dry density and 13.3% water content, with a 200 mm slope height and 70° inclination angle. The micropile is 5%H in diameter and 50%H in length (H = slope height). The micropiles made from 50% soil, 20% cement, and 30% RHA with a 90% water content. The test results show that (1) C-RHA micropiles effectively improve the slope stability if implemented at a 2.95×10-2 reinforcement area to slope area ratio, with the lowest micropiles row located at 23.5%H from the slope toe; (2) Temporary lateral support is required due to the small contribution of the micropiles in the early period after the installation. However, after 28 days of curing, the on-site-cast method provides higher slope stability than the precast method; (3) Short micropiles experience pull-out failure and do not significantly increase shear strength. Shear strength decrement was observed on the model with alveolate micropiles. The shear strength loss, indicated by the decrement of the gravity level to make the slope fail, was due to soil structure disturbance and poor replacement-material strength.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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