基于球孔擴張理論的軟黏土中載體樁樁端擠密加固效應

周航 劉漢龍 丁選明 王繼忠

摘 要：載體樁是近年來出現的一種新樁型，其主要利用柱錘對深層土體進行填料夯實，形成樁端擴大載體，從而大大提高樁體豎向承載力。雖然載體樁在實際工程中廣泛應用，但目前仍缺乏較為嚴格的理論分析，特別在關于評價載體的加固范圍和載體對土體的擠密效應方面，仍然研究較少，這大大制約了載體樁的推廣和發展。針對該問題，將柱錘對填料夯實的過程簡化為球孔擴張力學模型，軟黏土采用修正劍橋模型的本構關系來模擬，建立球孔擴張偏微分控制方程組，通過相似變換的求解技術將偏微分方程轉化為常微分方程組，利用微分方程數值求解技術獲得常微分方程組的數值解。開展參數分析，探討球孔擴張過程中孔周土體強度和剛度的變化、孔周土體擠密區的范圍等，從理論角度揭示載體樁載體成形過程中的加固機理，為建立考慮樁端擠密效應的載體樁豎向承載力計算方法提供理論基礎。

關鍵詞：載體樁;球孔擴張;加固機理;軟黏土;擠密效應

中圖分類號：TU473.1 文獻標志碼：A 文章編號：2096-6717（2020）06-0001-10

Abstract： Carrier pile is newly developed in recent years. It utilizes a column hammer to tamp the filling in the deep soil， which forms an expanded carried at the pile end. This will greatly increase the vertical pile bearing capacity. Although the carrier pile has been widely used in practice， rare theoretical analysis has been conducted to check the size of the reinforced area and the compaction effect. This greatly restricts the popularization and development of the carrier pile. Under this condition， the process of the tamping through a column hammer is simplified as the spherical cavity expansion model. The soft clay is described by the MCC model. Then， a series of partial differential equations （PDEs） for spherical cavity expansion is constructed. Similarity solution technique is used to transform the PDEs to ordinary differential equations （ODEs）， which can be numerically solved through the ODE solver. Subsequently， a series of parametric analyses were conducted to investigate the variation of the soil strength and stiffness after spherical cavity expansion and the size of the compaction zone. This reveals the reinforced mechanism of the formation of the carried part of the pile from the theoretical viewpoint and provides a theoretical basis for constructing the theoretical calculation methods for the vertical bearing capacity of the carrier pile considering the compaction effect.

Keywords：carrier pile; spherical cavity expansion; reinforced mechanism; soft clay; compaction effect

載體樁的施工工藝（如圖1）可以概括為：利用柱錘夯擊成孔;將護筒壓入地基;分批向孔內投入水泥砂拌合物填充料反復夯實擠密，并通過三擊貫入度進行密實度控制，當三擊貫入度滿足設計要求后，形成載體;根據需要可放置鋼筋籠;灌注混凝土或放置預應力管樁而形成樁體樁[1]。從載體樁施工工……