Full-Casing Bored Cast-in-Place Pile Construction

Technical Principle

Full-casing bored cast-in-place piles use continuously advanced steel casing to support and protect the borehole, improving bore stability under complex geological conditions.

During construction, the steel casing advances together with the drilling process, providing continuous support through loose soils, sand, cobble and gravel layers, rockfill and groundwater-rich formations. Depending on ground conditions, the system can be combined with double-head drilling, rotary drilling, DTH hammer rock breaking and specialized drilling tools for bore formation and rock socketing.

Where thick fill, large rock fragments, boulders and hard rock are present, DTH hammer drilling can be integrated with the full-casing system. Rock breaking and spoil removal are carried out within the protected bore, allowing bore stability, drilling efficiency and pile construction quality to be maintained simultaneously.

The method is suitable for projects where conventional slurry-supported drilling may face stability limitations, complex groundwater conditions or difficult rock and boulder obstructions. It can be applied to residential developments, public buildings, industrial facilities, major infrastructure and other deep foundation projects requiring reliable bore stability and pile quality.

Technical Features

• Continuous steel casing support improves bore stability in complex ground;
• Reduces the risk of bore collapse, necking, soil loss and bore-wall disturbance;
• Suitable for loose fill, sand, cobble and gravel layers, rockfill and groundwater-rich formations;
• Can be combined with double-head drilling, DTH hammers and specialized drilling tools to penetrate boulders and hard rock;
• Reduces reliance on large-volume slurry support and helps limit slurry-related environmental impacts;
• Allows flexible adjustment of casing, drilling tools and equipment combinations according to ground conditions;
• Suitable for large-diameter and deep rock-socketed pile foundations with demanding quality requirements.

Applications

Complex Ground Foundation Works

Full-casing bored piles are particularly suitable for pile construction in complex ground, including loose fill, sand, cobble and gravel layers, boulder-bearing fill, groundwater-rich formations and other conditions requiring reliable bore stability.

Kingjiu selects suitable casing systems, drilling equipment, DTH hammer configurations and construction parameters according to project-specific geology and construction requirements to achieve stable and high-quality pile installation.

Large-Diameter and Deep Rock-Socketed Piles

Where hard rock, boulders or large rock fragments are present beneath thick fill, full-casing construction can be combined with DTH hammer drilling.

Continuous casing support maintains bore stability while the DTH hammer breaks boulders and rock, providing an effective solution for large-diameter rock-socketed piles under difficult overburden conditions.

Urban Development and Mountainous Sites

For urban development, mountainous construction sites and projects close to existing roads or structures, full-casing bored piles can reduce ground disturbance and bore instability through continuous casing support.

The method is particularly suitable for sites with significant elevation differences, thick fill, complex groundwater conditions and ground where conventional drilling methods may have limited efficiency.

Representative Project

Pile Foundation Works for the Wencheng Yatoushan B-33 Plot Project

Kingjiu participated in the pile foundation construction for the Wencheng Yatoushan B-33 Plot Project in Xuekou Town, Wencheng County, Zhejiang Province.

The project covers a site area of approximately 68,957 m² and a total construction area of approximately 103,435.5 m², including high-rise and low-rise residential buildings together with an integrated basement. A total of 615 foundation piles were constructed.

The site is characterized by low mountainous and hilly terrain with a maximum elevation difference of approximately 43.21 m. Ground conditions include thick miscellaneous fill containing large rock fragments and boulders, underlain by hard moderately weathered tuff. Pore groundwater and bedrock fissure water are also present.

These conditions created significant challenges for conventional piling methods, including low drilling efficiency, high slurry demand, difficult rock socketing and unstable bore conditions.

To address these challenges, the project adopted a large-diameter DTH hammer full-casing bored cast-in-place pile method, with moderately weathered tuff used as the bearing stratum. Steel casing was advanced continuously to support the borehole, while DTH hammer drilling was used to break large rock fragments, boulders and the underlying rock.

Air-assisted bore cleaning was used to control bottom sediment thickness to no more than 50 mm. C30 concrete was placed through tremie pipes under water, followed by controlled casing extraction using a vibratory hammer and crawler crane to maintain concrete integrity and pile quality.

Two double-head full-casing piling rigs were deployed, operating continuously in two shifts over a planned 60-day construction period.

Through the combined use of full-casing support, DTH hammer rock breaking and coordinated equipment deployment, the project addressed major construction challenges including significant site elevation differences, boulder obstructions, hard-rock socketing and complex groundwater conditions.

All pile foundation test results met the relevant design and specification requirements, demonstrating the applicability of full-casing bored pile construction to complex mountainous fill and hard-rock formations.

技术原理

全套管钻孔灌注桩是一种采用钢护筒连续跟进支护的桩基施工技术，通过套管对孔壁进行约束和保护，提高复杂地层条件下的成孔稳定性。

施工过程中，钢护筒随着钻进过程同步下沉，对松散土层、砂层、卵砾石层、块石及地下水丰富地层形成连续支护，并可根据地质条件结合双动力钻进、旋挖钻进、潜孔锤破岩及专用钻具完成成孔和嵌岩施工。

对于存在厚层回填、大块石、漂石及坚硬岩层的复杂地层，可采用潜孔锤与全套管组合工艺，在钢护筒保护下进行破岩和排渣，从而兼顾孔壁稳定、钻进效率及施工质量。

该工法适用于传统泥浆护壁施工稳定性不足、地下水条件复杂或存在块石及岩层障碍的工程环境，可用于住宅、公共建筑、工业设施、大型基础设施及其他对成孔稳定性和桩基质量要求较高的深基础工程。

技术特点

• 钢护筒连续跟进支护，提高复杂地层中的成孔稳定性；
• 有效降低塌孔、缩径、土体流失及孔壁扰动风险；
• 适用于松散填土、砂层、卵砾石层、块石回填及富水地层；
• 可结合双动力钻进、潜孔锤及其他专用钻具穿越漂石和硬岩；
• 减少对大规模泥浆护壁的依赖，有利于降低泥浆污染；
• 可根据不同地质条件灵活调整套管、钻具及设备组合；
• 适用于高质量要求的大直径、深嵌岩桩基础工程。

工程应用

复杂地层基础工程

全套管钻孔灌注桩主要应用于复杂地质条件下的桩基础施工，包括松散填土、砂层、卵砾石层、块石及漂石回填、地下水丰富区域以及成孔稳定性要求较高的工程环境。

京久基础根据不同项目的地质条件和施工要求，结合钢护筒支护、钻进设备配置、潜孔锤破岩及施工参数优化，实现复杂环境下稳定、高质量的桩基础施工。

大直径及深嵌岩桩基础

对于厚层回填以下存在坚硬岩层、漂石或大块石的项目，可采用全套管与潜孔锤组合施工，通过钢护筒持续护壁，并利用潜孔锤处理块石、漂石及岩层，实现复杂覆盖层条件下的大直径嵌岩桩施工。

城市建设及复杂山地工程

针对城市建设、山地开发及邻近既有道路和建筑物的项目，全套管钻孔灌注桩可通过连续套管支护降低地层扰动和成孔风险。

该工法尤其适用于场地高差较大、回填层厚、地下水条件复杂以及传统钻进方式施工效率较低的工程场景。

代表性工程案例

文成鸭头山 B-33 地块工程项目桩基工程

京久基础参与该项目桩基础施工。

项目位于浙江省温州市文成县峃口镇鸭头山 B-33 地块，总用地面积约 68,957 m²，总建筑面积约 103,435.5 m²，包含高层、低层住宅及整体地下室，共施工桩基 615 根。

项目场地属于低山丘陵地貌，最大高差约 43.21 m。场地存在厚层杂填土，其中含大量块石和漂石，下伏坚硬中等风化凝灰岩，同时孔隙潜水和基岩裂隙水较为发育。复杂回填、块石及漂石障碍、硬岩和地下水条件，使传统工艺面临成孔效率低、泥浆污染较大及嵌岩施工困难等问题。

针对上述地质条件，项目采用大直径潜孔钻全套管钻孔灌注桩工法，以中等风化凝灰岩作为持力层。施工过程中钢护筒全程跟进护壁，利用潜孔锤破碎块石、漂石及岩层，并采用气压清孔，将孔底沉渣厚度控制在 50 mm 以内。

成孔完成后采用水下导管灌注 C30 混凝土，并通过振动锤配合履带吊进行套管振动起拔，以保障桩身混凝土密实性和成桩质量。

项目投入 2 台双动力全套管桩架，实行 24 小时两班连续作业，计划总工期 60 天。通过全套管护壁、潜孔锤破岩及设备协同施工，克服了山地高差大、块石漂石障碍、硬岩嵌岩及地下水复杂等施工难题。

项目桩基各项检测结果均满足设计及相关规范要求，体现了全套管钻孔灌注桩工法在复杂山地回填及硬岩地层中的施工适应能力。