Enhancing Soil and Rock Stability through Pressure Grouting of Self-Drilling Anchor Bolts

Pressure grouting is an indispensable technique in the field of construction and geotechnical engineering, particularly when it comes to fortifying the stability of soil and rock structures. Self-drilling anchor bolts are commonly employed for their effectiveness in providing structural support.

The Science Behind High-Pressure Grouting

High-pressure grouting involves injecting slurry into rock and soil, instigating a series of intricate reactions within the subsurface. As the high-pressure slurry infiltrates the ground, it initiates the formation of slurry bubbles, which exert complex three-dimensional stress on the surrounding rock and soil. In areas of weakness, this stress can overcome initial stress and compressive strength, leading to a splitting action.

The interaction between the slurry and the rock and soil is multifaceted. This includes the hydration reaction of cement forming tobermorite gel, the creation of Ca2+ and microcrystalline gel through the interaction of oxide and water in micro-fissures (insoluble in water), and ion exchange interactions between Ca2+ and Na+, which result in the formation of soil granular structures and stable clot bodies. These interactions collectively establish a network of slurry pulse within the ground.

Concurrently, the slurry exerts a filling and compaction effect, expelling free water and weakly bound water. This leads to the evaporation of water from the hydration reaction and a reduction in moisture through ion exchange. These processes ultimately enhance the physical properties of the rock and soil, contributing to the formation of induration and altering the soil's reaction mechanism.

High-pressure grouting primarily focuses on splitting as its primary objective, with penetrating, filling, and squeezing recombination actions serving as auxiliary processes. This transformation through grouting with rock bolts enhances the physical properties of the soil and rock, effectively restraining deformation.

Pressure Grouting Methods for Self-Drilling Anchor Bolts

Self-drilling anchor bolts are vital tools in geotechnical engineering, offering critical stability for foundations and retaining structures. Pressure grouting plays a pivotal role in ensuring their effectiveness, and there are three primary methods for pressure grouting with self-drilling anchor bolts:

1. Infiltration-Type Grouting

Infiltration-type grouting involves injecting slurry under pressure into cracks in soil and rock. This displaces water and gas without significantly altering the structure or volume of the substrate. This method is typically employed in construction projects involving medium sandy soil and rocks with existing cracks. The key theories guiding infiltration grouting are the spherical diffusion theory and cylindrical diffusion theory. Their application results in reduced porosity, enhanced foundation strength, decreased compressibility, prevention of shrinkage, and mitigation of uneven settlement.

2. Fracturing Grouting

Fracturing grouting entails creating fractures in the stratum by applying pressure to the slurry. This pressure overcomes the initial stress and tensile stress within the stratum, causing structural disturbances and destruction in the rock and soil body. This leads to a vertical split along a plane defined by the principal stress. Existing cracks extend, and new ones form as the slurry infiltrates deeper into the stratum. Fracturing grouting is particularly useful for enhancing objectivity and increasing the diffusion distance of the slurry within the stratum.

3. Compaction Grouting

Compaction grouting employs very high pressure to inject dense slurry into the soil. This process results in the formation of an aggregation at the end of the grouting pipe, inducing radial uplift force and causing localized elevation of the stratum. This method is best suited for reinforcing unsaturated soil, addressing uneven settlement, and performing foundation underpinning.

Regarding self-drilling anchor bolts, pressure grouting involves using slurry with a water-cement ratio of approximately 0.3 and grouting pressures typically ranging from 200-600 PSI (1.4-4.0 MPa). Pressure grouting significantly enhances the structural stability of soil and rock, reducing uneven settlement and preserving the integrity of the anchor bar.

Simultaneous drilling and grouting


Pressure grouting is a versatile and potent technique employed in construction and geotechnical engineering. When coupled with self-drilling anchor bolts, it becomes a formidable tool for enhancing the stability of soil and rock structures. Understanding the nuances of pressure grouting methods, including infiltration-type, fracturing, and compaction grouting, is crucial for engineers and construction professionals aiming to ensure the longevity and resilience of their projects. By harnessing the power of high-pressure slurry and its interactions with the subsurface, we can create enduring foundations and structures capable of withstanding the test of time. 
Sinorock's expertise in producing self-drilling anchor systems empowers builders to make informed choices, enhancing construction safety, efficiency, and stability. If you have any interest in self-drilling anchor systems, welcome contact us at sinorock@sinorockco.com.

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