compaction grout solution

Is Compaction Grout a Good Solution for Weak Soils?

In Commercial Blog Posts, Compaction Grout, Ground Improvement by John Topa

A Compaction grouting solution is often touted as the most effective way of combating the problem of weak soils. If you are familiar with engineering, you are likely already aware of how vital soil quality is when it comes to preparing building sites for commercial and industrial construction. Weak or granular soils filled with voids and cracks will settle over time, creating potentially serious foundation problems.

What Is Compaction Grouting?

Compaction grouting is a method for increasing the bearing capacity of the weak soils and to fill any fill voids. It involves injecting high-viscosity mortar, concrete, or another grouting material into the soil at a controlled flow rate to fill in any gaps or voids, allowing for lateral compaction without vibration.

Engineers in Florida often plan for the use of compaction grout to stabilize weak soil and treat it against liquefaction. In some cases, this procedure can also be used to lift settled structures.

Common Applications

Compaction grout can be used before new construction to improve the bearing capacity of weak or granular soils or increase the soil’s density beneath existing structures. That is not all it is used for, though. Here are a few other typical applications for compaction grout as a solution:

  • Remediating sinkholes
  • Stabilizing underground formations for pipes
  • Preparing sites for municipal engineering projects
  • Addressing foundation settling
  • Improving inadequately compacted fill
  • Contractors use compaction grouting to prepare sites for residential, commercial, and industrial construction projects. Engineers also use it to improve the soil before undertaking municipal projects.
Advantages of Compaction Grouting

Compaction grouting is not the only way to remediate weak soils, but it is arguably one of the most efficient methods of soil stabilization. Here are just a few of the unique advantages of using this procedure to stabilize subsoils and address sinkholes:

Cost Efficiency

Compaction grout is relatively easy to install compared to other soil stabilization and ground-shoring products and procedures. It creates only minimal disruptions to surrounding soils, structures, and landscapes, and uses inexpensive materials. The combined effect of these factors is that compaction grouting is a more cost-efficient alternative to most other compaction methods.

Requires Only Limited Access

It can be hard to remediate weak soil in areas that offer minimal access to construction sites. Since compaction grouting does not require as much heavy equipment, it is perfect for limited access projects.

residential compaction grout solution
Precise Application

Low mobility grout rheology allows for precise placement, which is perfect for highly populated areas. Compaction grouting can also be used for delicate applications that preclude vibration compaction methods.

Protection Against Liquefaction

Compaction grout can mitigate liquefaction potential. This helps to reduce the chances of soil damage following severe inclement weather events. Since Florida is prone to hurricanes and flooding, that’s excellent news for property owners.

Can Be Used to Address Foundation Settling

The precision associated with compaction grouting means it can be used to address foundation settling beneath existing commercial buildings. It can even be used beneath multi-story buildings, including both residential and commercial rental properties.

No Need for Connections to Existing Foundation Structures

Although compaction grouting can be used to resolve foundation settling in existing buildings, there is no need for connections to existing foundation structures. Compaction grouting can thus be performed before construction of new residential, industrial, or commercial buildings begins. Even when used to remediate existing foundation problems, the fact that there are no connections to the foundation structures makes compaction grouting easier than other methods.

Quick Results

Unlike some soil compaction procedures, which can take weeks to produce the desired results, compaction grouting almost immediately increases the ground’s bearing capacity. This helps keep construction and site remediation projects on-track.

Limitations of Compaction Grouting

There are two primary limitations of utilizing compaction grout as a weak soil solution. First, it is not suitable for clay-based soils with low permeability. Second, it cannot be used in areas with less than five feet of overburden. In these circumstances, limited overburden above the grouted zone can cause ground heaves.

Placement Sequence

Since every site is different, there is no way to standardize placement procedures and sequences or develop a universal guide for every possible application. Mixtures can be injected using a top-down or a bottom-up approach depending on the site conditions and desired results. Factors that influence placement sequence include:

  • Soil type
  • Site conditions
  • Soil test results
  • Pumping pressures
  • Injection rates
  • Injection volumes
  • Desired results
Top-Down Grouting

As a rule, top-down grouting is more time-consuming and expensive. It requires drilling through previously placed grout stages, which takes extra time and resources. However, this approach works best for improving the ground for incremental re-leveling of structures at ground depths of 3 to 15 feet.

Bottom-Up Grouting

Bottom-up placement is cheaper and less time-consuming. Technicians can use continuous pumping techniques to stabilize soils more than 15 feet deep. It is suitable for compacting soil to stabilize structures that require only minor re-leveling.

Combined Approach

It is often the case that a ground improvement company must use a combined approach to remediate soils, especially when the ground is soft to depths greater than 15 feet. The engineer will typically use bottom-up grouting from bedrock to around 10 feet below the surface or the lowest below-grade structural element, then use top-down grouting in the intermediate space. The bottom-up grouting procedure provides a stable base for top-down injection, helping to prevent further settlement.

Calculating Probe Spacing

Most compaction grouting companies space soil probes on eight-foot centers and foundation structural elements with a triangular grid on eight-foot spacing that spans the entire building footprint. Still, engineers use that as a general guide, not a dogmatic rule. Calculating optimal spacing requires taking other factors, such as the foundation system’s spanning capabilities, into account. New construction needs to determine these basic requirements before you contact a compaction grouting contractor.

Determining Stage Lengths

The first step is always to drill or drive a grout casing to the appropriate depth. There are three ways for engineers to assess pumping stages from there.

1. Predetermined grout volume

2. Predetermined pumping pressure

3. Presence of undesired ground movement

When the technicians have reached the end of the stage, they will move the grout casing up, then resume pumping. In most cases, stage lengths are measured in one-foot vertical increments, but they vary from site to site.

The Importance of Choosing the Right Contractors

Compaction grout for weak soils requires a lot of specialized tools, equipment, and expertise. Property owners and building contractors should only work with licensed and insured professionals with sufficient experience to understand local site conditions. Do not make a hasty choice.

Instead, take the time to thoroughly interview potential contractors, ask for references, and request a portfolio of completed projects. The ideal candidate will be able to produce a portfolio that contains similar projects and referrals or testimonials from previous clients in the area. Take all these factors into consideration before signing on the dotted line.

The Take-Away

Whether you want to prepare a site for new construction or shore up the foundations of multi-story buildings, compaction grouting provides a perfect solution. This quick, simple, and cost-effective strategy can be used to stabilize granular soils on just about any building site in Florida. It is also one of the most cost-effective ways to address foundation settling in existing buildings, exceptionally large commercial and industrial structures. Just make sure to hire an experienced compaction grouting company.