{"id":66542,"date":"2026-08-08T08:08:38","date_gmt":"2026-08-07T23:08:38","guid":{"rendered":"https:\/\/norimen.net\/?p=66542"},"modified":"2026-08-06T21:49:24","modified_gmt":"2026-08-06T12:49:24","slug":"where-is-the-construction-error-in-the-ground-anchor-work-a-complete-analysis","status":"publish","type":"post","link":"https:\/\/norimen.net\/en\/%e3%82%b0%e3%83%a9%e3%82%a6%e3%83%b3%e3%83%89%e3%82%a2%e3%83%b3%e3%82%ab%e3%83%bc%e5%b7%a5%e3%81%ae%e6%96%bd%e5%b7%a5%e3%83%9f%e3%82%b9%e3%81%af%e3%81%a9%e3%81%93%e3%81%a0%ef%bc%9f%e5%ae%8c%e5%85%a8\/","title":{"rendered":"Where Are the Mistakes in Ground Anchor Installation? The Complete Guide | How to Create Anchors That Won\u2019t Come Loose: Drilling, Grouting, Tensioning, and Head Finishing"},"content":{"rendered":"

Hello, everyone.<\/p>\n

This is Enta.<\/p>\n

I wrote a series of posts on this blog about construction errors in ground anchor work back in 2018, and I rewrote it again in 2023, but to be honest, both versions ended up feeling a bit half-baked lol.<\/p>\n

When I went back and reread my old posts this time, I found several instances where I thought, \u201cWait, this is the same thing I wrote about in Part 1,\u201d so I decided to go ahead and combine them all into a single post.<\/p>\n

\"Ground<\/p>\n

But that's beside the point.<\/p>\n

Ground anchor systems will provide the design-specified load-bearing capacity if installed correctly, but if you cut corners even in just one spot, they\u2019ll fail immediately.<\/p>\n

What makes it even more troublesome is that the cause of the hair loss is usually hidden in places that aren't visible to the naked eye.<\/p>\n

In this article, I\u2019ll share some of my own close calls on-site\u2014from drilling to head treatment\u2014while referencing the standards published by the Japanese Geotechnical Society,<\/p>\n

Here\u2019s a comprehensive summary of the areas where construction errors are most likely to occur.<\/p>\n

\u2460 Cleaning After Drilling | A Process Where You Don\u2019t Have to Aim for Perfection<\/h2>\n

Once drilling is complete, the inside of the casing will be cleaned.<\/p>\n

This is the process of removing slurry (muddy rock dust produced during drilling) that remains inside the casing.<\/p>\n

To be honest, I'm a bit skeptical about just how effective this cleaning really is.<\/p>\n

It\u2019s just a matter of \u201cbetter to do it than not,\u201d but when I was younger, I wasn\u2019t that particular about it.<\/p>\n

The reason is simple: at job sites where water-jet drilling is the primary method, the water pressure isn't high enough to warrant the use of a compressor.<\/p>\n

It was just a matter of turning the inner rod in a circular motion to let the water flow out; once a little slime came out, that was it.<\/p>\n

Recently, there has been an increase in machines that mix water and air, so we can now spray with greater force, but to be honest, it\u2019s still difficult to achieve a perfect clean.<\/p>\n

Therefore, just because this step isn't performed perfectly doesn't necessarily mean it will lead to an installation error.<\/p>\n

As long as the soil and cement slurry are thoroughly mixed, that's fine, and if it accumulates in the slime pool, that's fine too.<\/p>\n

However, while various construction manuals state to \u201crinse with clean water,\u201d they do not go so far as to say to \u201cblow it off completely with compressed air.\u201d<\/p>\n

I interpret this as merely a goal to \"reduce the number of remaining slimes as much as possible,\" lol.<\/p>\n

\"Borehole<\/p>\n

\n

\u2461 Tendon Insertion | Grease on the anchorage point can be fatal<\/h2>\n

Once cleaning is complete, it\u2019s time to insert the tendons (tensile members such as prestressed steel strands or twisted wires).<\/p>\n

The first thing to note here is the trumpet tube.<\/p>\n

If you insert the pipe without the bell mouth, you may damage the polyethylene hose that protects the free-length section.<\/p>\n

Be careful, because if the grout leaks, it might not be possible to inject it properly from the bottom of the hole.<\/p>\n

Another thing that tends to be overlooked is grease buildup at the tendon attachment points.<\/p>\n

The anchorage section is the part that adheres directly to the grout underground to generate frictional resistance.<\/p>\n

If there is oil on this part, it reduces friction, and in the worst case, the tendon could come out entirely.<\/p>\n

Checking to see if the gloves used during insertion are free of oil is a simple but important step.<\/p>\n

To be honest, I think this is the mistake on site that\u2019s most likely to go unnoticed\u2014even though it\u2019s often overlooked.<\/p>\n

Please make sure to properly protect only the bonding area.<\/p>\n

Also, please make sure to thoroughly wipe down the workers' gloves or cover the side where the adhesive is applied.<\/p>\n

\"Tendon<\/p>\n

\n

\u2462 Cement Slurry Injection | The Key to Anchor Work<\/h2>\n

This is the most important step in the ground anchor process.<\/p>\n

This is an absolutely crucial part!<\/p>\n

If you mess this up, you'll almost certainly fail.<\/p>\n

The first thing to check is the formulation.<\/p>\n

Isn't there too much water?<\/p>\n

If the cement slurry is too runny, or if you have concerns about its consistency or the mix ratio, you should definitely make a new batch without hesitation.<\/p>\n

A strength of around 24 kN is a value that can typically be achieved with a standard mix, but some people on-site casually add water to make the mix looser, claiming it\u2019s \u201ctoo hard.\u201d<\/p>\n

Please do not do this under any circumstances.<\/p>\n

If you want to loosen it when it's hard, you should use a mixing agent instead of water.<\/p>\n

That's still better. (You can currently add up to 2%\u2014Seikaseum.)<\/p>\n

Construction managers, please make sure to carefully review this mix design verification.<\/p>\n

In addition, the design calls for the use of ordinary cement.<\/p>\n

When mixing cement slurry with ordinary cement, it takes about 10 seconds in a flow cone.<\/p>\n

When cement slurry is mixed using fast-setting cement, the flow cone time is 14 seconds or more.<\/p>\n

Please note that the concentration varies depending on the type of cement.<\/p>\n

In addition, the dough tends to become harder when the ambient temperature or the mixing temperature is high.<\/p>\n

\"Hot<\/p>\n

Another golden rule is to always start the injection from the deepest (lowest) point.<\/p>\n

The same applies to the \"dip-and-inject\" method (a method in which grout is injected into the casing first after drilling, followed by the insertion of tendons); in this case as well, grout is injected from the very bottom to displace the drilling fluid.<\/p>\n

If a thick stream of cement slurry comes out of the mouth, there is likely no problem with the bonding area.<\/p>\n

It's a total joke if all that comes out is watery milk lol (though I doubt that would ever happen).<\/p>\n

As for blood pressure, to be honest, I personally don't think there's any need to be that concerned about it.<\/p>\n

The Japan Geotechnical Society\u2019s \u201cStandards for the Design and Construction of Ground Anchors and Explanatory Notes\u201d states that pressurization should be \u201ccarried out using an appropriate method based on the soil conditions surrounding the anchor body,\u201d but does not specify any concrete values.<\/p>\n

\"Pressurization<\/p>\n

On the other hand, the Anchor Association\u2019s materials provide the following guideline: \u201cThis prevents the borehole wall from loosening, but excessive pressure can actually cause it to loosen. The pressure is typically applied at around 0.1 to 0.5 MPa; if the anchorage depth is significant, the pressure should be greater than the groundwater pressure and less than twice the equivalent water level.\u201d<\/p>\n

By the way, the hose bursts at 0.5 MPa or higher lol<\/p>\n

So, in practical terms, 0.2 to 0.3 MPa is sufficient.<\/p>\n

That said, in actual field conditions, considerable pressure is already being exerted on the tendon anchorage points due to the difference in elevation alone.<\/p>\n

To be honest, I have some doubts about the necessity of going out of our way to apply additional pressure.<\/p>\n

Plus, since it\u2019s unloaded, it won\u2019t be under any more pressure lol<\/p>\n

What is the pressure condition at the fixation site during injection? (Is pressurization necessary?)<\/a><\/h1>\n

\"Anchor<\/p>\n

\n

\u2463 Stress Analysis | The Pitfall of the 1.25x Multiplier<\/h2>\n

When it comes to mistakes in prestressed concrete construction, they tend to occur more often on the construction management side than among the on-site craftsmen.<\/p>\n

One common misconception among managers regarding stress analysis is the method for calculating the maximum test load.<\/p>\n

There is a rule that the maximum test load must be set so that it does not exceed \u201cTd \u00d7 1.25,\u201d where Td is the design anchor force for Grade A.<\/p>\n

That's correct so far.<\/p>\n

However, I get the impression that in many workplaces, \u201ccalculating at 1.25 times\u201d has become an end in itself.<\/p>\n

What caught my attention was the fact that this standard does not mean tests can be conducted using a uniform \"1.25 times\" multiplier regardless of ground conditions.<\/p>\n

If the anchorage is in rock that's as hard as a rock, even 1.25 times the load should be no problem.<\/p>\n

But what if it\u2019s a slimy mudstone layer that\u2019s difficult to drill through when water gets in?<\/p>\n

Even with a long curing time, there\u2019s still some concern, and I think the general feeling on-site is that \u201cit could be a little lighter.\u201d<\/p>\n

What if we were working at a site where the setting length is set to the maximum of 10 meters?<\/p>\n

This means there's a possibility of breaking out at 1.25 times the current price.<\/p>\n

 <\/p>\n

So, it's totally fine to let that feeling\u2014that slight sense of nervousness\u2014show up in your test scores, lol.<\/p>\n

The following is stated in Sections 8.4 (Qualification Tests) and 8.5 (Verification Tests) of the commentary to the Japan Geotechnical Society\u2019s \u201cDesign and Construction Standards for Ground Anchors and Commentary Thereon\u201d:<\/p>\n

\"The maximum design load shall be determined by taking into account the strength characteristics of the tendons, the service life, and the classification based on the importance of the structure. However, it shall not exceed the loads specified below: Rank A: Design anchor force (Td) \u00d7 1.25; Rank B: Design anchor force (Td) \u00d7 1.10.\"<\/p>\n

In other words, 1.25 times is an \u201cupper limit,\u201d not a requirement that the load must reach that level.<\/p>\n

The intent is that, based on the actual conditions at the site and at the discretion of the responsible engineer, a lower limit may be set.<\/p>\n

I don\u2019t think there\u2019s a particularly strong need to test anchors\u2014which will remain in service for decades to come\u2014by applying loads right up to their maximum limit every single time.<\/p>\n

However, if you take set loss (the initial decrease in tension) into account, it is safer to use a multiplier between 1.10 and 1.20.<\/p>\n

Be careful\u2014set loss can sometimes reach 1.3 times the static load!!<\/p>\n

Personally, I use the same multiplier for both the aptitude test and the confirmation test, and in practice, I apply a multiplier of approximately 1.15 to 1.2 times.<\/p>\n

Since I don't have to change the numbers for each type of test, it makes it easier to keep track of things on the digital whiteboard lol<\/p>\n

 <\/p>\n

Another situation during a tension test that really gave me a scare was misreading the pressure gauge on the jack.<\/p>\n

\"Pressure<\/p>\n

A long time ago, when I was a site supervisor, there was an instance where a worker operating a jack pulled it right up to its breaking load.<\/p>\n

He said he \u201chad misunderstood,\u201d but to be honest, this gauge is pretty hard to read, and it\u2019s even harder to make out if you have presbyopia lol.<\/p>\n

Since then, we've been marking this pressure gauge with a Tepla label or a marker to indicate the different levels.<\/p>\n

Even if you write on it with a marker, you can easily erase it with paint thinner, so it's not a problem.<\/p>\n

\"Digital<\/p>\n

Alternatively, using a digital gauge reduces errors and allows for more creative solutions.<\/p>\n

Since we aren't the general contractor, we don't issue on-site instructions, but we do make suggestions when asked.<\/p>\n

\"Preventing<\/p>\n

\n

\u2464 Head Processing Technician | The mistake that gradually takes its toll the most in the long run<\/h2>\n

Last but not least is the head processing technician.<\/p>\n

This is the kind of mistake that isn\u2019t apparent right after construction and only comes to light several years later, so, to be honest, it\u2019s the most troublesome.<\/p>\n

The most important point is the rust on the anchor head.<\/p>\n

At construction sites, the practice of applying grease to the anchor head after tightening is, surprisingly, not carried out as thoroughly as one might expect.<\/p>\n

In many cases, the process tends to be as simple as applying grease to the head cap and closing the lid\u2014and that\u2019s it.<\/p>\n

For example, in the case of KTB caps, they are designed with grease inside the undercap, but,<\/p>\n

If you simply install the cap and call it a day, it will eventually rust over time.<\/p>\n

I\u2019ve written about this before, but in ground anchor construction, head treatment is a critically important process from a long-term perspective.<\/p>\n

Since this is important, I\u2019ll write it again.<\/p>\n

\"Head<\/p>\n

Once the tension has subsided, apply rust-preventative oil to the head as soon as possible.<\/p>\n

The goal is simple: to cut off the supply of water and oxygen\u2014which cause rust\u2014as early as possible.<\/p>\n

In addition, once PC steel strands are cut, the cut ends begin to rust immediately.<\/p>\n

Please apply either epoxy paint or rust-preventive oil to this area.<\/p>\n

In the section on head treatment in the Japan Geotechnical Society\u2019s \u201cDesign and Construction Standards for Ground Anchors and Explanatory Notes,\u201d<\/p>\n

\"The anchor head shall be treated promptly after tensioning and setting to provide corrosion protection and safeguard the anchor head.\"<\/p>\n

It clearly states, \u201cCover the anchor head with a cap and fill the cap with a rust-preventive material, such as rust-preventive oil.\u201d<\/p>\n

It also states that if the head of the anchor cannot be treated immediately after the tension has been set, temporary corrosion protection measures should be taken\u2014such as using rainwater\u2014to prevent the anchor and tendons from rusting.<\/p>\n

The fact that the standards manual goes out of its way to state this is, I think, a reflection of the fact that this is a process that tends to be put on the back burner in the field.<\/p>\n

Broadly speaking, there are five areas where errors are most likely to occur during ground anchor installation.<\/p>\n

I feel like there are still some other minor details, but I think the two most important points are the cement slurry mixture and the head treatment.<\/p>\n

These are the only two things I make sure not to skimp on, no matter how busy I am.<\/p>\n

\"Head<\/p>\n

\n

When you look at these five steps side by side, ground anchor work is less about \u201cglaring mistakes\u201d than<\/p>\n

As I was writing this, it struck me once again that many people end up falling behind because of the accumulation of \u201cmundane tasks that are easily overlooked.\u201d<\/p>\n

Don't use water to cut corners on the cement slurry mix.<\/p>\n

Don't overlook oil stains on the mounting surface.<\/p>\n

Do not blindly apply the factor of 1.25. (The same applies to each load stage.)<\/p>\n

And don't put off working on the head.<\/p>\n

There's nothing special about it\u2014it's just a matter of sticking to the basics\u2014but that's actually pretty hard to do in the field, lol.<\/p>\n

I can't say we're doing everything perfectly either!<\/p>\n

I hope we can look out for one another as we move forward.<\/p>\n

That\u2019s exactly why I believe it\u2019s important to put these seemingly mundane checkpoints into words and document them.<\/p>\n

 <\/p>\n

See you later.<\/p>\n

Head Processing Is the Same for Both People and Anchors | Carefully<\/a><\/p><\/blockquote>\n