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<\/p>\nHello, everyone.<\/p>\n
This is Enta.<\/p>\n
Even though we're already in the second half of September, it's still pretty hot during the day.<\/p>\n
Since this is the season for autumn rains and typhoons, be sure to inspect slopes more thoroughly than usual after it rains.<\/p>\n
But that's beside the point.<\/p>\n
You often hear the terms \u201clandslide\u201d and \u201crockfall\u201d on the news, don\u2019t you?<\/p>\n
Since both involve \u201csoil sliding down a slope,\u201d I think many people assume they\u2019re the same thing.<\/p>\n
Actually, even among young directors, there are quite a few who work without fully clarifying this point (or who confuse the two).<\/p>\n
However, these two are completely different in terms of their causes and how they work.<\/p>\n
And precisely because they are different, the order in which countermeasures should be taken and the \u201cthings you shouldn\u2019t do\u201d also vary.<\/p>\n
In this post, I\u2019ll try to write as much as possible based on the guidelines and without using difficult words.<\/p>\n
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First, let's start with the meaning of the word.<\/p>\n
A landslide is \u201ca phenomenon in which a portion of the land slides due to groundwater or other factors, or a phenomenon in which the land moves as a result.\u201d<\/p>\n
The key points are\"Groundwater\"<\/strong>This is the part where that phrase appears.<\/p>\n On the other hand, steep slopes are defined as \u201cland with a slope of 30 degrees or more.\u201d<\/p>\n The key points here are\"Steep Slope\"<\/strong>\u3002<\/p>\n To give you an idea, it looks something like this.<\/p>\n A \"surface collapse\" is like when only the frosting on the surface of a cake slips right off.<\/strong><\/p>\n A landslide is like a cake slowly sliding across a plate, base and all.<\/strong><\/p>\n This \"border between the plate and the food\" corresponds to what is commonly referred to asSliding surface<\/strong>That's it.<\/p>\n Here's what it looks like in a table.<\/p>\n So, how can you identify the location of a landslide at the site?<\/p>\n Even though it's deep in the mountains, there are flat terraces at the base of a steep cliff, with rice paddies and ponds.<\/p>\n This means that such places might be the remnants of landslides that occurred in the past.<\/p>\n Just be careful, though\u2014it\u2019s easy to mistake river terraces and the like for landslide features, lol.<\/p>\n If you come across terrain like this near a construction site, I think it\u2019s a good idea to get into the habit of asking yourself, \u201cCould this be a landslide-prone area?\u201d<\/p>\n Incidentally, the Road Earthwork Guidelines state that \u201cthe boundary between rockfall and landslides is not always clear.\u201d<\/p>\n I\u2019ve heard that when a large-scale collapse occurs, it can sometimes be difficult to clearly distinguish it from a landslide.<\/p>\n Although landslides generally move slowly, it is said that some can move or slide down suddenly.<\/p>\n It\u2019s not necessarily true that \u201clandslides always happen slowly.\u201d<\/p>\n So, it's okay if you find yourself wondering, \"Which one is this?\" while you're on the job.<\/p>\n Even pros get confused\u2014in the end, it's all just guesswork lol (I get it right sometimes, though!)<\/p>\n One thing that always comes up when considering landslide countermeasures is\"Safety Factor\"<\/strong>That's the phrase.<\/p>\n Simply put,How many times greater is the \"braking force\" compared to the \"sliding force\"?<\/strong>That's the figure.<\/p>\n It's easier to understand if you think of it as a tug-of-war.<\/p>\n The planning safety factor in the Technical Guidelines for Landslide Prevention is determined as follows:<\/p>\n So, you start your calculations based on the assumption that \u201cif they\u2019re moving, it\u2019s already a tie or a loss,\u201d right?<\/p>\n The reason for the range of 1.1 to 1.2 is that this value is based on empirical data derived from past experience\u2014including cases where landslides became more active simply because the safety factor decreased by approximately 5 to 10% in cut and fill slopes.<\/p>\n Incidentally, the Road Earthwork Guidelines state that the design safety factor should be set within the range of 1.05 to 1.2, and that 1.2 is typically used. (For major roads, the value is 1.2.)<\/p>\n Although the specific range varies slightly depending on the book, the general idea\u2014to \"increase it from around 1.0 to around 1.2\"\u2014remains the same.<\/p>\n This is a sentence from the Technical Guidelines for Landslide Prevention, but,<\/p>\n The safety factor referred to here is used to determine the scope of remedial work; it does not indicate the stability of the slope after the work is completed.<\/strong><\/p>\n It doesn't mean, \"Since it was designed with a safety factor of 1.2, there's absolutely no way it'll break,\" lol.<\/p>\n Young directors in particular tend to misunderstand this, so please keep it in mind. Especially you, Yakusho!!<\/p>\n In other words, measures to prevent landslides are,\"What steps do I need to take\u2014and to what extent\u2014to increase a slope with a gradient of about 1.0 to 1.2?\"<\/strong>It's a job where I determine things through calculations.<\/p>\n So, what about a typical cut slope?<\/p>\n In the design of slope stabilization works, empirical techniques are emphasized, with the exception of certain structural works. (As stated in the guidelines.)<\/p>\n A prime example of this is the classification system established for each type of soil and rock.Standard Slope Grade<\/strong>That's it.<\/p>\n This is a guideline based on experience that indicates, \u201cIf this type of soil is used, maintaining this slope will almost certainly prevent major damage.\u201d<\/p>\n To put it simply,<\/p>\n Since we\u2019re relying on calculations, we can\u2019t even get started unless we know where the slip surface is.<\/p>\n They are calling for borehole surveys, slope stability surveys, groundwater surveys, and other investigations to be conducted in order to understand the mechanisms behind landslides.<\/p>\n That difference determines the \u201corder of the countermeasures.\u201d<\/p>\n Landslide mitigation measures can be broadly divided into two categories.<\/p>\n *Guidelines for Road Earthwork: Cut Work and Slope Stabilization<\/p>\n To put it another way,\"Suppressive treatment\" refers to \"treatment that eliminates the cause of a disease,\" while \"immobilization treatment\" refers to \"treatment that involves immobilizing the affected area with a cast.\"<\/strong>It's something like that.<\/p>\n And the order is important.<\/p>\n <\/p>\n When landslide activity continues at a high rate, as a general rule, preventive measures should not be implemented first; instead, they should be introduced only after the activity has been reduced or halted through containment measures.<\/strong><\/p>\n In the case of fast-moving landslides, it is impossible to install retaining structures, and even if they are installed, they may fail; therefore, the key question is: \u201cHow can we control them!?\u201d<\/p>\n So, the basic premise is to rely primarily on containment structures and combine them with deterrent structures as needed, right?<\/p>\n When movement is continuing gradually and steadily, not only can containment measures not be expected to be effective, but the construction work itself can also be dangerous, so,First, perform the restraint work to limit movement, and then...<\/strong>This means we will carry out preventive maintenance.<\/p>\n <\/p>\n Regarding retaining pile work, if movement of 1 mm\/day or more is occurring (or is expected), the piles will act independently of one another unless they are installed simultaneously as planned, and the desired effect cannot be achieved. Therefore, installation should not begin until it has been confirmed that landslide activity has largely ceased.<\/p>\n A movement of 1 mm a day is so slight that you can hardly tell it with the naked eye. (It might even be caused by the wind... lol)<\/p>\n Still, driving a pile would be dangerous, wouldn't it? lol<\/p>\n Flowchart for Reviewing Road Earthwork Guidelines<\/p>\n I'm sure you know that \"groundwater\" is included in the definition of the Landslide Prevention Act. (Nah, you probably don't, lol.)<\/p>\n Eliminating the causes of landslides is generally considered the most effective countermeasure. Since many landslides are triggered by an increase in groundwater levels caused by heavy rain, prolonged rainfall, or snowmelt, surface water drainage and groundwater drainage works are regarded as the primary methods to consider.<\/p>\n If the problem is caused by water, drain the water first.<\/p>\n This is something I've been saying for a loooooong time, lol. Anyway, maybe I'll just drain some water first!?<\/p>\n This is the absolute basics.<\/p>\n By the way, when it comes to slope failures, the goal is to prevent them from occurring at the points where they might happen.Preventive Engineer<\/strong>And so, he caught the falling dirtProtective Measures (Preparedness Measures)<\/strong>It is common to consider this in terms of...<\/p>\n Since collapse happens all at once, the choice is: \u201cPrevent it from happening, or brace for it.\u201d<\/p>\n Since landslides occur slowly, the approach is to \u201creduce the causes and stop the rest.\u201d<\/p>\n The difference in speed directly translates into a difference in how we approach the problem.<\/p>\n This is something I really want young directors to keep in mind.<\/p>\n When it comes to ordinary slopes, you\u2019d naturally think, \u201cIf it looks like it\u2019s about to collapse, just make the slope gentler,\u201d right?<\/p>\n However, in the case of landslides, this can sometimes backfire.<\/p>\n When constructing a road through an area prone to landslides,Cut the top part (the head), and pile up the bottom part (the feet).<\/strong>That is our general policy.<\/p>\n Conversely, piling dirt on the head or cutting the base will significantly compromise stability, so these actions must be avoided.<\/p>\n To use a tug-of-war analogy,<\/p>\n In reality, when trying to make a road pass through a landslide-prone area more quickly by gently re-contouring the entire slope, it may appear safer at first glance, but this actually removes the soil at the base of the landslide, which can make the slope even more unstable and lead to a recurrence.<\/p>\n The same applies to the soil and debris that have collapsed onto the road: if you rush to clear it all away, you\u2019ll remove the \u201canchor\u201d at the base of the landslide, which could cause the collapse to extend further inland.<\/p>\n From the general public's perspective, people probably think, \"Just get it over with and let us through!\" but actually, that's all part of preventing it from happening again!<\/p>\n In fact, removing it can sometimes lead to dangerous consequences.<\/p>\n <\/p>\n And even the backfill method\u2014where soil is piled up at the base\u2014is not a one-size-fits-all solution.<\/p>\n In many cases, the soil at the base of an existing landslide is disturbed and soft; the weight of the fill can cause the ground to collapse or block the flow of groundwater, which can in turn trigger a landslide.<\/p>\n Retaining embankment work isWell-drained soil<\/strong>Since this involves piling material at the base, it\u2019s standard practice to incorporate groundwater drainage measures, taking into account the rise in the groundwater level behind the embankment.<\/p>\n And, as expected, \u201cwater comes first\u201d here, too.<\/p>\n <\/p>\n There are also precautions to take when performing topsoil removal.<\/p>\n When planning earth-excavation work, it is necessary to conduct a thorough investigation in advance to ensure that it does not trigger a landslide hidden within the slope above; if a landslide is present on the slope above, this construction method should be avoided.<\/p>\n Landslide Mountain\u2014if you cut off the top of Landslide Mountain, the slope above it would start sliding too, and that would be a problem, lol.<\/p>\n When working on a slope, it\u2019s easy to focus only on the slope right in front of you and think about \u201chow to stabilize it.\u201d<\/p>\n However, at a landslide site, that slope may be just a small part of a much larger mass of soil.<\/p>\n \"Where are the slippery spots?\" \"Where does the water come from?\" \"Which construction measures are most effective, and in what order?\"<\/p>\n Just by keeping these three things in mind, you'll understand the role that the collection wells and anchors you're currently working on play within the overall system.<\/p>\n Instead of just following instructions to the letter at the specified location, if you ask yourself, \u201cWhy here?\u201d while you work, the job site becomes many times more interesting.<\/p>\n I hope that young directors, in particular, will cherish this sense of \u201cWhy?\u201d<\/p>\n When my boss says, \u201cThat\u2019s just how it is,\u201d he\u2019s really just saying he doesn\u2019t know, lol.<\/p>\n In that case, let's learn more about it!<\/p>\n It'll make your work\u2014and slope work\u2014even more fun!!<\/p>\n <\/p>\n See you later.<\/p>\n\n
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\n \nItem<\/th>\n Slope Collapse (Surface Collapse)<\/th>\n Landslide<\/th>\n<\/tr>\n<\/thead>\n \n Where to Ski<\/td>\n Near the surface of the ground<\/td>\n A slip plane deep underground<\/td>\n<\/tr>\n \n Speed of Movement<\/td>\n Fast \u00b7 Sudden<\/td>\n Slowly, Gradually<\/td>\n<\/tr>\n \n Slope Gradient<\/td>\n Common on steep slopes<\/td>\n It can occur even on slopes that are less steep than those prone to landslides<\/td>\n<\/tr>\n \n Main Reason<\/td>\n Water that seeped in due to heavy rain, etc.<\/td>\n Groundwater, etc.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n
![\"A](\"https:\/\/norimen.net\/wordpress\/wp-content\/uploads\/2026\/09\/e68108462963e22a574285e06f3525da.jpg\")
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\nUnderstanding the \"Safety Factor\" Helps You Understand Landslide Prevention Measures<\/h2>\n
![\"Safety](\"https:\/\/norimen.net\/wordpress\/wp-content\/uploads\/2026\/09\/7c2c4867893b95a8aba931d6b6a8c826.jpg\")
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\nThe first step in landslide prevention is \"draining the water\"<\/h2>\n
![\"Drainage](\"https:\/\/norimen.net\/wordpress\/wp-content\/uploads\/2023\/10\/551c3d01c936777a1bc79be317feef7a.jpg\")
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\n \nCategory<\/th>\n Approach<\/th>\n Main Types of Construction Work<\/th>\n<\/tr>\n<\/thead>\n \n Retaining Structure<\/td>\n By managing water and terrain, we can reduce the very causes of landslides.<\/td>\n Canal construction, horizontal drilling, catch basin construction, drainage tunnel construction, spoil removal, and retaining embankment construction, etc.<\/td>\n<\/tr>\n \n Retaining Wall<\/td>\n Stopping Landslides with the Strength of Structures<\/td>\n Pile Work, Shaft Work, Ground Anchor Work<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n
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\nSince it might fall apart, \u201ccutting it loosely\u201d can sometimes backfire<\/h2>\n
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