Bad construction leads to the Geocell slope landslides
In Sep. 2022, I receive an email from a Thailand customer, they want to buy our Geocell accessory-pin head to repair their failed project, and also ask me to help them to analyze the reason for landslides in some areas and how to repair them. Let’s see all their project information and our suggestions below:
The project information told by the customer:
1, Total area of the project is 110,000m2, installed Geocell type height 100mm welding 445mm for slope protection.
2, Slope angle: Inside slope is 45 degrees, another side is 1:2(around 26.6 degrees), for now, only 45 degrees fail.
3, The Geocell panel size they installed is 2.52×10.2m/pc, they did not lay 2.52m as width, but 10.2m as width. For slope construction, should use 2.52 as width, and 10.2 as length. But they did it opposite. they lay like this because they don’t want to cut and have other waste.
4, The infill material is gravel and they did not compact earth fill as standard.
5, All the Geocell panels are separate, they don’t have connection holes and do not use any connection keys. They didn’t connect different adjacent Geocells to a big panel.
6, They use wooden sticks for 1st positioning, and 12mm diameter fiberglass with pin head, length 400mm, 1 sqm/ 1 pc.
Customer analysis of the reasons for landslides:
1, They do not design for trench or dedman lock on the top, and also do not install from top to toe.
2, Geocell size 2.5mx10m panel, used 2.5 m 4 panels connected from top to toe, then I think it separate panel. And no trench for locking the top part .. finally fail.
3, This typical section both sides use geocell on the top 2 sides they not using trench lock.
Customer wants to ask:
Now we want to consultant need to tie 2 geocell sides together with tendons, is it work? And increasing fiberglass pin 800mm x 1 sqm / 1 pc – as total of 110,000 pcs as I ask offer.
The failure reasons we analyzed:
Sir, let me tell you all information from our engineer. First, let’s organize the failed reasons.
1, For this project, all the embankments are soft soil subgrade? right? Which means all the embankments are newly constructed. This is the first reason, for soft soil subgrade, and low carrying capacity. If can’t fix the Geocell well, it is very easy to landslide.
2, As you said, not designed for trench or deadman. If no trench or deadman, we can lay more on the top of the slope, our engineer said for a 1:1 slope it is better to lay 80cm on the top, at least 40-50cm.
3, As you said, should lay from top to toe, 10.2m as one panel, not 2.52m as they laid. As like the below photo, should lay 10.2m from top to toe.
4, Didn’t use connection holes and connection keys to connect all the Geocells to a big panel. As you said, they are all separate panels, if one landslide, the around panels will landslide. They don’t form a whole panel.
5, The pin is too short, especially for soft soil embankments, 40cm doesn’t work. Our engineer recommends 75cm + 10cm(geocell height)=85cm as the suitable length.
And now your client wants to repair the failed area + reinforce the other area to avoid potential landslides, right?
Solutions to repair the landslide areas:
First for the method of repairing the failed area. can tie them with tendons. But you have laid them already and infilled the gravel, how do you tie the tendon? For the failed area, only can remove the landslide area and relayed Geocell, with tendons, or lay 80cm on the top or trench. Or as you said use tendon and deadman. Must lay this way, from top to toe, fix 2.52m in the top and stretch the 10.2m from top to toe. Not stretch the 10.2m from right to left( customer’s wrong way).
Solutions to reinforce the area which may easily to landslides:
And for other not fail areas, if you want to reinforce them, our engineer said that currently only can use the pins to fix them.
1, As you said, add the fiberglass pin length to 80cm. Based on your slope 1:1.5, the soil base subgrade, should use length (0.5-0.75)+Geocell height of 10cm, so the total length for pin 0.6-0.85m, so your length 80cm is no problem.
2, If possible, use the anchor head to connect the separate Geocell to a big panel.
3, 1 sqm/1pc for the inside no problem. It is better to connect them and should use 1pc for every cell in most outside. As like this, use the anchor head to connect adjacent Geocells to a big panel. And if you can’t connect them use Anchor heads, because you have already filled gravel, so you’d better use steel to machine to J-shaped or U-shaped to connect them. The requirements for J-pin.
And the Geocell already fill with gravel, it should very hard to use the pin.
1, for the pin, it is better to use the cuspidal pin. Because the geocells have already filled with gravel.
2, At the top of the slope, every cell must use one pin. As in the above photo, every cell. And inside can use 1pc/sqm.
So now you’d better ask the customer to connect different panels to a big panel, use anchor heads or steel J-pin as I told you yesterday.
Customer’s last question
If they want to tie both edges of geocells with steel wire for every cell, is it OK (better than using the cuspidal pin)?
We consider this for you, but your project has one problem. You did not connect different adjacent Geocells to a big panel.
You use the steel wire to tie, only tie the top two layers, the bottom panels can’t tie, right? Can you understand this? You only can tie the top two layers, the bottom panels can’t tie, because your Geocell did not connect. the bottom panels still need to reinforce, otherwise still easy to landslide.
All in all, in Geocell slope protection projects, the quality of the geocell is important, and the design and construction method are also very critical. Only in this way, the projects can be done well. Otherwise, may cause project failure.
This project is a very good lesson for us! We need to learn from this and prevent similar problems happen again.
