Ating's Blog: Sinkhole (Lubang Runtuhan)

Hi. I’m Riesty Rahajeng, but I’m often called Ating. I don’t know why, but in here right now, I'm not discuss about that, hehe.

I’m a student of Civil Engineering in Conservation University, Semarang State University.

My background to write this, except because task, I will share about the lesson that I’ve learned. Yeah, Mr. Alfa gives us (his student) a task for TIK lecture, to write anything about Civil Engineering. I have an idea to write about Sinkhole that my task in first semester.

Mr. Untoro, Rekayasa Geologi lecture, gave us a task for Final Exam to explain an accident about geology. I’m searched on internet and I found interest thing that happened in Guatemala. Sinkhole.

Sinkhole

A sinkhole, also known as a sink, snake hole, swallow hole, swallet, doline, or cenote, is a natural depression or hole in the Earth's surface caused by karst processes — for example, the chemical dissolution of carbonate rocks or suffosion processes insandstone. Sinkholes may vary in size from 1 to 600 metres (3.3 to 2,000 ft) both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may be formed gradually or suddenly, and are found worldwide. The different terms for sinkholes are often used interchangeably.

I took a case that happened on May, 2010, a vertical hole that appeared down town Guatemala. The hole measures approximately has diameter 20 m and depth 30 m, gulp a building three floors (shaped little factory), a house and several electricity poles.

This is the article about that case :

How To Fix a Giant Sinkhole

The cement method vs. the graded-filter technique.

A sinkhole, 65 feet across and 100 feet deep,swallowed up a small factory and some telephone poles in Guatemala City last weekend. Police have been stationed around the hole to prevent bystanders from falling in, and those who live nearby are staying elsewhere for the time being. How do you fill a massive sinkhole in the middle of a major urban area?

With cement or rocks. Sinkholes develop when water flows through pores in bedrock and gradually enlarges them. When these subterranean cavities get big enough, the ground above collapses and fills them in. Guatemala City's last major crater, which opened in 2007, dropped three houses 330 feet below the city's streets. The government spent $2.7 million redirecting sewer pipes around the area and filling the hole with cement. This week's sinkhole will probably be filled the same way.

It's not clear whether cement is the best option, however. A 6,500-cubic-foot wad of concrete may serve to concentrate water runoff in other areas, leading to more sinkholes. Many engineers prefer the graded-filter technique, in which the hole is filled with a layer of boulders, then a layer of smaller rocks, and, finally, a layer of gravel. This fills the hole, more or less, while permitting water to drain through the area.

No matter what is used to fill the crater, more sinkholes are on the way. Guatemala City's location and leaky sewage system make it particularly prone to these events. The capital lies downhill from seven major volcanoes, two of which are active members of the Pacific Ring of Fire. For hundreds of thousands of years, the gargantuan Amatitlan Calderadumped volcanic ash on the ground where the city now sits. As a result, the local bedrock consists mostly of loose volcanic pumice. (Many cities sit atop volcanic deposits, but the ash from Amatitlan has not had the time or the appropriate pressure and temperature conditions to compress into a solid, reliable foundation.)

Large sinkholes sometimes open up in North America, too. While the process is similar, the geology is different. The most sinkhole-prone parts of the U.S. consist of limestone and dolomite bedrock rather than volcanic ash. The easily-eroded materials are responsible for natural wonders like New Mexico's Carlsbad Caverns, but they can also lead to a terrific collapse. Florida and Kentucky are the most vulnerable states. In 1994, a15-story-deep sinkhole opened near Mulberry, Fla.

Cover-collapse sinkholes—the dramatic and instantaneous events that swallow up unsuspecting victims—are relatively rare. Most sinkholes happen slowly over time, and bottom out at a foot or two. As the bedrock erodes, the ground begins to subside at an imperceptible rate. When the soil finally lowers to the level of the groundwater, there is a small, visible drop.

But in my task that I wrote with bahasa, this is the Accident Mechanism and Completion Recommendation.

Mekanisme Kejadian (Accident Mechanism)

Hujan lebat dari badai tropis Agatha dan drainase yang buruk (adanya kebocoran pipa bawah tanah) memicu lubang runtuhan besar di Guatemala. Lubang runtuhan di Guatemala terjadi akibat pengikisan batuan di dasar, mengikis rongga bawah tanah yang kemudian runtuh. Resiko lubang alami jenis ini banyak terdapat di negara bagian Amerika Serikat. Secara keseluruhan, resiko terulangnya lubang alami di Guatemala adalah tinggi dan tidak terduga.

Kota Guatemala sendiri dikelilingi oleh gunung aktif dimana termasuk dalam jajaran Ring of Fire. Selama ratusan tahun, kaldera raksasa dari Amatlitan menumpuk tanah dimana kota berada, akibatnya fondasi lokal Kota Guatemala sebagian besar terdiri dari batu apung vulkanik lepas yang tidak mempunyai waktu dan tekanan yang tepat untuk mengepresnya menjadi padatan yang baik.

Dapat disimpulkan bahwa sinkhole ini terjadi dikarenakan pengikisan tanah yang terjadi karena adanya hujan deras badai tropis Agatha. Pengikisan ini dari air dari kebocoran pipa yang membawa partikel-partikel tanah (yang merupakan abu vulkanik) dan meninggalkan kelonggaran partikel-partikel yang secara bertahap membentuk suatu void. Permukaan yang semula baik dan utuh, tiba-tiba tidak mendapat dukungan dari dalam tanah, dan untuk mencapai suatu kestabilan maka lubang runtuhan itu tiba-tiba terjadi.

Rekomendasi Penyelesaian (Completion Recommendation)

Sinkhole yang terjadi di sini dikarenakan aliran yang membawa partikel tanah sehingga menjadi terkikis dan menyebabkan adanya lubang runtuhan. Lubang runtuhan yang terjadi berada di area jalan. Lokasi Guatemala sendiri didukung dengan sistem drainase yang buruk membuat wilayah Guatemala beresiko dengan adanya lubang runtuhan seperti ini, dan dapat terjadi lagi secara tidak terduga.

1. Mengetahui penyebab lubang runtuhan. Penyebabnya adalah adanya aliran air di bawah tanah yang mengikis tanah (abu vulkanik) dan meninggalkan void.

2. Menggali lubang runtuhan. Menggali hingga mencapai sublayer batuan di bawah tanah. Jika harus menggali lebih dalam, diperlukan bentuk parit untuk menahan sisi daerah digali. Akan lebih baik apabila menggali dan menemukan titik kerusakan utama kebocoran. Maka segeralah memperbaiki pipa dan mengisi lubang.

3. Mengisi void agar tidak terjadi erosi lebih lanjut setelah lubang digali. Mulai dengan penempatan beberapa batu besar dengan lapisan yang cukup tebal. Tambahkan di atasnya batu yang lebih membentuk lapisan yang cukup tebal juga. Tambahkan di atasnya batu lebih kecil secara terus menerus hingga lapisan paling atas untuk lapisan (ukuran) berpasir di bawah lapisan tanah yang gelap.

4. Meletakkan lapisan kain lansekap atas kerikil untuk menjaga pasir dan tanah dari pengikisan oleh air yang turun melalui lapisan batuan, dan mengisi ke atas lapisan subsoil dengan pasir. Memadatkan bawah pasir, dan mengisi lubang yang tersisa dengan tanah lapisan atas.

Memeriksa daerah untuk beberapa hari. Bila lubang terbuka lagi, maka konsultasikan dengan ahli geologi, memastikan agar tidak berpotensi merusak struktur di sekitarnya.

And I will show you other Sinkhole, beautiful Sinkhole or pity Sinkhole.

Picher, Oklahoma. Tin and zink mining activity during through years leave Picher City, Oklahoma full of sinkholes. The top of several mines can’t again support heavy of earth and causes many mines collapses. In this time, the city to be stacks of mine activity rubbish and leave many king sized sinkhole.

The Great Blue Hole, Belize. Great Blue Hole is sinkhole under water in the middle of sea. This hole has circle formed, the vast is more than 300 m and the depth is 124 m. how beautiful!