SirElliott
Plastic
- Joined
- May 22, 2016
Greetings,
I am in need of some advice. I am with a group of homeowners who find ourselves in a landslide. To date the slide has moved a couple of feet in the last 3 months. The slide has been studied by 2 geotechnical firms. They feel without mitigation, the slide will continue, possibly catastrophically.
Resources are limited, the terrain is challenging. After much research by the geotechnical engineers, the consensus is that we need to get the water off the slide area. Of the various methods to accomplish that, horizontal drains are very efficient for the cost. Normally horizontal drains are metal or PVC pipes that are placed in the slope with a slight up angle. They are placed in bored holes. The pipes are slotted with screen material to keep the soil out. They provide a path for the groundwater to move out of the ground and into collection systems.
Normal horizontal drains will not work in this situation because the ground is still moving. The movement shears off the pipes. After more research we have found a system that uses “wick drains” in place of rigid pipe. Wick drains are tubes made of geotextile fabric around a plastic core. Normally they are placed vertically.
The method that has been developed uses drill pipe that has an ID of at least an 1⅜” and an OD of about 1¾”. The wick drain is threaded into the bore of the drill pipe and fastened to a metal plate with a piece of rebar welded to it. The metal plate is placed over the end of the drill pipe. This push plate keeps soil out of the pipe and acts as an anchor for the end of the wick drain
The pipe is then pushed into the slope with an excavator bucket or a dozer. As each section is advanced, a new section of pipe is added with more wick drain. This is pushed in and repeated until somewhere between 75 and 150 feet of pipe has been placed. Once the pipe is deep enough, a short section of pipe with chain hooks welded to the body is attached, and the pipe withdrawn. The plate with the wick attached to the rebar is anchored in the soil and stays as the pipe is withdrawn. As each section is withdrawn it is removed from the string. When completed the wick provides a path for the water that has been “filtered” by the geotextile cloth tube.
Typically a group of these are placed in a fan pattern from the same place. The operation is moved to the next site. We may need to place as many as 500 drains total.
The problem we have encountered is the drill pipe. We had anticipated locating a used string of an appropriate size drill pipe. Unfortunately the size we need, (something like AQ wire-line drill pipe with an inner diameter of 1 ⅜”) is not very popular. The small sizes are primarily used in geologic core sampling.
We now feel the best course of action is to fabricate a ‘Push pipe system”. We have access to a college machining, metal fabrication, and welding programs. The machining shop has Haas CNC turning centers, as well as the normal manual shop machines.
Our need is the design of the threaded connections. The connections do not have to withstand the rotational forces of drilling since the will be driven into the soil. They do have to withstand the force of driving a 150’ of pipe into the soil, and then the force of withdrawal. We expect the total string to be +-160 feet, made up with 20’ pipes. They also need to be able to be connected and disconnected in difficult conditions. I would think a robust thread is needed. The connections need to have a bore of at least 1 ⅜” The outside diameter could have a diameter of 2 ¼”. I would think the connector should have a larger diameter than the tube.
We have the ability to manufacture the connectors on the CNC lathes, and then weld them to steel tube. Timing is important. A major rain event could trigger catastrophic movement.
Can someone point us to a connector design that is in the public domain (many drill pipe connectors are licenced) that would accomplish what we need?
I have links to engineering articles of the process, if needed. Thanks for your suggestions.
Elliott
Photo of the slide scarpe.
I am in need of some advice. I am with a group of homeowners who find ourselves in a landslide. To date the slide has moved a couple of feet in the last 3 months. The slide has been studied by 2 geotechnical firms. They feel without mitigation, the slide will continue, possibly catastrophically.
Resources are limited, the terrain is challenging. After much research by the geotechnical engineers, the consensus is that we need to get the water off the slide area. Of the various methods to accomplish that, horizontal drains are very efficient for the cost. Normally horizontal drains are metal or PVC pipes that are placed in the slope with a slight up angle. They are placed in bored holes. The pipes are slotted with screen material to keep the soil out. They provide a path for the groundwater to move out of the ground and into collection systems.
Normal horizontal drains will not work in this situation because the ground is still moving. The movement shears off the pipes. After more research we have found a system that uses “wick drains” in place of rigid pipe. Wick drains are tubes made of geotextile fabric around a plastic core. Normally they are placed vertically.
The method that has been developed uses drill pipe that has an ID of at least an 1⅜” and an OD of about 1¾”. The wick drain is threaded into the bore of the drill pipe and fastened to a metal plate with a piece of rebar welded to it. The metal plate is placed over the end of the drill pipe. This push plate keeps soil out of the pipe and acts as an anchor for the end of the wick drain
The pipe is then pushed into the slope with an excavator bucket or a dozer. As each section is advanced, a new section of pipe is added with more wick drain. This is pushed in and repeated until somewhere between 75 and 150 feet of pipe has been placed. Once the pipe is deep enough, a short section of pipe with chain hooks welded to the body is attached, and the pipe withdrawn. The plate with the wick attached to the rebar is anchored in the soil and stays as the pipe is withdrawn. As each section is withdrawn it is removed from the string. When completed the wick provides a path for the water that has been “filtered” by the geotextile cloth tube.
Typically a group of these are placed in a fan pattern from the same place. The operation is moved to the next site. We may need to place as many as 500 drains total.
The problem we have encountered is the drill pipe. We had anticipated locating a used string of an appropriate size drill pipe. Unfortunately the size we need, (something like AQ wire-line drill pipe with an inner diameter of 1 ⅜”) is not very popular. The small sizes are primarily used in geologic core sampling.
We now feel the best course of action is to fabricate a ‘Push pipe system”. We have access to a college machining, metal fabrication, and welding programs. The machining shop has Haas CNC turning centers, as well as the normal manual shop machines.
Our need is the design of the threaded connections. The connections do not have to withstand the rotational forces of drilling since the will be driven into the soil. They do have to withstand the force of driving a 150’ of pipe into the soil, and then the force of withdrawal. We expect the total string to be +-160 feet, made up with 20’ pipes. They also need to be able to be connected and disconnected in difficult conditions. I would think a robust thread is needed. The connections need to have a bore of at least 1 ⅜” The outside diameter could have a diameter of 2 ¼”. I would think the connector should have a larger diameter than the tube.
We have the ability to manufacture the connectors on the CNC lathes, and then weld them to steel tube. Timing is important. A major rain event could trigger catastrophic movement.
Can someone point us to a connector design that is in the public domain (many drill pipe connectors are licenced) that would accomplish what we need?
I have links to engineering articles of the process, if needed. Thanks for your suggestions.
Elliott
Photo of the slide scarpe.