We have been asked to check an area of hillside movement. There are several homes that have been damaged in a severe to moderate manner due to a hill sliding. There is a sand seam that has caused the problem. They aren't worried about movement of the homes, but movement of the earth itself. They have perfromed some drainage work and are trying to figure out if they have stopped the problem. They aren't worried about 1 or 2 hundredths of a foot of movement, but are looking for larger numbers like a tenth of a foot or more. Elevation is secondary, they are more worried about the horizontal movement.
The contractors plan was to drive some rods in the side yard behind the houses as it is the area behind the houses that is moving, and shoot them from the street in front of the house. We will come back latter and shoot these again in a few weeks or months latter. There will be 2 bars in each side yard behind each house, one about 30 feet and another at 60 feet behind the house. They are pretty sure the street isn't moving. I told him to drive in smooth bars about 5 feet long at these places and they will cut X's in the curbs in front of the houses to shoot the bars from. We have a premanent base in town we can use, I was going to shoot the X's with RTK just to get a rough idea that they aren't moving over time along with the street. I was going to run a traverse between the X's on the curb and just figure the location and elevations of the rods by using a total station. I was going to set a tripod and tribrach up to shoot the rods, just to get a little better accuracy.
Does this sound like a good plan? Once again, I'm not worried about trying to get this stuff shot to the nearest 0.005' The movement of the soil and houses is so great it can be measured in feet in the horizontal and vertical in places. It's pretty shocking. They are just trying to get a handle on if the movement has stopped in some places, but not others.
I'd drive longer rods for monitoring if it were me. Also, you said you would use RTK, but where will the base be? It must be in a stable environment to assure it hasn't moved either.
We've done a few of these over the years, and if I were you, I'd shoot the road as well. We have a street here we did this on and the developer cut a hill and now all of his curb and gutter is 3' inside the right-of-way line due to the hill sliding and pushing the street.
The base is permanent mounted on top of a 7 story building at the university.
I just plan on using the RTK to check and make sure the street isn't moving.
Should you be monitoring deep set rods and very shallow rods at surface?
RADU
This movement is man caused and compared to the movement over the last 50 years is sudden. Are the original ownership lines holding or are they moving with the monuments in that area?
jud
RADU, I don't know? I could set a spike near each rod and keep track of both.
JUD, these are duplexs and I'm not sure if they own very much ground outside the building, but I think they own a small yard. I don't think the people are worried about the boundary corners moving, but yes, they would have moved, some maybe as much as a few feet.
> I'd drive longer rods for monitoring if it were me.
The top layer of soil could be moving over a stable lower layer. I'd want long and short bars in pairs.
> I don't think the people are worried about the boundary corners moving, but yes, they would have moved, some maybe as much as a few feet.
Never mind the boundary, these are ready made long term monitoring points whose original position has been established.
Shouldn't a Geologist be consulted in this matter??
you need to be monitoring above and below the slip plane.