ysna
Geotechnical
- Aug 27, 2015
- 16
Hi, I'm working for a consulting engineering, responsible for designing restoration and retrofitting plans for a two story adobe masonry building of historical significance. The building is built upon an alluvial fan with more than 20 meters of horizontally bedded layers of gravel and sand alluvial deposits with little or no bond between aggregates with some boulders of more than 80 centimeters of diameter. Based on our crack pattern surveys of the building, rophly more than 90 percent of the cracks are vertical cracks that are more intensive at ground floor or at middle or bottom half of the walls. Most of these cracks are still active. We believe that there may be a mass wasting phenomenon happening underneath some parts of this building causing this cracks.
The building is built near the apron of the fan with approximately 10 percent slop in neighboring area. It is built in an area of semi-arid climate with cold winters and hot summers. There is also rapid changes in soil water content due to flash flood incidents common in the region. There is a water feature built around, so that water flows from a seasonal spring and rain water flows are directed towards three connected water ponds built in front side, inside and back side of the building. These ponds are not insulated so well, and there is some evidence of leakage in them. Given this situation, We think the soil underneath building is prone to creep.
The building site is underlain by a layer of loom fill (mostly SC) of approximately two meter thickness, probably brought here for gardening in a somewhat inhabitant layers of soil. Walls of the building is placed on top of a rockery layer which is built to level surface of natural soil.
Speaking of creep evidence, other than the forms of cracks on the building's walls and surrounding walls of the site (which are mostly vertical and active), one can say, there is no particular sign of creep incident in the region. The building is surrounded with trees, pavements and fences, but there is no recognizable evidence of creep on them. There is also a road alongside this fan from uphill to downhill, also with no recognizable evidence of creep on it.
Given these hopefully detailed information, I would greatly appreciate to have your comments on the followings:
1. In my opinion, because all the features other than the building itself, i.e. trees, fences, pavements and the road, are built in and upon a fill layer of approximately two meter depth, so there is no evidence of creep recognizable on them (the fill itself is not creep prone). Also I think, it is weight of the two story building (estimated about 1 ton per square meter) that triggers the creep behavior of the underlain soils. Is that sounds a logical argument to you?
2. Going around the neighboring area, I could find some evidence of creep on top layer of soil right behind the building's backyard wall (attached file). Considering that these ripples that flow the contour of slop, are caused by creep in top soil layer, can we say that creep behavior also happens in the underlain bed of the building?
3. From a geotechnical engineer's viewpoint, what is your recommendation to prevent active differential lateral movements of building parts that are the main cause of vertical cracks?
The building is built near the apron of the fan with approximately 10 percent slop in neighboring area. It is built in an area of semi-arid climate with cold winters and hot summers. There is also rapid changes in soil water content due to flash flood incidents common in the region. There is a water feature built around, so that water flows from a seasonal spring and rain water flows are directed towards three connected water ponds built in front side, inside and back side of the building. These ponds are not insulated so well, and there is some evidence of leakage in them. Given this situation, We think the soil underneath building is prone to creep.
The building site is underlain by a layer of loom fill (mostly SC) of approximately two meter thickness, probably brought here for gardening in a somewhat inhabitant layers of soil. Walls of the building is placed on top of a rockery layer which is built to level surface of natural soil.
Speaking of creep evidence, other than the forms of cracks on the building's walls and surrounding walls of the site (which are mostly vertical and active), one can say, there is no particular sign of creep incident in the region. The building is surrounded with trees, pavements and fences, but there is no recognizable evidence of creep on them. There is also a road alongside this fan from uphill to downhill, also with no recognizable evidence of creep on it.
Given these hopefully detailed information, I would greatly appreciate to have your comments on the followings:
1. In my opinion, because all the features other than the building itself, i.e. trees, fences, pavements and the road, are built in and upon a fill layer of approximately two meter depth, so there is no evidence of creep recognizable on them (the fill itself is not creep prone). Also I think, it is weight of the two story building (estimated about 1 ton per square meter) that triggers the creep behavior of the underlain soils. Is that sounds a logical argument to you?
2. Going around the neighboring area, I could find some evidence of creep on top layer of soil right behind the building's backyard wall (attached file). Considering that these ripples that flow the contour of slop, are caused by creep in top soil layer, can we say that creep behavior also happens in the underlain bed of the building?
3. From a geotechnical engineer's viewpoint, what is your recommendation to prevent active differential lateral movements of building parts that are the main cause of vertical cracks?