有geotech的吗，请教问题# CivilEngineering - 土木工程
G*O
1 楼
为个两层的公共建筑提供基础设计参数，暂时没有确定是桩基还是浅基础。
粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
t*d
2 楼
CU
【在 G*O 的大作中提到】
: 为个两层的公共建筑提供基础设计参数，暂时没有确定是桩基还是浅基础。
: 粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
【在 G*O 的大作中提到】
: 为个两层的公共建筑提供基础设计参数，暂时没有确定是桩基还是浅基础。
: 粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
G*O
3 楼
can I ask why? any details?
【在 t******d 的大作中提到】
: CU
【在 t******d 的大作中提到】
: CU
t*d
4 楼
not sure what is your concern. but for clay, typically settlement is a big
issue, and CU is used more extensively than UU for this purpose.
【在 G*O 的大作中提到】
: can I ask why? any details?
issue, and CU is used more extensively than UU for this purpose.
【在 G*O 的大作中提到】
: can I ask why? any details?
w*g
5 楼
I also think it should be 固结不排水（CU）.
【在 G*O 的大作中提到】
: 为个两层的公共建筑提供基础设计参数，暂时没有确定是桩基还是浅基础。
: 粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
【在 G*O 的大作中提到】
: 为个两层的公共建筑提供基础设计参数，暂时没有确定是桩基还是浅基础。
: 粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
G*E
6 楼
I don't know what to say, man.
【在 t******d 的大作中提到】
: not sure what is your concern. but for clay, typically settlement is a big
: issue, and CU is used more extensively than UU for this purpose.
【在 t******d 的大作中提到】
: not sure what is your concern. but for clay, typically settlement is a big
: issue, and CU is used more extensively than UU for this purpose.
G*E
7 楼
why?
【在 w*g 的大作中提到】
: I also think it should be 固结不排水（CU）.
【在 w*g 的大作中提到】
: I also think it should be 固结不排水（CU）.
G*E
8 楼
UU is for sure
CU is optional (in case you have deep foundation or need surcharge the area)
【在 G*O 的大作中提到】
: 为个两层的公共建筑提供基础设计参数，暂时没有确定是桩基还是浅基础。
: 粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
CU is optional (in case you have deep foundation or need surcharge the area)
【在 G*O 的大作中提到】
: 为个两层的公共建筑提供基础设计参数，暂时没有确定是桩基还是浅基础。
: 粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
t*u
9 楼
Both UU and CU are for strength testing. Consolidation test
is for settlement purpose. Normally UU yield less shear strength than
CU. So the answer for the original question is UU. The purpose is to
check bearing capacity.
【在 t******d 的大作中提到】
: not sure what is your concern. but for clay, typically settlement is a big
: issue, and CU is used more extensively than UU for this purpose.
is for settlement purpose. Normally UU yield less shear strength than
CU. So the answer for the original question is UU. The purpose is to
check bearing capacity.
【在 t******d 的大作中提到】
: not sure what is your concern. but for clay, typically settlement is a big
: issue, and CU is used more extensively than UU for this purpose.
t*d
10 楼
sorry, I was wrong about consolidation, but I think UU is used for soil that
has high permeability, for clay, should use CU to get shear strength (c and
phi), isn't that right?
area)
【在 G*******E 的大作中提到】
: UU is for sure
: CU is optional (in case you have deep foundation or need surcharge the area)
has high permeability, for clay, should use CU to get shear strength (c and
phi), isn't that right?
area)
【在 G*******E 的大作中提到】
: UU is for sure
: CU is optional (in case you have deep foundation or need surcharge the area)
m*y
11 楼
Is UU used for the soil with high permeability? why?
t*u
12 楼
Both UU and CU are for clay. Both UU and CU are for strength parameters (c
and phi). Neither of them has anything to do with permeability. UU test
yields phi=0 for saturated clay. UU test result is typically for short-term
strength analysis (undrained). CU test result can be used for either short-
term (short-term in the future) or long-term (with measured pore pressures)
purposes.
that
and
【在 t******d 的大作中提到】
: sorry, I was wrong about consolidation, but I think UU is used for soil that
: has high permeability, for clay, should use CU to get shear strength (c and
: phi), isn't that right?
:
: area)
and phi). Neither of them has anything to do with permeability. UU test
yields phi=0 for saturated clay. UU test result is typically for short-term
strength analysis (undrained). CU test result can be used for either short-
term (short-term in the future) or long-term (with measured pore pressures)
purposes.
that
and
【在 t******d 的大作中提到】
: sorry, I was wrong about consolidation, but I think UU is used for soil that
: has high permeability, for clay, should use CU to get shear strength (c and
: phi), isn't that right?
:
: area)
t*d
13 楼
Thanks, man
This clarity the difference, but still why should be UU for this case? since
CU can be used for both short and long term?
term
)
【在 t***u 的大作中提到】
: Both UU and CU are for clay. Both UU and CU are for strength parameters (c
: and phi). Neither of them has anything to do with permeability. UU test
: yields phi=0 for saturated clay. UU test result is typically for short-term
: strength analysis (undrained). CU test result can be used for either short-
: term (short-term in the future) or long-term (with measured pore pressures)
: purposes.
:
: that
: and
This clarity the difference, but still why should be UU for this case? since
CU can be used for both short and long term?
term
)
【在 t***u 的大作中提到】
: Both UU and CU are for clay. Both UU and CU are for strength parameters (c
: and phi). Neither of them has anything to do with permeability. UU test
: yields phi=0 for saturated clay. UU test result is typically for short-term
: strength analysis (undrained). CU test result can be used for either short-
: term (short-term in the future) or long-term (with measured pore pressures)
: purposes.
:
: that
: and
G*E
14 楼
Think about when the failure could happen
Case 1.During construction
Case 2.Shortly after construction
Case 3.Long time after construction
Clay material has low permeability, so in Case 1 & 2, you can consider it is
undrained condition. Therefore, pore pressure can easily be built upon and
the pore pressure will reduce the effective stress of clay. Most of the time
, Case 1 & 2 are more critical because of the undrained condition.
For LZ's question, you need make sure that the building can be bu
【在 t******d 的大作中提到】
: Thanks, man
: This clarity the difference, but still why should be UU for this case? since
: CU can be used for both short and long term?
:
: term
: )
Case 1.During construction
Case 2.Shortly after construction
Case 3.Long time after construction
Clay material has low permeability, so in Case 1 & 2, you can consider it is
undrained condition. Therefore, pore pressure can easily be built upon and
the pore pressure will reduce the effective stress of clay. Most of the time
, Case 1 & 2 are more critical because of the undrained condition.
For LZ's question, you need make sure that the building can be bu
【在 t******d 的大作中提到】
: Thanks, man
: This clarity the difference, but still why should be UU for this case? since
: CU can be used for both short and long term?
:
: term
: )
x*g
15 楼
什么样的两层公共建筑？为什么要做三轴？
一般土的承载力，我认为做直剪就够了，主要原因是Buget和时间的考虑。如果非要做
三轴，那么首先考虑的是UU.原因是UU相对于CU成本低，试验需要的时间短，据此设计
偏保守。对同一粘土层，如果做20个直剪和做一个CU相比，你感觉哪一种更可靠！
做CU的目的是为了获得高的土的强度参数来减少设计成本，但作为岩土工程师，没有人
愿意承担高的风险。
如果从学术角度来看，施加土的上部荷载进行固结，然后在建筑荷重下做不排水剪。
一般土的承载力，我认为做直剪就够了，主要原因是Buget和时间的考虑。如果非要做
三轴，那么首先考虑的是UU.原因是UU相对于CU成本低，试验需要的时间短，据此设计
偏保守。对同一粘土层，如果做20个直剪和做一个CU相比，你感觉哪一种更可靠！
做CU的目的是为了获得高的土的强度参数来减少设计成本，但作为岩土工程师，没有人
愿意承担高的风险。
如果从学术角度来看，施加土的上部荷载进行固结，然后在建筑荷重下做不排水剪。
p*o
16 楼
大多数情况下是排水，有些较特殊情况要考虑不排水，比如在施工阶段迅速增加的荷载
下，一般认为孔隙水没时间排出，这时就需要考虑不排水。
【在 G*O 的大作中提到】
: 为个两层的公共建筑提供基础设计参数，暂时没有确定是桩基还是浅基础。
: 粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
下，一般认为孔隙水没时间排出，这时就需要考虑不排水。
【在 G*O 的大作中提到】
: 为个两层的公共建筑提供基础设计参数，暂时没有确定是桩基还是浅基础。
: 粘土层的三轴试验是应该做固结不排水（CU）还是不固结不排水（UU）。
m*y
17 楼
UU and direct shear should be enough. There is no need to do CU.
G*E
18 楼
So you think 20 DS will be cheaper than 1 CU?
Typically, cost wise, 2 DS = 1 CU.
So you think 10 CU will be less reliable than 20 DS?
BTW: It does not make sense to compare DS with CU, because DS is hard to
control drainage and shear area. At least, I don't trust shear strength
results from DS for clay.
Don't understand. What do you mean "高的土的强度参数"? and why "没有人愿意承
担高的风险"?
【在 x*******g 的大作中提到】
: 什么样的两层公共建筑？为什么要做三轴？
: 一般土的承载力，我认为做直剪就够了，主要原因是Buget和时间的考虑。如果非要做
: 三轴，那么首先考虑的是UU.原因是UU相对于CU成本低，试验需要的时间短，据此设计
: 偏保守。对同一粘土层，如果做20个直剪和做一个CU相比，你感觉哪一种更可靠！
: 做CU的目的是为了获得高的土的强度参数来减少设计成本，但作为岩土工程师，没有人
: 愿意承担高的风险。
: 如果从学术角度来看，施加土的上部荷载进行固结，然后在建筑荷重下做不排水剪。
G*E
19 楼
Copied from a textbook.
Disadvantages of the DS test include:
1. Difficult or impossible to control drainage, especially for fine-grained
soils.
2. Failure plane is forced--may not be the weakest or most critical plane in
the field
3. Non-uniform stress conditions exist in the specimen.
4. The principal stresses rotate during shear, and the rotation cannot be
controlled.Principal stresses are not directly measured.
Because the drainage conditions during all stages of the test markedly
influence
【在 x*******g 的大作中提到】
: 什么样的两层公共建筑？为什么要做三轴？
: 一般土的承载力，我认为做直剪就够了，主要原因是Buget和时间的考虑。如果非要做
: 三轴，那么首先考虑的是UU.原因是UU相对于CU成本低，试验需要的时间短，据此设计
: 偏保守。对同一粘土层，如果做20个直剪和做一个CU相比，你感觉哪一种更可靠！
: 做CU的目的是为了获得高的土的强度参数来减少设计成本，但作为岩土工程师，没有人
: 愿意承担高的风险。
: 如果从学术角度来看，施加土的上部荷载进行固结，然后在建筑荷重下做不排水剪。
Disadvantages of the DS test include:
1. Difficult or impossible to control drainage, especially for fine-grained
soils.
2. Failure plane is forced--may not be the weakest or most critical plane in
the field
3. Non-uniform stress conditions exist in the specimen.
4. The principal stresses rotate during shear, and the rotation cannot be
controlled.Principal stresses are not directly measured.
Because the drainage conditions during all stages of the test markedly
influence
【在 x*******g 的大作中提到】
: 什么样的两层公共建筑？为什么要做三轴？
: 一般土的承载力，我认为做直剪就够了，主要原因是Buget和时间的考虑。如果非要做
: 三轴，那么首先考虑的是UU.原因是UU相对于CU成本低，试验需要的时间短，据此设计
: 偏保守。对同一粘土层，如果做20个直剪和做一个CU相比，你感觉哪一种更可靠！
: 做CU的目的是为了获得高的土的强度参数来减少设计成本，但作为岩土工程师，没有人
: 愿意承担高的风险。
: 如果从学术角度来看，施加土的上部荷载进行固结，然后在建筑荷重下做不排水剪。
r*8
20 楼
I would say UU & CU.
UU for short term, CU for long term.
For normally consolidated clay and loose sand, short term is critical, for
over-consolidated clay and dense sand, long term is critical.
SHANSEP is pretty good test, only using CU, if you can accumulate your local
data, because fewer tests and lower total cost.
UU for short term, CU for long term.
For normally consolidated clay and loose sand, short term is critical, for
over-consolidated clay and dense sand, long term is critical.
SHANSEP is pretty good test, only using CU, if you can accumulate your local
data, because fewer tests and lower total cost.
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