SPT >50 in CLAYEY SOIL 1

[Kpaudel]

Dear friends,


U ever found such a hard clayey soil having SPT nearly 80, specific gravity nearly 2.3, organic content nearly 30%, natural moisture nearly 80%, Liquid limit nearly 90%, unconfined compressive value 500 kPa...????? my senior officer cannot accept our findings. They said they never experience SPT more than 30 in clayey soil. They want to term it as rock but we are very clear its clay. i am going to recommend skin pile but they said open shallow foundation is OK.. Give me your opinion.. wts kind of footing is appropriate??? Load on bottom of footing is approximately 40000 KN from bridge superstructure and substructure......

 

[fattdad]

It would help to know the geologic setting. I mean it could be IGM (Intermediate geologic materials - a.k.a., highly weathered rock) derived from some claystone or such. It could be lacustrine deposits overriden by a glacier.

Are there any secondary disconuitities (folds, fractures, joints, faults)? Does the "soil" display any rock-like texture? Where in the world is the site?

Is the N>50 clay a 2 ft layer, a 20 ft layer or a 200 ft layer (i.e., how far did the borehole penetrate)?

f-d

¡papá gordo ain’t no madre flaca!

 

[cvg]

I have seen claystone /siltstone lying below Holocene stream deposits. Dry density from 60 - 120 pcf. Rock cores and samples were taken and had SPT up to 80, RQD up to 70, LL up to 69 and unconfined compressive strength ranging from 4,000 up to 26,000 (where there was some sandstone in the core also). It was classified as "extremely weak to locally very strong rock". But keep it dry because it gets really slick in the rain.

 

[Kpaudel]

For your reference,

It’s on river bank and outlet of lacustrine deposit, rock is found nearly 50m below, at a depth of 25m to 33m there is coarse clean sand, where SPT ranges from 20-30, SPT value is more than 50 at 3 m depth on clayey layer and SPT value is more than 80 at 15 m on clayey layer depth below general ground, if its weathered rock then what about organic content more than 30%...Unit weight (Bulk density) is nearly 1.9 to 2.1 t/m2.

As per geological information there is no fault and fold, about 500 m upstream there is gorge of an about 150 m depth contains sandstone on both banks.

 

[BigHarvey]

Just one question : are you living on March ?

 

[Kpaudel]

Hahaha no sir...its on south asia NEPAL...

 

[detate]

The N-values can be exaggerated by the organic material in the clay soil if it is fibrous or woody in nature. Otherwise, I agree with fattdad that decomposed/highly weathered mudstone or shale could test as a clay and have very high N-values.

Doug Tate
southeast USA

 

[oldestguy]

How about the rig? Are you sure it is not all fouled up with crud?