I am involved in the design of a ground improvement behind the quay wall in a project using the deep soil mixing. The deep Soil Mixing (DSM) is called Deep Mixing Method (DMM) in Japan. The quay wall for the project is an anchored type wall that consist of an embeddd wall anchored in a rear row of piles. The soft clay between the wall and the rear row of piles will be improved by the DSM. I was not involved in electing this general arrangement of the wall and ground improvement.
The DSM block may be founded on dense sand, or on a 3 to 4 metres of firm to very stiff clay above that sand, if the DSM rig can not form DSM columns in this relatively stiff clay, so as to found the block on the underlying sand. Hence, this DSM block is likely to be 45 m wide and about 16m or 20 m deep, and will either be founded on 3 to 4 m thick firm to very stiff clay (N60=9 to 20), or on the underlying dense sand. The DSM block and the soft clay behind it will be loaded by 13m high sand fill. Seven metre height of this sand fill will be for land reclamation, and the rest of the sand will be for surcharging the soft clay. The soft clay behind this DSM block will have band drains, i.e. will be improved by surcharging+band drains.
The applied lateral thrust/force on the back of the anchored wall is therefore likely to be = The active earth pressure on the DSM block - the slide resisting force at the base of this block. I think the highest active earth pressure on the wall is likely to be during the surcharging period. As during this period, the active earth pressures will be higher than the active earth pressure after construction, due to the low strength of the clay before surcharging, and due to the high surcharging fill (about 6m of the 13m high fill).
I have the following querries:
1- After placing the 13m thick fill of sand on the soft clay, the excess pore water pressure increment in the clay will initially be high (about 200 kPa) and dissipate with time during the surcharging period . The question would then be: is the total stress analysis suitable to assess the earth pressure on the gravity type wall despite the initial high pore water pressures in the clay? if not, are there publications that advise about how to select the design earth pressure at the begining of the surcharging period?
2- Are there design manuals/ design guides, or even previous case histories that recommend the soil adhesion that is used to assess the active earth pressure on the wall back and the anti slide resistance force at the wall base? The client wants to either follow the BS8002 (soil adhesion is about 67% of the undrained strength of the clay, i.e. cw= 0.67*cu) or follow a sort of formal design manuals/ design guides. Published case history could be useful to convince the client. The CDIT (2002) book compiled by Dr. Terashi & Dr. Kitazume, outlined the current design practices in Japan. The CDIT book recommended the angle of friction on the wall base (when the wall is founded on granular soil, like the dense sand) to be identical to the angle of internal friction of that soil. This proposed value do not match the BS8002 proposed value to be used in the absence of lab test results. The CDIT, however, did not mention the value of the adhesion on the wall bottom, for the walls floating in the clay layers.
to assess the friction resistance on the wall surfaces.
I would be very grateful if you could send me replies to these queries or information about useful publications that address them.
The DSM block may be founded on dense sand, or on a 3 to 4 metres of firm to very stiff clay above that sand, if the DSM rig can not form DSM columns in this relatively stiff clay, so as to found the block on the underlying sand. Hence, this DSM block is likely to be 45 m wide and about 16m or 20 m deep, and will either be founded on 3 to 4 m thick firm to very stiff clay (N60=9 to 20), or on the underlying dense sand. The DSM block and the soft clay behind it will be loaded by 13m high sand fill. Seven metre height of this sand fill will be for land reclamation, and the rest of the sand will be for surcharging the soft clay. The soft clay behind this DSM block will have band drains, i.e. will be improved by surcharging+band drains.
The applied lateral thrust/force on the back of the anchored wall is therefore likely to be = The active earth pressure on the DSM block - the slide resisting force at the base of this block. I think the highest active earth pressure on the wall is likely to be during the surcharging period. As during this period, the active earth pressures will be higher than the active earth pressure after construction, due to the low strength of the clay before surcharging, and due to the high surcharging fill (about 6m of the 13m high fill).
I have the following querries:
1- After placing the 13m thick fill of sand on the soft clay, the excess pore water pressure increment in the clay will initially be high (about 200 kPa) and dissipate with time during the surcharging period . The question would then be: is the total stress analysis suitable to assess the earth pressure on the gravity type wall despite the initial high pore water pressures in the clay? if not, are there publications that advise about how to select the design earth pressure at the begining of the surcharging period?
2- Are there design manuals/ design guides, or even previous case histories that recommend the soil adhesion that is used to assess the active earth pressure on the wall back and the anti slide resistance force at the wall base? The client wants to either follow the BS8002 (soil adhesion is about 67% of the undrained strength of the clay, i.e. cw= 0.67*cu) or follow a sort of formal design manuals/ design guides. Published case history could be useful to convince the client. The CDIT (2002) book compiled by Dr. Terashi & Dr. Kitazume, outlined the current design practices in Japan. The CDIT book recommended the angle of friction on the wall base (when the wall is founded on granular soil, like the dense sand) to be identical to the angle of internal friction of that soil. This proposed value do not match the BS8002 proposed value to be used in the absence of lab test results. The CDIT, however, did not mention the value of the adhesion on the wall bottom, for the walls floating in the clay layers.
to assess the friction resistance on the wall surfaces.
I would be very grateful if you could send me replies to these queries or information about useful publications that address them.
