1.0.1 This specification is formulated with a view to implementing the national technical and economic policies, achieving safety and usability, advanced technology and economic rationality, ensuring quality and protecting environment in the geotechnical investigation in soft clay area.
1.0.2 This specification is applicable to geotechnical investigation for construction fields and subsoils in soft clay areas.
1.0.3 For the geotechnical investigation in soft clay area, the characteristics in soft clay area shall be reflected, experience in the area emphasized, data extensively collected, construction and design requirements understood in detail, investigating and analyzing carefully, and putting forward true and accurate survey report with complete data and correct assessment.
1.0.4 For important buildings and soft clay subsoils with special requirements or engineering having influence on environment, in construction and application, monitoring should be carried out according to the need of engineering construction.
1.0.5 Geotechnical investigation in soft clay area shall not only meet the requirements stipulated in this specification but also comply with those in the current relevant ones of the nation.
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2 Terminologies and Symbols
2.1 Terminologies
2.1.1 Soft clay
Fine-grained soil with natural void ratio larger than or equal to 1.0, natural moisture content larger than the liquid limit, with high compressibility, low strength, high sensitivity, low permeability and high rheological property, and possibly occurring earthquake subsidence under the action of large earthquake force, including sludge, mucky soil, peat, peaty soil, etc.
2.1.2 Thin wall sampler
Linerless sampler with inner diameter of 75mm~100mm, area ratio not larger than 10% (inner clearance ratio of 0) or area ratio of 10％~13％ (inner clearance ratio of 0.5~1.0).
2.1.3 Sensitivity
Ratio of strength of undisturbed cohesive soil to that of remoulded soil with the same moisture content as undisturbed cohesive soil.
2.1.4 Rheological property
Soil property that the long term strength is smaller than the transient strength due to slow and long-term shear deformation under the action of long duration load.
2.1.5 Thixotropy
Cohesive soil property that its structure is damaged and strength lost under disturbance and strength gradually recovers after the disturbance stops.
2.1.6 Compressed layer
Generic term of soil layer within the subsoil subsidence calculation depth.
2.1.7 Soft clay earthquake subsidence
Phenomena of ground or subsoil subsidence caused by soft clay softening due to earthquake.
2.1.8 Ground subsidence, land subsidence
Subsidence of ground in large area due to soil layer consolidation and compaction, which is caused by groundwater recession for excessively pumping groundwater in large area, or subsidence of ground caused by large area loading.
2.1.9 Negative skin friction, dragdown
Downward friction generated by soil to pile side surface when the amount of subsidence of soil around the pile is larger than the amount of vertically downward displacement of the pile, with the direction opposite to that of the positive friction.
2.1.10 Water level for prevention of up floating
Groundwater level of field required upon the up floating prevention evaluation on the underground buildings (structures) and ensuring safe and reasonable prevention of up floating.
2.2 Symbols
Ap——Area of pile tip;
a——Compression coefficient;
a1-2——Compression coefficient at the vertical pressure of 100kPa~200kPa;
b——Foundation bottom width;
Cc——Compression exponent;
Ch——Radial consolidation coefficient;
Cs——Swelling index;
Cu——Vane-shear strength; undrained shear strength;
Cv——Vertical consolidation coefficient;
c——Cohesion;
d——Foundation embedded depth or pile diameter;
di——Thickness of the ith soil layer;
ds——Depth of static cone penetration test point;
dw——Depth of groundwater level;
Em——Pressuremeter modulus;
E0——Deformation modulus of soil;
Es——Compression modulus of soil;
e——Void ratio;
e0——Natural void ratio;
Flei—Liquefaction strength ratio;
fa——Characteristic value of subsoil bearing capacity after depth width correction;
fak——Characteristic value of subsoil bearing capacity;
fr——Rock saturated uniaxial ultimate compressive strength;
fs——Side wall skin friction of double bridge probe
H——Layer thickness;
IL——Liquidity index;
IlE——Liquefaction index;
IP——Plasticity index;
K——Safety factor;
k——Permeability coefficient;
L——Pile length, segment pile length or foundation length;
N一一Measured blow count of standard penetration test;
N10——Measured blow count of light dynamic penetration test;
Nr, Nq, Nc——Subsoil bearing capacity coefficient;
Ncr——Critical value of standard penetration blow count in liquefaction appraisal;
N0——Reference value of standard penetration blow count in liquefaction appraisal;
n——Number of soil layers;
p——Base pressure;
pc——Preconsolidation pressure of soil;
p0——Initial pressure of pressuremeter test; base additional stress;
pL——Ultimate pressure of pressuremeter test;
ps——Specific penetration resistance of single bridge probe;
psb——Average of specific penetration resistance by static cone penetration around pile end;
pscr, ps0——Critical value and reference value of specific penetration resistance respectively;
pz——Effective deadweight pressure of soil;
py——Critical edge pressure in pressuremeter test;
Qu——the vertical ultimate bearing capacity of single pile;
qc——Double bridge probe tip resistance;
qccr, qc0——Critical value and reference value of tip resistance respectively;
qpk——Standard value of ultimate end resistance;
qsik——Standard value of ultimate side resistance of the ith soil layer along pipe;
qsis——Ultimate side resistance of soil along pile;
qu——Unconfined compressive strength;
Ra——Characteristic value of vertical bearing capacity of single pile;
Rf——Friction-resistance ratio of cone penetration;
Sc——Foundation soil consolidation subsidence quantity;
Sr——Saturation;
St——Sensitivity;
s——Foundation subsidence quantity; loading test subsidence quantity;
u——Pile shaft circumference;
vse——Equivalent shear wave velocity of soil layer;
w——Water content;
wP——Plastic limit;
wL——Liquid limit;
wi——Weight function value of layer influence at the ith measuring point;
zn——Subsidence calculation depth;
αb——Pile end resistance correction coefficient;
β——Correction coefficient for side resistance of soil around pile;
ηd, ηb——Correction coefficient of characteristic value of subsoil bearing capacity for foundation embedded depth and width;
γ——Unit weight of soil;
γ0——Unit weight of soil above the foundation bottom;
φ——Internal friction angle;
ρc——Percentage of clay particles content;
ψs——Empirical coefficient of subsidence calculation;
μ——Poisson's ratio of soil;
K20——Permeability coefficient of specimen at standard temperature (20℃).
