Super practical basic knowledge of geotechnical engineering

      According to the type of rock formation 、 The characteristics of structural plane and the lithology and strength of its constituent rocks , The rock mass is divided into magmatic rocks 、 Metamorphic rock 、 Clastic rock 、 Carbonate rocks and special rocks 5 Engineering geological rocks . Each rock class is further divided into several rock formations , total 18 Rock formation . According to the genetic type of soil 、 Material composition and engineering characteristics , The soil mass is divided into two categories 11 A set of .

Engineering geological characteristics of rock mass

1、 Magmatic rocks

（1） hard — Weak block — Layered basic extrusive rock .

Volcanic lava is massive , Harder — hard , Dry compressive strength 48.0—193.0 MPa , Softening coefficient 0.64—0.99, The stability of rock mass is good ; Pyroclastic rocks are bedded like or bedded , weak — Harder , Dry compressive strength 10.9—56.0 MPa , Softening coefficient 0.43—0.54, The stability of rock mass is poor . The level of mechanical strength is related to the development of rock joints and fissures and the degree of weathering . Moderately weathered basalt is slightly weathered — caller 20—50%; Pyroclastic rocks are easily weathered , Moderately weathered and fragile by hammering .

（2） hard — In harder layers — Acid extrusive rock .

The dry compressive strength of rocks is usually greater than 108 MPa . The mechanical strength of rhyolite varies greatly in vertical and horizontal directions , Under certain conditions, it can become a relatively weak interlayer in the rock formation . Make the stability of rock mass worse .

（3） Hard block intrusive rock .

In the middle of the rock — Coarse grained or porphyritic structure , Massive structure , The fresh is dense and hard , Cracks are not developed , The mechanical strength is generally high , Especially fresh granite , The compressive strength is generally greater than 98 MPa .

2、 Metamorphic rocks

（1） Soft and hard alternate thin — Medium thick layered metamorphic sand shale .

The thickness of rock stratum varies , Soft and hard , The integrity and weathering resistance of rocks vary greatly , Anisotropy of mechanical strength .

Schist 、 Phyllite 、 Slate and other soft rocks , Joint fissures are relatively developed , Vertical dry compressive strength 12.0—113 MPa ; quartzite 、 Metamorphic sandstone 、 Siliceous rock and other hard rocks , Harder — hard , Vertical dry compressive strength 43.0—260 MPa , Highest up to 338 MPa . The dry compressive strength of weathered rock is only 40—90 MPa .

（2） Hard block migmatites .

The rock is massive , Good integrity , hard , Dry compressive strength 59—196 MPa , Strong weathering is 22 MPa .

（3） Weak cataclastic tectonic rock .

The rock is broken , Strong water permeability , The vertical saturated compressive strength of crushed granite is 73 MPa , Partially less than 20 MPa .

3、 Clastic rock

（1） weak — Harder , in — Thick layered red sandstone and mudstone .

The rocks are interbedded with unequal thickness . The mechanical strength varies with different lithology . Sandstone , Conglomerate and other rocks are hard , The dry compressive strength is more than 50 MPa , The dry compressive strength of weathered rock is generally less than 50 MPa . mudstone 、 The vertical dry compressive strength of clay rock is 11.8—17.0 MPa .

（2） Soft and hard alternate thin — Intermediate sand shale .

Shale is often intercalated with sandstone or interbedded with sandstone . The dry compressive strength of sandstone is 100—169 MPa , It is several to ten times higher than schist , The strength of sandstone is easily affected by weathering , Those who are weathered are 3.8—27 MPa , Semi weathered 60—70.3 MPa .

（3） hard — Relatively hard medium thick layered sandy conglomerate .

The rock is dense and hard , Strong water resistance and weathering resistance , High mechanical strength , The compressive strength is more than 98 MPa .

（4） Soft and hard layered clastic rocks intercalated with carbonate rocks .

Carbonate rock 、 Quartz sandstone 、 The compressive strength of siltstone is high , Shale has low compressive strength . However, carbonate rocks are developed due to karst , The strength decreases , Especially in the fracture zone .

4、 Carbonate rocks

The engineering geological characteristics of this rock are mainly related to the degree of rock dissolution .

（1） hard — Hard medium — Thick bedded strong rock dissolved carbonate rock .

Including limestone 、 Dolomitic limestone 、 Dolomite , Karst rate 8—35%, The compressive strength of fresh rock is generally greater than 98 MPa .

（2） hard — Hard medium — Thick layered medium rock molten carbonate rock .

Mainly limestone 、 Dolomitized limestone 、 Biological limestone 、 Dolomite, etc , Solution gaps are generally developed along the fault and fold axis 、 Karst cave 、 Underground river, etc . The karst rate is generally 1.2—3.3%, The depth of karst development is 100 Mi xinnei . Dry strength 69.5—107.7 MPa , Saturated compressive strength 51.0—75.5 MPa , Dry shear strength 8.0—12.7 MPa .

（3） hard — Hard medium — Thick layered weak rock dissolved carbonate rock .

The main rock is limestone 、 Argillaceous limestone 、 Dolomitic limestone 、 Siliceous limestone 、 Dolomite, etc , Fissures and karst are poorly developed , The compressive strength of limestone is 60.7—66.1 MPa .

（4） Soft and hard layered carbonate rocks with clastic rocks .

The main rock is limestone 、 Biological limestone 、 Dolomite 、 Marl mixed with quartz sandstone 、 Shale 、 Carbonaceous shale, etc . The rock strength varies greatly , The compressive strength of limestone can reach 123.2 MPa , The compressive strength of shale is generally 11.5—22.8 MPa , And easy to soften and muddy .

5、 Special rocks

（1） weak — It is hard and thin — Intermediate coal bearing 、 Oil shale red sandstone mudstone .

Fresh lignite is easy to oxidize into fragments , Compressive strength is only 1.82 MPa , Cohesion 202 kpa ; Oil shale foliation is developed , Compressive strength 1.1—2.8 MPa , Cohesion 48—292 MPa ; Gravel 、 Sandstone 、 Engineering geological characteristics and weakness of mudstone — The relatively hard red sandstone mudstone group is quite .

（2） Soft and hard alternate thin — Middle coal bearing sand shale .

The mechanical strength of rock varies greatly , The anisotropy is obvious . Mudstone and shale are easy to soften , And cracks are developed , The rock is broken , Its slope is prone to collapse and deformation .

（3） Soft and hard alternating layered gypsum 、 Calcareous red sandstone and mudstone .

Rocks are easy to soften and dissolve , Often form karst caves 、 Dissolved pore 、 Dissolution ditch, etc . North Guangdong Pingshi 、 Danxia 、 Meitang 、 The limestone conglomerate karst of Upper Cretaceous in pengwu basin is relatively developed , Often become heterogeneous foundation , Unfavorable to engineering construction .

（4） weak — Harder layered coral 、 Shell clastic rock .

The cementation degree of rock is poor . Except that the local strength of shell sandstone in modern intertidal zone is slightly higher , Other strengths are mostly low . According to a small number of samples of bioclastic rocks , The dry compressive strength is 0.9—40.8 MPa , Softening coefficient 0.83—0.91.

Engineering geological characteristics of soil

1、 Sedimentary soil

（1） General clayey soil .

The soil is generally wet — saturated , soft — plastic , Partially flow plastic or hard plastic . soft — The allowable bearing capacity of flow molders is generally less than 100 kpa , The allowable bearing capacity of plastic or hard plastic soil is generally 120 kpa .

（2） Old clay .

The soil is mainly hard plastic , in — Low compressibility , The old clayey soil above the aquifer , The allowable bearing capacity is general 200 kpa . However, there are great differences in the engineering properties of old clayey soils of different causes and ages .

（3） Sandy soil .

The soil has strong water permeability 、 Fast compaction and large internal friction angle . There are many factors affecting its mechanical strength , Generally, the deposition time is early 、 Buried deep , High strength , On the contrary, it is lower . The compactness is loose — There are many middle secret , Generally, from shallow to deep, from loose to dense . When it is below the groundwater level and the buried depth is less than 15 When rice , Sand liquefaction may be caused by strong earthquake or mechanical vibration .

（4） gravels .

Gravelly soil is mainly distributed in rivers 、 Upstream and tributary valleys , Scattered along the coast . Mostly buried under other soil groups , And it is often the bottom gravel layer . The soil has large pores 、 Strong water permeability 、 High shear strength , Slightly dense — Dense ( Naked people live in loose places ), High mechanical strength , Generally, it can be used as a good natural foundation .

（5） Special soil .

Special soil , Mainly muddy soil and peat soil . Muddy soil has high natural water content , And greater than the liquid limit , The void ratio is greater than 1, Strong hydrophilicity , Strong water permeability , Soft plastic — Flow plastic , High pressure contraction , The allowable bearing capacity is less than 90 kpa . The average shear strength of undisturbed soil is 8.4—64 kpa . Peat soil is mostly cow dung , Soft and light , Saturated or oversaturated , With large porosity 、 soft — Flow plastic 、 High compression 、 Thixotropic 、 Low mechanical strength and poor engineering performance . The number of light penetration is 1—17 blow , The allowable bearing capacity is less than 100 kpa .

Besides , There is also diatomite , Its nature is loose and light , High pressure contraction . Strong water absorption when dry , Easy to disintegrate , The intensity is very low .

2、 Slope residual soil

（1） Residual soil of intrusive rock slope .

The soil is clay 、 Sandy soil, etc , It generally contains more quartz gravel . In natural state, it is plastic hard plastic , Medium compressibility , Average compressibility 0.3—0.46 Per megapascal , Average SPT blow count 8.0—21.5 blow . High mechanical strength , And it increases with the increase of depth , The allowable bearing capacity is mostly up to 160 kpa .

（2） Ejected rock slope residual soil .

The soil is clay 、 Loam 、 Sandy soil, etc , Plastic — Hard plastic . According to the test results of two rhyolitic porphyry residual soils in Mei County , The liquid index is less than zero , The average compression coefficient is 0.01 Per megapascal , Compression modulus 16.2 MPa ; The pore ratio of basic volcanic residual soil in Leiqiong area is generally 0.966—2.548, The average compression coefficient is 0.029—0.289 Per megapascal , The allowable bearing capacity of foundation generally reaches 200 kpa .

（3） Clastic rock slope residual soil .

Mainly clay 、 Loam , plastic — Hard plastic , Average compressibility 0.196—0.36 Per megapascal , SPT average blow count 13.7—60 blow , High mechanical strength .

（4） Carbonate slope residual soil .

Mainly clay 、 Gravelly clay 、 Gravelly loam 、 Subsoil , Collectively referred to as red clay . The prominent engineering geological feature of soil mass is that it has certain expansibility , When losing water, the volume shrinks violently , The more serious the water loss , The greater the shrinkage , But the water absorption and expansion is weak , The inflation pressure is very low . Moisture content in natural state 、 Void ratio 、 Plasticity index is high , Mostly hard — Hard plastic . Mainly medium compressibility , The average compression coefficient is 0.008—0.048 Per megapascal .

（5） Metamorphic rock slope residual soil .

Mainly clay 、 Clay with gravel 、 Sandy soil, etc , The strength is generally high , The allowable bearing capacity is up to 250 kpa .

According to the type of rock formation 、 The characteristics of structural plane and the lithology and strength of its constituent rocks , The rock mass is divided into magmatic rocks 、 Metamorphic rock 、 Clastic rock 、 Carbonate rocks and special rocks 5 Engineering geological rocks . Each rock class is further divided into several rock formations , total 18 Rock formation . According to the genetic type of soil 、 Material composition and engineering characteristics , The soil mass is divided into two categories 11 A set of .

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Finite element method for seepage problems in Geotechnical Engineering ： theory 、 Modular programming 、 Open source program hands-on application 01 Preface This course is mainly aimed at the seepage problem in Geotechnical Engineering （ The strength problem will be carried out later 、 Topics such as consolidation problems ）, Use four nights https://mp.weixin.qq.com/s/WlTCSWZArtdm8oRJ1V6Hgg