土壤行为基础：詹姆斯·K·米切尔与肯尼思·索加

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"Fundamentals of Soil Behavior" 是一本由James K. Mitchell 和 Kenichi Soga合著的关于土力学基础的书籍，第三版由John Wiley & Sons, Inc.于2005年出版。本书深入探讨了土壤行为的基本原理，是土木工程、地质工程以及环境科学等相关领域的核心参考资料。它涵盖了土壤的物理性质、机械行为、土壤与水的关系、土壤的压缩和强度特性、土壤动力学以及土壤的稳定性和渗透性等多个关键主题。 1. 土壤的物理性质：书中详细介绍了土壤颗粒的大小分布（粒径分析）、孔隙结构、密度、湿度、含水量等基本概念，这些都是理解和预测土壤行为的基础。 2. 土壤力学：讲解了土壤的应力应变关系，包括弹性、塑性、剪切强度和抗压强度等。这部分内容对于分析建筑物地基的承载能力至关重要。 3. 土壤与水的相互作用：探讨了土壤中的水分状态，如饱和度、毛细现象、渗透率和排水性能，这些在地下水控制、土体稳定性分析和环境工程中都有重要应用。 4. 土壤的压缩和强度特性：讨论了土壤在荷载作用下的体积变化，包括即时和延迟压缩，以及有效应力原理。此外，还涵盖了Mohr-Coulomb破坏准则，用于预测土壤的剪切强度。 5. 土壤动力学：这部分内容涉及到地震工程，讲解了土壤对振动的响应，包括动态应力、地震波传播和场地效应，这对于地震区的建筑安全设计具有重要意义。 6. 土壤的稳定性和渗透性：分析了土壤的稳定性问题，如滑坡、土体流动等灾害，以及土壤的渗透性对液体流动的影响，对于防洪、排水系统设计和污染控制有指导作用。 7. 实验方法：书中也包含了各种实验技术，如直剪试验、三轴试验、孔隙压力测量等，这些实验方法是确定土壤参数和验证理论模型的关键工具。《土壤行为基础》为读者提供了全面而深入的土壤科学知识，适合大学土木工程专业学生和专业工程师作为教材或参考书，帮助他们理解并解决实际工程中的土壤相关问题。同时，它也是研究土壤环境影响、地基处理、地下结构设计等领域的科学家和实践者的重要参考资料。

SOIL FORMATION

Figure 2.5 Bowen’s reaction series of mineral stability. Each

mineral is more stable than the one above it on the list.

Mineralogy textbooks commonly list determinative

properties for about 200 minerals. The list of the most

common rock- or soil-forming minerals is rather short,

however. Common minerals found in soils are listed in

Table 2.1. The top six silicates originate from rocks by

physical weathering processes, whereas the other min-

erals are formed by chemical weathering processes.

Further description of important minerals found in

soils is given in Chapter 3.

2.5 WEATHERING

Weathering of rocks and soils is a destructive process

whereby debris of various sizes, compositions, and

shapes is formed.

The new compositions are usually

more stable than the old and involve a decrease in the

internal energy of the materials. As erosion moves the

ground surface downward, pressures and temperatures

in the rocks are decreased, so they then possess an

internal energy above that for equilibrium in the new

environment. This, in conjunction with exposure to the

atmosphere, water, and various chemical and biological

agents, results in processes of alteration.

A variety of physical, chemical, and biological proc-

esses act to break down rock masses. Physical proc-

esses reduce particle size, increase surface area, and

increase bulk volume. Chemical and biological proc-

esses can cause complete changes in both physical and

chemical properties.

A general deﬁnition of weathering (Reiche, 1945; Keller, 1957) is:

the response of materials within the lithosphere to conditions at or

near its contact with the atmosphere, the hydrosphere, and perhaps

more importantly, the biosphere. The biosphere is the entire space

occupied by living organisms; the hydrosphere is the aqueous enve-

lope of Earth; and the lithosphere is the solid part of Earth.

Physical Processes of Weathering

Physical weathering processes cause in situ breakdown

without chemical change. Five processes are impor-

tant:

1. Unloading Cracks and joints may form to

depths of hundreds of meters below the ground

surface when the effective conﬁning pressure is

reduced. Reduction in conﬁning pressure may re-

sult from uplift, erosion, or changes in ﬂuid pres-

sure. Exfoliation is the spalling or peeling off of

surface layers of rocks. Exfoliation may occur

during rock excavation and tunneling. The term

popping rock is used to describe the sudden spall-

ing of rock slabs as a result of stress release.

2. Thermal Expansion and Contraction The ef-

fects of thermal expansion and contraction range

from creation of planes of weakness from strains

already present in a rock to complete fracture.

Repeated frost and insolation (daytime heating)

may be important in some desert areas. Fires can

cause very rapid temperature increase and rock

weathering.

3. Crystal Growth, Including Frost Action The

crystallization pressures of salts and the pressure

associated with the freezing of water in saturated

rocks may cause signiﬁcant disintegration. Many

talus deposits have been formed by frost action.

However, the role of freeze–thaw in physical

weathering has been debated (Birkeland, 1984).

The rapid rates and high amplitude of tempera-

ture change required to produce necessary pres-

sure have not been conﬁrmed in the ﬁeld. Instead,

some researchers favor the process in which thin

ﬁlms of adsorbed water is the agent that promotes

weathering. These ﬁlms can be adsorbed so

tightly that they cannot freeze. However, the wa-

ter is attracted to a freezing front and pressures

exerted during the migration of these ﬁlms can

break the rock apart.

4. Colloid Plucking The shrinkage of colloidal

materials on drying can exert a tensile stress on

surfaces with which they are in contact.

5. Organic Activity The growth of plant roots in

existing fractures in rocks is an important weath-

ering process. In addition, the activities of

worms, rodents, and humans may cause consid-

erable mixing in the zone of weathering.

To appreciate this phenomenon, smear a ﬁlm of highly plastic clay

paste on the back of your hand and let it dry.

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WEATHERING

Table 2.1 Common Soil Minerals

Name Chemical Formula Characteristics

Quartz SiO

Abundant in sand and silt

Feldspar (Na,K)AlO

[SiO

]

CaAl

[SiO

]

Abundant in soil that is not leached extensively

Mica K

[Si

]

(OH)

[Si

]

(Mg,Fe)

(OH)

Source of K in most temperate-zone soils

Amphibole (Ca,Na,K)

2,3

(Mg,Fe,Al)

(OH)

[(Si,Al)

]

Easily weathered to clay minerals and oxides

Pyroxene (Ca,Mg,Fe,Ti,Al)(Si.Al)O

Easily weathered

Olivine (Mg,Fe)

SiO

Easily weathered

Epidote

Tourmaline

Zircon

Rutile

Kaolinite

(Al,Fe)

(OH)Si

NaMg

(OH,F)

ZrSiO

TiO

(OH)

Highly resistant to chemical weathering; used

as ‘‘index mineral’’ in pedologic studies

Smectite,

vermiculite,

chlorite

(Si,Al)

(Al,Fe,Mg)

(OH)

where M

⫽ interlayer cation

Abundant in clays as products of weathering;

source of exchangeable cations in soils

Allophane Si

 nH

O Abundant in soils derived from volcanic ash

deposits

Imogolite Si

 5H

Gibbsite Al(OH)

Abundant in leached soils

Goethite FeO(OH) Most abundant Fe oxide

Hematite Fe

Abundant in warm region

Ferrihydrate Fe

 9H

O Abundant in organic horizons

Birnessite (Na,Ca)Mn

 2.8H

O Most abundant Mn oxide

Calcite CaCO

Most abundant carbonate

Gypsum CaSO

 2H

O Abundant in arid regions

Adapted from Sposito (1989).

Physical weathering processes are generally the

forerunners of chemical weathering. Their main con-

tributions are to loosen rock masses, reduce particle

sizes, and increase the available surface area for chem-

ical attack.

Chemical Processes of Weathering

Chemical weathering transforms one mineral to an-

other or completely dissolves the mineral. Practically

all chemical weathering processes depend on the pres-

ence of water. Hydration, that is, the surface adsorption

of water, is the forerunner of all the more complex

chemical reactions, many of which proceed simulta-

neously. Some important chemical processes are listed

below.

1. Hydrolysis, probably the most important chemi-

cal process, is the reaction between the mineral

and H

⫹

and (OH)

⫺

of water. The small size of

the ion enables it to enter the lattice of minerals

and replace existing cations. For feldspar,

Orthoclase feldspar:

⫹⫺

K silicate ⫹ HOH

⫹⫺

→ H silicate ⫹ K OH (alkaline)

Anorthite:

⫹⫺

Ca silicate ⫹ 2H OH

→ H silicate ⫹ Ca(OH) (basic)

As water is absorbed into feldspar, kaolinite is

often produced. In a similar way, other clay min-

erals and zeolites (microporous aluminosilicates)

may form by weathering of silicate minerals as

the associated ions such as silica, sodium, potas-

sium, calcium, and magnesium are lost into so-

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10 2

SOIL FORMATION

Figure 2.6 Solubility of alumina and amorphous silica in

water (Keller, 1964b).

lution.

Hydrolysis will not continue in the presence of

static water. Continued driving of the reaction to

the right requires removal of soluble materials by

leaching, complexing, adsorption, and precipita-

tion, as well as the continued introduction of H

⫹

ions.

Carbonic acid (H

) speeds chemical

weathering. This weak acid is formed by the so-

lution in rainwater of a small amount of carbon

dioxide gas from the atmosphere. Additional car-

bonic acid and other acids are produced by the

roots of plants, by insects that live in the soil,

and by the bacteria that degrade plant and animal

remains.

The pH of the system is important because it

inﬂuences the amount of available H

⫹

, the solu-

bility of SiO

and Al

, and the type of clay

mineral that may form. The solubility of silica

and alumina as a function of pH is shown in Fig.

2.6.

2. Chelation involves the complexing and removal

of metal ions. It helps to drive hydrolysis reac-

tions. For example,

Muscovite:

K [Si Al ]Al O (OH)

⫹ 6COH ⫹ 8H O

2 6 2 420 4 242 2

⫹⫹

⫺

→ 2K ⫹ 6COAl ⫹ 6Si(OH) ⫹ 8OH

24 4

Oxalic acid (C

), the chelating agent, re-

leases C

⫺

, which forms a soluble complex

with Al

⫹

to enhance dissolution of muscovite.

Ring-structured organic compounds derived from

humus can act as chelating agents by holding

metal ions within the rings by covalent bonding.

3. Cation exchange is important in chemical weath-

ering in at least three ways:

a. It may cause replacement of hydrogen on

hydrogen bearing colloids. This reduces the

ability of the colloids to bring H

⫹

to unweath-

ered surfaces.

b. The ions held by Al

and SiO

colloids in-

ﬂuence the types of clay minerals that form.

c. Physical properties of the system such as the

permeability may depend on the adsorbed ion

concentrations and types.

4. Oxidation is the loss of electrons by cations, and

reduction is the gain of electrons. Both are im-

portant in chemical weathering. Most important

oxidation products depend on dissolved oxygen

in the water. The oxidation of pyrite is typical of

many oxidation reactions during weathering

(Keller, 1957):

2FeS

⫹ 2H O ⫹ 7O → 2FeSO ⫹ 2H SO

22 2 424

FeSO ⫹ 2H O → Fe(OH) ⫹ HSO

42 224

(hydrolysis)

Oxidation of Fe(OH)

gives

4Fe(OH)

⫹ O ⫹ 2H O → 4Fe(OH)

22 2 3

2Fe(OH) → Fe O  nH O (limonite)

3232

The H

formed in these reactions rejuvenates

the process. It may also drive the hydrolysis of

silicates and weather limestone to produce gyp-

sum and carbonic acid. During the construction

of the Carsington Dam in England in the early

1980s, soil in the reservoir area that contained

pyrite was uncovered during construction follow-

ing the excavation and exposure of air and water

of the Namurian shale used in the embankment.

The sulfuric acid that was released as a result of

the pyrite oxidation reacted with limestone to

form gypsum and CO

. Accumulation of CO

construction shafts led to the asphyxiation of

workers who were unaware of its presence. It is

believed that the oxidation process was mediated

by bacteria (Cripps et al., 1993), as discussed fur-

Copyrighted Material

WEATHERING

Figure 2.7 Microogranisms attached to soil particle sur-

faces: (a) bacteria attached to sand particle (from Robertson

et al. 1993 in Chenu and Stotzky, 2002), (b) bacterial mi-

croaggregate [from Robert and Chenu (1992) in Chenu and

Stotzky (2002)], and (c) bioﬁlm on soil surface (from Chenu

and Stotzky (2002).

ther in the next section.

Many iron minerals weather to iron oxide

(Fe

, hematite). The red soils of warm, humid

regions are colored by iron oxides. Oxides can

act as cementing agents between soil particles.

Reduction reactions, which are of importance

relative to the inﬂuences of bacterial action and

plants on weathering, store energy that may be

used in later stages of weathering.

5. Carbonation is the combination of carbonate or

bicarbonate ions with earth materials. Atmos-

pheric CO

is the source of the ions. Limestone

made of calcite and dolomite is one of the rocks

that weather most quickly especially in humid

regions. The carbonation of dolomitic limestone

proceeds as follows:

CaMg(CO )

⫹ 2CO ⫹ 2H O

32 2 2

→ Ca(HCO ) ⫹ Mg(HCO )

32 32

The dissolved components can be carried off in

water solution. They may also be precipitated at

locations away from the original formation.

Microbiological Effects

Several types of microorganisms are found in soils;

there are cellular microorganisms (bacteria, archea, al-

gae, fungi, protozoa, and slime molds) and noncellular

microorganisms (viruses). They may be nearly round,

rodlike, or spiral and range in size from less than 1 to

100



m, which is equivalent to coarse clay size to ﬁne

sand size. Figure 2.7a shows bacteria adhering to

quartz sand grains, and Fig. 2.7b shows clay minerals

coating around the cell envelope, forming what are

called bacterial microaggregates.

A few billion to 3

trillion microorganisms exist in a kilogram of soil near

the ground surface and bacteria are dominant. Micro-

organisms can reproduce very rapidly. The replication

rate is controlled by factors such as temperature, pH,

ionic concentrations, nutrients, and water availability.

Under ideal conditions, the ‘‘generation time’’ for bac-

terial ﬁssion can be as short as 10 min; however, an

hour scale is typical. These high-speed generation

rates, mutation, and natural selection lead to very fast

adaptation and extraordinary biodiversity.

Autotrophic photosynthetic bacteria, that is, photo-

autotrophs, played a crucial role in the geological de-

Further details of how microorganisms adhere to soil surfaces are

given in Chenu and Stotzky (2002).

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12 2

SOIL FORMATION

velopment of Earth (Hattori, 1973; McCarty, 2004).

Photosynthetic bacteria, cyanobacteria, or ‘‘blue-green

bacteria’’ evolved about 3.5 billion years ago (Proter-

ozoic era—Precambrian), and they are the oldest

known fossils. Cyanobacteria use energy from the sun

to reduce the carbon in CO

to cellular carbon and to

obtain the needed electrons for oxidizing the oxygen

in water to molecular oxygen. During the Archaean

period (2.5 billion years ago), cyanobacteria converted

the atmosphere from reducing to oxidizing and

changed the mineral nature of Earth.

Eukaryotic algae evolved later, followed by the mul-

ticellular eukaryotes including plants. Photosynthesis

is the primary producer of the organic particulate mat-

ter in shale, sand, silt, and clay, as well as in coal,

petroleum, and methane deposits. Furthermore, cyano-

bacteria and algae increase the water pH when they

consume CO

dissolved in water, resulting in carbonate

formation and precipitation of magnesium and calcium

carbonates, leading to Earth’s major carbonate forma-

tions.

Aerobic bacteria live in the presence of dissolved

oxygen. Anaerobic bacteria survive only in the absence

of oxygen. Facultative bacteria can live with or without

oxygen. Some bacteria may resort to fermentation to

sustain their metabolism under anaerobic conditions

(Purves et al., 1997). For example, in the case of an-

aerobic conditions, fermenting bacteria oxidize carbo-

hydrates to produce simple organic acids and H

that

are used to reduction of ferric (Fe

⫹

) iron, sulfate re-

duction, and the generation of methane (Chapelle,

2001). Microbial energy metabolism involves electron

transfers, and the electron sources and acceptors can

be both organic and inorganic compounds (Horn and

Meike, 1995). Most soil bacteria derive their carbon

and energy directly from organic matter and its oxi-

dation. Some other bacteria derive their energy from

oxidation of inorganic substances such as ammonium,

sulfur, and iron and most of their carbon from carbon

dioxide. Therefore, biological activity mediates geo-

chemical reactions, causing them to proceed at rates

that are sometimes orders of magnitude more rapid

than would be predicted solely on the basis of the ther-

mochemical reactions involved.

Bacteria tend to adhere to mineral surfaces and form

microcolonies known as bioﬁlms as shown in Fig. 2.7c.

Some bioﬁlms are made of single-type bacteria, while

others involve symbiotic communities where two or

more bacteria types coexist and complement each

other. For example, bioﬁlms involved in rock weath-

ering may involve an upper aerobic layer, followed by

an intermediate facultative layer that rests on top of the

aerobic layer that produces the weathering agents

(e.g., acids) directly on the rock surface (Ehrlich,

1998). Bioﬁlms bind cations in the pore ﬂuid and fa-

cilitate nucleation and crystal growth even at low ionic

concentrations in the pore ﬂuid (Konhauser and Urru-

tia, 1999). After nucleation is initiated, further mineral

growth or precipitation can occur abiotically, including

the precipitation of amorphous iron–aluminum sili-

cates and poorly crystallized claylike minerals, such as

allophone, imogolite, and smectite (Urrutia and Bev-

eridge, 1995; Ehrlich, 1999; Barton et al., 2001).

In the case of the Carsington Dam construction,

Cripps et al. (1993) hypothesized that autotrophic bac-

teria greatly accelerated the oxidation rate of the pyrite,

so that it occurred within months during construction.

The resulting sulfuric acid reacted with the drainage

blanket constructed of carboniferous limestone, which

then resulted in precipitation of gypsum and iron hy-

droxide, clogging of drains and generation of carbon

dioxide.

Weathering Products

The products of weathering, several of which will gen-

erally coexist at one time, include:

1. Unaltered minerals that are either highly resistant

or freshly exposed

2. Newly formed, more stable minerals having the

same structure as the original mineral

3. Newly formed minerals having a form similar to

the original, but a changed internal structure

4. Products of disrupted minerals, either at or trans-

ported from the site. Such minerals might include

a. Colloidal gels of Al

and SiO

b. Clay minerals

c. Zeolites

d. Cations and anions in solution

e. Mineral precipitates

5. Unused guest reactants

The relationship between minerals and different

weathering stages is given in Table 2.2. The similarity

between the order of representative minerals for the

different weathering stages and Bowen’s reaction se-

ries given earlier (Fig. 2.5) may be noted.

Contrasts in compositions between terrestrial and lu-

nar soils can be accounted for largely in terms of dif-

ferences in chemical weathering. Soils on Earth are

composed mainly of quartz and clay minerals because

the minerals of lower stability, such as feldspar, oli-

vine, hornblende, and glasses, are rapidly removed by

chemical weathering. On the Moon, however, the ab-

sence of water and free oxygen prevent chemical

weathering. Hence, lunar soils are made up mainly of

fragmented parent rock and rapidly crystallized

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