Uniaxial compression data

Uniaxial compression data from samples collected at three different depths (0-5, 10-15 and 20-25 cm) from different fields in Southern Minas Gerais state, Southeastern Brazil, annually cultivated with corn for silage production.
Samples were collected according to a spatially-stratified design. In each sampling point, six undisturbed soil samples were collected (within metallic cylinders 2.5 cm high and 6.4 cm wide), a replicate pair in each of the sampling depths: 0-5 cm, 10-15 cm, and 20-25 cm. A set of 76 sampling points was distributed in the three fields (field 1A: 22 points in 6.2 ha; field 1B: 29 points in 15.6 ha; field 2A: 25 points in 7.6 ha), totalling 456 samples.
The samples were saturated and set to equilibrate at water tensions of 10 or 100 kPa (half the samples at each water potential). These water tensions were chosen because silage harvesting usually occurs during the rainy season and the soil is therefore expected to be moist. The samples were then submitted to drained, confined uniaxial compression tests on electric-pneumatic consolidometers (model S-450, Durham GeoSlope, USA). A stress sequence of 25, 50, 100, 200, 400, 800 and 1600 kPa was applied to the samples for eight minutes per load step without decompression between each step.
reference: field, depth and water tension;
field: identifies sampling field r1, r2 and ed, respectively 1A, 1B and 2A in the attached figure;
depth: sampling depth (0-5, 10-15 and 20-25 cm);
psi: water potential (in kPa) as numeric variable (10 or 100 kPa);
tensao: water potential (in kPa) as categorical variable (10 or 100 kPa);
Dsmax: maximum bulk density from the standard Proctor test (Mg/m3);
sample: sample identification number (each undisturbed sample was collected within metallic rings 6.4 cm wide and 2.5 cm high);
load: applied loads (in kPa) during the uniaxial compression tests (25, 50, 100, 200, 400, 800 and 1600 kPa);
w: weght basis water content (g/g);
teta: volume basis water content (m3/m3);
db0: initial bulk density (that is, before compression) in Mg/m3;
e: initial void ratio (that is, before compression);
n: initial total porosity (that is, before compression) in m3/m3;
sat: initial degree of satuartion (that is, before compression);
air: initial air-filled porosity (that is, before compression), calculated as the difference between total porosity and water content;
dbi: bulk density at each applied load level;
GC: degree of compaction (dbi/Dsmax) at each applied load level;
ei: void ratio at each applied load level;
ni: total porosity at each applied load level;
strain: vertical deformation at each applied load level;
sati: degree of saturation at each applied load level;
airi: air-filled porosity at each applied load level;
deriv.ro: rate of change in bulk density at each load increment;
deriv.e: rate of change in void ratio at each load increment;
deriv.n: rate of change in total porosity at each load increment;
deriv.str: rate of change in strain at each load increment.

本数据集涵盖巴西东南部米纳斯吉拉斯州南部不同常年种植青贮玉米的农田中，采集自0-5 cm、10-15 cm、20-25 cm三个深度的土壤样品单轴压缩试验数据。

样品采用空间分层采样方案进行采集。每个采样点分别在0-5 cm、10-15 cm、20-25 cm三个深度采集6份原状土样，每个深度设置一组重复样品（两个平行样），使用高2.5 cm、直径6.4 cm的金属圆筒完成采样。本次研究共设置76个采样点，分布于3块农田：1A农田6.2公顷范围内布设22个采样点，1B农田15.6公顷范围内布设29个采样点，2A农田7.6公顷范围内布设25个采样点，总计采集456份土样。

将采集的土样进行饱和处理，并在10 kPa或100 kPa的水吸力下达到水分平衡，两种水势条件下各设置一半样品。选择该范围水吸力的依据为：青贮饲料收获通常处于雨季，此时土壤处于湿润状态。随后采用电动气压固结仪（型号S-450，Durham GeoSlope，美国）对样品开展排水、有侧限的单轴压缩试验。试验施加的荷载序列为25、50、100、200、400、800、1600 kPa，每级荷载持续8分钟，各级荷载间不进行卸压操作。

### 数据集字段说明
1. reference：采样综合标识，包含农田、采样深度与水势三项信息；
2. field：采样农田编号，对应附图中的r1、r2、ed，分别对应1A、1B、2A农田；
3. depth：采样深度（单位：cm），可选值为0-5、10-15、20-25；
4. psi：以数值型变量表示的水势（单位：kPa），可选值为10或100；
5. tensao：以分类变量表示的水势（单位：kPa），可选值为10或100；
6. Dsmax：标准普氏击实试验得到的最大干容重（单位：Mg/m³）；
7. sample：土样编号，每份原状土样均使用直径6.4 cm、高2.5 cm的金属环采集；
8. load：单轴压缩试验中施加的荷载（单位：kPa），可选值为25、50、100、200、400、800、1600；
9. w：重量含水率（单位：g/g）；
10. teta：体积含水率（单位：m³/m³）；
11. db0：压缩前初始干容重（单位：Mg/m³）；
12. e：压缩前初始孔隙比；
13. n：压缩前初始总孔隙度（单位：m³/m³）；
14. sat：压缩前初始饱和度；
15. air：压缩前初始充气孔隙度，通过总孔隙度与体积含水率的差值计算得到；
16. dbi：各级施加荷载下的干容重；
17. GC：各级施加荷载下的压实度，计算公式为dbi/Dsmax；
18. ei：各级施加荷载下的孔隙比；
19. ni：各级施加荷载下的总孔隙度；
20. strain：各级施加荷载下的竖向变形；
21. sati：各级施加荷载下的饱和度；
22. airi：各级施加荷载下的充气孔隙度；
23. deriv.ro：每级荷载增量下干容重的变化速率；
24. deriv.e：每级荷载增量下孔隙比的变化速率；
25. deriv.n：每级荷载增量下总孔隙度的变化速率；
26. deriv.str：每级荷载增量下竖向变形的变化速率。