Construction Inspection for Field Office Activities Subsurface Water

Construction Inspection for Field Office Activities Subsurface Water Collection (aka Drains and Filters) 11/26/2020 Subsurface Water Collection 1

Objectives To understand the purpose of subsurface water collection for drains, filters, and other practices. Review conservation practices using subsurface water collection To understand the importance of drains and filters in embankments To learn proper installation of drains and filters 11/26/2020 Subsurface Water Collection 2

What are drains and filters and what is the difference? 11/26/2020 Subsurface Water Collection 3

Filter separates soil from drain fill and keeps soil particles from plugging the drain Geotextile (sock around pipe) Sand Drains convey flow Perforated tubing or slotted pipe Gravel 11/26/2020 Subsurface Water Collection 4

Where are drains and filters used in NRCS projects? 11/26/2020 Subsurface Water Collection 5

Drains and filters in NRCS work? Embankments Drains (Dams/levees) Retaining wall/Foundation wall drains Water resource structure drains (structural spillways, concrete lined channels) Landscape drains (field drains) Foundation drains (Dams/waste storage ponds) 11/26/2020 Subsurface Water Collection 6

Typical sand gravel filter and drain 11/26/2020 Subsurface Water Collection 7

Seepage failure 11/26/2020 Subsurface Water Collection Sand boil at toe of levee. Uncontrolled underseepage can lead to failure of embankment 8

Sand boil at toe of levee. Uncontrolled underseepage can lead to failure of embankment 11/26/2020 Subsurface Water Collection 9

Typical Dam and Foundation Materials

Embankment and foundation drains • Foundation Trench Drain 11/26/2020 Subsurface Water Collection 11

Typical Dam and Foundation Materials

Foundation Trench Drain Installation 11/26/2020 Subsurface Water Collection 13

Embankment and foundation drains • Foundation Blanket Drain 11/26/2020 Subsurface Water Collection 14

Embankment and foundation drains • Embankment Chimney Filter/Drain 11/26/2020 Subsurface Water Collection 15

Embankment Chimney Drain Installation 11/26/2020 Subsurface Water Collection 16

Embankment Chimney Drain Installation 11/26/2020 Subsurface Water Collection 17

Where are drains used in NRCS projects? 11/26/2020 Subsurface Water Collection 18

Foundation drain 11/26/2020 Subsurface Water Collection 19

Drainage for walls 11/26/2020 Subsurface Water Collection 20

Materials 11/26/2020 Subsurface Water Collection 21

Foundation drain using geocomposite 11/26/2020 Subsurface Water Collection 22

Landscape/French drains 11/26/2020 Subsurface Water Collection 23

Landscape Drain AWSP - Seepage Collection ASTM C 33 sand, 6 in. thick 18 in. overlap 4 in. dia. slotted pipe CCL, 4 ft. thick Nonwoven geotextile ASTM C 33, Size 89 drain material

Landscape drains Plan view of Field drains 11/26/2020 Subsurface Water Collection 25

Landscape drains Field drains 11/26/2020 Subsurface Water Collection 26

Perforated Corrugated Plastic Pipe 11/26/2020 Subsurface Water Collection 27

Where else is subsurface water collection used in NRCS projects? 11/26/2020 Subsurface Water Collection 28

Spring Developments Installed watering facility near spring development Installation of Spring Box 11/26/2020 Subsurface Water Collection 29

Slotted PVC Pipe 11/26/2020 Subsurface Water Collection 30

Spring Developments Installed Spring Box 11/26/2020 Subsurface Water Collection Watering facility is 1700’ from spring box, 100’ of slotted collection pipe 31

Spring Developments Plan view typical installation 11/26/2020 Subsurface Water Collection 32

Spring Developments Section view typical installation 11/26/2020 Subsurface Water Collection 33

Why are filters important in embankments? 11/26/2020 Subsurface Water Collection 34

Filter Diaphragm vs. AS Collars Filter Diaphragm 11/26/2020 Subsurface Water Collection 35

Conservation Practice Standard 378, Ponds was last revised in May, 2011. It still allows use of anti-seep collars in structures that fall under that Standard. The current guidance given in 378 states that: “Seepage along pipes extending through the embankment shall be controlled by use of a drainage diaphragm, unless it is determined that anti-seep collars will adequately serve the purpose. ” 11/26/2020 Subsurface Water Collection 36

The NRCS criteria for larger embankments is contained in TR 60. It was revised in October 1985 as an amended TR 60. The revision required that anti-seep collars no longer be used as a design measure for seepage control along pipes for dams designed under TR 60. This amendment required that filter diaphragms be substituted for anti-seep collars in the design of all structures governed by this standard. 11/26/2020 Subsurface Water Collection 37

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Why Filters instead of Anti-Seep Collars? • Significant number of failures (dams, not ponds) attributed to poor soils • A filter was needed due to poor soils, eliminating the need for collars • For larger pipes, filters are easier to install than collars and result in better embankments 11/26/2020 Subsurface Water Collection 39

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Moisture Control? 11/26/2020 Subsurface Water Collection 42

Filter Diaphragm A filter diaphragm is a designed zone of filter material (usually well-graded, clean sand) constructed around a conduit. It has become a standard defensive design measure to prevent problems associated with seepage or internal erosion in earth fill surrounding the conduit. 11/26/2020 Subsurface Water Collection 43

Filter Diaphragm 11/26/2020 Subsurface Water Collection 44

Filter Diaphragm 11/26/2020 Subsurface Water Collection 45

Filter Diaphragm 11/26/2020 Subsurface Water Collection 46

Hydraulic fractures Hydraulic Fractures Conduit Foundation Excavation Limits 11/26/2020 Subsurface Water Collection 47

Proper filter location Sand Filter Drainage Diaphragm Hydraulic Fractures Conduit Foundation Excavation Limits 11/26/2020 Subsurface Water Collection 48

Improper filter location Sand Filter Drainage Diaphragm Hydraulic Fractures Conduit Foundation Excavation Limits 11/26/2020 Subsurface Water Collection 49

Something just doesn’t look right! 11/26/2020 Subsurface Water Collection 50

Filter Material Quality Sand Gravel Crushed Stone CLEAN! No organic matter, clay balls, soft particles or other substances. YES NO 11/26/2020 Subsurface Water Collection 51

Filter Materials Storage, Handling, and Placement The objective is to stockpile and place the material in a manner that will: Prevent segregation of particle sizes Prevent contamination Meet specified compaction requirements 11/26/2020 Subsurface Water Collection 52

Storage Larger particles roll down the side of the pile. 11/26/2020 Subsurface Water Collection Drainfill deposited on piles with steep sides tends to segregate. Tall piles tend to have steep sides. 53

Moisture for compaction Fine drainfill must be either very dry or very wet Fine drainfill that is very dry can be compacted to obtain the desired density. Complete saturation and drainage or flooding is often best for densifying fine drainfill. Moisture in sand causes bulking 11/26/2020 Subsurface Water Collection 54

Compaction Lift thickness: Drainfill shall be placed uniformly in layers not more than 12 inches deep before compaction. When compaction is accomplished by manually controlled equipment, the layers shall be not more than 8 inches deep. 11/26/2020 Subsurface Water Collection 55

Flood and Drain You can compact sands by flooding and draining them. Free water will stand on the surface when the sand is saturated. This method of compaction can be difficult. 11/26/2020 Subsurface Water Collection 56

Steel-drum vibrating roller • higher amplitude and a lower frequency than plate vibrators • Single drum vibratory rollers typically have a higher amplitude than double drum vibratory rollers • Vibratory rollers are effective in compacting sands but are usually not as efficient as the plate vibrator for thin lifts. 11/26/2020 Subsurface Water Collection 57

Plate vibrator • high frequency (2000 to 6000 blows per minute) and a low amplitude • produces a stress wave that travels through the soil and sets the particles in motion • does a good job but not as good as flooding the material in a 12 inch lift and draining. 11/26/2020 Subsurface Water Collection 58

T R E N C H 11/26/2020 S A F E T Y Subsurface Water Collection 59

Drain placement without forms earthfill T r e n c h earthfill sand 11/26/2020 Subsurface Water Collection When forms are not used chimney drains and drainage diaphragms are installed in a trench that is excavated after the adjacent fill has been placed 60

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Forms for Drain Placement 11/26/2020 Subsurface Water Collection 64

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Fill trench on each side of box at the same rate. This Form tends to shift Not this 11/26/2020 Subsurface Water Collection 66

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Chimney drain placement without forms Lateral Limits earthfill 11/26/2020 ill f n ai dr earthfill Subsurface Water Collection When forms or a trench are not used, chimney drains and drainage diaphragms are installed in a Christmas tree configuration 70

Improvements? 11/26/2020 Subsurface Water Collection 71

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Subsurface Water Collection Quality assurance checklist Safety - especially trench safety Location – Installed where planned and designed Materials – Geosynthetics and/or drainfill Pipes – Proper materials and installation covered in that topic Quantities – Volumes, lengths, etc. measured and calculated properly CPA-06 notes - (conservation assistance notes) and completion of As-Builts. 11/26/2020 Subsurface Water Collection 73