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Site Development Reviewer

Chapters 6 to 8: Developing the Site Form, Landscaping, Site Construction

Chapter 6: Developing the Site Form

6.1 Modification of the Site Form

- The site surface is shaped by both natural conditions and the building placed on it.

- Two basic design paths: preserve the original form (minimal disturbance) or modify it to fit the building and its functions.

- Modifying the form raises technical issues: long-term stability of the new form under weather and use, and the practical work needed to achieve and keep the desired shape.

6.2 Cut and Fill

- Cut — removal of existing surface material.

- Fill — building up the surface with added material.

- Together, cut and fill redefine the surface — comparing the before (original site) and after (finished, new surface).

- Before designing, gather:

- Geometry/shape of the existing surface

- Inventory of surface objects (trees, rock outcrops, streams)

- Subsurface information (soil borings, geotechnical reports, site inspection)

- Common goal: balance cut and fill volumes so material doesn't need to be hauled off-site or imported (saves cost).

- Complication: cut material isn't always usable as fill (junk, wrong soil type) — sometimes it must be removed and specially prepared fill imported instead.

- Cut surfaces versus filled surfaces behave differently:

- Cutting can expose subsurface geotechnical problems — needs review by a soils analyst.

- Filled ground needs time to settle as the new soil mass consolidates under gravity, water, and other forces — stabilizing it is a real design concern.

6.3 Grading

- Grading = the construction process that recontours the ground surface by sculpting surface materials to a newly defined profile.

- Typically requires cutting and/or filling; it is a multistage process, not just reaching one final dimension.

- Sequence: preliminary grading (strip unwanted material, set up a base for construction) to grading develops progressively as construction proceeds (excavated material may be reused as fill/backfill) to finished grade once buildings, pavements, and plantings are all in place.

- Range: the finished grade may be almost entirely defined by construction, or (other extreme) an almost fully preserved site where the finished grade is essentially the original grade, needing only final landscaping/topsoil work.

6.4 Drainage

- Core concern: managing water (rain, snowmelt, runoff) off the surface.

- Investigate early:

- Pattern of drainage — where the water actually goes

- Amount of flow — depends on catchment area size and rainfall intensity

- Velocity of flow — depends on slope angle and surface texture/absorption

- Bare soil/planted surfaces absorb some water; anything not "dead flat" sheds runoff.

- Roof drainage is part of total site drainage — must be planned (piped to storm sewer, or directed onto the site surface).

- Retaining soil on unpaved surfaces is a drainage-linked problem: plant roots and hard edging help hold soil; geotextiles can protect vulnerable surfaces until plants establish.

- Construction plays a major role in drainage management:

- Paved areas are sloped or crowned to shed water off the surface.

- Curbs at streets/drives can double as drainage channels.

- Large paved areas often need an underground piped storm-drain system.

- A site's drainage is part of a larger watershed pattern — a hillside site has both uphill and downhill neighbors, and maintaining goodwill (plus legal constraints) affects how drainage can be handled.

6.5 Site Edge Constraints

- Site edges are usually fixed — a designer generally can't alter neighboring properties or bordering streets, so shaping happens mostly within the site boundary.

- Edge concerns include:

- Site drainage to/from neighbors

- Access to breezes, sunlight, views (blocking these creates conflict)

- Unattractive views the site may expose to neighbors (building rear, trash area, parking lot)

- Construction right at the property edge (even a simple fence) is often restricted by code/regulation and may require negotiating with neighbors and local authorities.

- Edge plantings should also consider neighbors (overhanging growth, dropped material).

- Competing goals: prominence/visibility from the street side versus blending in/privacy toward other sides of the neighborhood.

6.6 Controlling the Site Form

- Site form is more than geometry — it must account for real soil behavior and construction feasibility, not just an abstract shape.

- Major concern: steep slopes — controlling erosion (from precipitation/irrigation) and structural stability.

- Stabilizing measures: deeply rooted plantings and various constructed/retaining elements (see Chapter 8).

6.7 Use of Site Construction

Site constructions (pavements, walls, drainage channels, etcetera) support site form development even when built for another purpose (traffic, drainage):

- Maintaining Discrete Areas — sidewalks, drives, drainage channels, and buildings divide the site into zones.

- Achieving Three-Dimensional Forms — retaining walls, high curbs, terraces, stairs, ramps create abrupt vertical changes in finished grade.

- Achieving Changes at Site Edges — abrupt elevation changes at the boundary handled with retaining/bracing structures.

- Range: a highly built-up urban site may have construction that nearly displaces the natural soil form entirely; an undisturbed site has minimal construction impact.

6.8 Building/Site Form Relations

- Horizontal Placement — the building footprint is usually the major site "element" planned first; it strongly limits how the rest of the site can be developed, especially on tight sites.

- Vertical Placement — the building's foundation/entry-floor level constrains site edge conditions (sidewalks, driveways, terraces) and drainage design (drainage should generally move away from the building).

- Strongly Controlling Site Drainage — the building can function as a major drainage device; on tight or problem sites, building edges may even collect site drainage that feeds into the sewer system.

Chapter 7: Landscaping

7.1 General Landscaping Work

- Landscape ≠ just plantings. It's the total experience of all site elements and their relationships, including how building/site interaction extends to the site's edges.

- Typical landscape work: soil grading, plantings, walkways, structures, plus utility installations (irrigation piping, fountains, lighting wiring).

7.2 Existing Features and Conditions

- Ground Form — a key early issue: what to do with the existing ground surface, tied to site edges, proposed uses, and how building and site integrate. Even where preservation is the goal, construction traffic and heavy equipment usually disturb the surface somewhat.

- Existing Site Material — treat existing materials as an inventory of available, essentially free resources. If unused, removal/disposal becomes a real cost.

- Surface materials matter most for finished grade, plant installation, and new pavements.

- Deeper materials matter for foundations — heavy elements may need deep foundations (driven piles, drilled piers).

- Watch for: potential fault movement, unstable/unsuitable soils, freeze-thaw cycles, and reduced groundwater absorption once the site is covered by buildings/pavement (continuous irrigation can noticeably raise soil water presence).

7.3 Preservation of Existing Elements

- Preservation can be simple (isolate an untouched portion) or difficult (protect elements while heavily reforming the surrounding surface).

- Buildings/pavements block water and air from reaching tree roots; heavy equipment compacts soil and can destroy roots. Severe pruning can offset construction damage but reduces the tree's long-term vigor — feasibility should be checked with a plant-growth professional.

- Grade changes near existing trees need special care:

- Raising the grade around a tree may need a retaining structure at the trunk so air/water still reach the roots.

- Lowering the grade (cutting) near a tree may need a slope-retaining structure to hold the soil mass at root level.

- Open-jointed retaining units let air in and moisture drain out, but can dry soil too fast in some cases — controlled permeability may be needed.

- Consider compatibility when adding new plantings near existing ones — some plants don't tolerate sharing a heavily planted space.

7.4 Planning the Landscape

- Landscape design is the major visual element of site design, but it's not simply display — it's an experience shared by everyone who uses the site.

- The designer should mentally "walk through" the site from the perspective of all users — not just building occupants, but passersby, and people/animals with a range of abilities and sensibilities.

- Sites are experienced continuously, across weather, time of day, and season — good design considers the site on a rainy morning, a sunny afternoon, at night, and in snow, not just under one ideal condition.

- Landscaping can extend the building's structural/spatial character into the site — shrubbery, trees, and trellis-like structures can create enclosed or semi-enclosed outdoor spaces.

7.5 Plantings

Three basic forms:

1. Ground Covers — low plantings that blanket the soil (grass, creeping ivy, low shrubs); good where heavy foot traffic or play activity is expected, and for stabilizing slopes/reducing erosion.

2. Single, Large Plants — individual large trees or shrubs used as standalone site elements.

3. Controlled Plant Groupings — rows of single trees, or shrubs trimmed to form a continuous hedge, bed, or similar grouped element.

- Plants may be installed directly in the ground or in a constructed container/planter (built-in or freestanding).

- Selection factors: appearance, cost, availability, climate compatibility, cultivation needs, growth rate, toxicity, and what the plant drops on the site (leaves, fruit, sap = maintenance/litter concern).

7.6 Requirements for Installation of Plantings

- Plants need adequate soil depth and volume for root growth and nourishment — required depth/volume depends on species and mature size.

- Site construction can conflict with planting needs: walls, pavements, or piping can restrict root growth, block sunlight/precipitation, or be lifted by growing roots.

- A well-coordinated design integrates functional elements (parking dividers, curbing, retaining walls) with plantings, which can soften them and reduce how much hard landscaping is needed.

7.7 Design for Maintenance and Growth

- Landscape design must anticipate continual growth — plants aren't static once installed; they grow, change, and eventually need active management (or die).

- Think in two timeframes:

1. Initial installation condition

2. Long-term condition — what will it look like in 5 to 10 years? Could overgrown foliage affect a neighbor's view or create liability?

- Expected maintenance level matters too: major institutional buildings can assume ongoing professional maintenance; other situations may only get "plant them and forget them" care — this affects which species/plantings are realistically feasible.

7.8 Irrigation and Sustenance

- Plants need: water, air, controlled sunlight, nutrients, and protection from frost, wind, and physical damage.

- Watering must be carefully controlled — too much can drown roots or leach out soil nutrients; too little can cause stunted growth or death.

- How plants are watered depends on region, soil type, and species — some rely on natural precipitation; others need supplemental irrigation, from occasional watering up to extensive, continuous, deep watering (costly in arid/hot regions).

- Site soil and drainage conditions affect how much water plants can actually use:

- Porous soils absorb irrigation water readily.

- Dense, slow-draining soils may hold water too long (causing rot) or fail to absorb it well.

- Regrading/drainage changes can alter existing water supply to established plants (for example, diverting water away from roots that depended on it) — a real concern when working around mature plantings.

- Because construction, drainage, and irrigation interact, all three need to be coordinated together in the design.

Chapter 8: Site Construction

8.1 Soil Structures

Soil is the primary "material" of site construction — it affects foundation design, pavement design, and general site development.

Slope Control

- Sloped sites are increasingly common as flat land runs out; requires careful study before construction.

- Cut slopes — stability depends on the soil's natural properties (angle of repose for loose sand; rock/cemented soil may allow much steeper or even vertical cuts).

- Fill slopes — stability depends on the character of the soil being built up.

- Slope failure mechanisms:

- Erosion — surface soil washed away (worsened by wind or heavy rainfall/irrigation).

- Slippage — the soil mass moves downhill, either as a vertical settling under gravity, or by sliding along a slip plane (one soil layer over another).

- Both are often triggered by increased soil moisture.

Retaining Devices for Slopes

- Surface treatments — hold the surface itself in place (plant roots, pavement cover, porous pavers, rocks, geotextiles). These do not prevent deeper slip-plane failure, only surface erosion/retention.

- Stepped slopes — subdividing a slope into steps (near-flat treads with retained risers) reduces the effective slope angle; steps can double as walkways, driveways, or roads on developed hillsides.

Temporary Bracing (used during construction to hold excavation sides)

- Braced cut — simple bracing across a shallow excavation.

- Steel sheet piling — driven sheets forming a temporary wall, allowing soil removal from one side.

- Lagging with soldier beams / steel H-piles — vertical beams ("soldiers") with horizontal boards/sheets ("lagging") between them.

- Cross-bracing — struts placed across the excavation.

- Sheet-pile or soldier-pile walls are sometimes left in place permanently (for example, becoming one side of a basement or cantilever wall's form).

8.2 Pavements

Common paving materials:

- Concrete — strongest common type; used for heavy-traffic roads and walks.

- Asphalt — oil-based (bituminous) binder with aggregate; less permanent than concrete, choice often driven by cost.

- Loose unit pavers — brick, cobblestone, cast interlocking units, cut stone, over a sand/gravel base; durable if properly installed.

- Loose materials — fine gravel, bark, wood chips; light traffic only, needs ongoing maintenance.

Concrete Slab Construction (top to bottom):

1. Concrete slab

2. Membrane (reinforced, water-resistant paper or plastic film) — where moisture intrusion is a concern

3. Coarse-grained pavement base (fine gravel/sand), compacted

4. Prepared (graded and compacted) soil surface

- Thickness: nominal 4-in. slabs are common for residential/light traffic; heavier vehicular loads may need approximately 5.5-in.; very heavy loads (trucks, warehouses) may need thicker slabs with more reinforcement.

- Reinforcement: usually welded wire mesh for 4-in. slabs; thicker slabs may add small rebar. Purpose is to control (reduce) cracking from shrinkage, temperature change, and uneven settlement — placed near the top of the slab, where cracking is most likely to start.

- Joints: control/construction joints are spaced to control where cracking happens (predictable, less visible locations — changes in width, corners, etcetera).

- Surface treatment: smooth troweled finish is common; anti-slip finishes (broomed, sandblasted, roughened) are often required where slabs get wet, especially in public areas.

- Framed pavements: where the ground below can't fully support the pavement (for example, over fill, or spanning a structure), the pavement is built as a spanning reinforced-concrete structure rather than resting directly on soil.

8.3 Retaining Structures

- Curbs — smallest retaining structures; used for elevation changes under about 18 in.; also function as pavement edging.

- Loose-laid retaining walls — unmortared stone or timber, banked/leaned into the cut they retain; naturally porous (lets groundwater seep through) — useful where the high side is heavily irrigated.

- Cantilever retaining walls — the strongest common type; structural masonry or concrete walls anchored to a large footing.

- Used for walls up to roughly 6 ft high.

- Must resist rotational (overturning) and horizontal sliding forces from soil pressure on the high side.

- Taller walls are often tapered (thicker at the base).

- Tall walls may be braced with buttresses (visible front face) or counterforts (hidden back side — usually preferred, since it doesn't affect appearance and needs less excavation/backfill).

- Miscellaneous: Gabions — wire baskets filled with stones, stacked to form a flexible, permeable wall. Timber walls are also still used, often reinforced with geotechnical fabric and drilled-in anchors.

8.4 Planters

- Edging — the simplest planter device; defines and restrains ground-cover plantings (can be a simple maintained trim line, or an actual built edge/curb).

- Planters as containers — built-in (integrated with a paved area or structure, sometimes doubling as seating) or freestanding (pots, tubs — movable, though often heavy).

- Watering/drainage must be planned:

- Built-in planters — usually connected to piped drainage/irrigation, since plants will eventually outgrow the planter and need replacement.

- Freestanding planters — watered more by hand or controlled leaking; drainage design should prevent both overwatering damage and moisture loss.

8.5 Site Service Elements

Utilitarian elements (signage, fire hydrants, drainage devices/meters, electrical transformers) must be planned into the general site design.

Channels

- Surface drainage naturally concentrates into channels as it follows ground contours (this is how creeks/rivers form).

- Constructed channels may be closed (piped, for example, into a sewer) or open (shaped as natural-looking streams, or lined with reinforced concrete where major flow control is needed).

Tunnels (for larger underground site development)

- Sewers — buried pipe (steel, cast iron, fiber-reinforced plastic, fired clay); larger pipes for greater flow capacity.

- Utilities — gas, water, electrical power, telephone lines, routed for ease of ongoing maintenance/alteration.

- Pedestrian or vehicular traffic — connects buildings, especially useful in extreme-cold climates; may also carry rail lines, waste collection, or delivery systems.

Utility Elements and Enclosures

- Some equipment must be above ground for access/maintenance (shutoff valves, meters); placement is often restricted to specific site/building entry points.

- Enclosures can be visually integrated into the landscape but must still meet functional access requirements.

8.6 Stairs and Ramps

- Needed wherever pedestrians must navigate meaningful vertical change; even a "flat" site still needs a slight pitch or crown for drainage.

- Ramps:

- Generally classed as ramps (rather than sloped sidewalks) at slope angles of roughly 5°–15°.

- Steepness limits may be governed by code, especially for accessibility (handicapped) use.

- Slip-resistance is critical when wet — achieved through surfacing choice (roughened concrete, gritted tiles, textured unit pavers).

- Ramps with significant rise typically require handrails.

- Stairs:

- Exterior stair risers are usually shallower than interior stairs, for safety.

- A minimum step height still matters — a single very low riser is actually a tripping hazard because it isn't obvious to pedestrians.

- Built in various materials/methods depending on traffic and structural support needed.

8.7 Construction as Site Sculpture

Functional "necessities" don't have to be purely utilitarian in appearance. Three general design approaches:

1. Aesthetic enhancement — improve appearance through finish/form while keeping full function.

2. Landscape integration — treat the element as a landscape feature itself (for example, worked in as planting edging, a planter, or a paved surface).

3. Concealment — hide the element from view using plantings, fences, or other construction.

8.8 Underground Buildings

Occurs where site surfaces are developed over underground building spaces — most commonly underground parking below a plaza, terrace, or partial site area.

Three basic development concerns:

1. Excavation and construction of the underground structure itself.

2. Redevelopment of the general finished surface grade (backfill, buildup over the structure).

3. Development of the finished site surface on top (plantings, pavements).

Structure

- The roof of an underground structure typically carries much larger loads than an ordinary roof (soil weight, or a plaza's live load — around 150 to 250 psf in most codes) plus its own structural loads — one of the heaviest types of sitecast concrete construction.

- Designers try to keep the structure's total depth to a minimum — commonly with two-way flat slab or two-way waffle systems, which give the smoothest underside and least overall depth (helpful when the underside stays exposed, for example, a parking garage ceiling).

Water Control

- The roof of an underground structure is essentially a flat roof, needing a fully watertight membrane, careful flashing/sealing, insulation, and often a vapor barrier.

- Drainage needs careful planning, since the "roof" is buried — once covered, the space is either fully watertight or is a serious, hard-to-fix problem (little middle ground).

Earth-Covered Roofs (top to bottom):

1. Earth fill for planting

2. Protective cover

3. Insulation

4. Drainage layer

5. Protective cover

6. Waterproof membrane

7. Concrete structure

- Plant roots need adequate soil depth — larger plants/trees may need raised or specially deepened planters set into the roof structure to get enough depth without over-thickening the entire roof.

Paved Roofs / Plaza Pavement (top to bottom):

1. Unit pavers

2. Mortar or sand setting bed

3. Structural paving slab

4. Insulation

5. Drainage layer

6. Protective layer

7. Waterproof membrane

8. Concrete structure

- A single underground roof may combine both paved and planted areas — this requires coordinating both systems' total thickness/dimensions together.

Quick Reference — Numbers and Terms to Remember

Table: Columns: Item, Value / Term. Row 1. Item: Ramp slope range. Value / Term: approximately 5 degrees –15 degrees. Row 2. Item: Curb height limit (before needing a full retaining wall). Value / Term: less than 18 in.. Row 3. Item: Cantilever retaining wall — typical max height for basic form. Value / Term: approximately 6 ft. Row 4. Item: Nominal residential slab thickness. Value / Term: 4 in. (actually 3.5 in.). Row 5. Item: Slab thickness for some vehicular loads. Value / Term: approximately 5.5 in.. Row 6. Item: Plaza/underground roof live load. Value / Term: 150 to 250 psf. Row 7. Item: Wall bracing on visible face. Value / Term: Buttress. Row 8. Item: Wall bracing on hidden/back face. Value / Term: Counterfort. Row 9. Item: Wire-and-stone retaining unit. Value / Term: Gabion. Row 10. Item: Soil layer sliding over another. Value / Term: Slip plane failure. Row 11. Item: Concrete floor systems for minimal underground roof depth. Value / Term: Two-way flat slab / two-way waffle slab.

Key distinctions to keep straight:

- Cut versus Fill — removing material versus adding material.

- Grading versus Drainage — grading shapes the surface; drainage is about controlling water movement across that shaped surface.

- Buttress versus Counterfort — both brace a tall retaining wall; buttress is on the front (exposed) face, counterfort is on the back (hidden) face.

- Erosion versus Slippage — erosion wears away the surface; slippage is a deeper failure of the soil mass along a slip plane.

- Earth-covered roof versus Paved roof — same underground structure concept, different surface treatment and layer stack-up.