die Sohle
sole
The bottom part of a shoe that has direct contact with the ground.
Der Schuster muss die abgelaufene Sohle meiner Stiefel erneuern.
The cobbler has to replace the worn-out sole of my boots.

sole
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sole
The bottom part of a shoe that has direct contact with the ground.
Der Schuster muss die abgelaufene Sohle meiner Stiefel erneuern.
The cobbler has to replace the worn-out sole of my boots.

To recognize the correct meaning of 'Sohle' (sole), pay attention to the signal words in the sentence. 'Schuh' (shoe) or 'Stiefel' (boot) point to the shoe part, 'Fuß' (foot) to the body part, and words like 'essen' (to eat) or 'Restaurant' (restaurant) to the fish.
Die Sohlen meiner neuen Schuhe sind sehr bequem.
The soles of my new shoes are very comfortable.
When talking about shoes, people often speak of 'abgelaufenen' (worn-out), 'neuen' (new), or 'rutschfesten' (non-slip) soles. Typical verbs are 'besohlen' (to resole) or 'erneuern' (to replace/renew).
Der Schuster kann deine alten Schuhe neu besohlen.
The cobbler can resole your old shoes.
In relation to the foot, 'Sohle' (sole) is often connected with sensations. Typical phrases are 'brennende Sohlen haben' (to have burning soles) or 'sich die Sohlen wund laufen' (to walk until the soles of one's feet are sore).
Beim Barfußlaufen auf dem heißen Asphalt habe ich mir fast die Sohlen verbrannt.
Walking barefoot on the hot asphalt, I almost burned the soles of my feet.
The term 'Sohle' (sole) for tough meat is a vivid and colloquial put-down. It compares the texture of the food to that of a tough shoe sole.
Das Steak war so trocken, es war eine einzige zähe Sohle.
The steak was so dry; it was just one tough piece of shoe leather.
The meaning 'Boden eines Tals oder Bergwerks' (floor of a valley or mine) is used almost only in the technical language of geography or mining. In everyday language, this use is very rare.
Die Geologen untersuchten die Beschaffenheit der Talsohle.
The geologists examined the structure of the valley floor.
reason / ground
'der Grund' and 'die Sohle' can both refer to the lowest part of something, for example a body of water. In this sense, 'der Grund' is the more normal word, especially when talking about the bottom of a lake or sea. 'die Sohle' is more specialized in this meaning and sounds more technical, for example with a valley, a mine, or sometimes a body of water. The words can be confused because both mean the area 'at the bottom'. In everyday language, however, people usually say 'der Grund des Sees' (the bottom of the lake), not 'die Sohle des Sees'.

Die Sohle des Tals bleibt im Winter lange im Schatten.
The valley floor stays in the shade for a long time in winter.
Am Grund des Sees liegen viele alte Äste.
There are many old branches at the bottom of the lake.